%0 Journal Article
%A V. V. Amel'kin
%A I. V. Gaishun
%T The periodic solutions of second order systems
%J Differencialʹnye uravneniâ
%D 1974
%P 1560-1564
%V 10
%N 9
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1974_10_9_a1/
%G ru
%F DE_1974_10_9_a1