You may use quotation marks:
" Double quotes around a phrase, matches only conceptions containing the complete phrase. For example: "mental mode" is different than just: mental model
You may also use a full set of boolean operators:
Place a + in front of a word to require it, - to exclude it
~ A leading tilde marks a word as less important. It's useful for marking noise words.
* An asterisk acts like a wildcard. Unlike the others it is placed AFTER the word and not before it.
( ) Parentheses are put around sub-expressions to give them higher precedence in the search.
For example you can search for:
- mental model
- "mental model"
- +mental -model
- (mental model) rhetoric