首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   116篇
  免费   3篇
  国内免费   35篇
化学   82篇
力学   61篇
数学   2篇
物理学   9篇
  2023年   3篇
  2022年   14篇
  2021年   7篇
  2020年   4篇
  2019年   8篇
  2018年   5篇
  2017年   1篇
  2016年   4篇
  2015年   6篇
  2014年   7篇
  2013年   2篇
  2012年   1篇
  2011年   4篇
  2010年   6篇
  2009年   7篇
  2008年   8篇
  2007年   8篇
  2006年   7篇
  2005年   2篇
  2004年   4篇
  2003年   5篇
  2002年   6篇
  2001年   5篇
  1999年   5篇
  1998年   4篇
  1997年   3篇
  1996年   4篇
  1995年   2篇
  1994年   2篇
  1993年   5篇
  1992年   2篇
  1990年   2篇
  1989年   1篇
排序方式: 共有154条查询结果,搜索用时 15 毫秒
41.
N-取代马来酰亚胺和苯乙烯的原子转移自由基共聚合   总被引:5,自引:0,他引:5  
近来,以卤代烷、铜(Ⅰ)卤素盐和2,2 联吡啶体系引发苯乙烯可进行活性聚合,即原子转移自由基聚合(ATRP),得到指定分子量和窄分子量分布的聚合物[1],开辟了活性聚合的一个新领域,引起了广泛的关注.利用ATRP方法,对合成较窄的分子量分布的均聚物...  相似文献   
42.
马来酸酐和苯乙烯是被广为研究的一对电荷转移复合物 (Chargetransfercomplex,简称CTC) ,而且能通过通常的自由基聚合发生交替共聚[1] .所得的聚合物由于酸酐基团的存在 ,很易进行大分子改性得到具有某些特殊功能的高分子 .不过 ,所得共聚物的分子量难以控制且分子量分布也较宽 .近年来发展起来的“活性” 可控自由基聚合越来越为人们所关注 ,因为采用这种方法不仅可对聚合物的分子量进行设计 ,同时分子量分布也较窄 ,也不需要活性离子型聚合那样严格的聚合条件 .关于烯类单体的活性自由基聚合迄今主要有氮氧自由基…  相似文献   
43.
Hydrophobic magnesium hydroxide (Mg(OH)2) nanoparticles were successfully synthesized via a one-step solution precipitation method with octadecyl dihydrogen phosphate (n-C18H37OPO3H2, ODP) as a surface modifier. The ODP was used to control the growth of crystal in the c direction (direction perpendicular to the layers) and to modify the surface property of the Mg(OH)2 particles produced from the precipitation. Measurements of relative contact angle and active ratio indicated that Mg(OH)2 samples were hydrophobic. The samples were characterized by using field emission scanning electron microscope (SEM), X-ray diffraction (XRD), infrared analysis (IR). The mechanism of influence of ODP on the surface property and morphology of Mg(OH)2 was discussed. Furthermore, from the results of the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests, it was confirmed that small amount of magnesium alkyl phosphate on the surface of Mg(OH)2 particles enhanced the thermal stability of the low density polyethylene(LDPE)/Mg(OH)2.  相似文献   
44.
A soapless emulsion polymerization method was applied to synthesize CaCO3/PMMA spherical composite with different loading of CaCO3. CaCO3 nanoparticles were pretreated with oleic acid after the carbonation process of Ca(OH)2 slurry by CO2, in order to improve the compatibility between the CaCO3 particles and MMA monomer in emulsion system. The results of photon correlation spectroscopy (PCS) showed the particles size of composites were bigger than the pure PMMA. And the size increased with the increase of the content of CaCO3 nanoparticles. TEM images showed that the morphology of the composite microspheres was uniform and CaCO3 nanoparticles can be well encapsulated in the polymeric microsphere, and were located at the edge of the spheres. The results of DTG and TG indicated that the CaCO3 nanoparticles could improve the thermal stability of PMMA. Moreover, capsulation of CaCO3 by PMMA can increase the acid-resistant of CaCO3 nanofillers.  相似文献   
45.
Stable hollow silica microspheres were synthesized by a solgel method in nonionic W/O emulsion; the mesoporous shell wall of the spheres could have potential applications as controlled release capsules for drugs, dyes, cosmetics and inks, artificial cells, catalysts, and fillers.  相似文献   
46.
多体动力学的几何积分方法研究进展   总被引:1,自引:0,他引:1  
动力系统的几何积分研究是近20年来工程计算领域非常活跃的方向.多体动力学方程(微分方程, 微分代数方程)是一类典型的动力系统,将其从Lagrange体系向Hamilton系统过渡,目的在于从欧氏几何过渡到辛几何形态, 将对偶变量引入到力学研究中,然后利用辛几何的数学框架对多体系统动力学方程进行数值计算,可以预知多体动力学系统的一些定性信息,并在数值离散时能保持这些定性性质特征,尤其在表示关键的物理意义时需要强调保持这些几何性质.简要介绍多体系统(无约束多刚体系统、完整约束多刚体系统和柔性多体系统)的Hamilton正则方程的建立和几何积分方法的构造,着重介绍了在多体动力学计算中非常有应用前景的高阶辛算法(合成辛算法、分裂合成辛算法和辛精细积分法)、多辛算法,以及广义Hamilton 系统与Lie 群积分方法等计算几何力学方法, 并对Lie群积分的投影方法、流形局部坐标法等方法进行了阐述.   相似文献   
47.
给出了空间拦截控制的非线性微分方程,并在非线性控制系统引入了结构力学中的多重子结构法,从而求出了空间拦截非线性最优末端导引规律,同时给出了相应的数值仿真。  相似文献   
48.
In the present paper, based on the precise integration method established in linear dynamic system, an improved precise integration method is presented for nonlinear dynamic system. Firstly, the nonlinear dynamic system is converted into an augmented Lie type dynamic system. Then the precise integration method is improved for solving the above augmented equation and preserving its group structure in the meantime. Finally, two numerical examples are presented to demonstrate the validity and effectiveness of the proposed method.  相似文献   
49.
In order to increase the accuracy of turbulence field reconstruction, this paper combines experimental observation and numerical simulation to develop and establish a data assimilation framework, and apply it to the study of S809 low-speed and high-angle airfoil flow. The method is based on the ensemble transform Kalman filter(ETKF) algorithm, which improves the disturbance strategy of the ensemble members and enhances the richness of the initial members by screening high flow field sensitivity ...  相似文献   
50.
The longitudinal wave propagating in an elastic rod with a variable cross-section owns wide engineering background, in which the longitudinal wave dissipation determines some important performances of the slender structure. To reproduce the longitudinal wave dissipation effects on an elastic rod with a variable cross-section, a structure-preserving approach is developed based on the dynamic symmetry breaking theory. For the dynamic model controlling the longitudinal wave propagating in the elast...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号