Apparently PubMed Central, which has a very large repository of articles (millions), costs about US$ 3 million per year to provide free-to-user access. They onl

Apparently PubMed Central, which has a very large repository of articles (millions), costs about US$ 3 million per year to provide free-to-user access. They only provide what publishers allow, however. https://www.ncbi.nlm.nih.gov/pmc/about/faq/ https://www.ncbi.nlm.nih.gov/pmc/about/faq/