To narrow or broaden search results, try using Boolean searches. Boolean searching is a method of using search tools called operators that modify search results using keywords to broaden and narrow search results. 

The operators are:

• AND, which combines words together to narrow a search
• OR, which searches for one term or another to broaden a search
• NOT, which excludes words from a search to narrow it

The modifiers are:

• an asterisk *, which is placed at the end of a word stem and pulls results with the same stem and different endings to broaden a search
• parenthesis (), which are used with OR statements to specify that the results should only mention one of the keywords
• quotation marks " ", which will return the exact word or phrase searched with no variants

Read this library guide page on Boolean searches to learn more.