Unpaywall consists of a database that includes a list of almost 20 million freely available scholarly articles. Most researchers access it using a browser plug-in that was released in 2017. The service works by searching for a queried paper’s unique digital tag — a string of numbers and letters known as its DOI, or digital object identifier — against those of articles gathered from 50,000 journals and repositories.

• Listing ID: 57559
• Access Url: https://unpaywall.org/
• Related Subject: Miscellaneous

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