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   321358篇
  免费   2771篇
  国内免费   1071篇
化学   176087篇
晶体学   5032篇
力学   12854篇
综合类   11篇
数学   34542篇
物理学   96674篇
  2020年   2543篇
  2019年   2800篇
  2018年   3760篇
  2017年   3604篇
  2016年   5372篇
  2015年   3239篇
  2014年   5002篇
  2013年   13491篇
  2012年   9824篇
  2011年   12259篇
  2010年   8480篇
  2009年   8116篇
  2008年   11462篇
  2007年   11587篇
  2006年   10984篇
  2005年   10210篇
  2004年   9075篇
  2003年   8312篇
  2002年   8062篇
  2001年   8871篇
  2000年   6926篇
  1999年   5338篇
  1998年   4634篇
  1997年   4635篇
  1996年   4390篇
  1995年   3840篇
  1994年   3738篇
  1993年   3758篇
  1992年   4063篇
  1991年   4142篇
  1990年   3969篇
  1989年   3948篇
  1988年   3881篇
  1987年   3871篇
  1986年   3648篇
  1985年   4863篇
  1984年   5093篇
  1983年   4174篇
  1982年   4740篇
  1981年   4441篇
  1980年   4244篇
  1979年   4474篇
  1978年   4707篇
  1977年   4631篇
  1976年   4627篇
  1975年   4397篇
  1974年   4281篇
  1973年   4607篇
  1972年   2998篇
  1967年   2814篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
141.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 613–618, October, 1991.  相似文献   
142.
143.
144.
Results of an experimental observation of the voltage oscillations associated with a discrete tunneling of holes in porous silicon at room temperature are presented. The noise characteristics of diode structures with a porous silicon interlayer formed on heavily boron-doped silicon single crystals are studied. Peaks of excessive noise are observed at frequencies of ~1 MHz, at which single-electron oscillations should be expected. The peak noise power is found to increase with current according to the ~2.5 power law and, at a current density of 0.15 A/cm2, to exceed the noise power of the receiver by three to four orders of magnitude. The complex shape of the noise spectrum and its extension to the higher frequency region with increasing current are explained by the three-dimensionality of the system of nanometer-sized silicon grains embedded in insulating silicon dioxide of porous silicon.  相似文献   
145.
146.
Binding energy spectra of the valence electrons of the open shell molecule NO have been obtained up to 55 eV at azimuthal angles of 0° and 7° using binary (e, 2e) spectroscopy at an impact energy of 1200 eV. The momentum distribution has been obtained for the least tightly bound (unpaired) electron, removal of which leads to formation of the X 1Σ+ ground state of NO+. Momentum distributions have also been measured at 21.0 and 40.5 eV. The measured momentum distributions are compared with several literature wavefunctions of varying complexity. They are found to be in excellent agreement with those calculated using the natural spin orbital wavefunctions of Kouba and Ohrn.  相似文献   
147.
148.
In the present work, a quantitative analysis of the phase compositions by Mössbauer effect spectroscopy of solid and conventional hydrogen disproportionated Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys was carried out. Significant amounts of intermediate borides t-Fe3B and Pr(Fe, Co)12B6 were detected after solid hydrogen disproportionation treatment in Pr13.7Fe80.3B6.0 and Pr13.7Fe63.5Co16.7Zr0.1B6.0 alloys, respectively. After conventional hydrogenation–disproportionation–desorption–recombination treatment these phases were not detected and in no case residual Pr2Fe14B-phase was found. It was observed that the amount of intermediate borides after disproportionation can be correlated with the degree of texture after recombination at various temperatures.  相似文献   
149.
Based on the analysis of the K2O-P2O5-D2O solubility phase diagram, the optimum conditions of KD2PO4 crystallization—the compositions of mother solutions and the temperature range of crystallization—in the KH2PO4-D2O system have been determined. The technique of K(DxH1 ? x )2PO4 growth is developed. The DKDP single crystals with deuterium concentration up to 88 wt % are grown on DKDP seeds from KH2PO4 solutions in D2O by the method of temperature decrease.  相似文献   
150.
This paper presents the development and laboratory evaluation of a PM10/2.5/1.0 trichotomous sampling inlet that consists of two main parts: a previously designed PM10 size‐selective inlet part and a PM2.5/1.0 two‐stage virtual impactor, which was newly fabricated and attached serially to the PM10 size selective inlet part. Particles are collected in three locations through the trichotomous sampling inlet to provide for not only particle concentration measurements of PM10, PM2.5 and PM1.0, but also those of PM2.5–10 and PM1.0–2.5.  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