@article{DAN_1963_148_2_a2,
     author = {Yu. G. Borisovich},
     title = {Periodic solutions of equations in differential operators with a small parameter multiplying the derivative},
     journal = {Doklady Akademii Nauk},
     pages = {255--258},
     publisher = {mathdoc},
     volume = {148},
     number = {2},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1963_148_2_a2/}
}