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   159篇
  免费   4篇
化学   112篇
晶体学   1篇
数学   27篇
物理学   23篇
  2018年   2篇
  2017年   4篇
  2016年   4篇
  2015年   3篇
  2014年   6篇
  2013年   9篇
  2012年   4篇
  2011年   7篇
  2010年   6篇
  2009年   4篇
  2008年   8篇
  2007年   13篇
  2006年   7篇
  2005年   7篇
  2004年   7篇
  2003年   5篇
  2002年   4篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   2篇
  1996年   5篇
  1995年   2篇
  1994年   2篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1986年   3篇
  1985年   4篇
  1984年   2篇
  1982年   3篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1978年   3篇
  1977年   1篇
  1974年   1篇
  1973年   3篇
  1972年   4篇
  1971年   2篇
  1968年   1篇
  1967年   2篇
  1956年   1篇
  1933年   2篇
  1932年   1篇
排序方式: 共有163条查询结果,搜索用时 10 毫秒
61.
In this thesis, we consider some aspects ofnoncommutative classical invariant theory, i.e., noncommutative invariants ofthe classical group SL(2, k). We develop asymbolic method for invariants and covariants, and we use the method to compute some invariant algebras. The subspaceĨ d m of the noncommutative invariant algebraĨ d consisting of homogeneous elements of degreem has the structure of a module over thesymmetric group S m . We find the explicit decomposition into irreducible modules. As a consequence, we obtain theHilbert series of the commutative classical invariant algebras. TheCayley—Sylvester theorem and theHermite reciprocity law are studied in some detail. We consider a new power series H(Ĩ d,t) whose coefficients are the number of irreducibleS m -modules in the decomposition ofĨ d m , and show that it is rational. Finally, we develop some analogues of all this for covariants.  相似文献   
62.
63.
The structure of verticillol diepoxide 4 has been established by direct single crystal X-ray analysis. The structure of verticillol 5 follows from the chemical correlation to the diepoxide 4 as well as from NMR-LIS studies on verticillol which also provide evidence for the conformation of this alcohol. The absolute configuration of verticillol 5 has been assigned on the basis of CD data for the verticillol norketodiepoxide 6a.  相似文献   
64.
In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials.  相似文献   
65.
Lamellar liquid crystalline phases containing sodium n-octanoate, water, and an alcohol have been studied by means of 2H NMR. Order parameters have been determined for the octanoate alkyl chain in systems containing ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol or 1, 8-octandiol. The straight chain alcohols yield decreasing octanoate order parameters with decreasing chain length. With 1, 8-octandiol the octanoate order parameters are somewhat smaller than with 1-propanol, indicating quite flexible octanoate hydrocarbon chains. Using mono-deuteriated benzyl alcohol. C6H5CHDOH, the SCD as well as the SHD (= SHH ) order parameters were determined in the same measurement. A typical measurement yields |S HD|-|SCD | = 0.04 ± 0.04, where the error estimation includes the uncertainties in the quadrupole and the magnetic dipole-dipole coupling constants. It is stressed that in order to ascertain a significant difference between SHH and SCD , it is necessary to know the coupling constants with high accuracy. The phase diagram for the system sodium n-octanoate/water/benzyl alcohol was determined, mainly by 2H and 23Na NMR.  相似文献   
66.
In answer to recent experimental force measurements between oppositely charged surfaces we here reproduce the repulsion in the presence of multivalent salt using Monte Carlo simulations within the primitive model. Our osmotic pressure curves are in good agreement with experimental results. In contrast with Poisson-Boltzmann calculations, both repulsion and charge inversion are seen in the simulations. Repulsion is observed only for conditions under which there is charge inversion at large separations. However, in these cases, the repulsion is present also at intermediate separations, where there is no charge inversion. The charge inversion is thereby not the cause of the repulsion. Instead the repulsion appears to be an effect of the large amount of excess salt in the slit. Both phenomena, however, are closely linked and a consequence of ion-ion correlations, promoted by a strong electrostatic coupling.  相似文献   
67.
We use high-order Raman scattering in a bulk dielectric to characterize coherent dynamics with precision typical for gas phase experiments. The experimental pump-probe approach allows for the simultaneous observation and separation in space and time of the individual contributions of different-order Raman processes to a coherent wave packet without relying on phase-matching conditions and within the same experimental geometry. We propose a novel technique to discriminate between stimulated excitation of vibronic levels in the impulsive and intermediate excitation regimes, futhermore allowing us to distinguish between different pathways contributing to the same fifth-order Raman processes.  相似文献   
68.
69.
70.
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