TY  - JOUR
AU  - A. P. Sadovskii
TI  - On the problem of distinguishing the center and focus for systems of nonlinear oscillations
JO  - Differencialʹnye uravneniâ
PY  - 1976
SP  - 2273
EP  - 2274
VL  - 12
IS  - 12
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1976_12_12_a19/
LA  - ru
ID  - DE_1976_12_12_a19
ER  -