The Dana-Farber Cancer Institute has a good explanation of some different types of biomedical research: Research Types Explained: Basic, Clinical, Translational.
PubMed has many different publication types. View a list of them here. Many times, you will be looking for basic research articles, but PubMed does not have every basic research article labeled as such.
You can look at the Publication Type for an article to find out if an article is of a type that you are NOT interested in: clinical trial, review, meta-analysis, etc. Example:
You can eliminate some common publication types from your search too.
1. Enter keywords that describe your topic in the search box, then click the ADD button to add your terms to the query box.
2. Choose the Publication Type index from the list of indexes to the left of the search box.
3. Enter specific terms from the PubMed list of publication types that you want to eliminate from your search. Combine multiple terms with OR:
4. Click the button to the right of the search box and choose "Add with NOT".
5. Your query now contains keywords for your topic and publication type terms that will result in article that have those publication types eliminated from your results.
