你必须考虑到一定数量的错误。

You have to allow for a certain amount of error.

《柯林斯英汉双解大词典》

人们注意到一定数量的其他欧洲国家(丹麦、意大利和乌克兰)虽然现在流感发病处在一个较低水平，但已呈现出增长态势。

An increasing trend has also been observed in a number of other European countries (Denmark, Italy and Ukraine) where influenza activity currently remains low.

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算例表明，当混沌搜索的次数达到一定数量时，混合优化方法可以保证算法收敛到全局最优解，且计算效率比混沌优化方法有很大提高。

Numerical examples illustrate that the present method possesses both good capability to search global optima and far higher convergence speed than that of chaos optimization method.

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So, if we want to go from that stable state to that less stable state, we need to put in a certain amount of energy to our system, that difference between the free electron and the electron bound to the metal.

所以，如果我们想使电子,从稳态到达不够稳定的状态，我们需要引入一定数量的,能量到系统中，即自由电子和束缚于金属的,电子的能量差。

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