[1]  Hilbert D. Grundz\"{u}ge Einer Allgeemeinen Theorieder Linearen Integralgleichungen. Leipzig: Teubner, 1912

[2]  Sun J X, Zhang G W.  Positive solutions of singular nonlinear Sturm-Liouville problems. Acta Math Sinica (in Chinese), 2005, 48: 1095--1104

[3]  Zhang G W, Sun J X.  Positive solutions of a class of singular two-point boundary value problems. Acta Math Appl Sinica (in Chinese), 2006, 29: 297--310

[4] Sun J X, Zhang G W. Nontrivial solutions of singular superlinear Sturm-Liouville problems. J Math Anal Appl, 2006, 313: 518--536

[5] Sun J X,  Zhang G W. Nontrivial solutions of singular sublinear Sturm-Liouville problems. J Math Anal Appl, 2007, 326: 242--251

[6]  Guo D J,  Sun J X.  Nonlinear Integral Equstions (in Chinese). Jinan: Shandong Sci Tech Press, 1987

[7] Sun J X. Nonzero solutions of superlinear Hammerstein integral equations and its applications. Chinese Annals of Mathematics (in Chinese), 1986, 7A: 528--536

[8] Sun J X. Positive solutions of nonlinear Hammerstein integral equations and its applications. Chinese Annals of Mathematics (in Chinese), 1988, 9A: 90--96

[9] Sun J X, Liu X Y. Computation of topological degree in ordered Banach spaces with lattice structure and its application to superlinear differential equations. J Math Anal Appl, 2008, 348: 927--937