BioMed Central: Free access to articles from a variety of journals on science, mathematics, and more.
Directory of Open Access Journals: "DOAJ is a community-curated online directory that indexes and provides access to high quality, open access, peer-reviewed journals."
PLOS: "PLOS publishes a suite of influential Open Access journals across all areas of science and medicine."
Artstor: "Artstor’s ever-growing public collections offer approximately 1.3 million freely accessible images, videos, documents, and audio files from library special collections, faculty research, and institutional history materials, as well as hundreds of thousands of open access images from partner museums. Anyone may view and download these collections; no subscription or login required."
Digital Public Library of America: "Discover 40,554,817 images, texts, videos, and sounds from across the United States"
Google Scholar: "Provides a simple way to broadly search for scholarly literature. From one place, you can search across many disciplines and sources: articles, theses, books, abstracts and court opinions, from academic publishers, professional societies, online repositories, universities and other web sites."
Library of Congress: Digital Collections: Archives, photographs, documents, and more from the Library of Congress.
ACLS Humanities E-Book: "ACLS Humanities E-Book (HEB) is a digital collection of over 5,400 seminal books in the humanities and related social sciences."
National Academies Press: Downloadable PDF ebooks on science, engineering, medicine, and more.
The Online Books Project: "An index of over two million online books freely readable on the Internet."
Open Textbook Library: "Open textbooks are textbooks that have been funded, published, and licensed to be freely used, adapted, and distributed. These books have been reviewed by faculty from a variety of colleges and universities to assess their quality. These books can be downloaded for no cost, or printed at low cost. All textbooks are either used at multiple higher education institutions; or affiliated with an institution, scholarly society, or professional organization. The library currently includes 788 textbooks, with more being added all the time."
Project Gutenberg: "A library of over 60,000 free eBooks. Choose among free epub and Kindle eBooks, download them or read them online. You will find the world's great literature here, with focus on older works for which U.S. copyright has expired. Thousands of volunteers digitized and diligently proofread the eBooks, for enjoyment and education."
Thesaurus Linguae Grecae: Digital library of Greek literature.
The Avalon Project: Historical documents separated by era archived by Yale Law School.
California Digital Newspaper Collection: Searchable, full text database of historic California newspapers.
Perseus Digital Library: Covers the history, literature and culture of the Greco-Roman world
BioMed Central: Free access to articles from a variety of journals on science, mathematics, and more.
Mathworld: Comprehensive, free mathematics encyclopedia.
Global Health and Human Rights Database: A free online database of health & human rights law.
GovInfo: Statistics, budgets, documents, and more from the US government.
UN iLibrary: UN iLibrary is the comprehensive global search, discovery, and viewing source for digital content created by the United Nations
BioMed Central: Free access to articles from a variety of journals on science, mathematics, and more.
Ciencia.gov: Ciencia.Science.gov busca en más de 60 bases de datos y en más de 2200 sitios web de 15 agencias federales, ofreciendo 200 millones de páginas de información científica de gran autoridad de los E.E.U.U., incluyendo resultados de investigación y desarollo. Spanish language version of Science.gov.
CiteSeerX: CiteSeerx is an evolving scientific literature digital library and search engine that has focused primarily on the literature in computer and information science.
PLOS: "PLOS publishes a suite of influential Open Access journals across all areas of science and medicine."
Science.gov: Science.gov searches over 60 databases and over 2,200 scientific websites to provide users with access to more than 200 million pages of authoritative federal science information including research and development results.
United States Census Bureau: Explore data in multiple formats taken from current and past US Census records.
ERSys: "Using maps, charts, reports, and relevant links, Ersys covers over 2600 US cities with detailed information on demographics, environmental factors, economic indicators, housing stats, media (newspaper, television, and radio), schools, transportation, local contacts, and much more!"
Google Dataset Search: Search for free online datasets.
Pew Research Center: "Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research."