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   790篇
  免费   24篇
化学   512篇
晶体学   5篇
力学   24篇
数学   92篇
物理学   181篇
  2023年   7篇
  2022年   7篇
  2021年   19篇
  2020年   14篇
  2019年   16篇
  2018年   13篇
  2017年   11篇
  2016年   31篇
  2015年   25篇
  2014年   23篇
  2013年   36篇
  2012年   51篇
  2011年   56篇
  2010年   37篇
  2009年   44篇
  2008年   47篇
  2007年   38篇
  2006年   31篇
  2005年   14篇
  2004年   19篇
  2003年   15篇
  2002年   12篇
  2001年   11篇
  2000年   7篇
  1999年   10篇
  1997年   8篇
  1996年   11篇
  1995年   5篇
  1994年   8篇
  1993年   5篇
  1989年   4篇
  1988年   7篇
  1987年   8篇
  1984年   5篇
  1983年   5篇
  1982年   4篇
  1980年   4篇
  1979年   6篇
  1978年   10篇
  1977年   15篇
  1976年   6篇
  1975年   3篇
  1973年   3篇
  1972年   5篇
  1971年   4篇
  1961年   5篇
  1943年   3篇
  1939年   4篇
  1938年   3篇
  1935年   4篇
排序方式: 共有814条查询结果,搜索用时 15 毫秒
81.
The experimental achievements and the results obtained so far with the LPCTrap device installed at GANIL are presented. The apparatus is dedicated to the study of the weak interaction at low energy by means of precise measurements of the β ? ν angular correlation parameter in nuclear β decays. So far, the data collected with three isotopes have enabled to determine, for the first time, the charge state distributions of the recoiling ions, induced by shakeoff process. The analysis is presently refined to deduce the correlation parameters, with the potential of improving both the constraint deduced at low energy on exotic tensor currents (6He1+) and the precision on the V u d element of the quark-mixing matrix (35Ar1+ and 19Ne1+) deduced from the mirror transitions dataset.  相似文献   
82.
83.
Upper critical field measurements of the A15 type compounds Nb~3Au,Nb3Au0.7Pt0.3 and Nb3Pt having Tc values of 10.7, 13.0 and 8.7K, respectively, show Hc2(0) values of 235, 295 and 125 kG, respectively. The data for the compounds containing Au fit closely calculations for a dirty type II superconductor with no paramagnetic limiting, but data for Nb3Pt are slightly above these calculations.  相似文献   
84.
The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τπv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction.  相似文献   
85.
86.
The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem? concentration varied from 0 to 75 μg/ml and the illumination time varied from 60 min to 240 min.The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at μW/cm2 level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources.  相似文献   
87.
Organobentonites were synthesized by treating Na-bentonites (Wyomingand Re?adiye) with cetylpyridinium chloride (CPC) using ion exchangemethod. The difference in the basal spacing by 0.65 Å and a higher massloss by 13.32% of organobentonite (Wyoming) in the temperature range 200–550°Ccomparing with that of organobentonite (Re?adiye) were in conformitywith the CEC values of organobentonites. The HOH stretching and bending peaksof bentonites became sharper following the treatment with the organo-cation.The intensity decrease of the Al–OH band for organobentonite (Re?adiye)and in particular, the significantly higher amount of m-cresolretained by the organobentonite of lower CEC than that by the organobentonite(Wyoming) indicate the influence of the CP cation on the adsorption process.  相似文献   
88.
The electrooxidation of ethylene glycol was studied using platinum–cadmium electrocatalysts supported on high surface area carbon Vulcan XC-72. This is the first instance of Cd being used as an electrocatalyst for glycol oxidation reaction. The catalysts were prepared with various Pt:Cd atomic ratios of 90:10, 80:20, and 70:30. All the catalysts prepared were synthesized by the alcohol reduction method with 20 wt.% metal on carbon. These materials were characterized morphologically by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) and electrochemically by cyclic voltammetry and chronoamperometry. The electrochemical measurements were carried out at 25, 35, 45, and 55 °C, and the products of the electrochemical reaction were monitored by high-performance liquid chromatography (HPLC). The XRD patterns of all the PtCd catalysts presented cubic face-centered structures, and TEM revealed a homogeneous particle distribution on the carbon support with low agglomeration. The average particle size was assumed to be the maximum of the Gaussian distribution curve of particle size, at close to 2.5 nm. The presence of Cd results in an improvement in the glycol oxidation reaction, as observed by cyclic voltammetry; linear sweep voltammetry shows a lower onset potential compared to that of pure platinum. At a constant potential of 0.50 V (vs. RHE) at ambient temperature, HPLC showed glycolaldehyde to be the main byproduct formed from ethylene glycol oxidation at potential constant of 0.50 V.  相似文献   
89.
90.
Zusammenfassung Die L?sung des Systems der nichtlinearen partiellen Differentialgleichungen der laminaren kompressiblen Grenzschicht bereitet erhebliche mathematische Schwierigkeiten. In dieser Arbeit wird ein Differenzenverfahren benutzt, um die Str?mung entlang einer gekrümmten Wand zu untersuchen. Analytische Bedingungen für seine Stabilit?t sind angegeben, und die Konvergenz der L?sung gegen die L?sung des Differentialgleichungssystems ist durch Vergleichsrechnungen mit verschiedener Schrittweite erprobt. Der Einfluss von beliebigen Druck- und Temperaturverteilungen ist an einer Reihe von Beispielen untersucht. Da das Verfahren Energiedissipation und Ver?nderlichkeit der Dichte und der Z?higkeit vollst?ndig berücksichtigt, sind seine Ergebnisse benutzt, um die Vereinfachungen kritisch zu diskutieren, die so oft angewendet werden, um die analytische L?sung des Problems zu erleichtern.

This research was supported by the Air Force Office of Scientific Research of the Air Research and Development Command under Contract AF 18(600)-1488.  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