Citoid: Add PMID to all citation objects with a DOI using PubMub API
completed by: ☃ unicodesnowman
See https://phabricator.wikimedia.org/T1088 for the corresponding bug report. In method addPMID() in the file lib/zotero.js, currently the PMID is extracted from the extra field in the citation object. However, the PMID is only found in the extra field when the metadata is being extracted from a link directly from http://www.ncbi.nlm.nih.gov/ , but not if a different URL to the paper is used, such as one on the publisher's website. If a citation object contains a DOI, you can use the DOI to look up the PMID and add that to the citation using the PubMed API: http://www.ncbi.nlm.nih.gov/pmc/tools/id-converter-api/
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