@article{DAN_1964_157_6_a17,
     author = {G. M. Zhislin and A. G. Sigalov},
     title = {On the mixed spectrum of certain higher-dimensional differential operators of quantum mechanics},
     journal = {Doklady Akademii Nauk},
     pages = {1329--1331},
     publisher = {mathdoc},
     volume = {157},
     number = {6},
     year = {1964},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1964_157_6_a17/}
}