@article{ZVMMF_1997_37_7_a5,
     author = {Yu. V. Zasorin},
     title = {On the {Newton} principle for the {Helmholtz} equation},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {828--840},
     publisher = {mathdoc},
     volume = {37},
     number = {7},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1997_37_7_a5/}
}