Geer LY, Marchler-Bauer A, Geer RC, Han L, He J, He S, Liu C, Shi W, Bryant SH. The NCBI BioSystems database. Nucleic Acids Res. 2009 Oct 23 [Epub 2009 ahead of print] [Full Text] [PDF]

Articles describing the source databases are provided in the references section of the help document.