PubChem provides information on the biological activities of small molecules. It is organized as three linked databases within the NCBI's Entrez information retrieval system. These are PubChem Substance, PubChem Compound, and PubChem BioAssay. PubChem also provides a fast chemical structure similarity search tool. Links from PubChem's chemical structure records to other Entrez databases provide information on biological properties.

http://pubchem.ncbi.nlm.nih.gov