@article{DAN_1958_122_6_a5,
     author = {M. A. Krasnosel'skii and E. I. Pustyl'nik},
     title = {The use of fractional powers of operators in studying {Fourier} series of eigenfunctions of differential operators},
     journal = {Doklady Akademii Nauk},
     pages = {978--981},
     publisher = {mathdoc},
     volume = {122},
     number = {6},
     year = {1958},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1958_122_6_a5/}
}