@article{DE_1970_6_5_a1,
     author = {L. A. Cherkas},
     title = {The absence of limit cycles for a certain differential equation that has a structurally unstable focus},
     journal = {Differencialʹnye uravneni\^a},
     pages = {779--783},
     publisher = {mathdoc},
     volume = {6},
     number = {5},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_5_a1/}
}