全文获取类型
收费全文 | 3051篇 |
免费 | 72篇 |
国内免费 | 4篇 |
专业分类
化学 | 1752篇 |
晶体学 | 28篇 |
力学 | 78篇 |
数学 | 381篇 |
物理学 | 888篇 |
出版年
2020年 | 26篇 |
2019年 | 22篇 |
2017年 | 22篇 |
2016年 | 72篇 |
2015年 | 53篇 |
2014年 | 45篇 |
2013年 | 118篇 |
2012年 | 102篇 |
2011年 | 102篇 |
2010年 | 91篇 |
2009年 | 76篇 |
2008年 | 112篇 |
2007年 | 120篇 |
2006年 | 104篇 |
2005年 | 80篇 |
2004年 | 80篇 |
2003年 | 67篇 |
2002年 | 65篇 |
2001年 | 70篇 |
2000年 | 66篇 |
1999年 | 62篇 |
1998年 | 41篇 |
1997年 | 38篇 |
1996年 | 50篇 |
1995年 | 50篇 |
1994年 | 50篇 |
1993年 | 42篇 |
1992年 | 73篇 |
1991年 | 42篇 |
1990年 | 57篇 |
1989年 | 40篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 46篇 |
1985年 | 55篇 |
1984年 | 47篇 |
1983年 | 40篇 |
1982年 | 43篇 |
1981年 | 41篇 |
1980年 | 51篇 |
1979年 | 57篇 |
1978年 | 35篇 |
1977年 | 49篇 |
1976年 | 32篇 |
1975年 | 39篇 |
1974年 | 27篇 |
1973年 | 25篇 |
1971年 | 28篇 |
1967年 | 28篇 |
1966年 | 26篇 |
排序方式: 共有3127条查询结果,搜索用时 0 毫秒
101.
102.
103.
104.
[RuCl2(PPh3)3] reacts with thallium(I) fluoride to give either [Tl(mu-F)3Ru(PPh3)3] (1) or [Tl(mu3-F)(mu2-Cl)2Ru2(mu2-Cl)(mu2-F)(PPh3)4] (2) depending on the excess of TlF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)2(H2)(PPh3)3] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu3-F)(mu2-F)(mu2-X)Ru2(mu2-Br)(mu2-F)(PPh3)4] (X=Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d6 and d8 complexes containing hard ligands (such as fluoro, oxo, and amido). 相似文献
105.
Hidenori Okamura Antony Crisp Sarah Hübner Sidney Becker Petra Rov Thomas Carell 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18864-18869
The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information‐carrying RNA oligomers able to self‐replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto‐RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis‐urea (biuret) and tris‐urea (triuret) are able to directly react with ribose. The urea‐ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides’ base‐pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea‐containing RNA bases are good candidates for a proto‐RNA world. 相似文献
106.
107.
Ferry Heus Martin Giera Gerdien E. de Kloe Dick van Iperen Joost Buijs Tariq T. Nahar August B. Smit Henk Lingeman Iwan J. P. de Esch Wilfried M. A. Niessen Hubertus Irth Jeroen Kool 《Analytical and bioanalytical chemistry》2010,398(7-8):3023-3032
One way to profile complex mixtures for receptor affinity is to couple liquid chromatography (LC) on-line to biochemical detection (BCD). A drawback of this hyphenated screening approach is the relatively high consumption of sample, receptor protein and (fluorescently labeled) tracer ligand. Here, we worked toward minimization of sample and reagent consumption, by coupling nano-LC on-line to a light-emitting diode (LED) based capillary confocal fluorescence detection system capable of on-line BCD with low-flow rates. In this fluorescence detection system, a capillary with an extended light path (bubble cell) was used as a detection cell in order to enhance sensitivity. The technology was applied to a fluorescent enhancement bioassay for the acetylcholine binding protein, a structural analog of the extracellular ligand-binding domain of neuronal nicotinic acetylcholine receptors. In the miniaturized setup, the sensitive and low void volume LED-induced confocal fluorescence detection system operated in flow injection analysis mode allowing the measurement of IC50 values, which were comparable with those measured by a conventional plate reader bioassay. The current setup uses 50 nL as injection volume with a carrier flow rate of 400 nL/min. Finally, coupling of the detection system to gradient reversed-phase nano-LC allowed analysis of mixtures in order to identify the bioactive compounds present by injecting 10 nL of each mixture. 相似文献
108.
109.
The high pressure behaviour of InI is studied by DFT‐calculations and compared with experimental data. The existence of a 5s2 electron pair in In+ represents an unfavourable bonding situation for high symmetry structures because of effective closed shell repulsion. Since cations with a ns2 electron pair are highly polarizable and the electronic situation is more favourable in the low symmetry structure InI prefers a TlI‐type structure at ambient pressure. A pressure induced transition to the more densely packed high symmetry CsCl‐type structure takes place at about 19 GPa according to our calculations. At ambient pressure the interactions are predominantly ionic. However with increasing pressure the distances between In+ cations in the TlI‐type structure diminish drastically, mainly due to the changing space requirement of the lone electron pair. Apart from ionic interactions further bonding interactions between the In+ cations occur. At elevated pressure the electron localization function (ELF) as well as the band structure diagrams suggest metallic bonding between the In+ within the zigzag chain, i. e. increasing bonding interactions between the In+ cations due to the electron pair and its s‐p‐mixing. At ambient pressure In‐In interactions are rather weak and the space requirement of the lone electron pair mainly determines the characteristic arrangement of the ions. At elevated pressure the In‐In interactions become stronger and stabilise themselves additionally the specific structural arrangement. 相似文献
110.
Günter Reck Roland Becker 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m134-m136
Bis(N,N‐di‐n‐butyldithiocarbamato‐κ2S,S′)(1,10‐phenanthroline‐κ2N,N′)zinc(II) ethanol hemisolvate, [Zn(C9H18NS2)2(C12H8N2)]·0.5C2H6O, (I), and bis(N,N‐di‐n‐hexyldithiocarbamato‐κ2S,S′)bis(1,10‐phenanthroline‐κ2N,N′)calcium(II), [Ca(C13H26NS2)2(C12H8N2)2], (II), are mixed‐ligand complexes. In the first compound, the Zn atom has a distorted octahedral coordination, while in the second compound, the Ca atom is eight‐coordinate, with four S and four N atoms forming a highly distorted cube. 相似文献