Scirus

Search engine that fetches only scientific websites.
http://www.scirus.com/

Online Journals Search Engine

A multi-search tool that permits queries of a number of scientific journals.
http://ojose.lanners.org/

SciSeek

Science search engine and directory. Also provides forums, tools and related news.
http://www.sciseek.com

Meta Search Engine for Scientific Literature

A multi-search tool that permits queries from scientific journals.
http://www.ojose.com/

ISI Highly Cited

A search tool to identify individuals, departments and laboratories that have made fundamental contributions to the advancement of science and technology in recent decades.
http://isihighlycited.com/

CiteSeer

Search engine for computer science and related matters. For all results number of citations are given which allows to estimate the importance of a paper in a given context. Most of the papers are cached and available for direct download as postscript or P
http://citeseer.ist.psu.edu/