By using the weak maximum principle, the uniqueness and stability of the solution of water vapour equation with the first, second and third boundary-value problems were proven.

利用该弱极大值原理，证明了对于第一类、第二类和第三类边值问题，水汽方程解的唯一性和稳定性。

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According to the principle, potential coefficients can be obtained directly in solving the mixed boundary value problems of first, second and third type.

根据这一原理可解第一、第二和第三边值问题的混合边值问题直接求得位系数。

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We show existence results for multiple sign-changing solution for third-order two- point boundary value problems by using the fixed point index and the topologic degree theory.

主要研究一类三阶两点边值问题变号解的存在性和多重性，利用不动点指数和拓扑度理论等得到了新的结论。

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