TY  - JOUR
AU  - N. L. Shcheglova
TI  - A criterion for the coexistence of a center and a focus of the equation $y'=(x+\lambda y+Q_3)/(-y+\lambda x+P_3)$
JO  - Differencialʹnye uravneniâ
PY  - 1991
SP  - 2001
EP  - 2005
VL  - 27
IS  - 11
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1991_27_11_a22/
LA  - ru
ID  - DE_1991_27_11_a22
ER  -