We recently added Scopus to our database lineup. Scopus is a citation and abstract database of peer-reviewed literature covering over 21,000 journals, books and conference proceedings in a wide range of fields including science, technology, medicine, and the social sciences. Its big claim to fame is citation indexing, which provides a way to judge the impact of a research article by tracking who cited it in later publications.
Update 7/1/20: Scopus is no longer available.