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   10742篇
  免费   1970篇
  国内免费   980篇
化学   7042篇
晶体学   83篇
力学   671篇
综合类   85篇
数学   1226篇
物理学   4585篇
  2024年   41篇
  2023年   242篇
  2022年   402篇
  2021年   438篇
  2020年   427篇
  2019年   422篇
  2018年   360篇
  2017年   341篇
  2016年   535篇
  2015年   508篇
  2014年   572篇
  2013年   788篇
  2012年   942篇
  2011年   1022篇
  2010年   641篇
  2009年   668篇
  2008年   668篇
  2007年   575篇
  2006年   530篇
  2005年   441篇
  2004年   343篇
  2003年   283篇
  2002年   257篇
  2001年   212篇
  2000年   219篇
  1999年   205篇
  1998年   215篇
  1997年   191篇
  1996年   151篇
  1995年   196篇
  1994年   170篇
  1993年   127篇
  1992年   101篇
  1991年   85篇
  1990年   90篇
  1989年   64篇
  1988年   43篇
  1987年   33篇
  1986年   35篇
  1985年   21篇
  1984年   18篇
  1983年   21篇
  1982年   12篇
  1981年   6篇
  1980年   10篇
  1979年   2篇
  1978年   4篇
  1975年   3篇
  1974年   2篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
为刻划一类权函数W,使具有N阶消失矩的函数f的Hilbert变换f满足带权L~P强型不等式Adams给出了一个充要条件。利用A_P权的性质,本文进一步完善了这个结果。  相似文献   
32.
This study aimed to elucidate the responses of a novel characterized Issatchenkia terricola WJL-G4 against citric acid stress by performing physiological analysis, morphology observation, and structural and membrane fatty acid composition analysis. The results showed that under citric acid stress, the cell vitality of I. terricola WJL-G4 was reduced. The cell morphology changed with the unclear, uncompleted and thinner cell wall, and degraded the cell structure. When the citric acid concentration was 20 g/L, I. terricola WJL-G4 could tolerate citric acid and maintain the cell structure by increasing the intracellular pH, superoxide dismutase activity, and contents of unsaturated fatty acids. As the citric acid concentration was ≥80 g/L, the stress has exceeded the cellular anti-stress ability, causing substantial cell damage. The cell membrane permeability, the content of membrane lipids, malondialdehyde and superoxide anion increased, but the intracellular pH and superoxide dismutase activities decreased, accompanying the increase of citric acid concentrations. The findings of this work provided a theoretical basis for the responsive mechanism of I. terricola WJL-G4 under high concentrations of citric acid, and can serve as a reference for biological acid reduction in fruit processing.  相似文献   
33.
Eleven triazolyl substituted tetrahydrobenzofuran derivatives were synthesized in high yields as novel H+/K+‐ATPase inhibitor via one‐pot CuI‐catalyzed three‐component click reaction of azide, secondary amine and 3‐bromopropyne under mild conditions in water. Their structures were characterized by NMR, IR, ESI‐MS, elemental analysis and single‐crystal X‐ray diffraction analysis. Most of the target compounds exhibited better H+/K+‐ATPase inhibitory activity than commercial omeprazole with IC50 values less than 15 µmol·L?1. The initial structure‐activity analysis suggested that the triazole substituted by cycloalkyl, aromatic ring or O‐containing side‐chain seemed to be beneficial for enhancing the activity.  相似文献   
34.
Electron-phonon coupling (EPC) in cuprate and iron-based superconducting systems, as revealed by Raman scat- tering, is briefly reviewed. We introduce how to extract the coupling information through phonon lineshape. Then we discuss the strength of EPC in different high-temperature superconductor (HTSC) systems and possible factors affecting the strength. A comparative study between Raman phonon theories and experiments allows us to gain insight into some crucial electronic properties, especially superconductivity. Finally, we summarize and compare EPC in the two existing HTSC systems, and discuss what role it may play in the HTSC.  相似文献   
35.
The hybridization between the outmost s orbitals of metal (Bi3+,Sn2+,Pb2+,Ag+) and O 2p orbitals has been widely employed to develop innovative semiconductors w...  相似文献   
36.
37.
38.
Summary In the present paper, a diffraction integral formula for a misaligned optical system is derived. The interference effects of opticalelement arrays are studied by means of such a formula. The possibility of eliminating interference fringes is discussed. The conclusion is that the interference fringes could be eliminated when the αβγδ condition for arrays is satisfied. The synthetical aberration is simultaneously eliminated. However, in this case, the synthetical image coincides with the individual images. For some special application, the synthetical image does not coincide with the individual images and the αβγδ condition is not fulfilled. But the interference fringes may disappear in some special cases.
Riassunto La formula di Collins, che esprime il cammino ottico fra un punto del piano oggetto e un punto del piano immagine nel caso di un sistema ottico centrato, è generalizzata al caso di un sistema ottico disallineato. La formula cosí ottenuta è applicata allo studio del fenomeno d’interferenza che ha luogo nel piano della cosiddetta ?immagine sintetica? fra i vari fasci emergenti da una cortina di elementi ottici. Si discutono infine le condizioni in cui non si hanno frange d’interferenza sull’immagine sintetica.
  相似文献   
39.
小世界生物神经网络的相干共振研究   总被引:1,自引:0,他引:1       下载免费PDF全文
周小荣  罗晓曙 《物理学报》2008,57(5):2849-2853
研究了无外界周期信号时Hodgkin-Huxley模型小世界生物神经网络的非线性响应.数值模拟结果显示:当噪声强度取某一有限值时,峰序列有序度可以达到最大,即产生相干共振现象.同时发现: 随着网络规模N的变化,相干共振系数cv的极小值不是一个,而是多个.这表明相干共振可发生在神经元集群数目特定的不同规模的网络中. 关键词: 相干共振 有序度 小世界网络 生物神经网络  相似文献   
40.
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