@article{MZM_1971_9_6_a4,
     author = {P. P. Zabreiko and S. O. Strygina},
     title = {Periodic solutions of evolutionary equations},
     journal = {Matemati\v{c}eskie zametki},
     pages = {651--662},
     publisher = {mathdoc},
     volume = {9},
     number = {6},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1971_9_6_a4/}
}