全文获取类型
收费全文 | 2261篇 |
免费 | 56篇 |
国内免费 | 2篇 |
专业分类
化学 | 1519篇 |
晶体学 | 8篇 |
力学 | 28篇 |
数学 | 256篇 |
物理学 | 508篇 |
出版年
2020年 | 20篇 |
2019年 | 23篇 |
2016年 | 43篇 |
2015年 | 35篇 |
2014年 | 30篇 |
2013年 | 78篇 |
2012年 | 67篇 |
2011年 | 77篇 |
2010年 | 46篇 |
2009年 | 48篇 |
2008年 | 73篇 |
2007年 | 63篇 |
2006年 | 69篇 |
2005年 | 57篇 |
2004年 | 41篇 |
2003年 | 48篇 |
2002年 | 39篇 |
2001年 | 36篇 |
2000年 | 33篇 |
1998年 | 19篇 |
1996年 | 49篇 |
1995年 | 60篇 |
1994年 | 33篇 |
1993年 | 48篇 |
1992年 | 44篇 |
1991年 | 32篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 27篇 |
1986年 | 28篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 39篇 |
1981年 | 41篇 |
1980年 | 30篇 |
1979年 | 39篇 |
1978年 | 29篇 |
1977年 | 35篇 |
1976年 | 39篇 |
1975年 | 29篇 |
1974年 | 45篇 |
1973年 | 33篇 |
1972年 | 22篇 |
1968年 | 30篇 |
1967年 | 37篇 |
1966年 | 43篇 |
1965年 | 29篇 |
1964年 | 42篇 |
1963年 | 37篇 |
排序方式: 共有2319条查询结果,搜索用时 15 毫秒
1.
Dr. Xiaoyan Sun Prof. Dr. Shaodong Zhou Dr. Lei Yue Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(14):3550-3559
Thermal gas-phase reactions of the ruthenium-oxide clusters [RuOx]+ (x=1–3) with methane and dihydrogen have been explored by using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. For methane activation, as compared to the previously studied [RuO]+/CH4 couple, the higher oxidized Ru systems give rise to completely different product distributions. [RuO2]+ brings about the generations of [Ru,O,C,H2]+/H2O, [Ru,O,C]+/H2/H2O, and [Ru,O,H2]+/CH2O, whereas [RuO3]+ exhibits a higher selectivity and efficiency in producing formaldehyde and syngas (CO+H2). Regarding the reactions with H2, as compared to CH4, both [RuO]+ and [RuO2]+ react similarly inefficiently with oxygen-atom transfer being the main reaction channel; in contrast, [RuO3]+ is inert toward dihydrogen. Theoretical analysis reveals that the reduction of the metal center drives the overall oxidation of methane, whereas the back-bonding orbital interactions between the cluster ions and dihydrogen control the H−H bond activation. Furthermore, the reactivity patterns of [RuOx]+ (x=1–3) with CH4 and H2 have been compared with the previously reported results of Group 8 analogues [OsOx]+/CH4/H2 (x=1–3) and the [FeO]+/H2 system. The electronic origins for their distinctly different reaction behaviors have been addressed. 相似文献
2.
3.
Dr. Shaodong Zhou Dr. Jilai Li Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3073-3076
Carbon‐atom extrusion from the ipso‐position of a halobenzene ring (C6H5X; X=F, Cl, Br, I) and its coupling with a methylene ligand to produce acetylene is not confined to [LaCH2]+; also, the third‐row transition‐metal complexes [MCH2]+, M=Hf, Ta, W, Re, and Os, bring about this unusual transformation. However, substrates with substituents X=CN, NO2, OCH3, and CF3 are either not reactive at all or give rise to different products when reacted with [LaCH2]+. In the thermal gas‐phase processes of atomic Ln+ with C7H7Cl substrates, only those lanthanides with a promotion energy small enough to attain a 4fn5d16s1 configuration are reactive and form both [LnCl]+ and [LnC5H5Cl]+. Branching ratios and the reaction efficiencies of the various processes seem to correlate with molecular properties, like the bond‐dissociation energies of the C?X or M+?X bonds or the promotion energies of lanthanides. 相似文献
4.
5.
6.
7.
Prof. Dr. Shaodong Zhou Dr. Xiaoyan Sun Dr. Lei Yue Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):2967-2971
The thermal gas-phase reactions of [Al2VO5]+ and [AlV2O6]+ with methane have been explored by using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry complemented by high-level quantum chemical calculations. Both cluster ions chemisorbed methane as the major reaction channels at room temperature. [Al2VO5]+ could break only one C−H bond to liberate CH3, whereas [AlV2O6]+ exhibited higher oxidizing ability such that it brings about the selective generation of formaldehyde. Mechanistic aspects are revealed and the crucial roles of the metal centers are discussed. 相似文献
8.
Prof. Dr. Helmut Schwarz 《Angewandte Chemie (International ed. in English)》2015,54(35):10090-10100
Gas‐phase investigations of judiciously doped oxide clusters permit to address fundamental challenges related to, for example, the low‐temperature oxidation of CO or the selective conversion of hydrocarbons. Modifying the size and composition of a free cluster in a controlled way enables the modification of local charge effects and of spin states, and spectroscopic studies in combination with computational work help to identify the active site of a catalyst and to unravel mechanistic details. Also, the interplay of the support material with the reactive part of a composite catalyst cluster can be addressed. Examples will be presented demonstrating how and why the gas‐phase reactivities of heteronuclear clusters, in comparison with their homonuclear counterparts, toward small, generally rather inert molecules can be increased, decreased, or not significantly affected. 相似文献
9.
On the Role of the Electronic Structure of the Heteronuclear Oxide Cluster [Ga2Mg2O5].+ in the Thermal Activation of Methane and Ethane: An Unusual Doping Effect 下载免费PDF全文
Dr. Jilai Li Dr. Xiao‐Nan Wu Dr. Maria Schlangen Dr. Shaodong Zhou Dr. Patricio González‐Navarrete Dr. Shiya Tang Prof. Dr. Helmut Schwarz 《Angewandte Chemie (International ed. in English)》2015,54(17):5074-5078
The reactivity of the heteronuclear oxide cluster [Ga2Mg2O5].+, bearing an unpaired electron at a bridging oxygen atom (Ob.?), towards methane and ethane has been studied using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). Hydrogen‐atom transfer (HAT) from both methane and ethane to the cluster ion is identified experimentally. The reaction mechanisms of these reactions are elucidated by state‐of‐the‐art quantum chemical calculations. The roles of spin density and charge distributions in HAT processes, as revealed by theory, not only deepen our mechanistic understanding of C? H bond activation but also provide important guidance for the rational design of catalysts by pointing to the particular role of doping effects. 相似文献
10.
Noah Schwarz Xiaofei Sun Dr. Ravi Yadav Dr. Ralf Köppe Dr. Thomas Simler Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12857-12865
Divalent lanthanide and alkaline-earth complexes supported by N-heterocyclic carbene (NHC) ligands have been accessed by redox-transmetalation between air-stable NHC-AgI complexes and the corresponding metals. By using the small ligand 1,3-dimethylimidazol-2-ylidene (IMe), two series of isostructural complexes were obtained: the tetra-NHC complexes [LnI2(IMe)4] (Ln=Eu and Sm) and the bis-NHC complexes [MI2(IMe)2(THF)2] (M=Yb, Ca and Sr). In the former, distortions in the NHC coordination were found to originate from intermolecular repulsions in the solid state. Application of the redox-transmetalation strategy with the bulkier 1,3-dimesitylimidazol-2-ylidene (IMes) ligand yielded [SrI2(IMes)(THF)3], while using a similar procedure with Ca metal led to [CaI2(THF)4] and uncoordinated IMes. DFT calculations were performed to rationalise the selective formation of the bis-NHC adduct in [SrI2(IMe)2(THF)2] and the tetra-NHC adduct in [SmI2(IMe)4]. Since the results in the gas phase point towards preferential formation of the tetra-NHC complexes for both metal centres, the differences between both arrangements are a result of solid-state effects such as slightly different packing forces. 相似文献