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   21篇
  免费   3篇
  国内免费   6篇
化学   11篇
数学   9篇
物理学   10篇
  2019年   1篇
  2017年   3篇
  2013年   3篇
  2012年   1篇
  2011年   2篇
  2010年   1篇
  2008年   2篇
  2007年   1篇
  2006年   1篇
  2004年   1篇
  2003年   1篇
  2002年   2篇
  2001年   2篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1993年   1篇
  1984年   1篇
  1965年   2篇
排序方式: 共有30条查询结果,搜索用时 44 毫秒
1.
The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann surfaces.More precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S~1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] 0,and(2) if the action is non-Hamiltonian, then there exists an S~1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ 0, then G must be trivial,(2) if λ = 0, then the G-action is non-Hamiltonian, and(3) if λ 0, then the G-action is Hamiltonian.  相似文献   
2.
A monodendron that over a broad temperature range self-assembles in quasi-spherical supramolecular aggregates organized on a thermotropic cubic Pm3n lattice was examined by TEM. Grain boundaries were found parallel to the (1 0 0) and (3 2 0) planes. In well annealed specimens, in which grain boundaries are rare, two types of stacking fault were numerous, suggesting their relatively low energy. In the original Pm 3n lattice and in the two stacking fault arrangements, the supramolecular aggregates are distorted to an oblate shape, which is likely to be favoured by a crowded microscopic interface between core and tail moieties. Symmetry and phase selection for the ordered arrangement of amphiphilic molecules is discussed.  相似文献   
3.
Abstract The effect of forestland availability under different ownership types on license sales for hunting in nine Southeastern states is empirically evaluated. An equation that represents license sales for hunting is estimated assuming the sale of hunting licenses in a particular county is related to the characteristics of that county as well as the characteristics and license sales for hunting in its neighboring counties. The positive effects of the amounts of both national and private forestland on license sales reaffirm the potential benefits of maintaining forestland to stimulate hunting. The positive spillover effect of national forests on license sales for hunting suggests that availability and close access to hunting in national forests within neighboring counties are important in supporting hunting license sales in a county. This study contributes to the general understanding of the drivers affecting individuals’ decisions to use natural resources for hunting. Advances in natural resource modeling, specifically the spatial process model and geospatial data used in this research, make it possible to examine the interactions between the spatial dynamics and ownership attributes of the natural system, allowing policy makers to design natural resource management practices that respond to a system characterized by these interactions.  相似文献   
4.
By using the sequential effect algebra theory, we establish the partitions and refinements of quantum logics and study their entropies.  相似文献   
5.
设λ,μ是两个序列空间并有符号弱滑脊性,(λ,μ)是变换λ进入μ的无穷矩阵算子所成的无穷矩阵代数,本文研究了这类代数的强,Mackey、弱乘法序列连续性问题。  相似文献   
6.
尿素法合成高结晶度类水滑石   总被引:25,自引:0,他引:25       下载免费PDF全文
尿素的高温分解特性被用于控制层状化合物合成过程中的pH值。室温下尿素可与硝酸盐形成均一溶液,当其高温分解时可以保证溶液内部各点的pH值始终一致,因而可获得高结晶度的水滑石样品。利用该法可合成出Mg-Al、Zn-Al及Ni-Al类水滑石,但难以合成出Co-Al,Mn-Al及Co-Cr类水滑石,相信这与不同金属离子发生沉淀时所需的pH值有关。  相似文献   
7.
8.
最强Orlicz-Pettis拓扑   总被引:4,自引:0,他引:4  
引进了lp(p≥1)空间的子集是本性紧概念,借此给出了抽象对偶系统(E,F)中最强Orlicz-Petits拓扑SOP(E,F)以及产生该拓扑的最大映射集族的表示.利用此结果搞清楚了现有两种Orlicz-Petits拓扑即Dierolf拓扑(M)和Twed-dle拓扑(E,T’)的确切意义以及它们之间的相互关系.指出了的最大性所蕴涵的理论意义和应用价值.证实了σ(F,E)-条件紧集和σ(F,E)-可数紧集都含于中。进而实质性地改进了矢位测度论中的Graves-Rness定理、抽象函数论中的Thomas定理等重要结果.  相似文献   
9.
CHO  Iwhan  PYUN  Kwang-Soo 《应用化学》2001,18(5):296-300
In recent years certain new technologies demand optically transparent high Tgpolymer materials.Some aliphatic polymers containing cyclic structure are in the marketalready and have been applied to manufacture various devices in optics industry.However,these polymers are usually of nonpolar character and their difficulties inadhesion and solubility in solvents limited their applicability in many technologies[1 ,2 ] .The polymerization of polar group-containing internal cyclic olefins by transit…  相似文献   
10.
A new method for measuring and exploiting the magnetic field dependence of chemically induced dynamic nuclear polarization (CIDNP) is described. A solution of an amino acid or protein together with a flavin photosensitizer is irradiated with laser light at a position in the bore of a superconducting NMR magnet where the field is between 0.1 T and 7.0 T. The polarized sample is then transferred by rapid injection into an NMR tube at the centre of the magnet (at 9.4 T), where the spectrum is recorded. The observed 1H CIDNP field dependence of tyrosine agrees well with the diffusion model of the radical pair mechanism. The field dependence of histidine, tryptophan and methionine CIDNP allows the g values of the transient radicals responsible for the polarization to be determined. Experiments in which amino acids compete for the photoexcited flavin indicate that methionine residues could be used as probes of surface accessibility, especially if the polarization is generated in low fields (~ 0.7 T) and detected in high fields (≥ 9.4 T). Possible extensions of the technique to study protein folding and the structures of partially denatured states of proteins are discussed.  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