PubChem

由美國國家生物技術資訊中心 (National Center for Biotechnology Information，簡稱 NCBI) 維護，專門針對查詢化學分子與生物活性的搜索引擎，擁有上百萬組化學結構和相關文字資料，並可免費經由 FTP 下載。

PubChem is the world's largest collection of freely accessible chemical information. Search chemicals by name, molecular formula, structure, and other identifiers. Find chemical and physical properties, biological activities, safety and toxicity information, patents, literature citations and more.