@article{AFM_2002_27_2_a1,
     author = {Yik-Man Chiang and Shi-An Gao},
     title = {On a problem in complex oscillation theory of periodic second order linear differential equations and some related perturbation results},
     journal = {Annales Fennici Mathematici},
     pages = {273--290},
     publisher = {mathdoc},
     volume = {27},
     number = {2},
     year = {2002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AFM_2002_27_2_a1/}
}