ChemSpider is a free chemical structure database providing fast text and structure search access to over 57 million structures from hundreds of data sources. Provided by the Royal Society of Chemistry.
PubChem is a NLM database of compounds, substances, and bioassays, focusing on the biological activities of small molecules. PubChem provides substance information, compound structures, and bioactivity data for small molecules in three primary databases, PCsubstance, PCcompound, and PCbioassay. PubChem also includes a chemical structure similarity search tool.
