全文获取类型
收费全文 | 363篇 |
免费 | 17篇 |
专业分类
化学 | 331篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 2篇 |
物理学 | 43篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 12篇 |
2013年 | 11篇 |
2012年 | 30篇 |
2011年 | 23篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 19篇 |
2007年 | 29篇 |
2006年 | 31篇 |
2005年 | 33篇 |
2004年 | 25篇 |
2003年 | 17篇 |
2002年 | 21篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有380条查询结果,搜索用时 15 毫秒
11.
Smectic layer structure of ferroelectric liquid crystal formed between fine polymer fibres 总被引:1,自引:0,他引:1
Hideo Fujikake Takashi Toyooka Takeshi Murashige Hiroto Sato Yoshiki Iino Masahiro Kawakita Hiroshi Kikuchi 《Liquid crystals》2002,29(7):881-887
This paper describes the alignment of ferroelectric liquid crystal (FLC) structures formed between aligned polymer fibres, where the FLC smectic layers are determined by polarising microscopy and X-ray diffraction. The FLC/polymer composite films were formed from a nematic phase FLC/monomer solution using a photopolymerisation-induced phase separation method. It was found that bending of the FLC smectic layers was induced in both the film plane and the cross-sectional plane at the phase transition from smectic A to chiral smectic C of the FLC material. The light transmittance properties of the composite film between crossed polarizers was analysed by light propagation simulation in several optical anisotropic media, based on the evaluated smectic layer model. 相似文献
12.
Hiroto Tachikawa Sten Lunell Christer Trnkvist Anders Lund 《International journal of quantum chemistry》1992,43(4):449-461
A vibrational coupling model to treat the solvation effects in chemical reaction rate calculations is proposed and applied to the intramolecular hydrogen transfer reaction CH3O· → ·CH2OH in the condensed phase. The effect of solvation is taken into account in two ways: (1) the solvent effect on the activation energy of the reaction is simulated by including 39 surrounding water molecules, represented by fractional charges at the assumed atomic positions, in the potential energy surface calculation; and (2) the vibrational couplings between the 10 nearest solvent molecules and the molecules constituting the reaction system are explicitly included in a vibrational frequency calculation. RRKM theory with Miller's tunneling correction included is employed to calculate the rate constants. The effect of solvation causes a significant change in the chemical reaction rate, mainly through a lowering of the activation energy. The vibrational coupling causes a slight increase of the rate constant in the tunneling region by perturbing the vibrational frequencies of the reactant and transition states, which appear in the rate-constant expression, but has little effect at higher temperatures. 相似文献
13.
14.
Chiral cationic palladium[bond]phosphinooxathiane complexes have been found to be effective catalysts for enantioselective Diels-Alder (DA) reaction of cyclopentadiene with acyl-1,3-oxazolidin-2-ones to give the corresponding DA adducts in good yield and high enantioselectivity up to 93% ee. 相似文献
15.
Nitric oxide (NO) is an important mediator responsible for numerous physiological phenomena. Transient levels of NO in biological systems usually range from nanomolar to micromolar concentrations, with a rapid return to basal levels normally seen following these increases. Because NO can diffuse only over a local area in limited time due to such low levels of production and due to its short life-time prior to degradation, high spatial and temporal resolutions are required for direct and continuous NO measurement if the physiological role of NO is to be investigated in any system. For such purposes, analytical methods based on bio-imaging and electrochemical techniques for the measurement of NO are useful. In this paper, we describe the successful application of these methods to a number of biological systems. Specifically, complementary application of these methods demonstrate that it is possible to detect real-time NO production from nervous tissue with high spatial and temporal resolutions. 相似文献
16.
Hironobu Tahara Yudai Tanaka Shoko Yamamoto Shigeki Yonemori Bun Chan Hiroto Murakami Takamasa Sagara 《Chemical science》2021,12(13):4872
Redox-active ionic liquids (RAILs) are gaining attention as a material that can create a wide range of functions. We herein propose a charge-transfer (CT) RAIL by mixing two RAILs, specifically a carbazole-based ionic liquid ([CzC4ImC1][TFSI]) as a donor and a viologen-based ionic liquid ([C4VC7][TFSI]2) as an acceptor. We investigated the effect of CT interaction on the physicochemical properties of the CT ionic liquid (CT-IL) using the results of temperature-dependent measurements of UV-vis absorption, viscosity, and ionic conductivity as well as cyclic voltammograms. We employed the Walden analysis and the Grunberg–Nissan model to elucidate the effect of the CT interaction on the viscosity and ionic conductivity. The CT interaction reduces the viscosity by reducing the electrostatic attraction between the dicationic viologen and TFSI anion. It also reduces the ionic conductivity by the CT association of the dicationic viologen and carbazole. The electrochemically reversible responses of the viologens in [C4VC7][TFSI]2 and CT-IL are consistent with the Nernstian and the interacting two-redox site models. Notably, the transport and electrochemical properties are modulated by CT interaction, leading to unique features that are not present in individual component ILs. The inclusion of CT interaction in RAILs thus provides a powerful means to expand the scope of functionalized ionic liquids.A redox-active ionic liquid (RAIL) consisting of a carbazole and viologen shows charge transfer (CT) interaction. The physicochemical properties are modulated by the CT interaction by comparison with the individual RAILs. 相似文献
17.
One-dimensional potential energy curves for the isomerization of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin (bR), i.e., isomerization from all-trans- to 13-cis-forms, have been calculated by means of time-dependent density functional theory (TD-DFT) calculations, in order to elucidate the mechanism of initial step in photo-absorption. The transition state of the isomerization in the first excited state is located at theta(13-14)=58 degrees , where theta(13-14) means twist angle around the C(13)=C(14) double bond of PSBR The potential barrier is formed by the avoided crossing between S(1) (B(u)-like) and S(2) (A(g)-like) states. The mechanism of the isomerization was discussed on the basis of theoretical results. 相似文献
18.
Hiroto Nagaoka Kaoru Kobayashi Toshiaki Okamura Yasuji Yamada 《Tetrahedron letters》1987,28(52):6641-6644
The sequential Michael reaction of (S)-4,5-di-O-isopropylidenepent-2- enoate
and
with lithium enolate
afforded diastereo- and enantioselectively bicyclo[2.2.2]octane
and
(or
), respectively. The adducts were efficiently converted into both enantiomeric keto aldehydes (−)-
and (+)-
. 相似文献
19.
Okuyama Y Nakano H Takahashi K Hongo H Kabuto C 《Chemical communications (Cambridge, England)》2003,(4):524-525
Easily prepared, chiral sulfideoxathiane ligands are described which give excellent enantioselectivity (up to 99% ee) in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with a range of alkyl malonate nucleophiles. 相似文献
20.
Hiroto Tachikawa Hiroshi Kawabata Kazumi Matsushige 《Journal of organometallic chemistry》2005,690(12):2895-2904
The structures and electronic states of phenyl-capped terthiophene (denoted by P3T) and the ionic species of P3T have been investigated by means of density functional theory (DFT) and direct MO dynamics calculations. P3T is one of the high-performance molecular devices, which has been utilized as a semi-conductor. The calculations indicated that the neutral P3T has a non-planar structure whose the phenyl rings in both ends of thiophene chain are largely deviated from the molecular plane. The cation and anion radicals, dication and dianion were considered as its ionic states. The structure for cation radical of P3T is close to more planar than that of neutral P3T. The structures for anion radical, dication and dianion take a pure planar structure. The first excitation energy of neutral P3T is calculated to be 2.90 eV at the TD-B3LYP/6-31G(d)//B3LYP/6-311+G(d) level, while the P3T cation and anion radicals have lower excitation energies (1.22 and 1.10 eV, respectively). The direct MO dynamics calculation showed that neutral, cation and anion hold near planar structure at 300 K. On the other hand, oligothiophene (n = 5) and its ionic species are strongly deformed from the planar structure, and thiophene rings in both ends of chain rotate rapidly by thermal activation. The mechanism of the electron conductivity in P3T was discussed on the basis of theoretical results. 相似文献