@article{10_1007_s10492_012_0024_9,
     author = {Zhang, Qiongfen and Tang, X. H.},
     title = {Periodic solutions for second order {Hamiltonian} systems},
     journal = {Applications of Mathematics},
     pages = {407--425},
     publisher = {mathdoc},
     volume = {57},
     number = {4},
     year = {2012},
     doi = {10.1007/s10492-012-0024-9},
     mrnumber = {2984611},
     zbl = {1265.34154},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10492-012-0024-9/}
}