The NLM Technical Bulletin recently released a Skill Kit for searching for phrases in PubMed®. The Skill Kit outlines the following steps:
1. Search the phrase first without quotes or search tags.
2. Check Search details to see how the search was translated.
3. Use quotes only when Search details indicate your phrase is broken apart.
Most often, phrases entered without quotation marks will be searched as phrases in all fields, as well as being subjected to Automatic Term Mapping . However, sometimes even quotes won’t work because not all phrases are recognized as phrases.