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   167篇
  免费   1篇
化学   95篇
力学   1篇
数学   10篇
物理学   62篇
  2023年   2篇
  2020年   2篇
  2019年   2篇
  2015年   1篇
  2013年   21篇
  2012年   11篇
  2011年   9篇
  2010年   8篇
  2009年   2篇
  2008年   2篇
  2007年   8篇
  2006年   4篇
  2005年   9篇
  2004年   2篇
  2003年   5篇
  2002年   1篇
  2001年   3篇
  2000年   4篇
  1999年   3篇
  1998年   2篇
  1997年   6篇
  1996年   1篇
  1995年   8篇
  1993年   4篇
  1992年   1篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1977年   2篇
  1975年   2篇
  1974年   2篇
  1973年   2篇
  1970年   1篇
  1968年   1篇
  1967年   4篇
  1962年   1篇
  1948年   1篇
  1939年   1篇
  1938年   2篇
  1935年   1篇
  1934年   1篇
  1933年   1篇
  1932年   1篇
  1931年   4篇
  1924年   2篇
排序方式: 共有168条查询结果,搜索用时 15 毫秒
21.
We report results of susceptibility χ and 7Li NMR measurements on LiVSi2O6. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement of V ions. The NMR results indicate antiferromagnetic ordering below TN=24 K. The intra- and interchain coupling J and Jp for LiVSi2O6, and also for its sister compounds LiVGe2O6, NaVSi2O6 and NaVGe2O6, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations. While Jp is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below TN, indicated by the variation of the NMR spin-lattice relaxation rate at T≪TN.  相似文献   
22.
23.
24.
The aim of our study was to modify the basis compound ß-TaON, which crystallizes in the monoclinic baddeleyite-type, by incorporation of appropriate dopant ions, in order to obtain anion-deficient cubic fluorite-type phases, which are of interest as solids with mobile nitrogen ions. For this purpose, scandium-doped tantalum oxide nitrides were prepared by ammonolysis of amorphous oxide precursors. An unexpected variety of phases with different structural features was observed: bixbyite-type phases of general composition ScxTa1−x(O,N)y with 0.33≤x≤1 and 1.7≤y≤1.9, yellow colored metastable anatase-type phases such as Sc0.1Ta0.9O1.2N0.8 or Sc0.15Ta0.85O1.3N0.7 and, additionally, anosovite-type phases ScxTa3−xO2xN5−2x with 0≤x≤1.05. Selected phases were investigated by UV/vis spectroscopy. Anatase- and anosovite-type compounds show brilliant colors. In the anatase-type phase, a possible anion ordering was examined by theoretical methods. Additionally, energy calculations on phase stability were performed for ScxTa1−xO1+2xN1−2x in the baddeleyite, rutile, and anatase structure types with varying amounts of dopants.  相似文献   
25.
26.
27.
28.
29.
Huber (1956) [8] considered the following problem on the hyperbolic plane H. Consider a strictly hyperbolic subgroup of automorphisms on H with compact quotient, and choose a conjugacy class in this group. Count the number of vertices inside an increasing ball, which are images of a fixed point xH under automorphisms in the chosen conjugacy class, and describe the asymptotic behaviour of this number as the size of the ball goes to infinity. We use a well-known analogy between the hyperbolic plane and the regular tree to solve this problem on the regular tree.  相似文献   
30.
We consider the physics of lattice bosons in the presence of either disordered on-site chemical potential or disordered on-site interparticle interactions. By means of analytical results using strong-coupling expansion, and numerical results based on quantum Monte Carlo calculations, we show that important qualitative changes in the zero temperature phase diagram are observed when comparing both cases. Although for both types of disorder superfluid, Mott-insulator and Bose-glass phases may be found, we show that in the case of random interactions the Mott-insulating regions shrink and eventually vanish for any finite disorder strength beyond a sufficiently large filling factor. Furthermore, at low values of the chemical potential both the superfluid and Mott insulator are stable towards the formation of a Bose-glass, leading to a possibly non-trivial tricritical point. We discuss possible experimental realizations of both types of disorder in the context of ultra cold atomic gases in optical lattices. PACS 03.75.Lm; 03.75.Ss; 05.30.Jp; 32.80.Pj  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