All databases that allow searching have an additional feature that allows for a more structured search.
NCBI provides a complete tutorial on this at: http://www.ncbi.nlm.nih.gov/books/NBK53592/
This example uses a SNP database search as a sample.
The Advanced function is link that can be found under the regular search bar:
Click on the "Advanced" link:
The "Builder" section is where you start adding our search terms:
The "All Fields" is a pull-down list of what fields are available. You can then add your specific terms in the empty field following. If you don't know the values to add, the "Show Index List" can be used to display the list of values.
As you add terms, the top search bar displays your new search query.
When you are satisfied with your search, click the "search" button to view your results.
If you plan to reuse this query, you can save the query string in your NCBI account.
Sign into your NCBI account and then click the 'Save search" link:
Click the "Save" button to save this search string.
This page also allows the creation of alerts. NCBI can be configured to run this saved search at various intervals automatically and be notified of the results vis email.