The boolean operators AND, OR are the most commonly used. AND Searches for specific information often needs two or more search terms to be combined. A paper on mathematics only will not be retrieved. This can be used to retrieve references which have indexed with either one topic or another or both. For example, adolescents or teenagers will provide references which have indexed either or both.
Many systems have a range of limit features which can be used to refine the search results.
These include year and languages. If your search produces too many references there are a number of procedures you can utilise including consider the first few records retrieved and identify perhaps other search terms which have been assigned to them. Consider the date for your search. Check subject headings assigned and search using this method. This will often retrieve fewer but more relevant references.