The best practice when searching in Enterprise is to enter your search term and leave the first drop down on "Everything" and either let the default "All Fields" stand on the second drop down or choose one (Author, Title, Subject, etc.) - then, click SEARCH.
Once you have a results set, see the detailed "Limit Search Results" in the left column. These can be used to include or exclude many different factors to help you pinpoint what you are looking for.
For further search assistance, please see the Enterprise Help page (found at the top right of the catalog, linked to the question mark icon).