全文获取类型
收费全文 | 511篇 |
免费 | 55篇 |
国内免费 | 3篇 |
专业分类
化学 | 487篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 37篇 |
物理学 | 39篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 15篇 |
2021年 | 19篇 |
2020年 | 35篇 |
2019年 | 37篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 33篇 |
2015年 | 35篇 |
2014年 | 38篇 |
2013年 | 24篇 |
2012年 | 44篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 13篇 |
2008年 | 31篇 |
2007年 | 24篇 |
2006年 | 18篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 12篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1968年 | 1篇 |
1961年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有569条查询结果,搜索用时 15 毫秒
61.
We apply two- and three-dimensional numerical calculations to study optical nanoantennae made of two coupled gold nanostructures, enclosing a single emitter in their gap. We show that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime. We examine the competition between the radiative and nonradiative processes in the presence of the antennae as a function of wavelength and antenna geometry. Our results hold great promise for improving the quantum efficiency of poor emitters such as silicon nanocrystals or carbon nanotubes. 相似文献
62.
Direct In Situ Investigation of Milling Reactions Using Combined X‐ray Diffraction and Raman Spectroscopy 下载免费PDF全文
M. Sc. Lisa Batzdorf Dipl.‐Chem. Franziska Fischer Dipl.‐Chem. Manuel Wilke Dipl.‐Ing. Klaus‐Jürgen Wenzel Dr. Franziska Emmerling 《Angewandte Chemie (International ed. in English)》2015,54(6):1799-1802
The combination of two analytical methods including time‐resolved in situ X‐ray diffraction (XRD) and Raman spectroscopy provides a new opportunity for a detailed analysis of the key mechanisms of milling reactions. To prove the general applicability of our setup, we investigated the mechanochemical synthesis of four archetypical model compounds, ranging from 3D frameworks through layered structures to organic molecular compounds. The reaction mechanism for each model compound could be elucidated. The results clearly show the unique advantage of the combination of XRD and Raman spectroscopy because of the different information content and dynamic range of both individual methods. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structures and thus obtaining reliable data for mechanistic studies. 相似文献
63.
Stability and Conversion of Tin Zintl Anions in Liquid Ammonia Investigated by NMR Spectroscopy 下载免费PDF全文
Franziska Fendt Dr. Carina Koch Dr. Maria Neumeier Dr. Stefanie Gärtner Prof. Dr. Ruth M. Gschwind Prof. Dr. Nikolaus Korber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14539-14544
Homoatomic polyanions of post‐transition main‐group metals, namely, Zintl anions, are precast in analogous Zintl phases and can react in solution to form new materials. Despite comprehensible reaction approaches, the formed products cannot be planned in advance, as hitherto undetected and therefore disregarded side reactions take place. The outcomes and interpretations of the reactions of Zintl anions are so far based mainly on crystal structures, which only allow characterization of the product that has the lowest solubility. Here we present the results of our investigation of the stability of highly charged tin Zintl anions in liquid ammonia, which is not exclusively based on solution effects but also on the oxidative influence of the solvent. This allows for a deeper understanding of the ongoing processes in solution and opens doors to the directed synthesis of transition metal complexes of Sn44?, here shown by its reactivity towards MesCu. 相似文献
64.
Rahn T Bendrath F Hein M Baumann W Jiao H Börner A Villinger A Langer P 《Organic & biomolecular chemistry》2011,9(14):5172-5184
Bis-cyclopropanated 1,3,5-tricarbonyl compounds were prepared by a sequence of Claisen condensations and cyclopropanations. The optimization of the conditions proved to be very important to suppress retro-Claisen reactions. The conformation of these molecules was studied by experimental and computational methods. The syn/syn;syn/syn conformation is present for all derivatives. It is exclusively present in the case of the derivative containing a phenyl group located at the terminal carbon atom. In most cases, equilibria with other conformers are found. 相似文献
65.
66.
67.
Gao YK Traeger F Kotsis K Staemmler V 《Physical chemistry chemical physics : PCCP》2011,13(22):10709-10718
The adsorption of alanine on the mixed-terminated ZnO(10 ?10) surface is studied by means of quantum-chemical ab initio calculations. Using a finite cluster model and the adsorption geometry as obtained both by periodic CPMD and embedded cluster calculations, the C1s, N1s and O1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra are calculated for single alanine molecules on ZnO(10 ?10). These spectra are compared with the spectra calculated for alanine in the gas phase and in its crystalline form and with experimental XPS and NEXAFS data for the isolated alanine molecule and for alanine adsorbed on ZnO(10 ?10) at multilayer and monolayer coverage. The excellent agreement between the experimental and calculated XP and NEXAFS spectra confirms the calculated adsorption geometry: A single alanine molecule is bound to ZnO(10 ?10) in a dissociated bidentate form with the two O atoms of the acid group bound to two Zn atoms of the surface and the proton transferred to one O atom of the surface. Other possible structures, such as adsorption of alanine in one of its neutral or zwitterionic forms in which the proton of the -COOH group remains at this group or is transferred to the amino group, can be excluded since they would give rise to quite different XP spectra. In the multilayer coverage regime, on the other hand, alanine is in its crystalline form as is also shown by the analysis of the XP spectra. 相似文献
68.
Synthesis and crystal structure of the isotypic rare earth thioborates Ce[BS3], Pr[BS3], and Nd[BS3]
Jens Hunger 《Journal of solid state chemistry》2010,183(3):702-4479
The orthothioborates Ce[BS3], Pr[BS3] and Nd[BS3] were prepared from mixtures of the rare earth (RE) metals together with amorphous boron and sulfur summing up to the compositions CeB3S6, PrB5S9 and NdB3S6. The following preparation routes were used: solid state reactions with maximum temperatures of 1323 K and high-pressure high-temperature syntheses at 1173 K and 3 GPa. Pr[BS3] and Nd[BS3] were also obtained from rare earth chlorides RECl3 and sodium thioborate Na2B2S5 by metathesis type reactions at maximum temperatures of 1073 K. The crystal structure of the title compounds was determined from X-ray powder diffraction data. The thioborates are isotypic and crystallize in the orthorhombic spacegroup Pna21 (No. 33; Z=4; Ce: , , ; Pr: , , ; Nd: , , ) . The crystal structures contain isolated [BS3]3‐ groups with boron in trigonal-planar coordination. The sulfur atoms form the vertices of undulated kagome nets, which are stacked along [100] according to the sequence ABAB. Within these nets every second triangle is occupied by boron and the large hexagons are centered by rare earth ions, which are surrounded by overall nine sulfur species. 相似文献
69.
Uwe Bhme Franziska Bendrath Betty Günther 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):o631-o632
In the title compound, C8H22Cl2N2Si3, the central Si atom is tetrahedrally coordinated by two Cl and two N atoms in a molecule that has crystallographically imposed C2 symmetry. Comparison is made with the isomorphous structure having titanium instead of silicon at the central position in the diazacyclopentane ring [Tinkler, Deeth, Duncalf & McCamley (1996). Chem. Commun. pp. 2623–2624]. 相似文献
70.
A regioselective synthesis of 2,4,6-trisubstituted pyridine is described starting from 2,6-dibromo-4-nitropyridine. All three different regioisomers of the 2,4,6-triamino substituted pyridine have been synthesized in four to five steps. The method described is a general route to unsymmetrical 2,4,6-trisubstituted amino pyridines. 相似文献