Web of Science is the most complete and comprehensive citation tracking database with coverage from 1900 to the present. It provides thorough coverage of ~5900 major journals. Includes cited author searching. Abstracts, keywords, and additional subject categories are included and searchable from 1991+.
Video Tutorial: http://scientific.thomson.com/support/recorded-training/wos/
Google has a specialized interface for searching the journal literature called Google Scholar that provides access to peer-reviewed papers, theses, books, abstracts and articles, from academic publishers, professional societies, preprint repositories, universities and other scholarly organizations. Although it is not as standardized, thorough, or reliable as BIOSIS, Web of Science and other literature databases, Google Scholar is the simple interface that has its advantages of those who are less experienced with searching the literature.
Provides International coverage of journal articles, selected web sites, and patents in the sciences and social sciences; provides citation tracking from 1996 to the present.
Interactive Tutorial: http://help.scopus.com/robo/projects/schelp/tutorials/sc_menu.html