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   522篇
  免费   5篇
  国内免费   6篇
化学   378篇
力学   14篇
数学   72篇
物理学   69篇
  2021年   3篇
  2020年   5篇
  2019年   5篇
  2018年   6篇
  2017年   3篇
  2016年   10篇
  2015年   9篇
  2014年   9篇
  2013年   20篇
  2012年   36篇
  2011年   44篇
  2010年   23篇
  2009年   27篇
  2008年   31篇
  2007年   32篇
  2006年   51篇
  2005年   40篇
  2004年   31篇
  2003年   29篇
  2002年   23篇
  2001年   7篇
  2000年   7篇
  1999年   5篇
  1998年   8篇
  1997年   4篇
  1996年   6篇
  1995年   2篇
  1994年   3篇
  1993年   5篇
  1992年   5篇
  1991年   6篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   4篇
  1981年   3篇
  1979年   1篇
  1978年   4篇
  1973年   2篇
  1970年   1篇
  1969年   2篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1919年   1篇
  1916年   1篇
  1896年   2篇
排序方式: 共有533条查询结果,搜索用时 15 毫秒
21.
The configuration interaction (CI ) method where the efficiency of the generators of the unitary group is most fully exploited is the internally contracted multireference CI method. In the most recent version of this method the semi-internal configurations were kept uncontracted, which means that the number of configurations can still be quite large. In the present study the necessary formulas are derived for the case where the semi-internal states are also contracted. The highest density matrix that appears in these formulas is of order 5, and the computational treatment of this large matrix is discussed in detail.  相似文献   
22.
23.
Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds. The olefin undergoes two types of palladium-catalyzed reactions: (a) arylation to provide C-3 arylated derivatives and (b) competing double bond isomerization. Addition of silver carbonate and thallium acetate fully suppressed the isomerization, and good yields of C-3 substituted compounds were achieved after arylation with aryl halides. With regard to aryl triflates as arylating agents, addition of lithium chloride was necessary to promote the Heck reaction. This additive excluded the use of silver and thallium salts, but high regioselectivity and good yields could be obtained by employing tri-2-furylphosphine as ligand. Arylation was rendered both regioselective and enantioselective (58% ee) with 1-naphthyl triflate as substrate utilizing a (R)-BINAP/thallium acetate combination. The C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.  相似文献   
24.
A halide-sensitive fluorescence probe was utilized to evaluate the miscibility of fluorocarbon and hydrocarbon surfactants in aqueous micellar systems. The fluorescence of 6-methoxy-N-1,1,2,2-tetrahydroheptadecafluorodecylquinolinium chloride, FC10MQ, was quenched by halide ions dissociated from the surfactant. The fluorescence in micellar solutions showed an initially rapid decay. This suggests that halide ions effectively quench FC10MQ fluorescence at the micellar surface. The subsequent slow decay corresponds to the quenching of FC10MQ fluorescence in the aqueous bulk phase by the free counterions. The Stern-Volmer plots for fluorescence quenching gave a distinct break at the critical micelle concentration of the cationic surfactants. The abrupt increase in fluorescence quenching is attributed to the solubilization of the probe in the micelles. The fluorescence quenching behavior provides direct information about the immiscibility of fluorocarbon and hydrocarbon species in micelles, and the results indicate that almost pure fluorocarbon micelles appear in surfactants mixtures.  相似文献   
25.
A flexible electrochromic active matrix addressed display, including 8 × 8 pixels, is demonstrated by using solution processing based on standard printing and coating manufacturing techniques. Each organic electrochromic display (OECD) pixel and its corresponding organic electrochemical transistor (OECT) are located on different sides of the flexible PET substrate. Electronic vias generated through the plastic substrate connects each OECD pixel with one addressing OECT. When comparing this display with actively addressed OECDs with all its components located on the same side, the present approach based on this electronic via substrate provides an enhanced pixel resolution and a relatively more simplified manufacturing process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012  相似文献   
26.
A bottle screening method to detect smuggling drugs was developed based on a series of rapid and automated magnetic resonance measurements. Liquid alteration is detected by evaluating chemical and physical properties of the liquid, scanning the bottle with a compact, non-contact magnetic resonance probe. Chemical and molecular diffusion changes are detected by means of the magnetic resonance relaxation time. The inspection device automatically detects the presence of concealed powders dissolved in liquids in a second timescale. The non-ionizing, non-contact method effectively screens bottles, regardless of their shape, size, and color. The proposed system configuration does not require a large magnet generating uniform magnetic fields; rather it inspects the liquid using a compact probe positioned on the wall of the bottle. For a variety of samples tested, the screening does not require detailed information on the expected content of the bottle.  相似文献   
27.
28.
ABSTRACT

Acyloxymethylation of an acylated silver salt of α-trinositol gives, after deprotection, membrane permeable 1D-myo-inositol 1,2,6-tris(ethoxycarbonyloxymethyl sodium phosphate). The acyl groups, 3-(4,5-methylenedioxy-2-nitrophenyl)propanoyl, are cleaved by hydrogenolysis.  相似文献   
29.
Abstract

The first completed chemical synthesis of Agrocinopine A (5) is presented. The key step in the synthesis was the pivaloyl chloride promoted condensation of a blocked arabinose 2-H-phosphonate derivative 3 with a protected sucrose derivative 1 having a free hydroxyl at 4′-OH. The resulting H-phosphonic acid diester was oxidised in situ with iodine to produce the corresponding phosphodiester 4, which was subsequently deblocked to give Agrocinopine A.  相似文献   
30.
A palladium(II)-catalyzed decarboxylative protocol for the synthesis of aryl ketones has been developed. The addition of TFA was shown to improve the reaction yield and employing THF as solvent enabled the use of solid nitriles and in only a small excess. Using this method, five different benzoic acids reacted with a wide range of nitriles to produce 29 diverse (hetero)aryl ketone derivatives in up to 94% yield.  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