• SCIRUS 460 million scientific items indexed at last count, it 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
  • Public Library of Science (PLoS) Includes PLOS Journals, Currents, and Blogs. Peer-reviewed content in the sciences.
  • National Academy Press Created by the National Academies. Publishes primarily in the sciences and medicine although some materials in behavior sciences are also present. PDF's can be downloaded.
  • Searches over 45 scientific databases and over 2000 websites from US federal agences.  Best to use advanced search option.
  • Science Commons Science resources using the Creative Commons licensing scheme.
  • Proceedings of the National Academy of Sciences Coverage in PNAS spans the biological, physical, and social sciences. PNAS is published weekly in print, and daily online in PNAS Early Edition
  • Science Accelerator gateway to science, including R&D results, project descriptions, accomplishments, and more, via resources from the Office of Scientific and Technical Information (OSTI), U.S. Department of Energy
  • Worldwide Science Online A federation of national science portals where research results are made available by participating nations. Includes results from, the CERN document server, arXiv, and more. Not all peer-reviewed, not all OA.
  • Eric Weisstein's World of Science contains budding encyclopedias of astronomy, scientific biography, chemistry, and physics