Why do some science journals capitalize the words in a title, and others don't?
Essentially, the way to check is to look at if the particular journal to which you want to submit a paper uses title case or sentence case for the capitalization of titles. I think a lot of it is publisher-specific. For example, in my field, I publish primarily in American Chemical Society journals, which use title case, and AIP/APS journals, which use sentence case.