@article{DAN_1958_118_1_a4,
     author = {V. A. Kondratiev},
     title = {On the oscillation of solutions of linear differential equations of the third and fourth order},
     journal = {Doklady Akademii Nauk},
     pages = {22--24},
     year = {1958},
     volume = {118},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_118_1_a4/}
}