TY  - JOUR
AU  - A. P. Sadovskii
TI  - The problem of distinguishing the center and a focus for systems with nonzero linear part
JO  - Differencialʹnye uravneniâ
PY  - 1976
SP  - 1238
EP  - 1246
VL  - 12
IS  - 7
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1976_12_7_a10/
LA  - ru
ID  - DE_1976_12_7_a10
ER  -