10 Excellent Science Search Engines

Scirus
Scirus searches over 450 million scientific items, and allows researchers to search for not only journal content but also scientists’ homepages, courseware, pre-print server material, patents and institutional repository and website information.

Scitopia.org
Scitopia.org is a free federated vertical search service which retrieves content provided by its twenty-one partner scholarly societies (Acoustical Society of America, American Geophysical Union, American Institute of Aeronautics and Astronautics, American Institute of Physics, American Physical Society, American Society of Civil Engineers, American Society of Mechanical Engineers, American Vacuum Society, Audio Engineering Society, The Electrochemical Society, The Institute of Electrical and Electronics Engineers, Institute of Physics Publishing, International Union of Crystallography, Optical Society of America , Professional Engineering Publishing, The Royal Society, Society of Automotive Engineers, Society for Industrial and Applied Mathematics, SPIE, and The Society for Information Display).

Science.gov
A new version has just been launched. Science.gov is a free, integrated single-search gateway to reliable science and technology information from 17 organizations within 13 federal science agencies.

Science Research

A free search engine allowing access to numerous scientific journals and public science databases.

Scitation
Searches more than one million documents from scholarly journals, magazines, conference proceedings, and other special publications from prestigious scientific societies and technical publishers. In addition, through Scitation, members of Heriot-Watt University can access the full text of several journals published by the American Institute of Physics and other learned societies, including the American Society of Civil Engineers, the American Society of Mechanical Engineers, and the Optical Society of America.

WorldWideScience.org
WorldWideScience.org is a global science gateway connecting you to national and international scientific databases and portals.

Science Accelerator
Science Accelerator searches science, including R&D results, project descriptions, accomplishments, and more, via resources made available by the Office of Scientific and Technical Information (OSTI), U.S. Department of Energy.

TechXtra
A free service provided by Heriot-Watt University which can help you find articles, books, the best websites, the latest industry news, job announcements, technical reports, technical data, full text eprints, the latest research, thesis & dissertations, teaching and learning resources and more, in engineering, mathematics and computing.

search.optics.org
A much more specific search engine. This one is a search tool that only returns results from websites that have been selected for their optics content