Automatic Term Mapping
When you use no quotation marks, tags or asterisks, PubMed uses an Automatic Term Mapping feature to search for:
- Subjects (using the Medical Subject Headings)
- Journals and
in that order.
As soon as PubMed finds a match, the mapping stops. That is, if a term matches a subject, PubMed does not continue to look for that term as a journal.
If no match is found, PubMed breaks apart the phrase and repeats the process until a match is found.
The phrases and individual terms are also searched in All Fields.
You can see this process at work by looking at your Search details.