全文获取类型
收费全文 | 4243篇 |
免费 | 77篇 |
国内免费 | 9篇 |
专业分类
化学 | 2889篇 |
晶体学 | 17篇 |
力学 | 69篇 |
数学 | 946篇 |
物理学 | 408篇 |
出版年
2020年 | 31篇 |
2019年 | 40篇 |
2016年 | 77篇 |
2015年 | 58篇 |
2014年 | 36篇 |
2013年 | 127篇 |
2012年 | 96篇 |
2011年 | 153篇 |
2010年 | 115篇 |
2009年 | 121篇 |
2008年 | 145篇 |
2007年 | 133篇 |
2006年 | 146篇 |
2005年 | 131篇 |
2004年 | 99篇 |
2003年 | 97篇 |
2002年 | 72篇 |
2001年 | 35篇 |
2000年 | 30篇 |
1999年 | 33篇 |
1998年 | 34篇 |
1997年 | 45篇 |
1996年 | 66篇 |
1995年 | 72篇 |
1994年 | 51篇 |
1993年 | 60篇 |
1992年 | 91篇 |
1991年 | 86篇 |
1990年 | 75篇 |
1989年 | 71篇 |
1988年 | 58篇 |
1987年 | 62篇 |
1986年 | 61篇 |
1985年 | 76篇 |
1984年 | 91篇 |
1983年 | 83篇 |
1982年 | 76篇 |
1981年 | 101篇 |
1980年 | 61篇 |
1979年 | 78篇 |
1978年 | 71篇 |
1977年 | 98篇 |
1976年 | 70篇 |
1975年 | 83篇 |
1974年 | 90篇 |
1973年 | 66篇 |
1972年 | 54篇 |
1971年 | 47篇 |
1970年 | 38篇 |
1962年 | 29篇 |
排序方式: 共有4329条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
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
5.
Lajos Attila Papp Gabriel Hancu rpd Gyresi Hajnal Kelemen Zoltn‐Istvn Szab Bla Noszl Pavel Dubský Gerg Tth 《Electrophoresis》2019,40(21):2799-2805
Novel capillary electrophoresis methods using CDs as chiral selectors were developed and validated for the chiral separation of lansoprazole and rabeprazole, two proton pump inhibitors. Fourteen different neutral and anionic CDs were screened at pH 4 and 7 in the preliminary analysis. Sulfobutyl‐ether‐β‐CD with a degree of substitution of 6.5 and 10 at neutral pH proved to be the most suitable chiral selector for both compounds. Various dual CD systems were also compared, and the possible mechanisms of enantiomer separation were investigated. A dual selector system containing sulfobutyl‐ether‐β‐CD degree of substitution 6.5 and native γ‐CD proved to be the most adequate system for the separations. Method optimization was carried out using an experimental design approach, performing an initial fractional factorial screening design, followed by a central composite design to establish the optimal analytical conditions. The optimized methods (25 mM phosphate buffer, pH 7, 10 mM sulfobutyl‐ether‐β‐CD/20 mM γ‐CD, +20 kV voltage; 17°C temperature; 50 mbar/3 s injection, detection at 210 nm for lansoprazole; 25 mM phosphate buffer, pH 7, 15 mM sulfobutyl‐ether‐β‐CD/30 mM γ‐CD, +20 kV voltage; 18°C temperature; 50 mbar/3 s injection, detection at 210 nm for rabeprazole) provided baseline separation for lansoprazole (Rs = 2.91) and rabeprazole (Rs = 2.53) enantiomers with favorable migration order (in both cases the S‐enantiomers migrates first). The optimized methods were validated according to current guidelines and proved to be reliable, linear, precise, and accurate for the determination of 0.15% distomer as chiral impurity in dexlansoprazole and dexrabeprazole samples. 相似文献
6.
7.
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
8.
9.
10.