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PolyU Library

Conduct a Literature Review

A guide to walk you through the process of doing a literature review

More Searching Tips

Here are some quick tips when you got too many or too few results. 

Too many results? Too few results?
  • Add extra search terms and combine them with AND operator. AND narrows your search.
  • Use more specific search terms, especially for terms that have different meanings in different disciplines/contexts, e.g. use "computing architecture" instead of "architecture".
  • Specify the search field, e.g. search within "Title", "Subject".
  • Use exact phrase search, i.e. add quotation marks " " around your search terms
  • Use filters to refine your search results, e.g. peer-reviewed journals, publication year range
  • Add synonyms or alternative search terms and combine them with OR operator. OR broadens your search.
  • Use truncations or wildcards, e.g. transmit* finds transmit, transmitted, transmission, etc.
  • Other than keyword searching, also perform subject heading searching, e.g. search MeSH, indexing terms in the database.
  • Use citation chaining to explore related articles

Still confused? Learn more details about searching techniques below. 

Do note that you do not need to use all of these techniques in every search you perform. However, understanding how they work can definitely help you better manage your search.

Boolean operators allow you to include multiple words and concepts in your searches. AND, OR, NOT are the most commonly used Boolean operators. Move your cursor over the Boolean operators to see how each one works!

  • AND
  • OR
  • NOT

Move your cursor over the Boolean operators to see how each one works.

AND combines search terms so that each result contains all of the terms. E.g. "youth AND drug" finds articles that contain both youth and drug.

OR combines search terms so that each result contains at least one of the terms. It is often used to connect synonyms or similar concepts. E.g. "youth OR teenager" finds articles that contain either youth or teenager or both.

NOT excludes terms so that each result does not contain the term. E.g. "drug NOT alcohol" finds articles that contain drug but exclude alcohol.

(Adapted from The Boolean Machine, by Rockwell Schrock)

Search Order of Boolean Operators

  • NOT AND > OR  (in most databases, including OneSearch) 
  • Use parentheses () if you need to override the order. 


  • youth OR teenager AND drug finds articles that contain either youth (only), or teenager and drug (both words are present);
  • (youth OR teenager) AND drug finds articles that contain either youth and drug (both words are present) or teenager and drug (both words are present).

Truncations (*) and wildcards (?, #) are used to include different spellings therefore broadens your search.


  • comput* searches computer, computers, computing
  • colo?r searches color, colour

Truncation and wildcard symbols may vary by database. Check the Help page in the database to learn the symbols and operators that database supports. (or, google database name + "operator" to locate the search help page directly).

Phrase search is used to search the specific expression or concepts. Usually quotation marks "" are used to search the exact phrase. Phrase search narrows your search.


  • "knowledge sharing" searches only the phrase "knowledge sharing" and will NOT search knowledge creation and sharing (additional words in between) or knowledge shared

In some databases, quotation marks cannot be used with truncation or wildcards. e.g.: "knowledge shar*". Do check the Help page in the database to learn the symbols and operators that database supports.

Keyword searching Subject Heading searching

Keywords are natural language words or phrases that describe the search topic.

Keyword searching looks for the keywords in any field of the record (if not specified).

Subject headings are a group of "controlled vocabularies" that describe the content of each item. These controlled vocabularies are usually given by subject specialists or indexers.

Subject heading searching looks for the subject heading terms in the subject heading field (e.g. Subject, Subject Terms) of the record.

Commonly used subject headings include  MeSH and Emtree, both are used to search biomedical literature.


  • Subject heading searching helps you find articles by "meaning".
    e.g. search "knowledge management" by Subject returns results that may not contain the phrase "knowledge management" but discuss organizational learning (which is a related subject to knowledge management).
  • Some databases can recommend subject headings when you do a keyword searching. After that you may select appropriate subject headings to search again.
    e.g. EBSCOhost uses "Suggest Subject Terms".