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   1324650篇
  免费   30291篇
  国内免费   8444篇
化学   661407篇
晶体学   20252篇
力学   74492篇
综合类   161篇
数学   240847篇
物理学   366226篇
  2021年   13551篇
  2020年   15986篇
  2019年   16090篇
  2018年   12165篇
  2016年   27703篇
  2015年   20842篇
  2014年   30516篇
  2013年   74538篇
  2012年   37531篇
  2011年   33791篇
  2010年   36869篇
  2009年   39391篇
  2008年   33352篇
  2007年   28868篇
  2006年   35451篇
  2005年   27827篇
  2004年   29083篇
  2003年   27607篇
  2002年   28755篇
  2001年   27360篇
  2000年   24173篇
  1999年   22197篇
  1998年   20911篇
  1997年   20915篇
  1996年   21098篇
  1995年   19171篇
  1994年   18610篇
  1993年   18161篇
  1992年   17945篇
  1991年   18216篇
  1990年   17401篇
  1989年   17456篇
  1988年   17008篇
  1987年   17018篇
  1986年   15986篇
  1985年   22418篇
  1984年   23702篇
  1983年   19911篇
  1982年   21624篇
  1981年   20830篇
  1980年   20198篇
  1979年   20296篇
  1978年   21654篇
  1977年   21231篇
  1976年   20968篇
  1975年   19617篇
  1974年   19283篇
  1973年   19743篇
  1972年   14276篇
  1967年   12462篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
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   
62.
63.
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   
64.
65.
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   
66.
67.
68.
69.
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   
70.
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