PubMed's search filters restrict the number of results so they focus on specific patient populations and literature types.
Look for the filters on the left side of the results page. The most important filters are Publication Dates, Article Types, and patient population.
"Publication Dates" retrieves articles that were published during the years you specify. You can immediately select articles from the last 5 or 10 years. If you click the "Custom Range" link, you can pick any range of years you like.
"Article Types" retrieves entries based on its type of research and its format.
"Sex" and "Ages" filter the patient populations in the literature according to their sex and age range.
If you don't see the filter you want, click the "Chose additional filters" link.
Do not use the "Free full text" or "Full text" filters. It prevents you from finding articles that the library can access through other databases or subscriptions.
Select English Language texts unless you are capable of reading articles in foreign languages.
There are a few other filters available in PubMed like "Species". Click the "Choose Additional Filters" link to see them. Experimenting with filters can drastically change your results.