%0 Journal Article
%A I. Berstein
%T On the problem of periodical solutions of non-linear systems with a small parameter
%J Doklady Akademii Nauk
%D 1957
%P 9-11
%V 113
%N 1
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1957_113_1_a0/
%G ru
%F DAN_1957_113_1_a0