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   454336篇
  免费   4111篇
  国内免费   1153篇
化学   225872篇
晶体学   7021篇
力学   23016篇
综合类   14篇
数学   56284篇
物理学   147393篇
  2021年   4184篇
  2020年   4436篇
  2019年   5137篇
  2018年   7229篇
  2017年   7513篇
  2016年   9877篇
  2015年   5367篇
  2014年   9309篇
  2013年   20729篇
  2012年   16029篇
  2011年   19151篇
  2010年   14626篇
  2009年   14754篇
  2008年   17564篇
  2007年   17416篇
  2006年   15956篇
  2005年   13924篇
  2004年   13131篇
  2003年   11727篇
  2002年   11830篇
  2001年   13815篇
  2000年   10247篇
  1999年   7966篇
  1998年   6792篇
  1997年   6564篇
  1996年   6099篇
  1995年   5401篇
  1994年   5309篇
  1993年   5198篇
  1992年   5586篇
  1991年   6004篇
  1990年   5746篇
  1989年   5714篇
  1988年   5394篇
  1987年   5580篇
  1986年   5229篇
  1985年   6606篇
  1984年   6662篇
  1983年   5614篇
  1982年   5711篇
  1981年   5414篇
  1980年   5215篇
  1979年   5684篇
  1978年   5812篇
  1977年   5865篇
  1976年   5933篇
  1975年   5559篇
  1974年   5497篇
  1973年   5663篇
  1972年   4230篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
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   
95.
96.
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   
97.
98.
99.
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   
100.
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   
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