PubMed Central (PMC) is the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature.
There are many full-text books available through Google Books. Using the Advanced Search screen, check off ”Full view only” under ”Search”.
HathiTrust is a massive full-text digital library comprising more than 10 million volumes contributed by more than 60 major research institutions and libraries.
Google Scholar enables you to search specifically for scholarly literature, including peer-reviewed papers, theses, books, preprints, abstracts and technical reports from all broad areas of research.
"Download free books and texts. The Internet Archive Text Archive contains a wide range of fiction, popular books, children's books, historical texts and academic books. The collection is open to the community for the contribution of any type of text, many licensed using Creative Commons licenses."
Open Library is an open, editable library catalog, building towards a web page for every book ever published
Open Access Publishing in European Networks: "Freely accessible academic books, mainly in the area of Humanities and Social Sciences."
Search engine for academic open access web resources.
CORE (COnnecting REpositories) aims to facilitate free access to scholarly publications distributed across many systems. CORE provides access to millions of scholarly articles aggregated from many open access repositories.
Search publications and datasets from open access repositories and journals.
This service lets you search the contents of the repositories listed in OpenDOAR, an authoritative directory of academic open access repositories, for freely available academic research information. Full text is available for most results.
"OAIster is a union catalog of millions of records representing open access resources.... includes more than 25 million records representing digital resources from more than 1,100 contributors."
Provides free and open access through the Internet to written and spoken words, sound recordings, still and moving images, prints, maps, and sheet music that document the American experience.
The DPLA serves as a portal to the openly available, digitized contents of America’s libraries, archives, and museums. It indexes materials in all formats.