In the Advanced Search, you can select a number of options related to research studies. Look for the Methodology section, and choose Quantitative.
There is no easy way to specify quantitative studies in Medline and CINAHL.
Randomized Controlled Trials (check box or in the Publication Type menu) are often quantitative, or at least have a quantitative aspect.
In CINAHL Advanced Search, you can select Tables/Charts, Statistics, and/or Equations & Formulas from the Publication Type menu. This will pull up any article that was noted to contain tablular or chart data, statistics, or formulas. This will include some qualitative studies, as well.
Another trick for both Medline and CINAHL is to select Graphs and Charts from the Image types at the bottom of the Search screen (with the Research check box in CINAHL. Some qualitative studies also use charts and graphs (and some studies are mixed method) and some quantitative studies won't have charts or graphs listed as images.
If you don't find anything, check the Research check box alone, and go through the studies manually.
In the Advanced Search, you can select a number of options related to research studies. Look for the Methodology section, and choose Qualitative.
Qualitative studies are an option under Clincial Queries in the Advanced Search of both Medline and CINAHL.