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   1470745篇
  免费   33157篇
  国内免费   13307篇
化学   753486篇
晶体学   21089篇
力学   78894篇
综合类   432篇
数学   253304篇
物理学   410004篇
  2021年   15441篇
  2020年   17678篇
  2019年   17961篇
  2018年   15995篇
  2017年   14490篇
  2016年   31035篇
  2015年   23315篇
  2014年   33331篇
  2013年   78199篇
  2012年   47075篇
  2011年   47138篇
  2010年   42308篇
  2009年   43804篇
  2008年   43716篇
  2007年   40018篇
  2006年   43782篇
  2005年   36381篇
  2004年   36196篇
  2003年   33076篇
  2002年   33592篇
  2001年   33923篇
  2000年   28290篇
  1999年   24829篇
  1998年   22402篇
  1997年   22251篇
  1996年   22107篇
  1995年   20025篇
  1994年   19416篇
  1993年   18855篇
  1992年   19331篇
  1991年   19484篇
  1990年   18627篇
  1989年   18534篇
  1988年   18062篇
  1987年   17915篇
  1986年   16975篇
  1985年   23287篇
  1984年   24306篇
  1983年   20384篇
  1982年   21958篇
  1981年   21129篇
  1980年   20467篇
  1979年   20876篇
  1978年   22011篇
  1977年   21652篇
  1976年   21428篇
  1975年   20151篇
  1974年   19852篇
  1973年   20278篇
  1972年   14736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