@article{DE_1969_5_11_a4,
     author = {E. L. Tonkov and G. I. Yutkin},
     title = {Periodic solutions, and stability of a linear differential equation with periodic coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1990--2001},
     publisher = {mathdoc},
     volume = {5},
     number = {11},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_11_a4/}
}