Science.gov Searches over 45 scientific databases and over 2000 websites from US federal agencies. Best to use advanced search option.
National Academies Press Maintained by the National Academy of Sciences, the website contains reports (some book-length) on science, engineering, medicine and health policy. Not all items are free open-access but much is.
WorldWideScience A federated search engine for scientific papers worldwide. Can be searched in multiple languages and contains much open-access material.
Information Bridge: DOE Scientific and Technical Information Full-text documents and bibliographic citations of Department of Energy research report literature. Areas covered are physics, chemistry, material sciences, biology, environmental sciences, energy technologies, engineering, computer and information science, and renewable energy.
InTechOpen Thousands of open-access scholarly books, articles and research papers in the sciences.
SciELO Once was largely Brazilian science journals, now contains journals in most subjects from South America and some other locations (e.g. South Africa, Portugal). Also has open access books, largely from Brazil.
PubMedCentral Archive of open-access biomedical and life sciences articles maintained by the National Institutes of Health. A separate link is found on Hofstra Univeristy Library's list of research databases.
arXiv.org Open access pre-prints in physics, mathematics, computer science, quantitative biology, quantitative finance and economics.
bioRXiv Open access pre-prints in the biological sciences, including some medicine related fields.
CiteSeerX A scientific literature digital library and search engine that focuses primarily on the literature in computer and information science. Contains some material on the philosophy of science.
PaleorXiv A community-led platform for paleontologists to upload and share open access pre-prints.
EarthArXiv Open access pre-prints in the earth sciences.
Cogprints Archive of preprints and publications in psychology, neuroscience, linguistics, computer science, philosophy of mind other areas of philosophy, and biology.
AfricArXiv Archive of preprints of scientists from Africa. Outputs in all scientific fields.
JASDL: Journal of the Analytical Sciences Digital Library Peer-reviewed articles on the pedagogy of the analytical sciences and related areas.
ScienceOpen Allows searching for open access science articles as well as open peer-review. Contains published open access articles and preprints.
BioOne Peer-reviewed articles in the biological sciences. Much is open-access. Go to advanced search and then limit search to "All content I have access to", which should allow you to search in open-access journals.
Biodiversity Heritage Library Literature on biodiversity.
Smithsonian Library: Digital Library Books and other materials. Included are the Annual Reports of the Regents of the Smithsonian Institution, Annual Reports of the Bureau of Ethnography, both going back to the 19th century. A rich collection of material on Native Americans and on natural history. Some of this is reproduced in the Biodiversity Heritage site.
DSpace Repository A very mixed collection from the Smithsonian Library. Much information on science and primary sources in the history of science.
J-STAGE - “Japan Science and Technology Information Aggregator, Electronic” (J-STAGE) is a platform developed by the Japan Science and Technology Agency (JST) to make available internationally Japanese scholarly journals and research papers published by learned societies and specialized organizations. The search interface allows for English-language materials to be searched exclusively.
OpenGrey Over 700,000 references to grey literature produced in Europe. Allows you to locate records and download documents. Covers sciences, technoogy, economics, social sciences, and the humanities.
The Public Library of Science is a non-profit publisher of open access, peer-reviewed scientific journals that are fully searchable. Also available on the site is PLOS Currents, a publication that aims to "minimize the delay between the generation and publication of new research."
Project Euclid A not-for-profit online publishing service that provides access to journals, monographs, and conference proceedings in the fields of theoretical and applied mathematics and statistics. Not all the material is open-access but much of it is. Books may be more likely to be open-access than articles.
PLOS Publisher of open-access journals in medicine and biology.
PeerJ Open access peer reviewed articles largely in the biological sciences, although some other areas are covered as well. PeerJ Computer Science and Preprints can also be accessed from this link.
RCAAP - Repositório Científico de Acesso Aberto de Portugal Digitial material on science from Portugal.
For others in this discipline search in the Directory of Open Access Journals using the Browse function to get a list of disciplines. All journals in the DOAJ can be searched by individual title using Hofstra University's Journal Finder. OneSearch should also pick up the content.
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.
Byrne's Euclid A reproduction of Oliver Byrne's 1847 first six books of Euclid's Elements with interactive material.
Issues in Science and Technology Librarianship Publishes peer-reviewed or board-accepted articles. It is the official publication of the Science & Technology Section of the Association of College & Research Librarians.
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