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   1353569篇
  免费   30394篇
  国内免费   8539篇
化学   680450篇
晶体学   20398篇
力学   75078篇
综合类   172篇
数学   242304篇
物理学   374100篇
  2021年   13572篇
  2020年   16018篇
  2019年   16102篇
  2018年   12806篇
  2016年   28038篇
  2015年   20943篇
  2014年   30542篇
  2013年   74635篇
  2012年   39123篇
  2011年   36644篇
  2010年   37768篇
  2009年   40060篇
  2008年   35726篇
  2007年   31573篇
  2006年   37397篇
  2005年   30129篇
  2004年   30887篇
  2003年   28929篇
  2002年   29917篇
  2001年   28925篇
  2000年   25189篇
  1999年   22667篇
  1998年   21100篇
  1997年   21062篇
  1996年   21178篇
  1995年   19210篇
  1994年   18655篇
  1993年   18214篇
  1992年   18167篇
  1991年   18453篇
  1990年   17624篇
  1989年   17650篇
  1988年   17225篇
  1987年   17212篇
  1986年   16163篇
  1985年   22591篇
  1984年   23808篇
  1983年   19996篇
  1982年   21678篇
  1981年   20873篇
  1980年   20247篇
  1979年   20422篇
  1978年   21728篇
  1977年   21318篇
  1976年   21067篇
  1975年   19749篇
  1974年   19404篇
  1973年   19883篇
  1972年   14401篇
  1967年   12571篇
排序方式: 共有10000条查询结果,搜索用时 15 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