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   800篇
  免费   26篇
  国内免费   7篇
化学   329篇
晶体学   16篇
力学   41篇
数学   173篇
物理学   274篇
  2023年   6篇
  2021年   7篇
  2020年   9篇
  2019年   11篇
  2018年   17篇
  2017年   6篇
  2016年   11篇
  2015年   11篇
  2014年   16篇
  2013年   21篇
  2012年   16篇
  2011年   26篇
  2010年   18篇
  2009年   11篇
  2008年   25篇
  2007年   49篇
  2006年   50篇
  2005年   27篇
  2004年   50篇
  2003年   30篇
  2002年   38篇
  2001年   29篇
  2000年   20篇
  1999年   16篇
  1998年   12篇
  1997年   15篇
  1996年   7篇
  1995年   16篇
  1994年   13篇
  1993年   13篇
  1992年   15篇
  1991年   13篇
  1990年   10篇
  1989年   15篇
  1988年   8篇
  1987年   12篇
  1986年   8篇
  1985年   14篇
  1984年   8篇
  1983年   7篇
  1982年   7篇
  1981年   9篇
  1978年   11篇
  1977年   12篇
  1976年   9篇
  1975年   6篇
  1974年   13篇
  1973年   7篇
  1972年   5篇
  1964年   5篇
排序方式: 共有833条查询结果,搜索用时 15 毫秒
31.
We review the argument that latent image formation is a measurement in which the state vector collapses, requiring an enhanced noise parameter in objective reduction models. Tentative observation of a residual noise at this level, plus several experimental bounds, imply that the noise must be colored (i.e., non-white), and hence frame dependent and non-relativistic. Thus a relativistic objective reduction model, even if achievable in principle, would be incompatible with experiment; the best one can do is the non-relativistic CSL model. This negative conclusion has a positive aspect, in that the non-relativistic CSL reduction model evades the argument leading to the Conway–Kochen “Free Will Theorem”.  相似文献   
32.
33.
The copper‐catalyzed carbomagnesiation reaction of cyclopropenyl esters 1 leads to various substituted cyclopropanes species 3 in good yields with very high diastereoselectivities. The reaction proceeds through a syn‐chelated carbomagnesiation reaction and could be extended to various cyclopropenylmethyl ester derivatives 5 . The potential of this approach was illustrated by the preparation of two consecutive all‐carbon quaternary stereocenters. However, the carbometalation reaction needs to be performed at temperature ranging from ?35 to ?20 °C to avoid subsequent fragmentation reaction into stereodefined β,γ‐nonconjugated unsaturated esters 4 . Alternatively, the carbocupration reaction with organocopper species could also be performed to leads to configurationally stable cyclopropyl copper species 2[Cu] . Additionally, when the Lewis acid character of the copper center is decreased (i.e., RCuCNLi), the reaction proceed with an anti‐selectivity. The diastereodivergent behavior of these organometallic species is of synthetic interest, since both diastereomers syn‐ 3 and anti‐ 3 can be obtained, at will, from the same precursor cyclopropenyl esters 1 .  相似文献   
34.
Polymer hydrogels as a kind of soft materials have attracted increasing scientific and technological interest in past several decades. These materials have been applied widely in many fields [1], such as molecular filter [2,3], superabsorbent [4], and contact lenses [5] etc. However, synthetic polymeric hydrogels are seldom used as mechanical devices due to the lack of mechanical strength. Therefore, it is very imperative to improve their mechanical properties for wider use of polymeric hydrog…  相似文献   
35.
In the anionic polymerization of polar monomers the nature of active centres is considerably influenced by the reaction conditions. In a survey, the present state of knowledge is represented and discussed for the polymerization of acrylonitrile. Analogous problems of methyl methacrylate and vinylpyridine polymerization are included in the considerations.  相似文献   
36.
Dynamic nuclear polarization (DNP) is a powerful method to enhance the sensitivity of solid-state magnetic nuclear resonance (ssNMR) spectroscopy. However, its biomolecular applications at high magnetic fields (preferably>14 T) have so far been limited by the intrinsically low efficiency of polarizing agents and sample preparation aspects. Herein, we report a new class of trityl-nitroxide biradicals, dubbed SNAPols that combine high DNP efficiency with greatly enhanced hydrophilicity. SNAPol-1, the best compound in the series, shows DNP enhancement factors at 18.8 T of more than 100 in small molecules and globular proteins and also exhibits strong DNP enhancements in membrane proteins and cellular preparations. By integrating optimal sensitivity and high resolution, we expect widespread applications of this new polarizing agent in high-field DNP/ssNMR spectroscopy, especially for complex biomolecules.  相似文献   
37.
To study a geometric model of the human spine we are led tofinding a constrained minimum of a real valued function definedon a product of special orthogonal groups. To take advantgeof its Lie group structure we consider Newton's method on thismanifold. Comparisons between measured spines and computed spinesshow the pertinence of this approach.  相似文献   
38.
Consider independent and identically distributed random variables {X,X nj , 1jn,n1} with density f(x)=px p–1 I(x1), where p>0. We show that there exist unusual generalized Laws of the Iterated Logarithm involving the larger order statistics from our array.  相似文献   
39.
Nanomechanical devices based on DNA   总被引:3,自引:0,他引:3  
  相似文献   
40.
The emission of H and He isotopes in the reactions of 120 MeV 20Ne with 27A1 has been studied using light particle-heavy ion coincidence measurements. The energy spectra and angular correlations of the light particles emitted in coincidence with products of Z ≧ 14 agree well with the predictions of the statistical model applied to the decay of the compound nucleus 47V. Results on α-particle emission associated with deep inelastic reactions leading to carbon and oxygen products are also reported.  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