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   684篇
  免费   21篇
  国内免费   5篇
化学   369篇
晶体学   7篇
力学   41篇
数学   137篇
物理学   156篇
  2023年   4篇
  2022年   16篇
  2021年   16篇
  2020年   25篇
  2019年   20篇
  2018年   27篇
  2017年   18篇
  2016年   30篇
  2015年   17篇
  2014年   20篇
  2013年   62篇
  2012年   44篇
  2011年   46篇
  2010年   31篇
  2009年   31篇
  2008年   30篇
  2007年   23篇
  2006年   24篇
  2005年   18篇
  2004年   22篇
  2003年   17篇
  2002年   8篇
  2001年   10篇
  2000年   6篇
  1999年   10篇
  1998年   5篇
  1997年   7篇
  1996年   2篇
  1995年   5篇
  1994年   12篇
  1993年   9篇
  1992年   8篇
  1991年   8篇
  1990年   8篇
  1989年   9篇
  1988年   9篇
  1987年   9篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   6篇
  1982年   5篇
  1981年   2篇
  1980年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1967年   2篇
  1956年   2篇
  1955年   2篇
排序方式: 共有710条查询结果,搜索用时 125 毫秒
561.
A series of 3‐carboxylic derivatives of disubstituted 1,5‐benzodiazepines (5–9) was synthesized by hetero‐cyclisation from 1,2‐diaminobenzene (1) with dibenzoylmethane (2) followed by bromination on position 3 and by introduction of the carboxylic group or introduction of the malonic moiety. Reduction of the hetero‐cycle gave the perhydro derivative diethyl (2,4‐diphenyl‐1,2,4,5‐tetrahydro‐3H‐1,5‐benzodiazepin‐3‐yl)malonate (9) .  相似文献   
562.
In this paper, biological investigations and a high-resolution UPLC-PDA-ESI-qTOF-HRMS technique were employed for Brassica oleracea L. var. capitata f. rubra DC. (red cabbage) of the family Brassicaceae (Cruciferae), cultivated in Egypt, for the first time. The positive ionization mode is usually performed to identify anthocyanins. However, this technique cannot differentiate between anthocyanins and corresponding non-anthocyanin polyphenols. Thus, the negative ionization mode was also used, as it provided a series of characteristic ions for the MS analysis of anthocyanins. This helped in identifying five kaempferol derivatives for the first time in red cabbage, as well as nine—previously reported—anthocyanins. For the biological investigations, the acidified methanolic extract of fresh leaves and the methanolic extract of air-dried powdered leaves were examined for their antioxidant, antimicrobial, and anticancer activities. The freshly prepared phenolic extract was proven to be more biologically potent. Statistical significance was determined for its anticancer activity in comparison with standard doxorubicin.  相似文献   
563.
In this paper, the fractional cumulative entropy is considered to get its further properties and also its developments to dynamic cases. The measure is used to characterize a family of symmetric distributions and also another location family of distributions. The links between the fractional cumulative entropy and the classical differential entropy and some reliability quantities are also unveiled. In addition, the connection the measure has with the standard deviation is also found. We provide some examples to establish the variability property of this measure.  相似文献   
564.
Journal of Analytical Chemistry - In this research, chemiluminescence (CL) of several aldehydes (such as oxalaldehyde, N-isovaleryl-3-amino-propanal as the bioluminescent earthworm luciferin,...  相似文献   
565.
Journal of Thermal Analysis and Calorimetry - In this work, the influences of heat generation/absorption and nanofluid volume fraction on the entropy generation and MHD combined convection heat...  相似文献   
566.
The reactions of Cu (II), Zn (II) and Cd (II) chloride or bromide with (E)-1-(3,4-dimethoxybenzylidene)-4-methylthiosemicarbazone (MTSVT) lead to the formation of new complexes. They were characterized by spectroscopic studies: IR, 1H and 13C NMR. The crystal structures of the compounds [MTSVT] ( L ), [ZnBr2(MTSVT)2] ( 2 ), [CdCl2(MTSVT)2] ( 3 ) and [CdBr2(MTSVT)2.H2O] ( 4 ) were determined by X-ray diffraction. For complexes 2 – 4 , the ion is coordinated through the sulfur atom. All compounds were tested for their antifungal activity against human pathogenic fungi Candida albicans and Aspergillus fumigatus, and for their antibacterial activity against Gram (+) Bacillus subtilis and Enterococcus faecalis as well as against Gram (−) bacteria such as Paracoccus yeei and Acinetobacter baumanii. The results indicated that the metal complexes exhibited a marked enhancement in antibacterial activity compared with the parent Schiff base.  相似文献   
567.
Russian Journal of Organic Chemistry - New diaryl-substituted pyridine, pyrimidine, pyrazole, and isoxazole derivatives bearing biphenyl-4-yl and 4-(dimethylamino)phenyl substituents have been...  相似文献   
568.
569.
ABSTRACT

A three-component one-pot synthesis of new thiazolyl coumarin derivatives was carried out by condensing 3-acetyl-4-hydroxycoumarin, arylaldehydes, thiourea and ammonium acetate at reflux in DMC. The optimization details of the developed novel protocol are recorded. In addition, we have also synthesized these compounds via another second route in two steps. High atom-economy, excellent yields, simple procedure, and mild reaction conditions are the important features of this one-pot protocol. The chemical structures of the newly synthesized compounds were elucidated by using analytical (IR, 1H NMR, 13C NMR). Further, all the compounds were screened for their antioxidant activities.  相似文献   
570.
Accreditation and Quality Assurance - The main objective of the current research was to evaluate nitrate content in different brands of bottled drinking waters sold in Iranian markets using the...  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