When sampling frequency is quite high, frequency spectrum distributing of digital natural sampling and natural sampling is similarity.
当采样频率比较高时，数字化自然采样法的频谱分布与自然采样法的频谱分布类似。
Methods in 1999, a cross-sectional study was carried out in a natural population of Beijing, using stratified-random sampling method.
方法1999年在北京市自然人群中采用分层随机抽样的方法进行横断面调查。
PFU can be used as a sampling method for detection of organic chloride pollutants in natural water body and concentration variety of organic chloride pollutants in continuous water body.
有机氯污染物检测结果与PFU微型生物参数变化趋势相吻合。 PFU法可用于天然水体中有机氯污染物的筛选，以及连续水体中有机氯污染物浓度变化的监测。
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