多重晶面时 Bragg方程 0,20-Bragg angles Incident wave front 2A=2dhkl sine-path difference 2△=nλ-constructive interference Reflected wavefront 0 (hkl) dnkl (hkl) 20 Braggs'law:nA=2dhkl sinhkl 6Bragg方程 6 多重晶面时