@article{Rudakov2014periodic,
author={Rudakov, I.. and Lukavyy, A..},
title={Periodic solutions of a quasilinear wave equations with variable coefficients.},
journal={Bulletin of Bryansk state technical university},
publisher={Bryansk State Technical University},
year={2014},
pages={147-155},
volume={2014},
issue={3},
}