  Elastic electromagnetic form factors of nucleons are investigated both for
the time-like and the space-like momentums by using the unsubtracted dispersion
relation with QCD constraints. It is shown that the calculated form factors
reproduce the experimental data reasonably well; they agree with recent
experimental data for the neutron magnetic form factors for the space-like data
obtained by the CLAS collaboration and are compatible with the ratio of the
electric and magnetic form factors for the time-like momentum obtained by the
BABAR collaboration.
