Scholarly journal article databases - These databases include only scholarly journals, most of which focus on primary research articles. Examples include:
General databases - these include scholarly journal articles, but also include other sources such as magazines, trade publications, newspapers, theses, etc. Generally, there is a tab, or another way to limit your results to just the scholarly or academic journal articles. [Primary research articles are just one type of scholarly article.]
Citation databases - these do not include the full text of an article, only the citation information and the abstract, if available. Usually they will include links to the full text article, if the library has access to it in another database. Examples:
If you get too many articles in your search results, you need to narrow your focus. Add another term to your keyword. If you can't think of one, look at the keywords used by the database or find the keywords in an article seems to be close to what you want. In an article, keywords are usually above or below the abstract.
If you get too few articles in your search results, you are probably using too many keywords in your search. Try removing the least important keyword and doing the search again. Check the spelling of your keyword(s) and look for alternative spellings (e.g., peroxisome was once called microbody).