paper-lookup

Use the NCBI E-utilities esearch endpoint with db=pubmed and your query term, then call esummary or efetch with the returned PMIDs to get titles, abstracts, and metadata. Without an API key you are limited to 3 requests per second.

Use PubMed for biomedical topics, arXiv for physics and CS preprints, OpenAlex or Semantic Scholar for cross-disciplinary search, and Crossref for DOI metadata. For open access PDFs, check Unpaywall or CORE after finding the paper.

Query the Unpaywall API with the paper's DOI and your email parameter. If is_oa is true, the best_oa_location.url_for_pdf field contains a direct link to a legal free copy, with oa_status indicating gold, green, hybrid, or bronze access.

No, the bioRxiv and medRxiv APIs only support date-range browsing and DOI lookup, with no keyword search. To search preprints by keyword, use Semantic Scholar, OpenAlex, or CORE, which index bioRxiv and medRxiv content.

Without an API key, Semantic Scholar uses a shared rate pool that frequently hits limits. Register for a free API key and pass it in the x-api-key header to get a dedicated 1 request per second allowance.

Use the PMC ID Converter API at pmc.ncbi.nlm.nih.gov/tools/idconv with the ids parameter. It accepts up to 200 comma-separated IDs and returns the corresponding PMID, PMCID, and DOI for articles present in PMC.