By default, semantic search automatically expands your keywords to similar words (searching for ai will also include results containg artificial intelligence as well as machine learning for instance). To disable keyword expansion and revert to classic (strict) search, use double quotes ("ai").
The operator AND can be used for conjunction: green AND carbon only retrieves documents containing both words in any order.
To also include documents containing either word, use green OR carbon.
To exclude one term from the results, you can you the - (NOT) operator : green -carbon (projects containing "green" but not "carbon").
You can also search for an exact expression using double quotes: "artificial intelligence" only returns results with the words in that order.
Additionally, you can use the star operator as a wildcard: govern* will match government, governing, governors, etc. (minimum 3 characters before the *).