References from several of the below mentioned databases are included in our Catalogue. When searching in All Content refine your results on the left site by collection, for example Hathitrust, PubMed Central, DOAJ, Project Gutenberg, or any collection with Repository in its name.

• Scholarly Publications provides access to scientific output of Leiden University.

• OpenAIRE (Europe) provides access to more than 8.000.000 of Open Access publications from 460+ data providers from 38 Eurean countires, with links to funding, datasets and more.

• Digital Commons Network (USA) provides access to almost 800.000 scientific publications from over 300 (mainly US) academic institutions.

• Oaister (worldwide) provides access to over 30 million records found by harvesting over 700 repositories and open access collections worldwide. It is integrated in WorldCat, but also available as separate catalogue.

• openDOAR (worldwide) is an authoritative directory of academic open access repositories worldwide. OpenDOAR lets you search for repositories or search repository contents. It uses Google Custom Search Engine to offer full-text search of repositories listed in OpenDOAR.

• Registry of Open Access Repositories (worldwide): similiar to openDOAR, it gives access to repositories worldwide and lets you search for repositories or search repository contents with Google Custom Search Engine, but, in contrast to openDOAR, it is filled automatically.

• ArXiv (worldwide, Beta Sciences) is an openly accessible, moderated repository for scholarly papers in the disciplines of Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics. It is owned and operated by Cornell University.

• PubMed Central Open Access Subset is a part of the complete collection of medical articles in PMC.

• Highwire Press, the online journal-production division of the Stanford University Libraries, provides free access to almost 2 million articles from different publishers.

• JSTOR Register & Read is a new, experimental program which offers free, read-online access to individual scholars and researchers who register for a MyJSTOR account. Includes approximately 1,200 journals from more than 700 publishers, a subset of the content in JSTOR.

• The Directory of Open Access Journals (DOAJ) contains almost 10.000 OA journals in many languages. More than half of these journals are searchable at article level. Contains a.o. the following collections: PLoS One, BMJ Open, SAGE Open, AIP Advances, Open Biology and BioMed Central (BMC) journals

• The Directory of Open Access Scholarly Resources (ROAD) gives access to a subset of the ISSN Register, which describes scholarly resources in Open Access which have been assigned an ISSN: journals, conference proceedings and academic repositories. ROAD is offered by the ISSN International Centre with the support of the Communication and Information Sector of UNESCO.

• Scientific Electronic Library Online (SciELO) is an electronic library covering a selected collection of Brazilian scientific journals

• Elektronische Zeitschriftenbibliothek (EZB) provides a world wide overview of (free) e-journals. With a large number of search options.

• Directory of Open Access Books (DOAB) is a discovery service for peer reviewed books published under an Open Access license. DOAB enables you to search the description of the books, not the full-text content, and gives links to the publications'full texts at the publisher’s website or repository. It is a service from the OAPEN Foundation.

• OAPEN Library contains the full text to many peer reviewed OA books. It enables you to search both the full-text contents and the description of the books The OAPEN Library and DOAB are both services provided by the OAPEN Foundation.

• Project Gutenberg contains almost half a million free e-books.

• Gallica is a digital library from the Bibliothèque Nacionale de France, which provides free access to millions of monographs, periodicals, manuscripts, sound recordings and other materials.

• Google BookSearch is a large, for the most part full text searchable, database with millions of scanned books from libraries or directly from publishers. In advanced search, you can select: search full view only.

• Hathi Trust is a partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world. Click 'advanced search' to search by format (book, serial, audio, etc.). Be sure to select "full view only" to find open access resources.

• Online Books Page is a website that facilitates access to over one million books that are freely readable over the Internet. It is hosted by the University of Pennsylvania Libraries.

• Internet Archive Text Archive contains more than 5 million books that are freely available. At the archive's site OpenLibrary you will find a friendly user interface to the published books and links to other online book collections.

• Internet Archive is a giant non-profit internet library which offers permanent access to historical collections that exist in digital format.

• Universal Digital Library is a project initiated by Carnegie Mellon University, and previously known as the Million Book Project. The objective of this project is to transfer all books into digital format, in partnerships with other scanning centers internationally, in order to create a Universal Digital Library (UDL) which fosters creativity and free access to human knowledge.

• BASE is one of the largest search engines especially for academic open access web resources. Operated by Bielefeld University Library. Filter option after search by Open Access.

• CORE is an experimental service, smaller then BASE, but with more advanced discovery tools. Key feature: if you find an article you like, CORE will find similar ones by analysing the text of that article.

• Google Scholar is a is web-based scholarly search engine. To find freely available articles, enter fyletype:pdf behind your search query.

There are more and more useful browser extensions that allow open access publications to be found. These extensions look automatically for open access copies of paywalled research articles and bring you with one click to their full text. Below you will find two widely used extensions that are free and simple to install and use.

Unpaywall: an extension for Google Chrome and Firefox that searches several large open access databases.

Open Access Button: an extension for Google Chrome, Firefox, Internet Explorer and Safari. It also searches several large open access databases, besides it sends a request to the author to open up an article that can't be found for free in any other way.