%0 Journal Article
%A A. P. Sadovskii
%T On the problem of distinguishing the center and focus for systems of nonlinear oscillations
%J Differencialʹnye uravneniâ
%D 1976
%P 2273-2274
%V 12
%N 12
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1976_12_12_a19/
%G ru
%F DE_1976_12_12_a19