There is a brief guide for using Lexis-Nexis in the Sciences. Coverage goes back to 1994. This is a good, interdisciplinary index with a unique feature which allows you to search for articles which CITE a particular article. There is a brief guide to using Web of Science, with more in-depth online help. Current Contents Connect - the web version of Current Contents.
Coverage goes back two years.
There is a brief guide to using CCC, plus lots of online help. Indexes scientific and technical journals and conference proceedings inphysics, electrical engineering and electronics, computing and control, and information technology. January 1969 to the present. Access to SPIN Abstracts, going back to 1975, plus Advanced SPIN Abstracts, for articles not yet published. SPIN has bibliographic citations, abstracts, plus full-text links to AIP journals.