NLK
Directory of Open Access Journals
from 1972
Free Medical Journals
from 1972
PubMed Central
from 1972
Europe PubMed Central
from 1972
Open Access Digital Library
from 1972-01-01
Open Access Digital Library
from 1972-01-01
ROAD: Directory of Open Access Scholarly Resources
from 1972
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AND or + signifies AND operation (intersection)
OR or | signifies OR operation (union)
- negates a single word
" wraps text to signify a phrase
* at the end of a term signifies a right-side expansion
( and ) signify precedence
~N after a word signifies edit distance (fuzziness)
~N after a phrase signifies words distance