@article{TAM_1982_8_1_a2,
     author = {Vojin S. Drenovac},
     title = {The normal vibration modes of some nonlinear systems},
     journal = {Theoretical and applied mechanics},
     pages = {21 },
     year = {1982},
     volume = {8},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAM_1982_8_1_a2/}
}