TY  - GEN 
AU  - Qian, Dingbian
AU  - Torres Villarroya, Pedro José
AU  - Wang, Peiyu
PY  - 2019
UR  - https://hdl.handle.net/10481/99458
LA  - eng
TI  - Periodic solutions of second order equations via rotation numbers
DO  - https://doi.org/10.1016/j.jde.2018.10.010
ER  -