@article{10_4064_ap105_1_1,
     author = {Chengfu Che and Xiaoping Xue},
     title = {Periodic solutions for second order {Hamiltonian} systems
 on an arbitrary energy surface},
     journal = {Annales Polonici Mathematici},
     pages = {1--12},
     publisher = {mathdoc},
     volume = {105},
     number = {1},
     year = {2012},
     doi = {10.4064/ap105-1-1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap105-1-1/}
}