全文获取类型
收费全文 | 241篇 |
免费 | 16篇 |
专业分类
化学 | 152篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 28篇 |
物理学 | 74篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 23篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 6篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 2篇 |
1967年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有257条查询结果,搜索用时 15 毫秒
1.
Vsevolod Khikhlovskyi Albert J. J. M. van Breemen Jasper J. Michels René A. J. Janssen Gerwin H. Gelinck Martijn Kemerink 《Journal of Polymer Science.Polymer Physics》2015,53(17):1231-1237
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237 相似文献
2.
Hotze AC van der Geer EP Caspers SE Kooijman H Spek AL Haasnoot JG Reedijk J 《Inorganic chemistry》2004,43(16):4935-4943
The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance. 相似文献
3.
4.
Eva Blokker Dr. Xiaobo Sun Prof. Dr. Jordi Poater Dr. Ir. J. Martijn van der Schuur Dr. Trevor A. Hamlin Prof. Dr. F. Matthias Bickelhaupt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(63):15616-15622
We have quantum chemically analyzed element−element bonds of archetypal HnX−YHn molecules (X, Y=C, N, O, F, Si, P, S, Cl, Br, I), using density functional theory. One purpose is to obtain a set of consistent homolytic bond dissociation energies (BDE) for establishing accurate trends across the periodic table. The main objective is to elucidate the underlying physical factors behind these chemical bonding trends. On one hand, we confirm that, along a period (e. g., from C−C to C−F), bonds strengthen because the electronegativity difference across the bond increases. But, down a period, our findings constitute a paradigm shift. From C−F to C−I, for example, bonds do become weaker, however, not because of the decreasing electronegativity difference. Instead, we show that the effective atom size (via steric Pauli repulsion) is the causal factor behind bond weakening in this series, and behind the weakening in orbital interactions at the equilibrium distance. We discuss the actual bonding mechanism and the importance of analyzing this mechanism as a function of the bond distance. 相似文献
5.
Bart W. H. Saes Dr. Martijn M. Wienk Prof. René A. J. Janssen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14221-14228
Introducing solubilizing α-branched alkyl chains on a poly(diketopyrrolopyrrole-alt-terthiophene) results in a dramatic change of the structural, optical, and electronic properties compared to the isomeric polymer carrying β-branched alkyl side chains. When branched at the α-position the alkyl substituent creates a steric hindrance that reduces the tendency of the polymer to π–π stack and endows the material with a much higher solubility in common organic solvents. The wider π–π stacking and reduced tendency to crystallize, evidenced from grazing-incidence wide-angle X-ray scattering, result in a wider optical band gap in the solid state. In solar cells with a fullerene acceptor, the α-branched isomer affords a higher open-circuit voltage, but an overall lower power conversion efficiency as a result of a too well-mixed nanomorphology. Due its reduced π–π stacking, the α-branched isomer fluoresces and affords near-infrared light-emitting diodes emitting at 820 nm. 相似文献
6.
Mengmeng Li Haijun Bin Xuechen Jiao Martijn M. Wienk He Yan Ren A. J. Janssen 《Angewandte Chemie (International ed. in English)》2020,59(2):846-852
It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (Tdis) is investigated as a powerful strategy for morphology control. Low Tdis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π–π stacking. The field‐effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high Tdis with a value approaching 1 cm2 V?1 s?1. Besides that, the solution kinetics reveal a higher growth rate of aggregates at low Tdis, and filtration experiments further confirm that the dependence of the fibril width in monolayers on Tdis is consistent with the aggregate size in solution. The generalizability of the Tdis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high‐mobility monolayer transistors. 相似文献
7.
Dr. Christianus M. A. Leenders Gijs Jansen Martijn M. M. Frissen René P. M. Lafleur Dr. Ilja K. Voets Dr. Anja R. A. Palmans Prof. Dr. E. W. Meijer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4608-4615
We introduce monosaccharides as versatile water‐soluble units to compatibilise supramolecular polymers based on the benzene‐1,3,5‐tricarboxamide (BTA) moiety with water. A library of monosaccharide‐based BTAs is evaluated, varying the length of the alkyl chain (hexyl, octyl, decyl and dodecyl) separating the BTA and saccharide units, as well as the saccharide units (α‐glucose, β‐glucose, α‐mannose and α‐galactose). In all cases, the monosaccharides impart excellent water compatibility. The length of the alkyl chain is the determining factor to obtain either long, one‐dimensional supramolecular polymers (dodecyl spacer), small aggregates (decyl spacer) or molecularly dissolved (octyl and hexyl) BTAs in water. For the BTAs comprising a dodecyl spacer, our results suggest that a cooperative self‐assembly process is operative and that the introduction of different monosaccharides does not significantly change the self‐ assembly behaviour. Finally, we investigate the potential of post‐assembly functionalisation of the formed supramolecular polymers by taking advantage of dynamic covalent bond formation between the monosaccharides and benzoxaboroles. We observe that the supramolecular polymers readily react with a fluorescent benzoxaborole derivative permitting imaging of these dynamic complexes by confocal fluorescence microscopy. 相似文献
8.
Grotenbreg GM Kronemeijer M Timmer MS El Oualid F van Well RM Verdoes M Spalburg E van Hooft PA de Neeling AJ Noort D van Boom JH van der Marel GA Overkleeft HS Overhand M 《The Journal of organic chemistry》2004,69(23):7851-7859
A practical gram-scale and high-yielding synthesis of the antimicrobial peptide gramicidin S is presented. An Fmoc-based solid-phase peptide synthesis protocol is employed for the generation of the linear decapeptide precursor, which is cyclized in solution to afford the target compound. The versatility of our method is demonstrated by the construction of eight gramicidin S analogues (15a-h) having nonproteinogenic sugar amino acid residues (4-7) incorporated in the turn regions. 相似文献
9.
Martijn A. Zwijnenburg Robert G. Bell Furio Corà 《Journal of solid state chemistry》2008,181(9):2480-2487
The energetics, structure and physical properties of tetragonal and orthorhombic SiS2 were calculated by periodic density functional theory (DFT) calculations, using both localized orbital and projected augmented wave basis-sets. All methods applied agree upon the relative energies of the different polymorphs but show differences in the predicted geometries, which are minimized upon improving the basis-set quality. The hybrid PBE0 functional was found to give the best match between experimental and calculated structures. When comparing SiS2 with its much better studied oxide analog silica, we observe that upon substituting sulphur for oxygen, the energy landscape changes dramatically. Other effects of changing S for O are found to be smaller Si-X-Si angles, a broader distribution of X-Si-X angles, a more flexible framework and a significantly reduced band gap. The latter is in line with the experimental observation of photoluminescence in related GaGeS2 compounds and suggests that SiS2 might find application in UV light emitting diodes. Finally, a comparison of the maximally localized Wannier functions demonstrates that the Si-S bonds in SiS2 have a considerably more covalent character than the Si-O bonds in silica. 相似文献
10.
Martijn D.P. Risseeuw Gijs A. van der Marel Herman S. Overkleeft Mark Overhand 《Tetrahedron: Asymmetry》2009,20(6-8):945-951
The design, synthesis and application of oxabicyclo[4.1.0]heptane amino acids as conformationally restricted sugar amino acid dipeptide isosteres are reported. 相似文献