This is a list of either licensed  licensed, or selected, freely available freely available high quality databases.
Database Further information Access
ACM Digital Library
  • full text collection of every article published by the Association of Computing Machinery (ACM)
  • includes over 50 years of archives
arXiv.org
  • Open Access e-prints archive with 550,000+ e-prints
  • Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics
CogPrints - Cognitive Sciences EPrint Archive
  • free Open Access archive in any area of Psychology, Neuroscience, and Linguistics
  • in many areas of Computer Science, Biology, Neurology, etc.
Eurographics Digital Library
  • computer graphics and all related visual disciplines
  • bibliographic and metadata content freely accessible
  • access to full text content requires membership
IEEE Computer Society Digital Library (CSDL)
  • access to 27 society magazines and transactions with all available archives
  • access to >3.300 conference publications (>200 proceedings titles) with a backfile to 1995
ISI Web of Knowledge online database with access to
MathSciNet
  • Mathematical Reviews on the Web
  • provided by the American Mathematical Society
  • coverage back to 1940
PubMed
  • service of the U.S. National Library of Medicine
  • 18+ Mio article citations from MEDLINE & life sciences journals
  • coverage back to 1948 incl. links to full texts
PubMedCentral
  • provided by the U.S. National Institutes of Health (NIH)
  • free digital archive of biomedical and life sciences journal literature