@article{SJIM_2020_23_4_a10,
     author = {M. V. Shamolin},
     title = {Families of portraits of some pendulum-like systems in dynamics},
     journal = {Sibirskij \v{z}urnal industrialʹnoj matematiki},
     pages = {144--156},
     publisher = {mathdoc},
     volume = {23},
     number = {4},
     year = {2020},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SJIM_2020_23_4_a10/}
}