@article{10_4064_ap89_3_2,
     author = {Bingwen Liu},
     title = {Existence and uniqueness of periodic solutions for
  a kind of {Duffing} equation with two deviating arguments},
     journal = {Annales Polonici Mathematici},
     pages = {247--258},
     publisher = {mathdoc},
     volume = {89},
     number = {3},
     year = {2006},
     doi = {10.4064/ap89-3-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap89-3-2/}
}