If a concept consisting of more than one term is entered into PubMed, it will be searched for in the phrase index. If it is not found, the program will use Automatic Term Mapping to process the search. Each term in the phrase will be searched in all fields and combined, often resulting in some off-target records. To focus the search specifically on the concept, it is possible to search for a phrase in PubMed using quotation marks, e.g. “kidney allograft.” Automatic Term Mapping will be bypassed and the exact phrase will be searched for in all fields. The retrieval will have fewer off-target records.
To access the indexed phrases, use the Advanced search builder show index list. After selecting a search field, (Text Word [tw] is recommended for subject searches), enter the beginning of a phrase and then click Show index list.