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   370299篇
  免费   5113篇
  国内免费   955篇
化学   191222篇
晶体学   5149篇
力学   16902篇
综合类   7篇
数学   45487篇
物理学   117600篇
  2021年   3546篇
  2020年   3918篇
  2019年   4343篇
  2018年   6084篇
  2017年   6140篇
  2016年   8684篇
  2015年   5364篇
  2014年   8229篇
  2013年   18440篇
  2012年   15273篇
  2011年   17842篇
  2010年   12786篇
  2009年   12373篇
  2008年   15755篇
  2007年   15742篇
  2006年   14413篇
  2005年   12768篇
  2004年   11720篇
  2003年   10220篇
  2002年   10008篇
  2001年   11095篇
  2000年   8271篇
  1999年   6409篇
  1998年   5309篇
  1997年   5109篇
  1996年   4871篇
  1995年   4120篇
  1994年   4125篇
  1993年   4008篇
  1992年   4425篇
  1991年   4573篇
  1990年   4352篇
  1989年   4267篇
  1988年   3998篇
  1987年   4122篇
  1986年   3857篇
  1985年   4879篇
  1984年   4928篇
  1983年   4031篇
  1982年   4201篇
  1981年   3916篇
  1980年   3829篇
  1979年   4118篇
  1978年   4094篇
  1977年   4061篇
  1976年   4097篇
  1975年   3836篇
  1974年   3813篇
  1973年   3835篇
  1972年   2670篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
81.
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed.  相似文献   
82.
83.
Oxidation catalysis is used to increase the performance of hydrogen peroxide in laundry bleach applications. Bleach catalysts provide cost‐effective, energy‐saving and environmentally friendly bleach systems yielding perfect stain removal at lower temperatures. This comparative study is based on the synthesis of bis[bis(salicylhydrazonephenoxy)manganese(III)] phthalocyaninatozinc(II) ( 2 ), bis[bis(salicylhydrazonephenoxy)cobalt(III)] phthalocyaninatozinc(II) ( 3 ) and bis[bis(salicylhydrazonephenoxy)iron(III)] phthalocyaninatozinc(II) ( 4 ) as tri‐nuclear complexes consisting of two Schiff base complexes substituting a zinc phthalocyanine. Complexion on the periphery to obtain complexes 2 , 3 , 4 was performed through the reaction of a Schiff base‐substituted phthalocyanine using MnCl2?4H2O, CoCl2?6H2O or FeCl3?6H2O salts in basic condition in dimethylformamide. Fourier transform infrared, 1H NMR, 13C NMR, UV–visible, inductively coupled plasma optical emission and mass spectra were applied to characterize the prepared compounds. The bleach performances of the three phthalocyanine compounds 2 , 3 , 4 were examined by the degradation of morin as hydrophilic dye. The degradation progress in the presence of catalysts 2 , 3 , 4 /H2O2 combination in aqueous solution was investigated using an online spectrophotometric method. It was found that the catalysts 2 , 3 , 4 exhibited better bleaching performance at 25 °C than tetraactylethylethylenediamine as bleach activator used in powder detergent formulations for stain removal. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
84.
85.
86.
Russian Journal of General Chemistry - 8-Phenyltetrazolo[5,1-b][1,3,4]thiadiazepine was obtained as a result of intermolecular cyclization of 1-amino-1H-tetrazole-5-thiol and 3-phenyl-2-propynal....  相似文献   
87.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
88.
89.
90.
Russian Chemical Bulletin - Quantum chemical calculations and a comparative analysis of Raman spectra of 3,4,5-triphenyl-1-propyl-1,2-diphosphole (1),...  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