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   1356224篇
  免费   29580篇
  国内免费   7717篇
化学   683792篇
晶体学   20091篇
力学   74704篇
综合类   104篇
数学   242684篇
物理学   372146篇
  2021年   13502篇
  2020年   15934篇
  2019年   16075篇
  2016年   27548篇
  2015年   20746篇
  2014年   30499篇
  2013年   74549篇
  2012年   39279篇
  2011年   36178篇
  2010年   36788篇
  2009年   38933篇
  2008年   35414篇
  2007年   30962篇
  2006年   38455篇
  2005年   29742篇
  2004年   31266篇
  2003年   29388篇
  2002年   30619篇
  2001年   30131篇
  2000年   25850篇
  1999年   23051篇
  1998年   21295篇
  1997年   21218篇
  1996年   21227篇
  1995年   19263篇
  1994年   18700篇
  1993年   18258篇
  1992年   18399篇
  1991年   18642篇
  1990年   17840篇
  1989年   17867篇
  1988年   17445篇
  1987年   17323篇
  1986年   16341篇
  1985年   22733篇
  1984年   23911篇
  1983年   20065篇
  1982年   21780篇
  1981年   20977篇
  1980年   20293篇
  1979年   20527篇
  1978年   21817篇
  1977年   21411篇
  1976年   21151篇
  1975年   19885篇
  1974年   19597篇
  1973年   20048篇
  1972年   14515篇
  1968年   12345篇
  1967年   12673篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
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   
63.
64.
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   
65.
66.
Experimental Techniques - The analysis of residual stress in glass is usually carried out by means of photoelastic methods. This article considers the automation of the white light photoelastic...  相似文献   
67.
68.
69.
70.
In this communication, we report the synthesis of small‐sized (<10 nm), water‐soluble, magnetic nanoparticles (MNPs) coated with polyhedral oligomeric silsesquioxanes (POSS), which contain either polyethylene glycol (PEG) or octa(tetramethylammonium) (OctaTMA) as functional groups. The POSS‐coated MNPs exhibit superparamagnetic behavior with saturation magnetic moments (51–53 emu g?1) comparable to silica‐coated MNPs. They also provide good colloidal stability at different pH and salt concentrations, and low cytotoxicity to MCF‐7 human breast epithelial cells. The relaxivity data and magnetic resonance (MR) phantom images demonstrate the potential application of these MNPs in bioimaging.  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