TY  - JOUR
AU  - E. D. Zhitelzeif
TI  - Tests for the existence of limit cycles for systems of limit cycles for systems of the form $\dot{x}=y$, $\dot{y}=-\sum_{k=0}^n f_k(x)y^k$
JO  - Differencialʹnye uravneniâ
PY  - 1975
SP  - 1702
EP  - 1704
VL  - 11
IS  - 9
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1975_11_9_a19/
LA  - ru
ID  - DE_1975_11_9_a19
ER  -