@article{DE_1999_35_8_a5,
     author = {V. N. Laptinskii and V. L. Titov},
     title = {On the theory of periodic solutions of semilinear differential systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1036--1045},
     publisher = {mathdoc},
     volume = {35},
     number = {8},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_8_a5/}
}