@article{DE_1982_18_10_a2,
     author = {A. A. Zevin},
     title = {Estimates of periodic solutions of second-order nonlinear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1673--1679},
     publisher = {mathdoc},
     volume = {18},
     number = {10},
     year = {1982},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1982_18_10_a2/}
}