A Digital Object Identifier (DOI) is a unique string of letters and numbers assigned to articles or documents to provide a persistent link to it's location on the web. These codes are registered by the International DOI Foundation, who assigns them to works from participating publishers.
Each DOI is made up of two parts, a prefix and a suffix separated by a forward slash. Every DOI prefix begins with the number 10 followed by a series of four or more numbers assigned to a particular organization. The suffix will be a mix of numbers and letters assigned by the publisher.
Adding https://doi.org/ to the beginning of a DOI provides a direct link to access the article.
DOI Examples:
10.1080/10304312.2019.1567685
10.1080/07491409.2004.10162472
A PubMed Identifier (PMID) is a unique numerical identifier assigned by the NIH National Library of Medicine for biomedical literature indexed in PubMed. PubMed is a free resource containing citations and abstracts that links to full-text articles when available through PubMed Central (PMC).
The PMID should be a 1-8 digit number and can be found at the end of a citation in PubMed.
PMID Examples:
36377759
30203088