全文获取类型
收费全文 | 580篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 461篇 |
晶体学 | 8篇 |
力学 | 4篇 |
数学 | 13篇 |
物理学 | 109篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 39篇 |
2011年 | 39篇 |
2010年 | 23篇 |
2009年 | 19篇 |
2008年 | 32篇 |
2007年 | 36篇 |
2006年 | 52篇 |
2005年 | 41篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 32篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1966年 | 3篇 |
排序方式: 共有595条查询结果,搜索用时 15 毫秒
591.
Endo H Kawamoto T Mori T Terasaki I Kakiuchi T Sawa H Kodani M Takimiya K Otsubo T 《Journal of the American Chemical Society》2006,128(28):9006-9007
A newly prepared organic conductor, (EDT-TSF)(2)GaCl(4), shows considerable nonlinear conductance in the insulating state below 20 K, and a metallic state is restored by the application of moderate currents. This conductor has a stacking structure with a quasi-one-dimensional open Fermi surface, similar to the sulfur analogues. Since the interchain interaction is enhanced by the selenium substitution, the static magnetic susceptibility as well as ESR does not show any anomaly around 20 K, and low-temperature X-ray investigation does not show any extra spots. Isostructural (EDT-TSF)(2)FeCl(4) shows similar conducting properties, although the magnetic interaction of the anion is weak. Like this, nonlinear conductance is a versatile tool to restore a metallic state when the metal-insulator transition is almost suppressed. 相似文献
592.
Permethylated 6-O-modified beta-cyclodextrins 2a-2d were synthesized as novel photosensitizing hosts with a flexible skeleton. Circular dichroism (CD) and 2D NMR spectral examinations of benzoate 2a revealed that the benzoate moiety is deeply included into its own cavity in aqueous solution. Upon addition of (Z)-cyclooctene (1Z) to a 50% aqueous methanol solution of 2a at 25 degrees C, the benzoate moiety of 2a was gradually excluded from the cavity as indicated by the CD spectral changes; the Job's plot revealed the formation of a 1:1 complex of 2a with 1Z. The binding constants for the complexation of 1Z by 2a were determined by CD spectral titration in 50% aqueous methanol at various temperatures. The van't Hoff analysis of the obtained data afforded the thermodynamic parameters (DeltaH degrees = -3.1 kJ mol(-1), DeltaS degrees = 48.5 J mol(-1) K(-1)), demonstrating the entropy-driven complexation by the permethylated cyclodextrin. This is in sharp contrast to the complexation of 1Z by nonmethylated beta-cyclodextrin benzoate that is driven by enthalpy (DeltaH degrees = -31.8 kJ mol(-1) and DeltaS degrees = -51.1 J mol(-1) K(-1)). Upon supramolecular photosensitization with 2a-2d, 1Z isomerized to the (E)-isomer (1E) in moderate enantiomeric excesses (ee's), which however displayed significant temperature dependence with accompanying switching of the product's chirality in an extreme case. Such dynamic behavior of ee is very different from that reported for the photosensitization with nonmethylated cyclodextrin benzoate, where the product's ee is controlled by host occupancy. Eyring treatment of the ee obtained at various temperatures (<0 degrees C) gave the differential activation parameters for the enantiodifferentiation process occurring in the supramolecular exciplex, revealing the crucial role of entropy, as indicated by the DeltaDeltaS(++) value changing dynamically from +4 to -24 J K(-1) mol(-1). The origin of the contrasting behavior of permethylated versus nonmethylated cyclodextrin hosts is inferred to be the conformational flexibility of the former host, which enables the entropy-driven guest complexation in the ground state and the entropy-controlled enantiodifferentiation in the excited state. 相似文献
593.
Yang C Nakamura A Fukuhara G Origane Y Mori T Wada T Inoue Y 《The Journal of organic chemistry》2006,71(8):3126-3136
A series of secondary-face-substituted and skeleton-modified gamma-cyclodextrins (gamma-CDs) were prepared as chiral hosts for enantiodifferentiating [4+4] photocyclodimerization reactions of 2-anthracenecarboxylic acid (AC). These gamma-CD derivatives form stable ternary complexes with ACs, with altroside-bearing gamma-CDs undergoing induced-fit conformational changes upon complexation, and the photocyclodimerization of AC was, thus, dramatically accelerated. The enantiomeric excess (ee) of anti-head-to-head cyclodimer 3 was greatly enhanced in general with altroside-bearing gamma-CDs 7-9. Although mono-altro-gamma-CD 9 and 3A-azido-3A-deoxy-altro-gamma-CD 7 gave 2 in ee's smaller than those obtained with native gamma-CD, 3A-amino-3A-deoxy-altro-gamma-CD 8 yielded 2 in much higher ee's, which is likely to be ascribed to the combined effects of the less-symmetric cavity and the electrostatic interactions. The influence of temperature and high pressure on the supramolecular photochirogenic reaction has been investigated in depth. An ee as high as 71% was obtained for cyclodimer 2 in the photocyclodimerization of AC mediated by 8 at 210 MPa and -21.5 degrees C. 相似文献
594.
Kenji Yamamoto Takako Tsuboi Toshiya Ohashi Takehiko Tawara Hideki Gotoh Atsushi Nakamura Jiro Temmyo 《Journal of Crystal Growth》2010,312(10):1703-1708
We report the structural and optical properties of wurtzite-structure Zn(Mg,Cd)O ternary alloys. Wurtzite (0 0 0 1) Zn1−xCdxO and MgyZn1−yO films were grown on (11–20) sapphire substrates using remote-plasma-enhanced metalorganic chemical vapor deposition. The large bowing parameters of Zn1−xCdxO and MgyZn1−yO ternary alloys are 3.0 and 3.5, respectively, which reflects the large difference of each binary’s electronegativity. We have analyzed the broadening of photoluminescence (PL) in Zn(Mg,Cd)O alloys on alloy content by taking into account the statistical alloy fluctuation and the localization of the exciton, and have clarified that the localization of the exciton strongly affects to PL full-width at half-maximum (FWHM) in Zn(Mg,Cd)O alloys. The alloy broadenings in steady-state PL of Zn(Mg,Cd)O alloys are in good agreement with the calculated tendency by the theoretical model based on the statistical alloy fluctuation, while PL FWHM of Zn1−xCdxO is three times larger than the calculated results. Moreover, as another way to confirm alloy broadening, we also have done time-resolved PL measurements and derived the localized depth of the exciton in ZnO-based system, indicating a good agreement with the tendency of PL FWHM broadening. 相似文献