Periodic solutions of second order equations via rotation numbers Qian, Dingbian Torres Villarroya, Pedro José Wang, Peiyu 2025-01-17T07:38:09Z 2025-01-17T07:38:09Z 2019-04-05 journal article https://hdl.handle.net/10481/99458 https://doi.org/10.1016/j.jde.2018.10.010 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional