Filters (sometimes referred to as "hedges") help a researcher refine search results in order to retrieve more precise matches to their information need. Filters can specify publications years, document type, study type, and other attributes sometimes offered as options in bibliographic databases. They are widely used in health sciences literature searching and there are many online examples of these available for researchers to adapt to their own work.
Methodology Oriented Locators for Evidence-based Searching
Leonard Gibbs and their co-authors suggest terms -- which they label MOLES -- to use in order to identify specific types of articles. For example, if you want to find research syntheses, you may use terms such as "meta-analysis," "systematic review," etc. Gibbs, et. al., offer this planning sheet, in their book Evidence-based practice for the helping professions: A practical guide with integrated multimedia, to provide ideas of terms to locate a range of research.
Other Sources for Filters
This is a sample. There are many others that you can find freely available on the internet.