The variation of frequency curve's mode peak content with the increasing of depth, shows not only the trend of chemical weathering but also variation gradient of weathering extent.
频率曲线众数峰含量随深度的变化，不但指示了化学风化趋势，而且反映了风化程度的变化梯度。
Generalized into local frequency from integral frequency, the method of joint time-frequency distribution effectively analyzes the signal based on the variation of frequency with time.
联合时频分布方法把整体频谱推广到局部频率，根据频率随着时间的变化情况，对信号进行有效的分析。
Still, the mathematical models used to rank results are usually some variation of the common term-frequency/inversed document frequency model, which is well-mapped territory.
尽管如此，用于排序结果的数学模型通常是常用的 词频/倒排文档频率模型的变体，而对于这种模型，已有很好的研究基础。
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