@article{SM_1998_189_1_a6,
     author = {V. A. Sadovnichii and V. E. Podolskii},
     title = {A~class of {Sturm{\textendash}Liouville} operators and approximate calculation of the first eigenvalues},
     journal = {Sbornik. Mathematics},
     pages = {129--145},
     year = {1998},
     volume = {189},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1998_189_1_a6/}
}