全文获取类型
收费全文 | 925篇 |
免费 | 190篇 |
国内免费 | 64篇 |
专业分类
化学 | 833篇 |
晶体学 | 42篇 |
力学 | 3篇 |
综合类 | 3篇 |
数学 | 3篇 |
物理学 | 295篇 |
出版年
2024年 | 4篇 |
2023年 | 8篇 |
2022年 | 33篇 |
2021年 | 27篇 |
2020年 | 40篇 |
2019年 | 34篇 |
2018年 | 27篇 |
2017年 | 22篇 |
2016年 | 58篇 |
2015年 | 46篇 |
2014年 | 64篇 |
2013年 | 101篇 |
2012年 | 62篇 |
2011年 | 46篇 |
2010年 | 38篇 |
2009年 | 41篇 |
2008年 | 51篇 |
2007年 | 43篇 |
2006年 | 53篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 39篇 |
2002年 | 48篇 |
2001年 | 21篇 |
2000年 | 33篇 |
1999年 | 17篇 |
1998年 | 35篇 |
1997年 | 22篇 |
1996年 | 27篇 |
1995年 | 17篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1179条查询结果,搜索用时 359 毫秒
21.
A. V. Safronova L. N. Bochkarev N. E. Stolyarova I. K. Grigorieva I. P. Malysheva G. V. Basova G. K. Fukin E. V. Baranov Yu. A. Kurskii G. A. Abakumov 《Russian Chemical Bulletin》2006,55(2):218-221
New germanium-containing tungsten carbyne complexes Ph3GeC≡W(CH2R)3 (R = But or SiMe3) were synthesized by the reaction of the alkoxy derivative Ph3GeC≡W(OBut)3 with alkyllithium reagents RCH2Li. The new compounds were isolated in individual form as crystals in 95 and 90% yields, respectively, and were characterized
by elemental analysis, 1H and 13C NMR spectroscopy, and X-ray diffraction. X-ray diffraction study showed that the coordination environment of the W and Ge
atoms in the Ph3GeC≡ W(CH2But)3 and Ph3GeC≡W(CH2SiMe3)3 complexes can be described as a distorted tetrahedron.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 213—216, February, 2006. 相似文献
22.
A. A. Isaeva A. I. Baranov Th. Doert M. Ruck V. A. Kulbachinskii R. A. Lunin B. A. Popovkin 《Russian Chemical Bulletin》2007,56(9):1694-1700
New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni5.68SiSe2, Ni5.46GeSe2, and Ni5.42GeTe2, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten
flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M7−δEX2-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors
in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the
intergrowth structure type under consideration are discussed.
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007. 相似文献
23.
Michael Chariss Andrea Zickgraf Heike Stenger Elmar Bru Cristelle Desmarquet Martin Drger Silke Gerstmann Dainis Dakternieks James Hook 《Polyhedron》1998,17(25-26)
44 members of thecompound series Ph4−nMRn (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph3Sn (o-Tol) and PhSn (o-Tol)3 were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. 29 Si-, 119 Sn- and 207 Pb-NMR chemical shifts were determined in solution and in the solid state. 73 Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups. 相似文献
24.
S. Agnello R. Boscaino F. La Mattina S. Grandi A. Magistris 《Journal of Sol-Gel Science and Technology》2006,37(1):63-68
We have studied the generation mechanisms of H(II) paramagnetic centers in Ge-doped silica by investigating up to 104 mol ppm sol-gel Ge-doped silica materials. We have considered materials with the same concentrations of Ge but that are produced
by two different densification routes that give rise to different concentrations of Ge-related oxygen deficient centers (GeODC(II)).
These centers are characterized by an optical absorption band at ∼5.2 eV (B2β band) and two related emissions at ∼3.2 eV and ∼4.3 eV. The GeODC(II) content was estimated by absorption and emission measurements.
The H(II) centers were induced by room temperature γ-ray irradiation and their concentration was determined by electron paramagnetic
resonance measurements.
The comparison between the two kinds of materials, obtained by different preparations, shows that the GeODC(II) concentration
increases with the Ge content and is enhanced by vacuum densification. The comparison of irradiated samples shows that beyond
the already known process of conversion of preexisting GeODC(II) into H(II) centers, another generation process of H(II) centers
is effective that involves irradiation induced GeODC(II). 相似文献
25.
Wei Jiang Zheng-Long Yang Ding Weng Jun-Wei Wangb Yun-Feng Lu Min-Juan Zhang Zhen-Zhong Yang 《中国化学快报》2014,25(6):849-853
PbTe/SnTe hybrid nanocrystals with designed shape, chemical composition and narrow size distribution were synthesized by an efficient solvothermal approach. This approach enables mass and economical synthesis of PbTe-based nanocrystals. The organic ligands were completely removed by pretreatment with a super-hydride solution, making it possible to fabricate fully dense and robust thermoelectric devices with increased electrical conductivity. 相似文献
26.
The advent of multiple collector–inductively coupled plasma–mass spectrometry (MC-ICP-MS) has made the high-precision determination of Ge isotopes possible, which leads to the widespread application of Ge isotopes in earth, ocean, and cosmochemistry fields. This paper reviews the history of Ge isotope analysis, chemical dissolution and purification, and mass spectrometry measurements. Concentrated HNO3 is sufficient to dissolve nearly all types of samples and HF is also involved for Si-rich samples. Low-temperature ashing prior to dissolution is an alternative way to preconcentrate Ge in organic-rich samples. For different matrices, Ge isotopes can be determined by MC-ICP-MS coupled with a traditional nebulizer system or hydride generation system after two-step separation, one step cation/anion-exchange separation, or Mg/Fe co-precipitation protocols. Ion-exchange column methods are suitable for samples with elevated matrix and Ge content such as sulfides, iron oxides, silicate rocks, and coals, whereas Mg or Fe coprecipitation methods are particularly suitable for all kinds of water. Hydride generation systems are improved over traditional nebulizer system due to the smaller sample quantity and fewer matrix-related interferences. Sample-standard bracketing, double spike, and external Ga isotope normalization are used to mass bias correction and yield consistent results. Analytical methods involving Ge-poor samples and Ge isotope analyses based on different Ge species or specific Ge compound in natural environment will be important prospects in the further study. For further applications of Ge isotopes in mineral deposits such as sulfide and iron oxide deposits, sulfides, and iron oxides reference materials should be developed in the future. 相似文献
27.
《Mendeleev Communications》2022,32(1):19-21
A method for the facile synthesis of chiral germanium(IV) binaphthoxide complexes from the corresponding binaphthols and an organogermanium trichloride has been developed, which allows these unusual types of compounds to be synthesized in high yields. The crystal structure of one such complex, (S)-[Ge{O2C20H10(SiMe3)2-3,3'}{Cl}{Ph}], has been determined. 相似文献
28.
Dr. Todor Baramov Bianca Schmid Ho Ryu Jinhoon Jeong Dr. Karlijn Keijzer Dr. Leonard von Eckardstein Prof. Dr. Mu-Hyun Baik Prof. Dr. Roderich D. Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(28):6955-6962
The E. coli siderophore enterobactin, the strongest FeIII chelator known to date, forms hexacoordinate complexes with SiIV, GeIV, and TiIV. Synthetic protocols have been developed to prepare non-symmetric enterobactin analogues with varying denticities. Various benzoic acid residues were coupled to the macrocyclic lactone to afford a diverse library of ligands. These enterobactin analogues were bound to SiIV, GeIV, and TiIV, and the complexes were investigated through experimental and computational techniques. The binding behavior of the synthesized chelators enabled assessment of the contribution of each of the phenolic hydroxy groups in enterobactin to metal-ion complexation. It was found that at least four O-donors are needed for enterobactin derivatives to act as metal binders. Density functional theory calculations indicate that the strong binding behavior of enterobactin can be ascribed to a diminished translational entropy penalty, a common feature of the chelate effect, coupled with the structural arrangement of the three catechol moieties, which allows the triseryl base to be installed without distorting the preferred local metal-binding geometry of the catecholate ligands. 相似文献
29.
Dr. Ting Ouyang Sheng Huang Xiao-Tong Wang Prof. Zhao-Qing Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14024-14035
One of the most effective ways to cope with the problems of global warming and the energy shortage crisis is to develop renewable and clean energy sources. To achieve a carbon-neutral energy cycle, advanced carbon sequestration technologies are urgently needed, but because CO2 is a thermodynamically stable molecule with the highest carbon valence state of +4, this process faces many challenges. In recent years, electrochemical CO2 reduction has become a promising approach to fix and convert CO2 into high-value-added fuels and chemical feedstock. However, the large-scale commercial use of electrochemical CO2 reduction systems is hindered by poor electrocatalyst activity, large overpotential, low energy conversion efficiency, and product selectivity in reducing CO2. Therefore, there is an urgent need to rationally design highly efficient, stable, and scalable electrocatalysts to alleviate these problems. This minireview also aims to classify heterogeneous nanostructured electrocatalysts for the CO2 reduction reaction (CDRR). 相似文献
30.
Hengfeng Fan Huafeng Zhou Chaolong Ma Yiqing Huang Yan Li 《Molecular Crystals and Liquid Crystals》2014,593(1):232-242
The effect of humidity on the holographic grating diffraction efficiency and transmittance kinetics in the E204Q BR gelatin film is investigated. We found a correlation between the accumulation of the red-light absorbing O intermediate in the later part of the E204Q BR photocycle and sharpness (decay to the steady-state) of the holographic recording kinetics. As shown, at humidity exceeding 95% the ratio between the peak and steady-state of the diffraction efficiency for the weak probe beam (670 nm) can reach 8.7 in the E204Q BR film, which is sufficient for realization of an efficient novelty filter. 相似文献