Regression on a constant and time

Hello guys!
I have panel data and I want to calculate a regression with a constant and time as independent variable, to see if time plays an important role in explaining the evolution of my dependent variable. But there are so many types of regressions availabe in Stata. Which one do I have to use for my purpose? First i want to do a regression on my full sample (several countries) and furthermore on my subsamples (everysingle country that is included in the full sample). Or do you need more information to answer this question? If so, what else do I have to consider?

Cheers,
Jamie