In most databases the default search uses a basic index consisting of title words, descriptors (keywords) and words from the abstracts to retrieve relevant articles.
By limiting your search to the title or descriptor field, you will probably find fewer references but those retrieved are likely to be more relevant.
When you are looking for documents by a specific author, limit your search to the author field. Authors are often not included in the basic index. When searching for authors, it is advisable to look up the author in the index of the database, to see how his name and initials have been entered.
Other limiting options are publication year, document type and language. They can be very useful to refine your search.
Most databases have specific limiting options. Consult the help screens and documentation to find out what they are.
In this example from Medline, the question was whether there are any new drugs that can help you quit smoking.
|2||7363||smoking in ti|
|3||267161||SH = "DRUG-THERAPY"|
|4||182||#2 and (SH = "DRUG-THERAPY")|
|5||325428||PY > "1997"|
|6||21||#4 and (PY > "1997")|