
Google Scholar
A freely accessible web search engine indexing the full text or metadata of scholarly literature across an array of publishing formats and disciplines.
Unpaywall finds free versions of paywalled research papers, legally.

Unpaywall is a browser extension and open database that provides free access to research papers that are usually behind paywalls. It works by automatically searching for open access versions of articles as you browse scholarly journals and databases. When Unpaywall finds a free version, it displays a prominent link, allowing users to access the paper without paying a subscription fee. The underlying technology relies on a comprehensive index of open access content harvested from legal sources worldwide. Unpaywall primarily targets researchers, students, librarians, and anyone who needs access to scientific literature but lacks institutional subscriptions. It helps overcome barriers to knowledge access and promotes wider dissemination of research findings.
Unpaywall is a browser extension and open database that provides free access to research papers that are usually behind paywalls.
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Unpaywall automatically detects when a user is viewing a paywalled article and searches its database for a free, legal alternative using the DOI.
Maintains a large and up-to-date database of open access articles harvested from thousands of legal sources.
Uses the DOI (Digital Object Identifier) of an article for precise matching with open access versions, ensuring accuracy.
Provides an API for programmatic access to the Unpaywall database, enabling integration into other research tools and platforms.
Only links to legal open access versions of articles, ensuring compliance with copyright laws and ethical research practices.
Install the Unpaywall browser extension for Chrome or Firefox from the Unpaywall website.
Browse any website hosting academic articles, such as journal pages or Google Scholar.
Unpaywall automatically checks for a free, legal version of the article.
A green tab appears on the right side of the browser window if a free version is found.
Click the green tab to directly access the open access version of the article.
If no free version is found, no tab appears, indicating the article is likely behind a paywall.
Use the Unpaywall API for programmatic access to open access data (requires registration).
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Verified feedback from other users.
"Unpaywall is generally well-received by researchers and students for its ease of use and ability to find free, legal versions of paywalled articles. Users appreciate the convenience and cost savings it provides."
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