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排序方式: 共有108条查询结果,搜索用时 15 毫秒
91.
2012年全国高考理综全国卷有两道题背景相同,一道是新课标卷21题,试题如下.【题目1】假设地球是一半径为R,质量分布均匀的球体.一矿井深度为d.已知质量分布均匀的球壳对壳内物体的引力为零.矿井底部和地面处的重力加速度大小之比为 相似文献
92.
李雅卿 《应用泛函分析学报》2000,2(1):22-25
本分别给出了使在无穷维欧氏空间中球体和球面具有有限的,但又不是无穷小的测度的半径集合。 相似文献
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XianYunXU XiaoGuangLI 《中国化学快报》2003,14(7):759-762
NanocrystaUine MoS2 with hollow spherical morphology has been prepared by the hydrothermal method. The products are characterized by means of X-ray powder diffraction,transmission electron microscopy and high-resolution transmission electron microscopy. The experimental results give the evidence that the sample is consists of hollow spheres 400~600nm in diameter, and there is much whisker on the surface of MoS2 hollow sphere. 相似文献
95.
Ri-shengYao Wen-xiaGao JingSun Ya-huaYou 《高分子科学》2005,(4):401-405
The method of preparing uniform dextran microspheres with a narrow diameter distribution was introduced and the adsorbability of these microspheres was evaluated. The microspheres were prepared in W/O microemulsion using 0.5% dextran solution as the aqueous phase and n-hexane as the oil phase. Characteristics of the prepared dextran microspheres were examined with laser light blocking technique, optical microscope and ultraviolet spectrometer. The results show that the prepared dextran microspheres have uniform morphology and narrow diameter distribution, nearly 92% of them having a diameter of 56.6μm. In vitro evaluation of adsorbability, wet dextran microspheres have good adsorption of 98.32mg/g of model drug methylene blue in 20.86mg/L methylene blue solution at 25℃, The adsorption of dried dextran microspheres under the same condition is 132.15mg/g, which is even higher. And the adsorbability of dextran microspheres has significant relationship with the concentration of methylene blue and temperature. The adsorbability is better at lower temperature and higher concentration of methylene blue. 相似文献
96.
Composite microspheres composed of monodispersed poly(St-co-MAA) latices with diameter about 260 nm as core and Ag nanocrystals as shell were prepared by an in situ reduction method. The shell thickness could be controlled in the range of 15--45 nm by this coating process. The structure and the composition of the core-shell microspheres were characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TG). The formation of the composite microspheres is explained by the nucleation of silver on the surface of the latices followed by growth of the silver shell. 相似文献
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99.
针对现阶段 A P物理教学中引力有关定律推导问题, 采取与以往建立微分式不同的方法, 即利用高斯
定律来求解空心引力场值: 地球谐振子模型和空心球壳, 为广大教师提供一个新的授课思路 相似文献
100.
A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived.The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal models and it explains the mono-energetic electron trajectory more accurately,especially at the relativistic region.The maximum energy of electrons is calculated and it is shown that the maximum energy of the spheroid model is less than that of the spherical model.The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons △E/E for the spheroid model under the conditions reported here is half that of the spherical model and it is in good agreement with the experimental value in the same conditions.As a result,the quasi-mono-energetic electron output beam interacting with the laser plasma can be more appropriately described with this model. 相似文献