@article{10_4064_ap94_1_2,
     author = {Weiwen Shao and Fuxing Zhang and Ya Li},
     title = {Existence and uniqueness of periodic solutions for a kind of
 nonlinear $n$th order differential equations with delays},
     journal = {Annales Polonici Mathematici},
     pages = {15--27},
     publisher = {mathdoc},
     volume = {94},
     number = {1},
     year = {2008},
     doi = {10.4064/ap94-1-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap94-1-2/}
}