%0 Journal Article
%A M. A. Krasnosel'skii
%T An alternative principle for the existence of periodic solutions for differential equations with retarded argument
%J Doklady Akademii Nauk
%D 1963
%P 801-804
%V 152
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1963_152_4_a7/
%G ru
%F DAN_1963_152_4_a7