中文说明：
一种积分变换，它来源于函数的傅里叶积分表示。积分 （1） 称为? 的傅里叶积分。周期函数在一定条件下可以展成傅里叶级数，而在（－∞，∞）上定义的非周期函数?，显然不能用三角级数来表示。但是J.-B.-J.傅里叶建议把?表示成所谓傅里叶积分的方法。
English Description：
An integral transformation derived from the Fourier integral representation of a function. The integral (1) is called the Fourier integral of. The periodic function can be expanded into Fourier series under certain conditions, while the aperiodic function defined on (- ∞, ∞) can not be expressed by trigonometric series. But J. - B. - J. Fourier suggested that? Be expressed as a so-called Fourier integral.