Often called "LinkedIn for researchers," this platform allows authors to share their work. If the PDF isn't public, you can use the "Request full-text" button to ask the author directly.
Many universities use this service. You can navigate to libkey.io/[your-DOI] to see if your institution provides immediate access.
Search for the DOI directly. If a free PDF is available, a link will appear on the right side of the search results. download doi journal free
An essential browser extension that harvests Open Access content from over 50,000 publishers and repositories. When you visit a paywalled paper, a small green lock icon appears if a free version is available elsewhere.
A massive archive for papers in physics, mathematics, and computer science. Many researchers upload their work here before it even hits a journal. You can navigate to libkey
Unpaywall: An open database of 20 million free scholarly articles
Authors often upload "preprints" (versions of their papers before final formatting) to free databases. These are usually 100% legal to download. An essential browser extension that harvests Open Access
Many papers are legally available for free through "Open Access" (OA). These platforms allow you to input a DOI and find a legal, full-text version of the article.