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Free database with large amount of information about properties, structures, and biological activities of small organic molecules.
On the results page the "Substance" section finds including chemical structures, chemical names and related comments; the "Compound" section finds chemical structures and information about pharmacology, commerical uses, toxicity, etc.; and the "BioAssay" section searches bioactivity screens of the chemical substances described in PubChem Substance. The "pathway" section lists information about interactions among molecules within a cell that leads to a certain product or a change in the cell, and there are also sections to help you find relevant literature and patents.