@article{MZM_1997_61_4_a5,
     author = {S. V. Zelik},
     title = {The {Mathieu--Hill} operator equation with dissipation and estimates of its instability index},
     journal = {Matemati\v{c}eskie zametki},
     pages = {543--560},
     publisher = {mathdoc},
     volume = {61},
     number = {4},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1997_61_4_a5/}
}