%0 Journal Article
%A L. I. Burkina
%A G. A. Leonov
%T Frequency conditions for the existence of circular motions and second-order limit cycles in phase systems
%J Izvestiâ vysših učebnyh zavedenij. Matematika
%D 1980
%P 15-21
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/item/IVM_1980_2_a1/
%G ru
%F IVM_1980_2_a1