The particle diameters of the nano chitin and the derivative thereof are further reduced, so the skin care effect is also improved.
纳米甲壳质及其衍生物粒径更微细化，使得其美容护肤效果更佳。
Formulae on the base vectors and the coordinate variables derivative going with fluid particle and their application;
因为标量与坐标系无关，故两个矢量的点积称为标量不变量。
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