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   163篇
  免费   4篇
  国内免费   4篇
化学   121篇
晶体学   2篇
力学   5篇
数学   20篇
物理学   23篇
  2020年   4篇
  2019年   2篇
  2018年   1篇
  2016年   6篇
  2015年   3篇
  2014年   4篇
  2013年   9篇
  2012年   8篇
  2011年   16篇
  2010年   3篇
  2009年   2篇
  2008年   7篇
  2007年   10篇
  2006年   7篇
  2005年   6篇
  2004年   6篇
  2003年   2篇
  2002年   6篇
  2001年   10篇
  2000年   3篇
  1999年   4篇
  1998年   1篇
  1997年   2篇
  1995年   2篇
  1994年   2篇
  1990年   1篇
  1989年   5篇
  1988年   3篇
  1987年   1篇
  1986年   2篇
  1983年   2篇
  1982年   1篇
  1981年   5篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   2篇
  1973年   1篇
  1970年   3篇
  1969年   1篇
  1968年   1篇
  1966年   1篇
  1961年   1篇
  1955年   1篇
  1940年   1篇
  1936年   2篇
  1934年   2篇
  1928年   1篇
排序方式: 共有171条查询结果,搜索用时 15 毫秒
31.
32.
In this paper, we extend to the non-convex case the affine invariant geometric heat equation studied by Sapiro and Tannenbaum for convex plane curves. We prove that a smooth embedded plane curve will converge to a point when evolving according to this flow. This result extends the analogy between the affine heat equation and the well-known Euclidean geometric heat equation.

  相似文献   

33.
The synthesis of the first two arylenealkyne conjugated macrocycles containing a long alkylene bridge via Glaser coupling of template-directed tetraacetylenes was reported. Tetraacetylene intermediates with complex structures were constructed rapidly via quadruple Hagihara coupling of monoprotected bisacetylenes to appropriate tetraiodides and subsequent desilylation. The characterization of such compounds was carried out by NMR, GPC and UV-Vis spectra. Unfortunately, the two compounds were not liquid crystals and had no biaxial nematic mesophase character as expected. __________ Translated from Chemical Journal of Chinese Universities, 2007, 28(1): 65–70 [译自: 高等学校化学学报]  相似文献   
34.
Fourier transform infrared extinction spectra of a variety of CO ice aerosols, generated at low temperatures in a liquid helium cooled collisional-cooling cell, have been analyzed. Different operation modes of the cooling system were used for the generation of spherical and nonspherical CO nanoparticles at temperatures between 5 and 35 K and with diameters between 10 and 1000 nm. In contrast to the predominantly amorphous CO films described in the literature the presented CO particles are (poly)crystalline. A Mie inversion iterative scheme is presented and used to infer the optical constants of CO ice for the cases compact particles have been produced. The spectra of nonspherical CO aerosol particles are interpreted by modeling the extinction using the discrete dipole approximation procedure combined with the retrieved optical constants. A global positive matrix factorization scheme allows us to infer the dominant shapes in the observed particle distribution and can be used as a guide for further experiments. Near 25 K a pronounced shape evolution of smaller particles from spherical toward longish structures was observed at low buffer-gas pressure over 400 s.  相似文献   
35.
Phenylacetylene‐based [2]rotaxanes were synthesized by a covalent‐template approach by aminolysis of the corresponding prerotaxanes. The wheel and the bulky stoppers are made of phenylene–ethynylene–butadiynylene macrocycles of the same size. The stoppers are large enough to enable the synthesis and purification of the rotaxane. However, the wheel unthreads from the axle at elevated temperatures. The deslipping kinetics and the activation parameters were determined. We described theoretically the unthreading by state‐of‐the‐art DFT‐based molecular‐mechanics models and a string method for the simulation of rare events. This approach enabled us to characterize in detail the unthreading mechanism, which involves the folding of the stopper during its passage through the wheel opening, a process that defies intuitive geometrical considerations. The conformational and energetic features of the transition allowed us to infer the molecular residues controlling the disassembly timescale.  相似文献   
36.
37.
Shape-persistent macrocycles with interiors in the nanometer regime were prepared by the oxidative cyclization of the appropriate bisacetylene precursors under high-dilution conditions. These compounds contain polycyclic aromatic hydrocarbons in the ring backbone and are decorated with extra annular oligoalkyl or silyl side groups. Interestingly, after depositing them on different surfaces and investigating the self-assembled structures by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), various nanostructures were observed. STM showed that these macrocycles are organized in two-dimensional (2D) layers, whereas AFM showed, in addition, the formation of 2D crystallites and one-dimensional fibrils. These results reveal the importance of the extra annular substitution of the macrocycles in creating patterned surfaces and nanoscale objects.  相似文献   
38.
39.
40.
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