%0 Journal Article
%A E. K. Ershov
%T On the number of cycles of some differential equations on a two-dimensional torus
%J Differencialʹnye uravneniâ
%D 1991
%P 2167-2169
%V 27
%N 12
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1991_27_12_a20/
%G ru
%F DE_1991_27_12_a20