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   1241篇
  免费   28篇
  国内免费   2篇
化学   975篇
晶体学   27篇
力学   10篇
数学   76篇
物理学   183篇
  2021年   8篇
  2020年   8篇
  2019年   14篇
  2018年   8篇
  2016年   18篇
  2015年   21篇
  2014年   15篇
  2013年   70篇
  2012年   37篇
  2011年   43篇
  2010年   30篇
  2009年   42篇
  2008年   64篇
  2007年   61篇
  2006年   48篇
  2005年   53篇
  2004年   48篇
  2003年   53篇
  2002年   59篇
  2001年   17篇
  2000年   26篇
  1999年   20篇
  1998年   17篇
  1997年   16篇
  1996年   24篇
  1995年   5篇
  1994年   11篇
  1993年   11篇
  1992年   16篇
  1991年   18篇
  1990年   7篇
  1989年   12篇
  1988年   9篇
  1987年   10篇
  1986年   7篇
  1985年   25篇
  1984年   21篇
  1983年   14篇
  1982年   24篇
  1981年   23篇
  1980年   40篇
  1979年   38篇
  1978年   32篇
  1977年   28篇
  1976年   8篇
  1975年   18篇
  1974年   12篇
  1973年   13篇
  1971年   5篇
  1969年   5篇
排序方式: 共有1271条查询结果,搜索用时 15 毫秒
81.
Capillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (= 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions.  相似文献   
82.
83.
84.
An improved lattice action for gauge theories with Wilson fermions is presented.  相似文献   
85.
86.
An optical method for measuring the thickness of heterogeneous materials has been studied. The method is based on the light attenuation theory. A complete system has been constructed in order to demonstrate the applicability of the present method for industrial use. The experimental set-up consists of semiconductor lasers, focusing lenses, photo-diodes serving as a power meter and a personal computer with an A/D converter for data acquisition. Averaging of numerous measurements is required in the present method because the heterogeneous cell structure of the foam material yields large fluctuations in transmitted light levels. The fluctuations can be reduced to below 1% of the transmitted light power by 80 times averaging. The error of the measurement is considered to be a few tens of micrometers in thickness. The present system is capable of sampling data at a rate of 400 Hz and has been successfully applied to a manufacturing process.  相似文献   
87.
Allylazetidinones 9, 10, prepared by coupling of allylcoppers 8 with chloroazetidinones 6, 7, were converted into carbapenem esters 16, 2831 using an Emmons-Horner reaction to introduce the 6-side chain and an intramolecular Wittig reaction to form the carbapenem ring system.  相似文献   
88.
The microwave spectra of four isotopic species of dichlorine monoxide (OCl2) have been observed, and the rotational constants have been obtained. The rm structure for each isotopic species has been determined by Watson's method. The equilibrium structure has been estimated by taking proper averages of rm structures to be re(OCl) = 1.69587(7) A? and ∠eClOCl = 110.886(6)°. The general applicability and the merit of the present method for estimating the equilibrium structure are pointed out.  相似文献   
89.
Galvanomagnetic effects in tellurium with carrier concentrations ranges from 1014 ∽7×1015cm-3 were measured at liquid helium temperatures in intense magnetic fields up to 90 kOe. In slightly doped crystals, whose carrier concentrations were about 3 ∽ 7 × 1015cm-3, the magnetic field dependences of the Hall coefficient and the transverse magnetoresistance were found to be different from those in purer crystals. The results can be explained by assuming the existence of an impurity band and by taking into account the complicated structure of the Landau levels.  相似文献   
90.
A lower bound {14(4q + 5)}12 + 32 is given for the minimum weight of the symmetry code C(q) over GF(3), which is introduced by Pless [3].  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