NLM Style Guide: ReferenceTypes
NLM Citing Medicine Table of Contents
For detailed rules and various examples, use the Table of Contents https://www.ncbi.nlm.nih.gov/books/NBK7256/ to navigate to the appropriate type of reference.
Reference Types - Quick Guide
NLM : https://www.nlm.nih.gov/bsd/uniform_requirements.html
Details, including fuller citations and explanations, are in Citing Medicine. (Note Appendix F which covers how citations in MEDLINE/PubMed differ from the advice in Citing Medicine.) For datasets (Item 43 below) and software on the Internet (Item 44 below), simplified formats are also shown.
Reference Types
Cite as print or online source?
NLM's Citing Medicine recommends that you always cite the version that you saw.
If you read the article online, do not cite the article as if it were the print version.