[1]Yau S T. Differential geometry. Beijing:Science Press

[2]Watson G N. A treatise on the theorey of bessel function. The syndics of the cambridge university press,1952

[3]Deng Y B. The estimates of eigenvalues for laplace operator. Lecture notes in pure and applied mathe-matics, 176.15-20

[4]Zong J Q, Yang H C. On the estimate of the first eigenvalue of compact Riemennian manifold. Scientia,1983,A9:812-820

[5]Opial Z. Sur une inegalte. Ann Polon Math, 1960,8:29-32

[6]Olech C. A simple proof of a certain result of Z Opial. Ann Polon Math, 1960,8:61-63

[7]Bessack P R. On an integral inequlity of Z Opial. Trans Amer Math Soc, 1960,104:470-475

[8]Mallow. An even simpler proof of Opial inequality. Proc Amer Math Soc, 1960,15:565-566

[9]Gilbarg D, Trudinger N S. Elliptic partial differential equatations of second order. Second Edition.Berlin,Heidelberg,New York,Tokyo:Springer-verlag,1983

[10]He X G. A short proof of a generalization of Opial inequality. J Math Anal Appl, 1984,182:299-300

[11]Liang Z J. The Opial-Hua inequality. J C C N U, 1980,2:33-37