全文获取类型
收费全文 | 398篇 |
免费 | 19篇 |
专业分类
化学 | 345篇 |
晶体学 | 4篇 |
力学 | 5篇 |
数学 | 3篇 |
物理学 | 60篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 24篇 |
2011年 | 15篇 |
2010年 | 19篇 |
2009年 | 12篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有417条查询结果,搜索用时 15 毫秒
331.
Treatment of (NH4)[Au(D‐Hpen‐S)2](D‐H2pen = D‐penicillamine) with CoCl2·6H2O in an acetate buffer solution, followed by air oxidation, gave neutral AuICoIII and anionic AuI3CoIII2 polynuclear complexes, [Au3Co3(D‐pen‐N,O,S)6]([ 1 ]) and [Au3Co2(D‐pen‐N,S)6]3? ([ 2 ]3?), which were separated by anion‐exchange column chromatography. Complexes [ 1 ] and [ 2 ]3? each formed a single isomer, and their structures were determined by single‐crystal X‐ray crystallography. In [ 1 ], each of three [Au(D‐pen‐S)2]3?metalloligands coordinates to two CoIII ions in a bis‐tridentate‐N,O,S mode to form a cyclic AuI3CoIII3 hexanuclear structure, in which three [Co(D‐pen‐N,O,S)2]? octahedral units and six bridging S atoms adopt trans(O) geometrical and R chiral configurations, respectively. In [ 2 ]3?, each of three [Au(D‐pen‐S)2]3? metalloligands coordinates to two CoIII ions in a bis‐bidentate‐N,S mode to form a AuI3CoIII2 pentanuclear structure, in which two [Co(D‐pen‐N,S)3]3? units and six bridging S atoms adopt ∧ and R chiral configurations, respectively. 相似文献
332.
Shinichirou Minemoto Kazutaka Takahashi Jun Matsumoto Masako Iseda Akira Terasaki Hideo Imoto Tamotsu Kondow 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):13-16
Optical absorption spectra of cobalt cluster ions, Co n + , and vanadium cluster ions, V n + , were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co 4 + , Co 3 + , and V 4 + have, respectively, a tetrahedral structure with a bond distance of 2.00Å, an equilateral triangle with a bond distance of 2.30Å, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Å and one of 2.89Å. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co 3 + , Co 4 + , and V 4 + , respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively. 相似文献
333.
[reaction: see text] Catalytic asymmetric allylic amination of cycloalkenyl carbonates (methyl cyclohexen-2-yl carbonate, methyl cyclohepten-2-yl carbonate, methyl 5-methoxycarbonylcyclohexen-2-yl carbonate, methyl cyclohexenyl carbonate, tert-butyl 5-methoxycarbonyloxy-1,2,5,6-tetrahydropyridinedicarboxylate) with dibenzylamines ((C6H5CH2)2NH, (C6H5CH2)(4-CH3OC6H4CH2)NH, (4-CH3OC6H4CH2)2NH) was achieved in water under heterogeneous conditions by use of a palladium complex of (3R,9aS)-3-[2-(diphenylphosphino)phenyl]-2-phenyltetrahydro-1H-imidazo[1,5-a]indole-1-one anchored on polystyrene-poly(ethylene glycol) copolymer resin to give the corresponding cycloalkenylamines with high enantiomeric selectivity (90-98% ee). 相似文献
334.
Taka-aki Hisashima Takeshi Matsushita Toshio Asada Shiro Koseki Azumao Toyota 《Theoretical chemistry accounts》2008,120(1-3):85-94
The dissociation energies of MH4 (M = La, Hf–Hg) were computed using full optimized reaction space (FORS) multi-configuration self-consistent field (MCSCF) and second-order multi-reference Møller–Plesset perturbation methods with the SBKJC basis sets augmented by a set of polarization functions (SBKJC(f,p)). It was shown that of the molecules examined, only four tetra-hydrides HfH4, TaH4, WH4, and OsH4 with Td symmetry are lower in energy than the corresponding dissociation limits. For WH4 and OsH4, the potential energy surfaces from the D4h to the Td structure were explored from both theoretical calculations and symmetry arguments based on the pseudo-Jahn- Teller effect. As for WH4, it is found that the ground state could be 3Eg, 3A2g, or 3B2g at the D4h structure. The present calculations suggest that the ground state is 3Eg, and that this state is stabilized by the eu deformation into a C2v structure (3B1) and then sequentially to the most stable Td structure (3A2). If the molecular system is promoted to the lowest 3B2g state, the D4h structure can directly deform into the most stable Td structure along the b2u vibrational mode. For OsH4, the ground state (5B1g) at the D4h structure deforms into a D2d structure and the resulting 5B2 state strongly interacts with the lowest 3E and 1A1 states due to the spin-orbit couplings (SOCs). As a result, it was shown that the relativistic potential energy of the lowest spin-mixed state (ground state) monotonically decreases along the D2d deformation path from the D4h to the Td structure. 相似文献
335.
Catalytic fluorination of 1,3-dicarbonyl compounds with aqueous hydrofluoric acid proceeded efficiently with the aid of iodoarene catalysts in the presence of m-CPBA as a terminal oxidant. o-Iodotoluene, o-iodoanisole, and o-ethyliodobenzene showed a high catalytic efficiency to give 2-fluoro-1,3-dicarbonyl compounds in good yields. 相似文献
336.
Shibo Xu Kazutaka Takamatsu Prof. Dr. Koji Hirano Prof. Dr. Masahiro Miura 《Angewandte Chemie (International ed. in English)》2018,57(36):11797-11801
A Ni(OAc)2‐catalyzed C?H coupling of 8‐aminoquinoline‐derived benzamides with epoxides has been developed. The reaction proceeds with concomitant removal of the 8‐aminoquinoline auxiliary to form the corresponding 3,4‐dihydroisocoumarins directly. Additionally, the nickel catalysis is stereospecific, and the cis‐ and trans‐epoxides are converted into the corresponding cis‐ and trans‐dihydroisocoumarins with retention of configuration, which is complementary to previously reported palladium catalysis. Moreover, while still preliminary, the C ?H functionalization is also achieved in the presence of modified NiCl2 catalysts. 相似文献
337.
Quality evaluation of pearls has been traditionally performed by well-trained experts with the naked eye. Among several characteristics, interference color is a key factor for determining pearl quality. The interference color largely stems from the structure of the pearl’s nacre. In the present study, a method for the optical measurement of the interference color and the determination of its relation to the subjective quality of pearl from the spectral characteristics of light transmitted through the pearl is proposed. The spectral characteristics of the interference colors showed a clear dependence on the subjective quality. To quantify and visualize pearl quality, the wavelength of the interference color that shows a high correlation with subjective quality was selected. A validation test with another set of pearls confirmed that the results of the proposed method were highly correlated with those of expert visual evaluation. 相似文献
338.
Hymenosides G--J were newly isolated from the Japanese fern Hymenophyllum barbatum, in addition to hymenosides A--F. The structures of hymenosides were elucidated by extensive two-dimensional nuclear magnetic resonance and/or chemical evidence. The structures of those aglycones were divided into three types, 1,4-dihydroxy-2-hydroxymethyl-but-2-ene, 1,4-dihydroxy-2-methyl-but-2-ene, and 3-hydroxy-5-hexanolide. The sugar moieties were also established by chemical and spectroscopic methods, which were acylated by phenylacetic acid derivatives. These glycosides had a bitter or weakly pungent taste. 相似文献
339.
Experimental and numerical study on formability of friction stir welded TWB sheets based on hemispherical dome stretch tests 总被引:1,自引:0,他引:1
Wonoh Lee Kyung-Hwan Chung Daeyong Kim Junehyung Kim Chongmin Kim Kazutaka Okamoto R.H. Wagoner Kwansoo Chung 《International Journal of Plasticity》2009,25(9):1626
In order to investigate formability performance and also to obtain guidelines for the stamping process design of friction stir welded TWB (tailor welded blank) sheets, the hemispherical dome stretching test was experimentally performed and the results of the base and friction stir welded samples were compared. Also, in order to better understand the experimental results, numerical analysis was performed. In this work, five automotive sheets, 6111-T4, 5083-H18, 5083-O aluminum alloy, dual-phase steel (DP590) and AZ31 magnesium alloy sheets were considered by (friction stir) welding the same materials. To represent mechanical properties for the numerical analysis, the non-quadratic orthotropic yield function, Yld2000-2d, was utilized for the aluminum alloy and DP590 sheets, while the Cazacu anisotropic/asymmetric yield function was applied for the AZ31 sheet considering different hardening behavior in tension and compression. 相似文献
340.
Guoqiang Xie Minghui Song Kazutaka Mitsuishi Kazuo Furuya 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):564
Self-standing W-nanodendrite structures were grown on SiO2 substrate using an electron-beam-induced deposition (EBID) process with various accelerating voltages from 400 to 1000 kV. Effect of accelerating voltage on crystallization of the nanodendrites was investigated. The nanodendrites consisted of nano-sized grains and amorphous structures. The nano-sized grains were determined to be W crystal in BCC structure. The higher was electron beam accelerating voltage, the higher was crystallinity of the as-fabricated nanodendrites. It is suggested that high-energy electron irradiation enhances diffusion of W atoms in the nanodendrites, promotes crystallization of W grains. 相似文献