可以将字符类看作是规则表达式的“原子”，通常会将那些原子组合成“分子”。
You can think of character classes as the "atoms" of regular expressions, and you will usually want to group those atoms into "molecules."
首先，给出了宽带雷达信号具有高分辨能力的直观解释，推导了频率步进雷达合成高分辨一维距离像的通用数学表达式。
First, the basic expression of high-resolution one dimensional range profile of the stepped frequency (SF) is deduced to explain the high resolution of the wideband signals.
文中推导出了各种传播系数的表达式，计算出各不确定度的分量并将其合成。
Expression of various propagation coefficients, component of uncertainty and the combined uncertainty were deduced and calculated.
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