Here is an example:
Aim: This study attempts to test the hypothesis ... (present)
Background: Smith and Smith in their 1909 paper, showed that
Methods: Lab rats were used ..
Results: We found ...
Discussion: It seems ... (present)
Naturally, you'll use different tenses within each section depending on what you're trying to say. But I think that actually checking a few theses in your own field is your best option.