PubChem provides information on the biological activities of small molecules. Includes substance information, compound structures, and BioActivity data in three primary databases, Pcsubstance, Pccompound, and PCBioAssay, respectively
This is the most comprehensive scientific research tool on the web. With over 450 million scientific items indexed, it allows researchers to search for not only journal content but also scientists' homepages, courseware, and other scientific data.
Science.gov searches over 40 databases and over 2000 selected websites, offering 200 million pages of authoritative U.S. government science information, including research and development results. Science.gov is governed by the interagency Science.gov Alliance