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   516篇
  免费   12篇
  国内免费   1篇
化学   261篇
晶体学   9篇
力学   5篇
数学   15篇
物理学   239篇
  2023年   7篇
  2022年   17篇
  2021年   9篇
  2020年   15篇
  2019年   10篇
  2018年   19篇
  2017年   13篇
  2016年   25篇
  2015年   14篇
  2014年   26篇
  2013年   28篇
  2012年   42篇
  2011年   42篇
  2010年   31篇
  2009年   22篇
  2008年   24篇
  2007年   38篇
  2006年   22篇
  2005年   9篇
  2004年   10篇
  2003年   5篇
  2002年   8篇
  2001年   3篇
  2000年   4篇
  1999年   4篇
  1998年   7篇
  1997年   3篇
  1996年   2篇
  1995年   3篇
  1994年   3篇
  1992年   4篇
  1988年   3篇
  1987年   3篇
  1985年   9篇
  1981年   2篇
  1980年   4篇
  1979年   3篇
  1978年   4篇
  1977年   4篇
  1976年   3篇
  1975年   3篇
  1973年   2篇
  1967年   2篇
  1965年   1篇
  1964年   1篇
  1963年   2篇
  1962年   3篇
  1961年   2篇
  1960年   1篇
  1959年   1篇
排序方式: 共有529条查询结果,搜索用时 15 毫秒
31.
We have observed low-macroscopic field electron emission from wide bandgap nanocrystalline Al doped SnO2 thin films deposited on glass substrates. The emission properties have been studied for different anode-sample spacings and for different Al concentrations in the films. The turn-on field and approximate work function were calculated and we have tried to explain the emission mechanism from this. The turn-on field was found to vary in the range 5.6–7.5 V/μm for a variation of anode sample spacing from 80–120 μm. The turn-on field was also found to vary from 4.6–5.68 V/μm for a fixed anode-sample separation of 80 μm with a variation of Al concentration in the films 8.16–2.31%. The Al concentrations in the films have been measured by energy dispersive X-ray analysis. Optical transmittance measurement of the films showed a high transparency with a direct bandgap ∼3.98 eV. Due to the wide bandgap, the electron affinity of the film decreased. This, along with the nanocrystalline nature of the films, enhanced the field emission properties. PACS 81.20.Fw; 61.10.-i; 79.70.+q  相似文献   
32.
A pulsed master oscillator fiber power amplifier working in nanosecond range has been developed. An ytterbium-doped double-clad (large mode area) optical fiber was used as an amplifying medium. Actively Q-switched Nd:YVO laser was used as a seed of light pulses. The system worked at the repetition rate from 10 kHz to 40 kHz. At the amplifier output, pulses of 10.9 kW peak-power were achieved. The laser system worked at the slope efficiency of 30%.  相似文献   
33.
34.
We derive simple expressions for the asymptotic variance of the kernel-density estimator of a stationary continuous-time process in one and d dimensions and relate convergence rates to sample path smoothness. Important applications include methods for selecting optimal smoothing parameters and construction of confidence bands for testing hypotheses about the density. In a simulation study the results are applied to bandwidth selection for discrete-time processes that can be modelled as continuous-time processes sampled at a high rate.  相似文献   
35.
Sodium cholate and sodium deoxycholate dissolved in formamide were applied as stationary phases in gas chromatography. The critical micelle concentration of sodium cholate and deoxycholate in formamide was determined by surface tension measurements. The relation of retention times vs. concentration of bile salts was investigated for isomers of monoterpenes and xylenes. The enthalpy of binding of selected compounds with sodium cholate and sodium deoxycholate monomers and micelles was determined.  相似文献   
36.
Batch extraction of uranium(VI) from uranyl nitrate solutions using TiAP in ionic liquids ([BMIM]PF6 and [HMIM]PF6) is studied. Effects of acidity, TiAP concentration in ionic liquid and temperature on distribution coefficient are studied. Results show that distribution coefficient increases with an increase in acidity and reduces with an increase in the alkyl chain length of the cation of the ionic liquid. Extraction of uranium(VI) by TiAP-[HMIM]PF6 system is found to involve two molecules of the extractant per metal ion and extraction is found to change from being exothermic to endothermic as the percentage of the extractant is increased.  相似文献   
37.
38.
39.
40.

Background  

Two main genes encoding the catalytic subunits Cα and Cβ of cyclic AMP dependent protein kinase (PKA) have been identified in all vertebrates examined. The murine, bovine and human Cβ genes encode several splice variants, including the splice variant Cβ2. In mouse Cβ2 has a relative molecular mass of 38 kDa and is only expressed in the brain. In human and bovine Cβ2 has a relative molecular mass of 47 kDa and is mainly expressed in lymphoid tissues.  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