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   2421篇
  免费   35篇
  国内免费   14篇
化学   1703篇
晶体学   31篇
力学   117篇
综合类   1篇
数学   265篇
物理学   353篇
  2024年   33篇
  2023年   24篇
  2022年   154篇
  2021年   107篇
  2020年   68篇
  2019年   66篇
  2018年   62篇
  2017年   51篇
  2016年   90篇
  2015年   75篇
  2014年   84篇
  2013年   197篇
  2012年   151篇
  2011年   156篇
  2010年   87篇
  2009年   76篇
  2008年   83篇
  2007年   89篇
  2006年   73篇
  2005年   57篇
  2004年   55篇
  2003年   56篇
  2002年   63篇
  2001年   41篇
  2000年   50篇
  1999年   17篇
  1998年   23篇
  1997年   18篇
  1996年   23篇
  1995年   20篇
  1994年   23篇
  1993年   11篇
  1992年   12篇
  1991年   19篇
  1990年   15篇
  1989年   17篇
  1988年   9篇
  1987年   16篇
  1986年   12篇
  1985年   22篇
  1984年   19篇
  1983年   19篇
  1982年   19篇
  1981年   14篇
  1980年   11篇
  1979年   9篇
  1978年   6篇
  1977年   10篇
  1975年   10篇
  1973年   5篇
排序方式: 共有2470条查询结果,搜索用时 0 毫秒
31.
Dimethyl and diethyl fluoromalonates were prepared from hexafluoropropene by its exhaustive alcoholysis or alternatively its ammonolysis and alcoholysis. Fluoromalonates thus obtained or their alkylated derivatives were condensed with o-phenylenediamine or its substituted derivatives to give a number of 1H-3-fluoro-1,5-dibenzodiazepin-2,4(3H,5H)-diones.  相似文献   
32.
33.
Journal of Thermal Analysis and Calorimetry - This paper presents a comparison between the numerically determined soot volume fraction (SVF) in a momentum-dominated turbulent diffusion strained jet...  相似文献   
34.
Ibrahim  I.  Idris  S. O.  Abdulkadir  I.  Onu  A. D. 《Transition Metal Chemistry》2020,45(3):211-216
Transition Metal Chemistry - The kinetics of redox reaction between N,N′-phenylenebis-(salicylideneiminato)iron(III), hereafter referred to as [FeSalphen]+, and hypophosphorous acid was...  相似文献   
35.
36.
The reaction of the tripod ligand hydrotris(N-(2-methylphenyl)-2-thioimidazol-1-yl)borate, Tt with zinc(II) chloride yielded the chloro complex [TtZn–Cl] 1. The hydrolytic reactivity of its hydroxo complex [TtZn–(μ-OH)ZnTt]Cl 2 towards p-nitrophenyl acetate was hampered due to the formation of the stable phenolate complex [TtZn–O–Ar–p-NO2] 3 as a product inhibition. The X-ray structure analysis of complex 3 was determined and showed that its Zn[S3O] coordination sphere includes three thione donors from the ligand Tt and one oxygen donor from the hydrolysed product p-nitrophenolate in an ideally tetrahedral arrangement around the zinc(II) centre.  相似文献   
37.
The essential oil of the leaves of Cupressus sempervirens L. was isolated by hydrodistillation and tested against gram positive and gram negative bacteria, showing remarkable antimicrobial activity against Bacillus subtilis with minimum inhibitory concentration (MIC) 75%. The antiviral activity of the essential oil was tested against Herpes simplex virus type 1 (HSV-1), showing antiviral activity with virucidal percentages of 68.0% and 53.2% at concentrations of 1:32 and 1:64, respectively. We firstly reported the isolation of two epi-betulin esters of fatty acids from the CHCl3 fraction of Cupressus sempervirens L. leaves, which were isolated and purified using HPLC, and identified using PMR and MS. The CHCl3 fraction showed significant cytotoxicity against HeLa cells. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 265–268, May–June, 2009.  相似文献   
38.
Kinetics of β″ and β′ precipitations in an AlSiMg have been studied under non-isothermal conditions using differential scanning calorimetry (DSC) technique. The variation of the activation energy as a function of transformed fraction is determined using two isoconversional methods of Kissinger–Akahira–Sunose (KAS) and Friedman. The results obtained using the two methods show a change in the activation energy for both metastable phases precipitations as a function of transformed fraction. The results obtained from KAS method as compared with those obtained from Friedman method, show some major disagreements between the two methods. The growth exponent, determined by Ozawa method, decreases as a function of temperature for both phases.  相似文献   
39.

Abstract  

New ferrocenyl ketones were obtained as precursors of novel π-conjugated ferrocene-dithiafulvalene (Fc-DTF) and π-extended-ferrocenedithia-fulvalenes (π-exFc-DTF) as electron-donor conducting materials from ferrocene by a direct aroylation process using the Friedel–Crafts reaction. Novel Fc-DTF conjugates were synthesized using the Wittig–Horner reaction and their structures were determined. The redox behavior of the ferrocenyl carbonyl compounds Fc-DTF and Fc-π-exDTF was investigated in comparison to the parent ferrocene by means of cyclic voltammetry. A one-electron redox behavior was observed for carbonylferrocenes as one wave potential, while a two-electron process was observed as two oxidation waves for the conjugates. Introduction of electron-withdrawing groups led to increasing E pa values and decreasing ΔE p values. The UV–Vis spectra of some compounds were studied in comparison with ferrocene. The absorption spectra showed a red-shift with a slight increase in the absorption intensities.  相似文献   
40.

Background

One of the most popular techniques for cancer detection is the nuclear medicine technique. The present research focuses on Platelet-12-lipoxygenase (P-12-LOX) as a promising target for treating and radio-imaging tumor tissues. Curcumin was reported to inhibit this enzyme via binding to its active site.

Results

A novel curcumin derivative was successfully synthesized and characterized with yield of 74%. It was radiolabeled with the diagnostic radioisotope technetium-99m with 84% radiochemical yield and in vitro stability up to 6 h. The biodistribution studies in tumor bearing mice confirmed the high affinity predicted by the docking results with a free binding energy value of (ΔG ?50.10 kcal/mol) and affinity (13.64 pki) showing high accumulation in solid tumor with target/non-target ratio >6.

Conclusion

The newly synthesized curcumin derivative, as a result of a computational study on platelet-12 lipoxygenase, showed its excellent free binding energy (?G ?50.10 kcal/mol) and high affinity (13.64 pKi). It could be an excellent radio-imaging agent that targeting tumor cells via targeting of P-12-LOX.
Graphical abstract This novel curcumin derivative was successfully synthesized and radiolabeled with technetium-99m and biologically evaluated in tumor bearing mice that showed high accumulation in solid tumor with target/non-target ratio >6 confirming the affinity predicted by the docking results. Predicted binding mode of a new curcumin derivative in complex with 12-LOX active site. b Curcumin itself in the 12-LOX active site biological distribution of 99mTc-curcumin derivative complex in solid tumor bearing Albino mice
  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