%0 Journal Article
%A V. V. Amel'kin
%A N. A. Lukashevich
%T Tests for the existence of the center, and its isochronism
%J Differencialʹnye uravneniâ
%D 1974
%P 585-590
%V 10
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1974_10_4_a1/
%G ru
%F DE_1974_10_4_a1