PubMed / PubMed Central (PMC)
PubMed is the reference index for biomedical research, covering journal articles across medicine, nursing, life sciences, and related fields. Each record holds a citation, an abstract where available, and structured tags from the Medical Subject Headings (MeSH) vocabulary, which is useful for filtering a corpus by topic.
PubMed Central (PMC) is the companion archive that stores free full-text articles rather than just citations. Its Open Access subset is the part you can redistribute and process at scale, making it a common base for biomedical RAG systems.
Both are run by the National Library of Medicine, part of the US National Institutes of Health. You can pull records in bulk over FTP as XML. Citation metadata is public domain, but full-text article licences vary, so check the terms on each article in the Open Access subset before reuse.
Related sources
arXiv
An open-access preprint server for physics, mathematics, computer science, quantitative biology, statistics, and more, holding over 2.5 million papers. You can pull the full archive in bulk from Amazon S3, or harvest the metadata through OAI-PMH, a standard protocol for sharing records between repositories.
CORE
An aggregator of open-access research papers that harvests from thousands of repositories and journals worldwide. It holds over 300 million metadata records and more than 40 million full-text articles, all reachable through one search API.
Crossref
A nonprofit DOI registration agency that publishes metadata for over 150 million scholarly works, including journal articles, books, and conference proceedings. A DOI is the permanent identifier assigned to each work, and Crossref shares its metadata through a free API.
OpenAlex
A free, open catalogue of the world's scholarly works, authors, venues, institutions, and research topics. It succeeds Microsoft Academic Graph and holds hundreds of millions of works with rich metadata and citation links.