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   1353984篇
  免费   38587篇
  国内免费   17387篇
化学   685912篇
晶体学   20728篇
力学   77996篇
综合类   653篇
数学   246734篇
物理学   377935篇
  2022年   12278篇
  2021年   16329篇
  2020年   18990篇
  2019年   20042篇
  2018年   13128篇
  2016年   30890篇
  2015年   24673篇
  2014年   35289篇
  2013年   80432篇
  2012年   41682篇
  2011年   35561篇
  2010年   40018篇
  2009年   42739篇
  2008年   34249篇
  2007年   28044篇
  2006年   36047篇
  2005年   26816篇
  2004年   28647篇
  2003年   27418篇
  2002年   29246篇
  2001年   26280篇
  2000年   24115篇
  1999年   23012篇
  1998年   21824篇
  1997年   21787篇
  1996年   22119篇
  1995年   20128篇
  1994年   19412篇
  1993年   18751篇
  1992年   18187篇
  1991年   18444篇
  1990年   17595篇
  1989年   17531篇
  1988年   17005篇
  1987年   17037篇
  1986年   15862篇
  1985年   22320篇
  1984年   23632篇
  1983年   19898篇
  1982年   21588篇
  1981年   20823篇
  1980年   20129篇
  1979年   20110篇
  1978年   21513篇
  1977年   21067篇
  1976年   20731篇
  1975年   19403篇
  1974年   19021篇
  1973年   19495篇
  1972年   14026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.
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.  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