TY  - JOUR
AU  - A. P. Sadovskii
TI  - A solution for the problem of center and focus for certain systems of non-linear oscillations
JO  - Differencialʹnye uravneniâ
PY  - 1978
SP  - 380
EP  - 382
VL  - 14
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1978_14_2_a25/
LA  - ru
ID  - DE_1978_14_2_a25
ER  -