BASE is a search engine specifically for open access academic resources. It indexes over 400 million documents from more than 11,000 repositories and journals, including preprints, theses, and peer-reviewed articles. Unlike Google Scholar, which mixes freely available and paywalled content, BASE focuses exclusively on material that can be accessed without payment. You can filter by document type, language, year, and access rights.

The search interface is straightforward and the results include direct links to the full text where available. It's particularly useful for researchers who want to ensure their literature search is limited to open access sources, or for anyone who needs to find a freely available version of a paper that is paywalled elsewhere. Maintained by Bielefeld University Library in Germany.