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   107395篇
  免费   19087篇
  国内免费   9807篇
化学   89282篇
晶体学   1284篇
力学   4741篇
综合类   617篇
数学   10283篇
物理学   30082篇
  2024年   240篇
  2023年   1452篇
  2022年   2765篇
  2021年   3045篇
  2020年   4011篇
  2019年   5075篇
  2018年   3332篇
  2017年   2999篇
  2016年   6545篇
  2015年   6776篇
  2014年   7370篇
  2013年   9172篇
  2012年   9471篇
  2011年   8682篇
  2010年   7335篇
  2009年   7020篇
  2008年   6937篇
  2007年   5834篇
  2006年   5210篇
  2005年   4776篇
  2004年   3894篇
  2003年   3348篇
  2002年   3919篇
  2001年   2848篇
  2000年   2566篇
  1999年   1855篇
  1998年   1239篇
  1997年   1147篇
  1996年   1128篇
  1995年   1028篇
  1994年   861篇
  1993年   745篇
  1992年   636篇
  1991年   557篇
  1990年   479篇
  1989年   359篇
  1988年   289篇
  1987年   233篇
  1986年   230篇
  1985年   218篇
  1984年   127篇
  1983年   128篇
  1982年   78篇
  1981年   63篇
  1980年   40篇
  1979年   26篇
  1976年   20篇
  1975年   22篇
  1972年   19篇
  1957年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources.  相似文献   
12.
研究了拉曼放大器中放大的自发拉曼散射对拉曼开-关增益的影响,并提出了一种利用自发拉曼散射谱来调整拉曼放大器位曼开-关增益平坦的方法,实验采用4个波长为14xx nm的激光二极管作为抽运源,75km的G.652光纤作为传输介质,获得了C波段附近的光放大,同时对此给出了合理的理论解释。  相似文献   
13.
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds.  相似文献   
14.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
15.
The synthesis and characterization of several fullerene-based organometallic complexes containing Mo and W is reported.  相似文献   
16.
The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution.  相似文献   
17.
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described.  相似文献   
18.
19.
A graph G is N2locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005  相似文献   
20.
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated.  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