I wish sci-hub had a "donate paper" button. I've published things that are open access but the published obsfucate or make hard to find yet get SEO'd to the top of the rankings. I'd love to just upload a pdf, say, of a book chapter.
Edit: I added some additional info.
It mandates that within 1 year of journal publication the authors are to make the article available for download on pubmed...
"Before you sign a publication agreement or similar copyright transfer agreement, make sure that the agreement allows the paper to be posted to PubMed Central (PMC) in accordance with the NIH Public Access Policy. Final, peer-reviewed manuscripts must be submitted to the NIH Manuscript Submission System (NIHMS) upon acceptance for publication, and be made publicly available on PMC no later than 12 months after the official date of publication."