中国科学院数学与系统科学研究院期刊网
The Existence of Periodic Solutions for High Order Duffing Equations
Wen Bing LIU(1),Yong LI(2)
Acta Mathematica Sinica, Chinese Series . 2003, (1): 49 -56 .  DOI: 10.12386/A2003sxxb0008