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   509716篇
  免费   5248篇
  国内免费   1699篇
化学   262458篇
晶体学   8200篇
力学   23119篇
综合类   20篇
数学   63152篇
物理学   159714篇
  2021年   3847篇
  2020年   4157篇
  2019年   4641篇
  2018年   7273篇
  2017年   7691篇
  2016年   9719篇
  2015年   5912篇
  2014年   9219篇
  2013年   22592篇
  2012年   18886篇
  2011年   21647篇
  2010年   15578篇
  2009年   15273篇
  2008年   18125篇
  2007年   18319篇
  2006年   16962篇
  2005年   18492篇
  2004年   17016篇
  2003年   14025篇
  2002年   12313篇
  2001年   14456篇
  2000年   10932篇
  1999年   8586篇
  1998年   7131篇
  1997年   7021篇
  1996年   6691篇
  1995年   5892篇
  1994年   5778篇
  1993年   5594篇
  1992年   6439篇
  1991年   6475篇
  1990年   6274篇
  1989年   6217篇
  1988年   5924篇
  1987年   6044篇
  1986年   5658篇
  1985年   7373篇
  1984年   7380篇
  1983年   6171篇
  1982年   6439篇
  1981年   6144篇
  1980年   6035篇
  1979年   6378篇
  1978年   6672篇
  1977年   6478篇
  1976年   6440篇
  1975年   6095篇
  1974年   6017篇
  1973年   6060篇
  1972年   4202篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
84.
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   
85.
86.
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   
87.
88.
89.
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   
90.
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