Unpaywall

Unpaywall is an open database with over 20 million free scholarly articles harvested from over 50,000 journals and open-access repositories around the globe. Sources for these articles include repositories run by renowned universities, governments, and scholarly societies. Unpaywall is integrated into thousands of existing search engines, library platforms, and information products, making articles easy to find, track, and use for your scholarly communication needs.

The Unpaywall database has a very simple structure: it has one record for each article with a Crossref DOI. It harvests from many sources to find Open Access content, and then matches this content to these DOIs using content fingerprints. So for any given DOI, we know about any OA versions that exist anywhere.

To fetch entries from Unpaywall indirectly through Crossref, choose Search → Web search, and the search interface will appear in the side pane. Select Crossref in the dropdown menu. To start a search, enter the words of your query, and press Enter or the Fetch button.

The results are displayed in the import inspection window. In case an error occurs, it is shown in a popup.