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When you use no quotation marks, tags, or asterisks, PubMed uses Automatic Term Mapping feature to search for (in this order)
As soon as a match is found, PubMed searching stops. If no match is found, PubMed breaks apart the phrase and repeats the process until a match is found. Phrases and search words are searched in All Fields.
Search hedges are standardized search strings designed to comprehensively search on a concept. Other names are search filters, canned searches, clinical queries, or optimal search strategies. They are specific to a database and are not interchangeable to other databases. They are sometimes published and shared.
Below are some short search hedges for the PubMed database developed by different librarians to find human subjects/patients or to limit to a particular age group. But some can be very long and complex. And notice that there is not only one way to search.
PubMed, a free service of the National Library of Medicine, provides access to over 30 million citations for biomedical literature from health and life science journals, and online books via interface access to many individual life science databases and websites, including MEDLINE.
The PubMed search system defaults to the PubMed database of bibliographic information, which is drawn primarily from MEDLINE and PREMEDLINE. The MEDLINE file contains bibliographic citations and author abstracts from approximately 3,900 current biomedical journals published in the United States and 70 foreign countries. The PREMEDLINE database includes basic citation information and abstracts created prior to the full, completed records are prepared and added to MEDLINE. New records are added to PREMEDLINE daily.
In addition, for participating journals that are indexed selectively for MEDLINE, PubMed includes all article records from that journal, not only those that are included in MEDLINE content. Finally, PubMed is part of the NCBI's Entrez system which provides access to many microbiology databases. Coverage extends from 1966 to now. Selected content goes back to 1781.
Citations may include links to full-text content from PubMed Central and publisher web sites. If a publisher has a website that offers full text of its journals, PubMed provides links to that site.
The National Center for Biotechnology Information (NCBI) provides analysis and retrieval resources that include the GeneBank, Entrez, MyNCBI, PubMed, Entrez Gene, BLAST, BLAST Link (BLink), Electronic PCR, UniGene, HomoloGene, ProtEST, Cancer Chromosomes, Entrez Genomes, among many others.
PubMed includes over 26 million citations for biomedical literature from MEDLINE, life science journals, and online books. PubMed citations and abstracts include the fields of biomedicine and health, covering portions of the life sciences, behavioral sciences, chemical sciences, and bioengineering. Select full-text is available via PubMed Central.