Scirus
Search engine that fetches only scientific websites.

Phibot
An intelligent internet information retrieval tool for scientists.

Online Journals Search Engine
A multi-search tool that permits queries of a number of scientific journals.

SciSeek
Science search engine and directory. Also provides forums, tools and related news.

Meta Search Engine for Scientific Literature
A multi-search tool that permits queries from scientific journals.

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.