According to SPARC (the Scholarly Publishing and Academic Resources Coalition), "Open Access is the free, immediate, online availability of research articles coupled with the rights to use these articles fully in the digital environment. Open Access ensures that anyone can access and use these results—to turn ideas into industries and breakthroughs into better lives."
Here is a great article that goes into more detail: "What Is "Open Access"?"
Unpaywall is a Google Chrome web browser extension available for free at http://unpaywall.org/products/extension.
How it works
When a user lands on a paywall-blocked scholarly resource's webpage, if there's an open access version available somewhere else on the web for free that Unpaywall has previously located, a neon green icon will light up on the right side of the user's screen. Click on it, and you will be redirected to the freely available version of it! This is a legal and legitimate way to find scholarly content if you are performing open web searching (e.g. Google Scholar).
Open Access Button allows users to avoid paywalls and request research to get free, legal research articles delivered instantly. If the article isn't located for you in an OA repository, it will give you a hyperlink to request the article for free from the author(s). (You can see which aggregated repositories they pull their resources from at: https://openaccessbutton.org/about.)
How can I use it?
To learn more about the creators of Open Access Button supported by SPARC, check out this: https://sparcopen.org/our-work/innovator/open-access-button/.
ClinicalTrials.gov is a database of privately and publicly funded clinical studies conducted around the world. from the National Institues of Health > U.S. National Library of Medicine.
Digital Commons Network [Highly recommended] brings together free, full-text scholarly articles from hundreds of universities and colleges worldwide. Curated by university librarians and their supporting institutions, the Network includes a growing collection of peer-reviewed journal articles, book chapters, dissertations, working papers, conference proceedings, and other original scholarly work. See a video demo on the left side of this LibGuide for this database.
Directory of Open Access Repositories: OpenDOAR is the quality-assured global directory of academic open access repositories. It enables the identification, browsing and search for repositories, based on a range of features, such as location, software or type of material held.
DOAJ (Directory of Open Access Journals) is an online directory that indexes and provides access to high quality, open access, peer-reviewed journals. It was launched in 2003 at Lund University, Sweden, with 300 open access journals and today contains more than 12,000 open access journals covering all areas of science, technology, medicine, social science and humanities.
Google News Archive Search provides an easy way to search and explore historical archives for events, people, or ideas. Newspapers are alphabetized, and show the date range they cover, and number of issues available.
Paperity: The first multidisciplinary aggregator of Open Access journals and papers. Keep on top of recent discoveries and never hit a paywall with over 2.5 million papers and over 8,000 journals.
Public Library of Science (PLoS) is a nonprofit publisher, innovator and advocacy organization with 215,000+ peer-reviewed articles free to access, reuse and redistribute. Topical searches are available in: Biology, Computational Biology, Neglected Tropical Diseases, Medicine, Genetics, & Pathogens.
PubMed from the U.S. National Library of Medicine (NLM) within the National Institutes of Health, comprises more than 29 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites.
SpringerOpen's portfolio has grown tremendously since its launch in 2010, and it now offers researchers from all areas of science, technology, medicine, the humanities and social sciences a place to publish open access in journals and books. Publishing with SpringerOpen makes your work freely available online for everyone, immediately upon publication, and our high-level peer-review and production processes guarantee the quality and reliability of the work.
Taylor & Francis Open publishes high quality, rigorously peer-reviewed open access (OA) research across all disciplines.
Treesearch allow users to search for scientific articles written or published by the U.S. Forest Service, departmental child to the U.S. Department of Agriculture. Some resources are full-text, but many are bibliographic.
"There is an imminent danger of all new knowledge getting locked up and released into the public domain only when the middlemen publishers get rich enough. Released only when the knowledge itself is reasonably old and loose [sic] their cutting edge, especially for the economically tender third world." (Narasimhan, 2012).
There is a broad argument to be made, and that is already being made by many respected librarians, scientists, scholars, and researchers, that opening access to research is a moral imperative for humankind, and that urgency is compounded for those without the advantages of information privilege, which is "the idea that the information that one has access to is largely dependent on one’s status, affiliation, or power. " (Harmon, 2018)
Appedu, Sarah. (2018). Open access, social justice, and the moral imperative: Why OA publishing matters to WGS [PDF document]. Retrieved from https://cupola.gettysburg.edu/cgi/viewcontent.cgi?article=1100&context=librarypubs.
Harmon, Ian. (2018). Reflections on Information Privilege. Retrieved from https://hacklibraryschool.com/2018/05/08/reflections-on-information-privilege/.
Narasimhan, Arunn. (2012). Myths of and urgency for open access journals. Retrieved from https://home.iitm.ac.in/arunn/myths-of-and-urgency-for-open-access-journals.html.
SPARC. (n.d.). Open Access. Retrieved from https://sparcopen.org/open-access/.