%0 Journal Article
%A A. P. Sadovskii
%T The problem of distinguishing the center and a focus for systems with nonzero linear part
%J Differencialʹnye uravneniâ
%D 1976
%P 1238-1246
%V 12
%N 7
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1976_12_7_a10/
%G ru
%F DE_1976_12_7_a10