@article{10_4064_am32_3_5,
     author = {A. Raouf Chouikha},
     title = {Monotonicity of the period function for
 some planar differential systems.
 {Part} {I:} {Conservative} and quadratic systems},
     journal = {Applicationes Mathematicae},
     pages = {305--325},
     publisher = {mathdoc},
     volume = {32},
     number = {3},
     year = {2005},
     doi = {10.4064/am32-3-5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/am32-3-5/}
}