TY  - JOUR
AU  - A. P. Sadovskii
TI  - The problem of the center and focus for analytic systems with a zero linear part. I
JO  - Differencialʹnye uravneniâ
PY  - 1989
SP  - 790
EP  - 799
VL  - 25
IS  - 5
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1989_25_5_a7/
LA  - ru
ID  - DE_1989_25_5_a7
ER  -