TY  - JOUR
AU  - V. V. Amel'kin
AU  - N. A. Lukashevich
TI  - Tests for the existence of the center, and its isochronism
JO  - Differencialʹnye uravneniâ
PY  - 1974
SP  - 585
EP  - 590
VL  - 10
IS  - 4
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1974_10_4_a1/
LA  - ru
ID  - DE_1974_10_4_a1
ER  -