@article{DE_1993_29_5_a0,
     author = {V. V. Amel'kin and Ching Zan Dang},
     title = {Strong isochronism of the center of dynamical systems with second-degree polynomials},
     journal = {Differencialʹnye uravneni\^a},
     pages = {739--743},
     publisher = {mathdoc},
     volume = {29},
     number = {5},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1993_29_5_a0/}
}