全文获取类型
收费全文 | 280篇 |
免费 | 6篇 |
国内免费 | 3篇 |
专业分类
化学 | 229篇 |
力学 | 10篇 |
综合类 | 1篇 |
数学 | 6篇 |
物理学 | 43篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 10篇 |
2007年 | 17篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有289条查询结果,搜索用时 31 毫秒
71.
Twenty different tris(phenylcarbamate)s of cellulose were synthesized and evaluated as chiral stationary phases for HPLC. Optical resolving power of the tris(phenylcarbamate)s depends on the substituents introduced on the phenyl groups. Optical resolving abilities of amylose tris(phenylcarbamate)s were also evaluated. In most cases, either cellulose tris(3,5-dimethylphenylcarbamate) or amylose tris(3,5-dimethylphenylcarbamate) exhibited the highest optical resolving ability. Aralkylcarba-mates such as benzyl- and 1-phenylethylcarbamates of cellulose and amylose were also tested as chiral stationary phases. (S)-1-Phenylethylcarbamate of amylose showed a high optical resolving power. 相似文献
72.
We have investigated the binding of noble-gas (Ng) atoms (Ng=Ar,Kr,Xe) with Pt atom by the ab initio coupled-cluster CCSD(T) method, taking into account the relativistic effects. It is shown that two Ng atoms can bind with Pt atom in linear geometry in the singlet lowest state where the second Ng atom attaches to Pt with the larger binding energy than the first Ng atom. The binding energy is evaluated as 8.2, 17.9, and 33.4 kcal/mol for Ar-Pt-Ar, Kr-Pt-Kr, and Xe-Pt-Xe, respectively, relative to the triplet ground state of the dissociation limit Pt ((3)D)+2Ng. The present results indicate that these Ng-Pt-Ng compounds are possible new gas-phase or matrix species. 相似文献
73.
Ab initio configuration interaction through‐space/bond interaction analysis was proposed for the examination of specific intramolecular interactions including the effect of electron correlations. To test the effectiveness of our method, we applied it to rotational barrier in ethane. The results of our test suggest that the insensitivity of the ethane barrier to geometric relaxations is intimately connected with the cancellation of interactions through orbital overlaps and other factors. The orbital overlaps include exchange repulsion and hyperconjugation; other factors include classic Coulomb interaction and changes in bond orbital energy. The rotational state without the barrier (pure through‐bond state) can be achieved by deleting not only the “vicinal” interactions between the C? H bonds that belong to different methyl groups but also the “geminal” interactions within the methyl groups. Our mixing analysis of molecular orbitals supports the superiority of the staggered conformer by hyperconjugation. Moreover, it was demonstrated that our treatment could be applied to excited states as well as to the ground state, including electron correlation effects. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
74.
M. Oyaidzu A. Yoshikawa Y. Nishikawa K. Munakata M. Nishikawa K. Okuno 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(3):657-660
The annihilation behavior of irradiation defects induced in neutron-irradiated Li2TiO3 and Li2ZrO3 were investigated with the tritium release behavior. It was revealed that the common characteristics in both samples were
that the annihilation process of irradiation defects consisted of two first-order processes and E’-center could act as tritium
trapping site, and otherwise was the way how the E’-center annihilated. The difference was suggested to attribute to the mobility
of M as M4+ (or M3+, etc.). 相似文献
75.
A Zn chlorophyll-a derivative, Zn chlorin-e6 (ZnChl-e6), adsorbed onto a nanocrystalline TiO2 film (ZnChl-e6/TiO2) electrode was prepared, and the photovoltaic properties of the ZnChl-e6/TiO2 electrode were studied. The absorption peaks of ZnChl-e6/TiO2 observed at 420, 654, and 795 nm were attributed to the ZnChl-e6 molecules aggregating onto TiO2 film. The fluorescence attributed to the ZnChl-e6 monomer and aggregate was observed at 710 and 820 nm, respectively, and the fluorescence in both cases was quenched by TiO2 particles. The maximum of the incident photon-to-current conversion efficiency (IPCE) value in the photocurrent action spectrum was 800 nm, and the IPCE value was 7.0%. ZnChl-e6 molecules formed aggregates on a nanocrystalline TiO2 film electrode. From the photocurrent-photovoltage characteristics of the ZnChl-e6/TiO2 electrode irradiated with 100 mW cm(-2), the short-circuit photocurrent (I(SC)) was found to be 0.19 mA cm(-2) and the open-circuit photovoltage (V(OC)) was found to be 375 mV. The maximum power was estimated to be 28.7 microW cm(-2), and the fill factor (FF) was estimated to be 40.1%. A near-IR light induced photovoltaic conversion system using a ZnChl-e6 aggregate formed onto a nanocrystalline TiO2 film electrode was achieved. 相似文献
76.
Munakata H Imai H Nakagawa S Osada A Uemori Y 《Chemical & pharmaceutical bulletin》2003,51(5):614-615
Water-soluble porphyrins containing four platinum(II) complexes per molecule, [5alpha,10beta,15alpha,20beta-tetrakis(2-trans-(alpha,beta,alpha,beta-trans-Pt) and cis-(alpha,beta,alpha,beta-cis-Pt) [PtCl(NH(3))(2)]N-2-aminophenylporphyrin)], were synthesized and characterized. The binding of synthetic nucleotide polymers (poly(dG)-poly(dC), poly(dA)-poly(dT)) to the porphyrins was examined spectrophotometrically in aqueous solution. UV-vis spectral data suggested that these porphyrins bind to the nucleic acids by coordinative and Coulomb interactions. 相似文献
77.
In order to understand the origin of good thermoelectric (TE) properties in the transition metal oxides with the lattice structure isomorphous to the 232-structure, the bond nature between Co and O ions in Bi1.5Pb0.5Ca2−xMxCo2O8−δ-system has been tried to vary by replacing M with Sc3+, Y3+ or La3+ and by changing x from 0 to 0.3. The resistivity is minimum at x = 0.1 in Sc- and Y-systems, but very high in La-system. The large thermopower is obtained in every compound. The experimental TE properties have been discussed mainly within the framework of the charge-transfer scheme in which the ionic radii of Sc3+ and Y3+ smaller than Ca2+ reduce the energy between O 2p levels and Co eg parentages but the large ionic radius of La3+ expands it. The oxygen solubility in the compounds and the lattice distortion peculiar to the 232-structure are also likely to contribute somewhat to the experimental results. 相似文献
78.
Furuya K. Munakata F. Matsuo K. Akimune Y. Ye J. Okada A. 《Journal of Thermal Analysis and Calorimetry》2002,69(3):873-879
An advanced silicon nitride material with high isotropic thermal conductivity (149 W m-1 K-1) has been developed. This high thermal conductivity was achieved with a process that combines high-quality seed crystals
with a suitable additive system to promote grain growth. In this process, the addition of β-Si3N4 seed crystals was found to be effective in improving thermal conductivity due to their low defect and impurity concentrations.
The seed crystals seem to work as nuclei for controlling grain growth during the sintering process. Controlling the growth
of elongated grains so that they do not interact with each other seems important for suppressing the generation of new defects
inside the grains.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
79.
Honoh Suzuki Yuriko Abe Shin‐ichi Ishiguro 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):721-722
The title compound, dibromobis[tris(dimethylamino)phosphine oxide]cobalt(II), [CoBr2(C6H18N3OP)2], displays tetrahedral coordination about cobalt. The molecule has twofold crystallographic site symmetry. The short P—N bonds and the planarity of the dimethylamino groups indicate the importance of dπ–pπ interactions. One of the NMe2 groups has an irregular conformation about the P—N bond and deviates from planarity. It is ascribed to the steric hindrance induced by coordination at the O atom of hexamethylphosphoric triamide. 相似文献
80.
In low‐dimensional molecular crystals that exhibit Peierls instability, the intercolumnar interaction plays an important role in the determination of the conducting property. To predict the crystal structure that exhibits an electronic conduction, we proposed a simple formula based on the molecular orbital theory. In this approach, analytical molecular orbitals of polyene were extended to be applicable for molecular crystals of charge–transfer complexes, and the Peierls distortion was represented by using the first‐ and second‐order perturbation theory. It was concluded that the energetic behaviors and structures calculated by the analytical method developed in the present work are identical to those obtained by the tight‐binding ab initio molecular orbital calculation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献