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   642篇
  免费   4篇
  国内免费   5篇
化学   218篇
晶体学   16篇
力学   39篇
数学   139篇
物理学   239篇
  2021年   6篇
  2019年   4篇
  2018年   9篇
  2017年   4篇
  2016年   8篇
  2014年   8篇
  2013年   16篇
  2012年   10篇
  2011年   13篇
  2010年   13篇
  2009年   10篇
  2008年   16篇
  2007年   35篇
  2006年   38篇
  2005年   16篇
  2004年   35篇
  2003年   23篇
  2002年   27篇
  2001年   27篇
  2000年   19篇
  1999年   12篇
  1998年   9篇
  1997年   15篇
  1996年   6篇
  1995年   15篇
  1994年   10篇
  1993年   12篇
  1992年   13篇
  1991年   12篇
  1990年   10篇
  1989年   14篇
  1988年   8篇
  1987年   12篇
  1986年   6篇
  1985年   14篇
  1984年   8篇
  1983年   7篇
  1982年   7篇
  1981年   9篇
  1980年   4篇
  1978年   10篇
  1977年   11篇
  1976年   9篇
  1975年   6篇
  1974年   12篇
  1973年   7篇
  1972年   5篇
  1971年   3篇
  1964年   5篇
  1921年   4篇
排序方式: 共有651条查询结果,搜索用时 15 毫秒
11.
12.
13.
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   
14.
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   
15.
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   
16.
17.
18.
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   
19.
Phytotoxicity assessment of diclofenac and its phototransformation products   总被引:2,自引:0,他引:2  
The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the non-steroidal anti-inflammatory drug diclofenac is ubiquitously present in most of the surveyed surface waters, worldwide. Phototransformation of diclofenac was reported from laboratory assays as well as in natural water systems, raising the question of possible adverse effects of the phototransformation products of diclofenac to aquatic organisms. In this study the phytotoxicity of diclofenac exposed to natural sunlight was evaluated using synchronized cultures of the unicellular chlorophyte Scenedesmus vacuolatus. Diclofenac dissolved in ultra-pure water at 50 mg L−1 was exposed to natural midsummer sunlight for a maximum of 145 h. Twice a day subsamples were taken for chromatography and parallel phytotoxicity assessment. Inhibition of algal reproduction of the initial diclofenac solution was in the mg L−1 range indicating no specific toxicity of diclofenac towards S. vacuolatus. Fast degradation of diclofenac was observed with half lives between 3.3 and 6.4 h during the first and the third day of exposure, respectively. Phytotoxicity increased after 3.5 h of exposure of diclofenac to sunlight and showed a maximum of sixfold enhanced toxicity after 53 h of exposure to sunlight. Several phototransformation products were found during the experiment. The time courses of the relative concentration of three transformation products significantly correlated with enhanced phytotoxicity during the experiment. This indicates a high toxicity potential of phototransformation products of diclofenac at concentration levels that may come close to environmental concentrations of residual diclofenac after degradation. We conclude that toxicity assessment of phototransformation products should be included in the risk assessment of pharmaceuticals in the environment.  相似文献   
20.
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   
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