Singularly perturbed boundary value problems for a class of semi-linear second-order elliptic e-quations are studied.The formal approximation of the problem is constructed by using the method of composite expansions,and the existence and asymptotic behavior of solutions are proved by Harten's fixed point theorem.%研究了一类半线性二阶椭圆型方程的奇摄动边值问题。利用合成展开法构造出问题的零次形式近似，并应用椭圆型算子的最大值原理和改进的不动点定理证明解的存在性及解的渐近性质。
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