PubChem This link opens in a new windowContains the chemical structures of small organic molecules and information on their biological activities. Also includes substance information, compound structures, and bioactivity data in three primary databases, PCSubstance, PCCompound, and PCBioAssay, respectively. Integrated with Entrez, NCBI's primary search engine, it also provides compound neighboring, sub/superstructure, similarity structure, bioactivity data, and other searching features.