@article{INTO_2021_202_a3,
     author = {M. V. Shamolin},
     title = {Families of phase portraits for dynamical systems of pendulum type},
     journal = {Itogi nauki i tehniki. Sovremenna\^a matematika i e\"e prilo\v{z}eni\^a. Temati\v{c}eskie obzory},
     pages = {70--98},
     publisher = {mathdoc},
     volume = {202},
     year = {2021},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTO_2021_202_a3/}
}