Pubmed

https://www.ncbi.nlm.nih.gov/pmc/tools/get-metadata/

https://www.ncbi.nlm.nih.gov/pmc/tools/developers/#use-cases

Get article metadata

This E-Summary call retrieves article metadata for a PMCID:

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esummary.fcgi?db=pmc&id=3539452&retmode=json

The returned data includes the PubMed ID (PMID) for this article, so you can do a further call to get PubMed metadata for the same article:

https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esummary.fcgi?db=pubmed&id=22368089&retmode=json