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   270篇
  免费   4篇
化学   183篇
数学   31篇
物理学   60篇
  2022年   3篇
  2016年   7篇
  2015年   7篇
  2014年   2篇
  2013年   12篇
  2012年   4篇
  2011年   10篇
  2010年   10篇
  2009年   6篇
  2008年   11篇
  2007年   9篇
  2006年   16篇
  2005年   11篇
  2004年   11篇
  2003年   6篇
  2002年   3篇
  2001年   6篇
  2000年   4篇
  1999年   3篇
  1998年   4篇
  1997年   4篇
  1995年   4篇
  1994年   3篇
  1993年   2篇
  1992年   6篇
  1991年   4篇
  1990年   4篇
  1989年   5篇
  1988年   4篇
  1985年   2篇
  1984年   8篇
  1981年   5篇
  1980年   4篇
  1974年   2篇
  1973年   2篇
  1972年   2篇
  1966年   2篇
  1943年   3篇
  1936年   2篇
  1933年   3篇
  1929年   2篇
  1928年   5篇
  1927年   2篇
  1926年   6篇
  1925年   5篇
  1923年   4篇
  1922年   4篇
  1920年   2篇
  1919年   2篇
  1881年   2篇
排序方式: 共有274条查询结果,搜索用时 0 毫秒
271.
For a family of n mutually disjoint unit disks in the plane, we show that if any four disks are intersected by a line then there is a line that intersects at least n − 1 disks of . Supported by an NSERC Discovery Grant. Supported by OTKA Grant F042959. Supported by CONACYT CCDG 50151.  相似文献   
272.
The presence and absence of alkane isomers in petroleum and petroleum derivatives depend on the complexity of these structures. It was assumed that the more complex the structure is the less probable it is that that the molecule can be detected in any petroleum derivative. Complexity is a vague concept, which has not been defined in quantitative terms yet, and therefore there is no experimental method, which could be used to determine 'complexity'. Mass spectrometry and infrared spectroscopy in combination with gas chromatography were used to identify the various structural isomers of alkanes in petroleum ether. The isomers were categorised in quantitative terms by using topological indices and linear discriminant analysis. It was found that alkanes possessing a more complex, highly branched structure are less probable to be detected in petroleum ether than isomers with a simpler backbone structure. It was proposed that the experimental 'measure' of the complexity of isomer(i) should be proportional to 1/C(i), where C(i), denotes the concentration of isomer(i) in a (primary) petroleum derivative.  相似文献   
273.
New results are reported from large scale lattice simulations of a frequently discussed strongly interacting gauge theory with a fermion flavor doublet in the two-index symmetric (sextet) representation of the SU(3) color gauge group. We find that the chiral condensate and the mass spectrum of the sextet model are consistent with chiral symmetry breaking in the limit of vanishing fermion mass. In contrast, sextet fermion mass deformations of spectral properties are not consistent with leading conformal scaling behavior near the critical surface of a conformal theory. A recent paper could not resolve the conformal fixed point of the gauge coupling from the slowly walking scenario of a very small nearly vanishing β-function (DeGrand et al. [3]). It is argued that overall consistency with our new results is resolved if the sextet model is close to the conformal window, staying outside with a very small non-vanishing β-function. The model would exhibit then the simplest composite Higgs mechanism leaving open the possibility of a light scalar state with quantum numbers of the Higgs impostor. It would emerge as the pseudo-Goldstone dilaton state from spontaneous symmetry breaking of scale invariance. We will argue that even without association with the dilaton, the scalar Higgs-like state can be light very close to the conformal window. A new Higgs project of sextet lattice simulations is outlined to resolve these important questions.  相似文献   
274.
Perfectly alternating copolymers can be synthesised by reacting diacrylates with terminal dienes using alternating diene metathesis polycondensation (ALTMET). This novel method is very versatile and allows preparation of diverse structures of polymers, including main‐chain liquid crystalline polymers.

Main‐chain liquid crystalline polymer obtained by ALTMET.  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