Is it advisable to get copyright on a research proposal and an academic article before submitting them?
A copyright exists on your original work from the moment it is created and fixed in a tangible form.  No marking or registration is needed.

Here in the US, this may be helpful:  Copyright in General

(In 1989, the US became a party to the Berne Convention, now followed by 171 countries.  So the law here should be similar to where you live.  But check your government's site or with an IP attorney if a lot is at stake.)