Searching in the library's resources depends on the keywords - or search terms - you use. Instead of searching for a whole question or sentence, break your topic into keywords. Mix and match different combinations of keywords to get different results when searching. Also, think of similar or related terms you can search for.
Research question: How do community policing techniques affect crime rates in urban areas?
Possible keyword combinations:
Mix and match different keywords to find different articles.
Watch this video for more help on brainstorming keywords: