麦克斯韦方程中有某些特性是恒定不变的——磁场强度、电位移场以及描述电磁场电通量的坡印廷矢量。
Maxwell's equations conserve certain properties-the magnetic field intensity, the electric displacement field and the Poynting vector that describes the electric flux of an electromagnetic field.
根据偏微分方程在无穷小变换下的不变性理论，研究经典场的对称性质和守恒量。
According to the invariance theory of partial differential equations under the infinitesimal transformations, the symmetries and conserved quantities of classical fields are studied.
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