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Search Help

How does the search work?

The search box appears at the top of every page on the National Library of Medicine (NLM) Web site.

To search the Web site, type a word or phrase into the search box. Click the 'Go' button, or press the 'Enter' key on your keyboard. The results page shows your first 10 matches. If your search yields more than 10 results, click on the ‘Next’ or page number links at the bottom of the page to view more.

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 including:

The NLM search engine does not include content NLM databases such as PubMed or Clinical Trials.

You may filter your search on one part of the site by navigating to an individual collection of results such as 'NLM Programs and Services' and 'Health Information – MedlinePlus'. For more information about the different collections, see What do the links under 'All Results' mean in the 'Refine by Type' box?

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What do the links under 'All Results' mean in the 'Refine by Type' box?

Your initial search results show matches from the Library’s Web sites. The links in the 'Refine by Type' box under 'All Results' represent sets of content, known as collections. The collections help you narrow your search by displaying results exclusively from one collection. For example, you can limit your search results to the news releases by clicking the ‘News and Announcements’ link in the 'Refine by Type' box.

There are nine collections:

  • The NLM Databases collection includes home pages for NLM databases such as PubMed, MedlinePlus, Pillbox, Profiles in Science, ToxMap, and Clinical Trials.
  • The NLM Programs and Services collection includes biomedical information resources, research activities, 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).
  • The Health Information – MedlinePlus collection includes health information on diseases, conditions and drug information from MedlinePlus.
  • The News and Announcements collection includes NLM news and press releases as well as NIH clinical alerts and advisories.
  • The FAQs and Factsheets collection includes Frequently Asked Questions (FAQs) and Factsheets about NLM’s programs and services.
  • The Newsletters and Publications collection includes NLM in Focus, the NLM Technical Bulletin, NCBI News, Citing Medicine, A History of the National Library of Medicine and other publications.
  • The Reports and Plans collection includes NLM’s Annual Reports, Board of Regents Minutes, the Long Range Plans as well as other reports and plans.
  • The Exhibits and Digital Collections collection 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 Repository.
  • The NLM Web Archives includes documents stored in the National Library of Medicine Web Archives. All pages in the archives are considered to be of permanent value. For more information see About the NLM Archives.

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What do the links in the 'Refine by Keyword' box mean?

The ‘Refine by Keyword’ box organizes your search results into clustered groups based on the most frequent words in the top 200 results. For example, a search on "PubMed" might return a cluster of documents that contain the phrase "Working with Search Results". Clustering helps you narrow down a large set of results quickly to find what you're looking for.

If there is a plus sign (plus sign) next to a cluster, click on it to view smaller clusters.

If there is a vertical line separating two or more clusters, they have the same number of matches for each term. For example, a search on "PubMed" might return a cluster labeled: Genome | Structure (11).

Click 'remix' to see additional clusters.

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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.

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Are Boolean searching and wildcards allowed?

These Boolean operators are available to you: OR, NOT, -, +

The asterisk '*' can be used as a wildcard character.

Note: Using AND is not necessary. All words are searched by default.

Boolean TermDescription
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"

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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.

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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)

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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".

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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".

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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.

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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.

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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, NLM's online catalog.

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What does the infinity symbol next to a search result mean?

The symbol next to a search result is an infinity symbol, and appears for all documents that NLM has assigned permanence ratings and other metadata. Click on the infinity symbol to view the permanence information for that document. Permanence information includes: title, URL, date last updated, date first published, permanence level, and a link to all of the metadata for the document. Click 'Permanence level' to see the definitions of NLM's four permanence levels. NLM uses permanence levels to indicate which NLM Web documents can change and which will remain permanently available. For more information, please see Developing Permanence Levels and the Archives for NLM's Permanent Web Documents.

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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.

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