The following are the most commonly used chemistry databases. For other chemistry related databases, see here.

SciFinder provides online access to Chemical Abstracts, other Chemical Abstract Services databases, MedLine, and chemical patents. SciFinder offers various search options including reference searching, structure searching, and reaction searching.

Reaxys is a web-based search and retrieval system for chemical compounds, bibliographic data and chemical reactions. Combined data from three sources: The Beilstein Database, The Gmelin Database, and The Patent Chemistry Database.

e-EROS is the online version of Encyclopedia of Reagents for organic synthesis with new reagents added semiannually. e-EROS provides both full text searching and structure searching options. Users can also browse by reagent name. For downloading and installing software and plug-ins for structure searching function, see here.

CHEMnetBASE provides online access to information from the Combined Chemical Dictionary, The CRC Handbook of Chemistry & Physics, Polymers: A Property Database, Properties of Organic Compounds, and some other chemistry dictionaries.

Web of Science
Web of Science is a multidisciplinary citation database that provides access to the journals and conference proceedings in the sciences, social sciences, arts, and humanities, with coverage to 1900.

Derwent Innovations Index
The Derwent Innovations Index available through the ISI Web of Knowledge interface, is a Web-accessible product that merges the Derwent World Patents Index with the Derwent Patents Citation Index. It provides access to more than 14,800,000 patents with links to cited and citing patents, cited articles, and full-text patent data sources. This resource gives users a comprehensive and international overview of inventions in three categories: chemical, electrical and electronic, and engineering.

PubMed includes over 15 million citations for biomedical articles back to 1947. These citations are from MEDLINE and additional life science journals. Includes links to many sites providing full text articles and other related resources.

ChemSpider is a free chemical structure database providing fast text and structure search access to over 28 million structures from hundreds of data sources.