They are actually written in whatever tense and person is logically needed to convey the thought.
When talking about the past, we write in the past ("..protein was expressed in Escherichia coli, puriļ¬ed and refolded as reported earlier", "analysis of the backbone geometry revealed")
When talking about the present, we write in the present ("we propose a novel mechanism", "spectrum is shown in fig. 5.2")
When talking about the future, we write in the future "The data accumulated will open up possibilities for..."
Scientific merit and clarity of thought are more important than any sort of preset language rules. If the editors disagree, they can correct what they don't like to fit the journal style, that's their job.
(as for active vs. passive, I agree with oikos)