@article{10_1007_s10492_005_0037_8,
     author = {L\"u, Haishen and O'Regan, Donal and Agarwal, Ravi P.},
     title = {On the existence of multiple periodic solutions for the vector $p${-Laplacian} via critical point theory},
     journal = {Applications of Mathematics},
     pages = {555--568},
     publisher = {mathdoc},
     volume = {50},
     number = {6},
     year = {2005},
     doi = {10.1007/s10492-005-0037-8},
     mrnumber = {2181026},
     zbl = {1099.34021},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10492-005-0037-8/}
}