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   330651篇
  免费   3692篇
  国内免费   957篇
化学   165866篇
晶体学   4424篇
力学   15646篇
综合类   7篇
数学   39091篇
物理学   110266篇
  2021年   3221篇
  2020年   3422篇
  2019年   3905篇
  2018年   5321篇
  2017年   5527篇
  2016年   7564篇
  2015年   4269篇
  2014年   7226篇
  2013年   16305篇
  2012年   12602篇
  2011年   15073篇
  2010年   11179篇
  2009年   11072篇
  2008年   13411篇
  2007年   13370篇
  2006年   12303篇
  2005年   10657篇
  2004年   9954篇
  2003年   8796篇
  2002年   8802篇
  2001年   10445篇
  2000年   7736篇
  1999年   6018篇
  1998年   5002篇
  1997年   4768篇
  1996年   4193篇
  1995年   3780篇
  1994年   3753篇
  1993年   3632篇
  1992年   4031篇
  1991年   4241篇
  1990年   4012篇
  1989年   3927篇
  1988年   3712篇
  1987年   3863篇
  1986年   3626篇
  1985年   4584篇
  1984年   4641篇
  1983年   3842篇
  1982年   3925篇
  1981年   3663篇
  1980年   3604篇
  1979年   3889篇
  1978年   3874篇
  1977年   3889篇
  1976年   3871篇
  1975年   3649篇
  1974年   3599篇
  1973年   3631篇
  1972年   2585篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
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   
73.
74.
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   
75.
76.
77.
Journal of Thermal Analysis and Calorimetry - Nanofluids are attractive alternatives for the current heat transfer fluids due to their remarkably higher thermal conductivity which leads to the...  相似文献   
78.
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   
79.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
80.
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