@article{DAN_1989_304_2_a6,
     author = {Nguyen Thi Thien Hoa},
     title = {The oscillation property of the operator $D(D^2+1^2)\cdots},
     journal = {Doklady Akademii Nauk},
     pages = {289--293},
     publisher = {mathdoc},
     volume = {304},
     number = {2},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_304_2_a6/}
}