Open Access, is described in the Budapest Open Access Initiative as scholarly research that is given to the world without expectation of payment. "The only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited.”
Unpaywall
Read paywalled research papers for free.
Unpaywall is a browser add-on that will alert you when an online article is available free from the author. Click the green tab and skip the paywall. It's fast, free, and legal, powered by their database of millions of author-uploaded PDFs.
Unpaywall finds Open Access content in many ways, including using data from open indexes like Crossref and DOAJ where it exists. However, the majority of our Open Access content comes from independently monitoring over 50,000 unique online content hosting locations.