TY  - JOUR
AU  - V. V. Amel'kin
TI  - On the question of the isochronism of the center of two-dimensional analytic differential systems
JO  - Differencialʹnye uravneniâ
PY  - 1977
SP  - 971
EP  - 980
VL  - 13
IS  - 6
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1977_13_6_a0/
LA  - ru
ID  - DE_1977_13_6_a0
ER  -