PMC FAQs

Below are answers to many of the questions PMC frequently receives. If you cannot find an answer to your question, please contact the PMC Help Desk at pubmedcentral@ncbi.nlm.nih.gov.

General Interest FAQs

FAQs for Publishers

FAQs for Authors

General Interest FAQs

What is PubMed Central (PMC)?

PubMed Central (PMC) is a free archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine (NIH/NLM). It is a repository for journal literature deposited by participating publishers, as well as for author manuscripts that have been submitted in compliance with the NIH Public Access Policy and similar policies of other research funding agencies.

Since its inception in 2000, PMC has grown from comprising only two journals, PNAS: Proceedings of the National Academy of Sciences and Molecular Biology of the Cell, to an archive of millions of articles from thousands of journals.

Participation by publishers in PMC is voluntary, although participating journals must meet certain scientific and technical standards. PMC, itself, is not a publisher.

Access to the material in PMC is free, but use of the material still is subject to the copyright and/or related license terms of the respective authors or publishers. See the PMC Copyright Notice for more information.

What is the difference between PMC and PubMed?

PubMed is a database of citations and abstracts. PMC is an electronic archive of full-text journal articles, offering free access to its contents.

For more details, please see "MEDLINE, PubMed, and PMC (PubMed Central): How are they different?"

Who operates PMC?

PMC was developed and is operated by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) at the U.S. National Institutes of Health (NIH).

Does any independent group oversee the operation of PMC?

The National Library of Medicine (NLM) Board of Regents provides oversight of PMC, which is part of the NLM Collection.

The PMC National Advisory Committee also advised on the content and operation of the repository from 1999 through 2017.

What journals are currently available in PMC?

See the PMC Journal List for a list of currently available journals.

How current is the material in PMC?

The currency and age of material in PMC varies by journal. Many journals make their content available in PMC as soon as it is published. Others may embargo (delay release of) content in PMC for anywhere from a few months to more than a year after publication. Most journals provide free access to full text in PMC within a year of publication.

How far back in time does the archive reach?

PMC has material dating back to the 1800s for some journals. Please visit the PMC Back Issue Digitization page for details about NLM’s back issue digitization projects.

Does PMC contain the complete contents of all the journals that are in its archive?

No. Journals that deposit their articles in PMC fall into one of three categories:

  1. Full Participation: These journals deposit the complete contents of each issue or volume, starting with a particular volume/issue or publication date.
  2. NIH Portfolio: These journals deposit all NIH-funded articles as defined by the NIH Public Access Policy, starting with a particular volume/issue or publication date. The publisher may also choose to deposit other, non-NIH-funded articles.
  3. Selective Deposit: Selective Deposit journals deposit a more loosely defined set of content than Full Participation and NIH portfolio journals. This category is intended for the deposit of a subset of articles from a collection of journals. It is frequently used by publishers who offer a hybrid publishing model, i.e., subscription-based journals in which selected articles are published as Open Access, or publishers who wish to support the policies of a particular funder which require articles to be made available in PMC under specific license terms.

The PMC Journal List includes information about what content is available from each journal; Selective Deposit journals are grouped under the Special Collections tab. A full description of each participation category is available on the Participation Agreements and Options page.

In addition to the articles from these journals, PMC contains author manuscripts of selected articles from other journals. See Who may contribute to PubMed Central for more information. These manuscripts are accessible via a PMC search or a link from the corresponding PubMed abstract.

How can I find out when PMC adds a new journal to its archive?

On the PMC Journal List page, there is a tab labeled "New", where you can see the list of all the Full Participation and NIH Portfolio journals added in the last 60 days.

How can I find out about changes to PMC?

News and announcements about PMC can be obtained via the methods below:

PMC-Announce email list: Add your name to the list to be notified by email whenever there important announcements about PMC.

New in PMC Page/RSS feed: Check the New in PMC/RSS feed for recent PMC developments or features.

How is PMC related to PMC International?

PMC International (PMCI) is a collaborative effort between: NIH / NLM; publishers and U.S. funding agencies that contribute content to the PMC archive; and funding organizations in other parts of the world that also wish to preserve and provide free access to journal articles authored by the researchers they support.

The PMCI network currently comprises (U.S. / NLM) PMC and Europe PMC. NLM’s collaboration with Europe PMC is based on a formal agreement between NLM and Europe PMC's sponsors concerning the management of any content the center gets from PMC. A second PMCI center, PMC Canada, was operational from October 2009 to February 2018.

Read more about PMCI on the PMC International page.

Are there any restrictions on the use of the material in PMC? Can I download a batch of articles from PMC for research or other purposes?

Although access to the material in PMC is free, the use of the material still is subject to the copyright and/or related license terms of the respective authors or publishers. See the PMC Copyright Notice for more information.

You may NOT use any kind of automated process to download articles in bulk from the main PMC site. PMC will block the access of any user who is found to be violating this policy.

However, there are a few Text Mining Collections within PMC where bulk retrieval of files for text mining and other purposes is permitted. License terms may vary by collection or even within a collection. To download a collection in PMC, you must use a designated service, such as the PMC FTP service. See the full listing of APIs that you can use for accessing PMC data on the PMC Developer Resources page.

What is the PMC Open Access subset? Isn't everything in PMC open access?

The PMC Open Access Subset contains articles that are still protected by copyright, but are made available under a Creative Commons or similar license that generally allows more liberal redistribution and reuse than a traditional copyrighted work. See the PMC Open Access Subset page for more information on how you may retrieve and use these articles.

The majority of the articles in PMC are subject to traditional copyright restrictions. They are free to access, but they are not Open Access articles in the specialized sense of that term.

Who may contribute to PMC?

PMC accepts articles from journals that meet PMC’s scientific, editorial, and technical standards and sign a PMC participation agreement with the National Library of Medicine (NLM). To become a PMC-participating journal, the publisher must submit a formal application after which NLM will review the scientific and editorial quality of the content as well as the technical quality of the journal’s digital files (see How to Participate in PMC).

In addition to PMC-participating journal content, PMC accepts individual author manuscripts that are deposited via the NIH Manuscript Submission (NIHMS) system or a similar manuscript processing system. This submission route is available only for manuscripts that are covered by the public access policies of approved funding agencies (see PMC and Research Funder Policies). Author manuscripts in PMC are clearly identified as such.

What types of material may be deposited in PMC?

As an archive, PMC strives to collect and preserve everything that is published in a participating journal. It has cover-to-cover digital copies of the early issues of any journal that came into PMC through NLM's Back Issue Digitization Project. For more recent material, which a journal must supply in XML form, PMC accepts any editorial content that can be represented accurately with the Journal Article Tag Suite (JATS) or a compatible DTD. In this context, "editorial content" refers to articles and article-like items, including book reviews, news items and obituaries.

At this time, PMC will not accept promotional material for pharmaceutical or other products, even if presented in the form of an article.

In general, a participating journal must deposit the final, published version of an article. However, when PMC serves as the repository for a funding agency's access program (e.g., NIH Public Access Policy), PMC will accept an author's peer reviewed manuscript, as accepted for publication. Manuscripts may be deposited via the NIH Manuscript Submission (NIHMS) system in a number of electronic word-processing formats. For more information, please see the How Papers Get Into PMC page, and the related FAQ, Who may contribute to PMC?

Does PMC include articles written in languages other than English?

Most of the articles in PMC are written in English. However, some journals in PMC publish material in more than one language and PMC may display some abstracts or full text articles in another language.

For those older issues of a journal that were scanned under NLM's digitization program, the PMC archive may also include some articles published exclusively in languages other than English.

Additionally, to support the MEDLINE Policy on Indexing Electronic Journals, PMC will archive the complete contents of any MEDLINE journal that applies to PMC, regardless of language, if the journal can meet PMC’s technical standards. Please see the Language Guidelines section on the PMC Policies page for additional details.

NIHMS is also able to process non-English manuscripts submitted to PMC that fall under the NIH Public Access Policy, as long as they are written in Latin scripts. Submissions written in other scripts (e.g., Cyrillic, kanji) cannot be processed by NIHMS.

What is the NIH Public Access Policy?

The NIH Public Access Policy ensures that the public has access to the published results of NIH-funded research. It requires scientists to submit final peer-reviewed journal manuscripts that arise from NIH funds to PMC upon acceptance for publication. The Policy requires that these final peer-reviewed manuscripts be accessible to the public on PMC to help advance science and improve human health.

I want to report a bad link or a typo in a PMC article. What do I do?

To report a problem with an article in PMC, please contact the PMC Help Desk at: pubmedcentral@ncbi.nlm.nih.gov. If you are the author of the article, please email the publisher and send a copy ("cc") of your message to the PMC Help Desk at pubmedcentral@ncbi.nlm.nih.gov.

What does embargo mean and can I get the article anyway?

When an article is under an embargo it means that there is a delay, as specified by the publisher, between when the article is published and when its full version can be made freely available in PMC. The default embargo for each journal in PMC can be found under the "Free Access" column on the PMC Journal List. The exact release date for each article under embargo is displayed in PMC search results, on the table of contents for the issue, or in the corresponding PubMed record. To obtain access to an article prior to its availability in PMC, you will need to contact the respective journal publisher directly.

Where can I get permissions to reproduce articles or images?

NLM does not hold the copyright for any of the material in PMC and cannot grant others permission to reuse or reproduce any of it (see PMC Copyright Notice). Many articles in PMC have a license (e.g., a Creative Commons license) that explicitly allows some degree of reuse or redistribution of the content. The licenses vary in what they allow; you need to determine whether a particular license permits your intended use. NLM cannot interpret the licenses for you. If an article has standard copyright protection and no special license, or if you are unsure of what the license allows, you should contact the respective journal publisher for permission.

What happens if a journal ceases its participation? Will the existing articles be removed?

PMC does not remove articles that have been deposited into its archive when a journal ceases participation. The journal will be designated as "No longer participating" in the Participation Level column on the Journal List and all the material deposited previously remains available.

FAQs for Publishers

What are a publisher’s options for depositing articles in PMC?

A paper can get into PubMed Central (PMC) as either:

  1. The final published version of the article, deposited directly in PMC by the publisher (i.e., PMC-participating journal), or
  2. An author manuscript version (i.e., peer-reviewed, accepted manuscript) that goes through the NIH Manuscript Submission (NIHMS) system into PMC.

See an overview of these paths on the page, How Papers Get Into PMC.

How soon after publication must articles be made available through PMC?

Publishers are encouraged to make their content viewable in PMC at the time of publication, or soon after, but may choose to have a release delay (embargo) for up to a year or more. See "Embargoes" on the PMC Policies page for further details.

Who controls copyright privileges for the material archived in PMC?

Copyright to all material deposited in PMC remains with the publisher or individual authors, whichever is applicable. PMC is an archive and does not claim copyright on any material in the archive. For more information, see the PMC Copyright Notice.

In what electronic formats may data be submitted to PMC?

A journal must provide PMC the full text of articles in an XML format that conforms to an acceptable journal article DTD (Document Type Definition). PMC does not accept articles in HTML format. The original high-resolution, digital image files must also be provided for all figures. A PDF version, if one exists, must be deposited in PMC in addition to the XML version (but not as the only form) of an article. Supplementary material, in the form of video, audio or data files that may be available with an article, must also be deposited. See the File Submission Specifications for further details.

Why does PMC require the full text of every article in XML? Why not accept just a PDF or HTML file?

We believe that XML is the most effective archival format for the textual portion of a journal article. It essentially is software- and hardware-independent, and therefore adapts easily to changes in technology. XML lets you preserve the structure and meaning of an article in a relatively simple and human readable form.

With a well-documented DTD, which serves as the "code book" for a piece of XML, you have something that people will still be able to decipher and use several generations from now, regardless of changes in technology. This characteristic lends XML to being converted to a more advanced text recording format in the future. XML tagging also makes it easier to automatically parse the content of an article, which can help with more focused searching and with linking the article to related content in other databases, e.g., links to factual reference data.

All of the articles in XML provided by a publisher will be normalized by PMC to conform to the NISO JATS Journal Publishing DTD, the standard XML format used in the archive.

What is the cost of participating in PMC?

There is no charge to publishers for including journal content in the PMC archive. A publisher is responsible only for any costs incurred in creating files that meet PMC's technical standards and transmitting them to PMC.

What do publishers gain by depositing their content in PMC?

Publishers receive the benefit of a permanent and freely accessible archive, managed by the National Library of Medicine. Every publisher can request from NLM and receive, free, a copy of their archived content at any time.

The journal also benefits from the integration of its full text with citations in PubMed and NCBI's numerous other databases, and the increased exposure that this brings.

Why does PMC require the deposit of complete articles, rather than linking to a journal site for full text?

NLM's journal abstract database, PubMed, already has links to full text at the online sites of thousands of journals that participate in the freely available LinkOut service. One of the primary goals of PMC is the creation of a digital archive of journal literature which, by definition, means the full text must be deposited in PMC.

How are article citations submitted to PubMed?

Details are available on the PMC Policies page in the PubMed Citations section.

What kinds of usage statistics does PMC provide to participating journals?

Each publisher has password-controlled access to a web site that has usage reports for that publisher's journal(s). The reports, updated daily and aggregated by month, include counts of available articles, total access by type of page (e.g., full-text HTML or PDF); unique IP addresses; and most frequently retrieved or cited articles. Any report may be downloaded as a CSV or XML file.

Monthly use at an individual article level is also available in CSV and XML format.

NLM's privacy policy does not allow the identification of use made by specific individuals, organizations or IP addresses. Therefore, the usage reports do not include this level of data.

PMC usage stats follow COUNTER guidelines on excluding access by robots and crawlers and not counting double clicks. However, PMC is not formally COUNTER compliant because the NLM privacy policy prevents us from reporting use by institution. Additionally, PMC statistics do not support some of the access mechanisms, such as SUSHI, or some of the specific report formats.

Participating publishers should contact their PMC journal manager for assistance with accessing the statistics web site.

What is PMC’s policy on accepting articles that are Ahead-of-Print/Online First?

Please see the Online First (OLF) articles entry on the PMC Policies page for information on PMC’s policy on accepting articles that are published Ahead of Print/Online First.

What is PMC’s policy on retractions?

PMC will not remove articles from its archive. For information on our retractions policy, see "Retractions" on the PMC Policies page.

FAQs for Authors

I need to have a PMCID for my article, how do I get one?

An article gets a PMCID when the full text is deposited in PMC, in the form of either the final published version or an author manuscript. A number of journals have agreed to deposit the final published version of all NIH-funded articles directly in PMC. See this page for a list. If your journal is not on this list, you must get the article into PMC via the NIHMS. For further details, see Submission Methods on the NIH Public Access page.

If the final published version is deposited in PMC directly by the publisher, a PMCID will be assigned once the files are received and PMC staff completes a check of the accuracy of the technical files.

If the author manuscript (i.e., final peer-reviewed version) is submitted to PMC via the NIHMS system (either by the publisher or author), a PMCID will be assigned only after the files have been converted into PMC format, the reviewing author has approved the PMC version, and the NIHMS record has been matched to a PubMed record.

What is the difference between a PMCID and a PMID?

A PMCID is a unique identifier for an article in PMC. A PMID is a unique identifier for a citation in PubMed. An article may be in both PMC and PubMed or in only one of the two. See "What is the difference between PMC and PubMed?"

The PMC reference number (PMCID) is different from the PubMed reference number (PMID). The PMCID links to full-text papers in PMC, whereas the PMID links to citations in PubMed. Only PMCIDs, not PMIDS, can be used as evidence of compliance with the NIH Public Access Policy.

What is the relationship between PMC and the NIH Manuscript Submission system?

The NIH Manuscript Submission System (NIHMS) takes in final peer-reviewed manuscripts covered by the NIH Public Access Policy and formats them for inclusion in PMC. Authors deposit the files for a final peer-reviewed manuscript (e.g., Microsoft Word document and figures) into the NIHMS. The files are converted to the Journal Article Tag Suite (JATS) DTD, and then reviewed in HTML and PDF formats by the author to confirm that the converted final peer-reviewed manuscript is faithful to the original. The NIHMS transfers the final peer-reviewed manuscript to PMC when it is ready to be made available publicly.

I’ve been told I have to submit my manuscript to PMC, how do I do it?

For information on submitting a manuscript, please see Author Manuscripts in PMC.

How can I find out how many times my article has been accessed, viewed or downloaded from PMC?

By agreement with the publishers, PMC is only able to give out usage data to the publisher who deposits an article. You will need to contact the publisher to request the usage data for your article. In the case of author manuscripts, PMC is only able to give out usage data to the author who releases it to PMC via the NIH Manuscript Submission System.

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Last updated: Tues., 23 Oct 2018