@article{RM_1965_20_2_a21,
     author = {A. Yu. Levin},
     title = {Integral criteria for the equation $\ddot x+q(t)x=0$ to be nonoscillatory},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {20},
     number = {2},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1965_20_2_a21/}
}