Online Library

Library

• Curriki
• Digital Health Resources Library (The Digital Medicine Society (DiMe) collaborated with the Clinical and Translational Science Institute (CTSI) and Center for Health + Technology (CHeT) at the University of Rochester, to create a crowdsourced library of what the community has found to be the most valuable and useful resources in digital health.)

• Internet Archive
  Internet Archive is a non-profit library that contains millions of free books, movies, software, music, websites, and other resources.

• Library Genesis (This fantastic digital shadow library, also known as libgen, gives you free access to millions of your favorite books and papers in epub, pdf, mobi, and many other formats as eBooks, from romance to science fiction, and everything in between. It includes textbooks and journal articles, academic works, graphic novels, and comics.)
• National Library of Medicine (Digital Collections provides access to the National Library of Medicine's distinctive digital content in the areas of biomedicine, health care and the history of medicine. Our unique digital collections are freely available for download worldwide and in the public domain unless otherwise indicated.)
• Open Library (Open Library is a non-profit project of the Internet Archive that has been funded in part by grants from the California State Library and the Kahle/Austin Foundation. Open Library is an open project: the software is open, the data is open, the documentation is open, and we welcome your contributions.)

• Open Access Library

Open Access Library (OALib) consists of:
• the Search Engine, based on a database with metadata of Open Access (OA) papers
• the Journal with OALib Articles,
• the Index with metadata entries of external OA journal articles,
• the Repository with own OALib PrePrints as well as external preprints and postprints, all stored in one of the 322 OALib Disciplinary Repositories.

OALib currently hosts links and metadata for over 5,706,041 open-access articles from a variety of academic disciplines. You can download all full-text articles from your search results for free.

• Project Gutenberg
  Project Gutenberg is a free eBook library with over 60,000 free eBooks. Choose from free epub and Kindle eBooks to download or read online. The world's great literature can be found here, with a focus on older works whose U.S. copyright has expired. Thousands of volunteers digitized and proofread the eBooks for your enjoyment.

• The National Science Digital Library
• The Free Library
• The Cochrane Library is a collection of databases that contain different types of high-quality, independent evidence used by healthcare decision-makers to make informed decisions.
• The OER Commons is a public digital library of open educational resources. Explore, create, and collaborate with educators around the world to improve curriculum.

Database

• arXiv e-Print Archive
  The arXiv e-Print Archive, which is run by Cornell University Library and curated by volunteer moderators, now provides open access to over one million e-prints.
  The database includes advisory committees for all eight subjects. The arXiv e-Print Archive is an excellent STEM resource, with a stated commitment to a "emphasis on openness, collaboration, and scholarship."

• Bielefeld Academic Search Engine
  The Bielefeld Academic Search Engine (BASE) is run by the Bielefeld University Library in Germany and contains over 240 million documents from over 8,000 sources. Sixty percent of its content is open access, and you can narrow your search results accordingly.

• BioMed Central
  BioMed Central offers open access research from over 300 peer-reviewed journals. While initially focused on physical sciences, math, and engineering resources, BioMed Central has expanded to include journals from a broader range of disciplines, with the goal of providing a single platform with OA articles for a variety of research needs. These journals can be browsed by subject or title, or you can search all articles for a specific keyword.

• CORE
  CORE is a multidisciplinary OA research aggregator. CORE has the most comprehensive collection of OA articles available. It allows users to search over 219 million open-access articles. While the majority of these point to the full-text article on the original publisher's website or to a PDF that can be downloaded, five million are hosted directly on CORE.

• CIA World Factbook
  The CIA World Factbook differs from the other resources on this list in that it is not a journal directory or repository online. It is, however, a useful free online research database for academics across the board.

• Directory of Open Access Journals
  The Directory of Open Access Journals (DOAJ), a multidisciplinary, community-curated directory, provides researchers with access to high-quality peer-reviewed journals. It has over two million articles from 17,193 journals archived, and you can browse by subject or search by keyword.

• Digital Library of the Commons Repository
  The Digital Library of the Commons (DLC) Repository, managed by Indiana University, is a multidisciplinary journal repository that allows users to access thousands of free and open access (OA) articles from around the world. You can browse by document type, date, author, title, and more, or search for keywords related to your topic.

• dblp Computer Science Bibliography
  The dblp Computer Science Bibliography is an online index of major publications in computer science. dblp was founded in 1993, but it was a university-specific database at the University of Trier in Germany until 2010. The Schloss Dagstuhl - Leibniz Center for Informatics currently maintains it.

• Dryad
  Dryad is an open-access digital repository of curated scientific research data. It was founded in 2009 and is run by a non-profit membership organization with a community of institutional and publisher members for whom their services are tailored. Members include Stanford, UCLA, and Yale, as well as publishers such as Oxford University Press and Wiley.

• Education Resources Information Center
  The Institution of Education Sciences' Education Resources Information Center (ERIC) allows you to search for educational resources by topic. Links take you to other websites where you may have to pay for the information, but you can only search for full-text articles. You can also limit your search to only peer-reviewed sources.

• EconBiz
  EconBiz is an excellent resource for economic and business research. It is a service of the Leibniz Information Centre for Economics that provides online access to full texts with the option of searching only for OA material. Their literature search includes multiple international databases.

• EThOS
  The E-Theses Online Service (EThOS), operated by the British Library, allows you to search over 500,000 doctoral theses in a variety of disciplines. All of the doctoral theses available on EThOS have been awarded by UK higher education institutions.

• Google Scholar allows you to search scholarly literature across many disciplines and sources from a variety of databases.

• JURN
  JURN, a multidisciplinary search engine, provides links to scholarly websites, articles, and journals that are open access (OA). JURN has indexed nearly 5,000 repositories in the arts, humanities, business, law, nature, science, and medicine to help you find exactly what you're looking for.

• MEDLINE primarily contains citations from journals with articles that are indexed with MeSH (Medical Subject Headings).

• OpenDOAR
  The Directory of Open Access Repositories, or OpenDOAR, is a comprehensive resource for finding free OA journals and articles. Using Google Custom Search, OpenDOAR searches OA repositories all over the world for relevant research in all disciplines.

• PubMed Central (PMC) contains full-text articles from journals that have been selected by NLM for archiving. 

• Public Library of Science
  PLOS (Public Library of Science) is a major player in the world of open-access science. The nonprofit organization is dedicated to promoting openness in academic research by publishing 12 open-access journals. "All PLOS content is at the highest possible level of OA," according to the website, "meaning that scientific articles are immediately and freely available to anyone, anywhere."

• Paperity
  Paperity claims to be the "first multidisciplinary aggregator of open access journals and papers." Their primary goal is to assist you in avoiding paywalls while connecting you to authoritative research. Paperity seeks to help authors reach their audiences and journals increase their exposure to boost readership, in addition to providing readers with easy access to thousands of journals.

• ScienceOpen
  ScienceOpen, which operates as a research and publishing network, provides open access to over 74 million articles in all fields of science. Although registration is required to view the full text of articles, registration is free. The advanced search function is extremely detailed, allowing you to find precisely what you're looking for.
• ScienceDirect is a medical search engine that allows you to find articles from medical journals.
• Scopus is an abstract and citation database.

• Science Huβ
  ScienceHuβ is a global science and technology publisher that offers free access to research articles and the most recent research information to the scientific community.

• Semantic Scholar
  Semantic Scholar, a one-of-a-kind and user-friendly resource, describes itself not only as a research database but also as a "search and discovery tool." Semantic Scholar uses artificial intelligence to sort through millions of science-related papers based on your search terms.

• Social Science Research Network
  The Social Science Research Network (SSRN) is a repository for papers in the social sciences. It is a highly interdisciplinary platform for searching for scholarly articles on 67 different social science topics. SSRN has a number of research networks for the various topics covered by the free scholarly database.

• Traditional Chinese Medicine Dadabase@Taiwan
  TCM Database@Taiwan: The World's Largest Traditional Chinese Medicine Database for Drug Screening In Silico. The Databases aim to bridge the East-West divide of drug discovery.

• Zenodo
  Zenodo was launched in 2013 and is powered by the European Organization for Nuclear Research (CERN). Zenodo, named after Zenodotus, the first librarian of Alexandria's ancient library, is a tool "built and developed by researchers to ensure that everyone can participate in open science." Zenodo accepts research in any file format from any discipline.

Others

• AI Computing Answers_Wolfram Alpha
• Bookshelf is an archive of books and reports within the biomedical and life sciences field.
• Encyclopedia Britannica
• Find Articles
• Google Books has more than 10 million free books available for users to read and download. Google's free books are made available to read through careful consideration of and respect for copyright law globally: they are public-domain works, made free on request of the copyright owner, or copyright-free, e.g. US government documents.

• OpenStax
  OpenStax creates high-quality, peer-reviewed, openly licensed college textbooks that are free online and inexpensive in print.

• Pubmed is the most popular and free-to-use medical search engine. It allows you to search for biomedical and life sciences literature, and also covers related fields such as bioengineering, behavioral sciences, and chemical sciences.

• The Free eBook
  Discover 1000's of New Authors in Hundreds of Categories
  Fiction and Non-Fiction --- Free Every Month!

• The Traditional Chinese Medicine Resource Platform has online resources on traditional Chinese medicine. It provides multiple resources and valuable reference documents for the traditional Chinese medicine industry and related industries, including electronic pharmacopeia, traditional Chinese medicine-related databases, scientific data resource search, traditional Chinese medicine policies and regulations, and pharmaceutical production quality management documents (GMP SOP) and registration requirements for proprietary Chinese medicines, etc.