The premise of a polling pattern is a periodic sampling of a target metric.

轮询模式的前提是对目标指标的定期采样。

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Methods a questionnaire was conducted among target population by multistage sampling.

方法采取多阶段抽样，对目标人群进行询问式问卷调查。

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Moreover, the chromatography separate condition, sample clean-up, the distributes regulation of target compounds in gas and particles, and the trap efficiency of sampling instrument is also studied.

并对色谱分离条件、样品净化方式、目标化合物在气相和颗粒物上的分布规律及采样器的捕集效率进行了实验。

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