@article{DE_1983_19_8_a3,
     author = {O. A. Veliev},
     title = {The spectrum and spectral singularities of differential operators with periodic complex-valued coefficients},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1316--1324},
     year = {1983},
     volume = {19},
     number = {8},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_8_a3/}
}