@article{ND_2010_6_1_a4,
     author = {S. A. Korolev and A. D. Morozov.},
     title = {On periodic perturbations of self-oscillating pendulum equations},
     journal = {Russian journal of nonlinear dynamics},
     pages = {79--89},
     publisher = {mathdoc},
     volume = {6},
     number = {1},
     year = {2010},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ND_2010_6_1_a4/}
}