[1] R. P. Agarwal and D. O’Regan, Singular boundary value
problems, Nonlinear Anal. 27 (1996), 645-656.
[2] L. H. Erbe, S. Hu and H. Wang, Multiple positive solutions of some
boundary value problems, J. Math. Anal. Appl. 184 (1994), 640-648.
[3] D. Guo and V. Lakshmikantham, Nonlinear problems in abstract
cones, Academic Press, New York, 1988.
[4] D. Guo and J. Sun, Calculation and application of topological
degree, J. Math. Res. Expro. 8 (1998), 469-480.
[5] C. P. Gupta, Existence and uniqueness theorems for the bending of
an elastic beam equation, J. Math. Anal. Appl. 26 (1998), 289-304.
[6] J. Henderson and H. Wang, Positive solutions for nonlinear
eigenvalue problems, J. Math. Anal. Appl. 208 (1997), 252-259.
[7] Y. Li, Positive solutions of second-order boundary value problems
with sign changing nonlinear terms, J. Math. Anal. Appl. 282 (2003),
232-240.
[8] R. Ma, Positive solutions of singular second order boundary value
problems, Acta. Math. Sinica. 41 (1998), 1225-1230 (in Chinese).