@article{DE_2004_40_8_a7,
     author = {L. A. Cherkas and I. L. Shevtsov},
     title = {Normal-Size {Limit} {Cycles} of {Quadratic} {Systems} with a {Structurally} {Unstable} {Focus}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1076--1084},
     publisher = {mathdoc},
     volume = {40},
     number = {8},
     year = {2004},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2004_40_8_a7/}
}