General Search Help
Can I search a phrase?
To search for phrases, type the phrase in quotation marks. For example, type "health services research" in quotes in the search box.
Are Boolean searching and wildcards allowed?
The Boolean operators 'OR', 'NOT', '-', and '+' may be used in your query. Using 'AND' is not necessary. All words are searched by default.
The asterisk '*' can be used as a wildcard character.
| Boolean Term | Description |
|---|---|
| OR | Use 'OR' when you only need at least one of the search words to appear in the results. Example: "aspirin OR tylenol" |
| NOT or - | Use 'NOT' or '-' when you do not want a particular term to appear in the results. Examples: "heart defects NOT attack" or "heart defects -attack" |
| * | Use '*' as a wildcard to search on all words that contain the letters you enter. You must enter a minimum of three letters plus the '*' character. Example: "mammo*" would find "mammogram" or "mammography" or "mammoplasty" |
| + | Use '+' when you require the exact word to appear in all of the results. For multiple words, you must use put a + sign in front of each word that must be exact. Example: search on "+lipitor cholesterol" if you only want to retrieve results with the brand name "Lipitor" and the word "cholesterol", and no results with the generic synonym "Atorvastatin" |
What types of files are searched?
The search engine finds these file types:
- Web pages (.html, .htm)
- Adobe® Acrobat PDF (.pdf)
- Microsoft® PowerPoint (.ppt)
- Microsoft® Word (.doc)
- Plain text (.txt)
Will the search automatically expand my search words to include synonyms?
Yes, searches are expanded using a thesaurus. The thesaurus contains a list of synonyms from NLM's MeSH® (Medical Subject Headings) and other sources. When there is a match between a search term and a word in the thesaurus, the synonym(s) for that word are automatically added to the search.
For example, if you search for the word "journal", results are automatically retrieved for "serial" and "periodical" too.
If you search for "native american health", results are automatically retrieved for "american indian health" too.
Stemming: The search engine will also 'stem' your search words. Stemming removes suffixes such as '-ing,' '-ed,' '-en,' and 's.' For example, a search on "coughing" would also retrieve any results that include the word "cough". A search on "leg" would also retrieve results containing the term "legs".
Is the search case-sensitive?
No, the search engine is not case-sensitive. For example, a search on "MEDLINE" will also return pages containing "medline". A search on "aids" will also return pages containing "AIDS".
Will the search check my spelling?
Yes, the search engine checks your search words against all of the words collected from the web site. When a word appears to be misspelled, the search engine looks at all the words it knows and offers you a word that could replace it.
What about entering special characters, like ñ or ö?
The search engine does not require foreign language words to contain accented symbols, but you may enter them if you want to. For example, searching on "Albert Szent-Györgyi" and "Albert Szent-Gyorgyi" will both return the same results from the Profiles in Science site.
What do I do if I get a message saying no results found for the search?
There are a few reasons why you could have received this message:
- Your word may be misspelled and the search engine can't find a substitute for it.
- For example, if you had typed in "dyabeets" when you meant "diabetes", the search engine won't be able to recognize it.
- The kind of information you are looking for may not be available from the NLM web site search.
If you are looking for journal articles, try searching PubMed, NLM's bibliographic database of journal article citations and abstracts.
If you are looking for the title of a book or other materials in the Library's collections, try searching LocatorPlus Catalog, NLM's online catalog.
What if this FAQ doesn't answer my question?
If the Search Help does not answer your questions, contact Customer Service and we will do our best to assist you.
Searching the NLM Main Website
How does the search work?
The search box appears at the top of every page on the National Library of Medicine (NLM) Web site. The default display for NLM searches is a comprehensive list of 'All Results'. The results are displayed in order of relevance. They are retrieved from the Library's Web sites. The NLM search engine does not include content from NLM databases such as PubMed Central or Clinical Trials. However, the first three article citations from Pubmed related to your search will display in a search widget.
What links are included in the facets at the top?
The facets help you narrow your search. There are four facets:
- NLM Programs and Services includes biomedical information resources, publications, and outreach programs from the Library, the National Center for Biotechnology Information (NCBI), the Lister Hill National Center for Biomedical Communications, and Specialized Information Services (SIS).
- Health Information includes health information on diseases, conditions and drug information from MedlinePlus.
- Exhibits and Collections includes exhibitions from NLM's History of Medicine, manuscripts, photographs, audiotapes, and other materials from Profiles in Science, and digitized books and films from the Digital Collections.
What does the Search Web Archives button do?
Search phrases can be applied to NLM’s various web archive collections hosted by the Internet Archive. Clicking the Search Web Archives button will perform the same search using the search engine of the NLM’s Internet Archives collection repository and take you to its search results page. For more information see NLM Web Collecting and Archiving.
What is included in the search widgets on the right side?
The search spotlight displays different widgets depending on the search terms(s):
- "NLM Recommended Resources" highlights selected NLM products and services
- "MedlinePlus Health Information" highlights the most relevant MedlinePlus health topic
- "Most Recent PubMed Articles" highlights the first three article citations as returned by PubMed
Search for PubMed Identifiers (PMIDs), author names, journal title abbreviations, grant numbers, or other PubMed fields. Search tags may be included with the search term(s), but they are not necessary. For example, smith j and smith j [au] retrieve the same results, just as they would in PubMed.
Can I restrict my search to a certain site, like MedlinePlus?
The MedlinePlus site has pages on diseases and conditions that link to the Web sites of selected government agencies and health-related organizations. To search MedlinePlus and these links, too, use the MedlinePlus search.
To restrict your search to other NLM Web sites, add the word 'site:' and the domain or URL to your search words. For example, a search on "aids site:profiles.nlm.nih.gov" will return results on AIDS from the Profiles in Science site only.
Last Reviewed: June 10, 2021