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   43556篇
  免费   1560篇
  国内免费   152篇
化学   23305篇
晶体学   211篇
力学   1120篇
综合类   5篇
数学   7271篇
物理学   13356篇
  2023年   280篇
  2021年   365篇
  2020年   561篇
  2019年   451篇
  2018年   559篇
  2017年   559篇
  2016年   1187篇
  2015年   903篇
  2014年   1032篇
  2013年   2105篇
  2012年   2002篇
  2011年   2172篇
  2010年   1413篇
  2009年   1194篇
  2008年   2033篇
  2007年   1921篇
  2006年   1804篇
  2005年   1669篇
  2004年   1420篇
  2003年   1167篇
  2002年   989篇
  2001年   906篇
  2000年   725篇
  1999年   528篇
  1998年   449篇
  1997年   468篇
  1996年   570篇
  1995年   518篇
  1994年   534篇
  1993年   561篇
  1992年   605篇
  1991年   434篇
  1990年   428篇
  1989年   388篇
  1988年   362篇
  1987年   361篇
  1986年   342篇
  1985年   536篇
  1984年   514篇
  1983年   434篇
  1982年   470篇
  1981年   466篇
  1980年   450篇
  1979年   439篇
  1978年   433篇
  1977年   425篇
  1976年   396篇
  1975年   390篇
  1974年   379篇
  1973年   318篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Journal of Fluorescence - A simple microwave-assisted synthesis of nitrogen-doped carbon dots with high oxygen content (O-N-CDs) was carried out with citric acid as a carbon source and...  相似文献   
2.
3.
Kleer  Pieter  Schäfer  Guido 《Mathematical Programming》2021,190(1-2):523-560
Mathematical Programming - We study the computation and efficiency of pure Nash equilibria in combinatorial congestion games, where the strategies of each player i are given by the binary vectors...  相似文献   
4.
The European Physical Journal E - The interstitial tumor microenvironment is composed of heterogeneously organized collagen-rich porous networks as well as channel-like structures and interfaces...  相似文献   
5.
Noble-metal aerogels (NMAs) have drawn increasing attention because of their self-supported conductive networks, high surface areas, and numerous optically/catalytically active sites, enabling their impressive performance in diverse fields. However, the fabrication methods suffer from tedious procedures, long preparation times, unavoidable impurities, and uncontrolled multiscale structures, discouraging their developments. By utilizing the self-healing properties of noble-metal aggregates, the freezing-promoted salting-out behavior, and the ice-templating effect, a freeze–thaw method is crafted that is capable of preparing various hierarchically structured noble-metal gels within one day without extra additives. In light of their cleanliness, the multi-scale structures, and combined catalytic/optical properties, the electrocatalytic and photoelectrocatalytic performance of NMAs are demonstrated, which surpasses that of commercial noble-metal catalysts.  相似文献   
6.
7.
8.
Quantitative determination of omega-6 and omega-3 polyunsaturated fatty acids in human plasma and urine with high accuracy and precision provides significant information to monitor the underlying etiology of several diseases. In this regard, liquid chromatography-mass spectrometry is a good choice owing to its great selectivity and sensitivity. Additionally, the hybrid quadrupole–time of flight–mass spectrometer systems provides easy identification of target compounds with superior mass measurements. In this study, an analytical method has been developed for simple, accurate and simultaneous determination of linoleic acid, arachidonic acid, docosahexaenoic acid and eicosapentaenoic acid in a short chromatographic analysis period. The developed method is suitable for the quantitative detection of these four compounds with detection limits ranging between 1.1–3.0 ng ml−1 and its applicability was assessed in human urine and plasma samples. As a result, acceptable accuracy (between 83 and 111%) and good precision (<6%) were obtained for target compounds using matrix matching calibration strategy.  相似文献   
9.
In this paper we study the domain of the generator of stable processes, stable-like processes and more general pseudo- and integro-differential operators which naturally arise both in analysis and as infinitesimal generators of Lévy- and Lévy-type (Feller) processes. In particular we obtain conditions on the symbol of the operator ensuring that certain (variable order) Hölder and Hölder–Zygmund spaces are in the domain. We use tools from probability theory to investigate the small-time asymptotics of the generalized moments of a Lévy or Lévy-type process (Xt)t0,
limt0?1t(Exf(Xt)?f(x)),xRd,
for functions f which are not necessarily bounded or differentiable. The pointwise limit exists for fixed xRd if f satisfies a Hölder condition at x. Moreover, we give sufficient conditions which ensure that the limit exists uniformly in the space of continuous functions vanishing at infinity. As an application we prove that the domain of the generator of (Xt)t0 contains certain Hölder spaces of variable order. Our results apply, in particular, to stable-like processes, relativistic stable-like processes, solutions of Lévy-driven SDEs and Lévy processes.  相似文献   
10.
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis.  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