全文获取类型
收费全文 | 198篇 |
免费 | 8篇 |
专业分类
化学 | 173篇 |
晶体学 | 2篇 |
数学 | 14篇 |
物理学 | 17篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 12篇 |
2011年 | 17篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 18篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1996年 | 1篇 |
1993年 | 2篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 5篇 |
1966年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有206条查询结果,搜索用时 15 毫秒
201.
G. G. Dvoryantseva M. M. Kaganskii I. S. Musatova A. S. Elina 《Chemistry of Heterocyclic Compounds》1974,10(11):1366-1370
The electronic spectra of neutral molecules and monocations of N-oxides of 2- and 3-substituted pyrazines and quinoxalines were measured, and their ionization constants in water were determined. The position of the protonation center in the investigated compounds was established. 相似文献
202.
N. E. Britikova L. A. Belova O. Yu. Magidsoh A. S. Elina 《Chemistry of Heterocyclic Compounds》1974,10(1):117-119
10-Chloro-2,4-dioxo derivatives of pyrimido[5,4-b]quinoline have been synthesized, and nucleophilic substitution reactions in these compounds have been studied. 相似文献
203.
Löfman M Koivukorpi J Noponen V Salo H Sievänen E 《Journal of colloid and interface science》2011,360(2):633-644
A series of amino- and hydroxyalkyl amides of bile acids have been synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), (1)H and (13)C nuclear magnetic resonance spectroscopy (NMR), as well as electrospray ionization mass spectrometry (ESI-MS) measurements. The ability of the synthesized molecules to promote gel formation was systematically investigated. Out of 396 combinations formed by 11 compounds and 36 different solvents, 22 gel-containing systems were obtained with 1% (w/v) gelator concentration. Apart from one exception, the gelator compounds were lithocholic acid derivatives. This challenges the general trend of bile acid-based physical gelators, according to which the gelation ability of lithocholic acid derivatives is poor. A correlation between the values of Kamlet-Taft parameters and solvent preferences for gelators was observed. The morphologies of the solid and gel structures studied with scanning electron microscopy (SEM) showed variability from fibers to spherical microscale aggregates, the latter of which are unique among bile acid-based organogels. The gels exhibited more complex behavior than was previously established with bile acid derivatives, judging by the microscale diversity present in gelating and non-gelating systems and the tendency for polymorphism. This study underlines the importance of both the molecular and colloidal scale aspects of the gelation phenomenon. 相似文献
204.
Massera C Melegari M Kalenius E Ugozzoli F Dalcanale E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(11):3064-3068
Guest-switchable crystals: A solid-state guest exchange of the tetraphosphonate cavitand Tiiii[H,CH(3),Ph] as host promotes single-crystal-to-single-crystal transformations (see graphic). The strong preference for methanol over water is observed in all three phases (gas, liquid, solid), thus demonstrating the fundamental role played by the preorganized cavity through synergistic H-bonds and C-H???π interactions. 相似文献
205.
Gita Sakale Maris Knite Valdis Teteris Velta Tupureina Santa Stepina Elina Liepa 《Central European Journal of Physics》2011,9(2):307-312
Polymer-nanostructured carbon composites (PNCC) using three different polymers as composite matrix materials (polyvinylacetate
(PVAc), polyethylene glycol (PEG) and ethylene-vinylacetate copolymer (EVA)) have been developed. High structure carbon black
Printex XE2 (Degussa AG) was used as a composites filler. Ethanol vapour sensor-effect of composites was determined as a change
of electrical resistance as the composite was held in ethanol vapour for 30 seconds. Reversibility of electrical resistance
of PNCC, response stability and repeatability have been measured and compared. The electrical resistance response of EVA-nanostructured
carbon composite (EVA-NCC) to ethanol vapour as a function of vinylacetate content in the copolymer has been evaluated. Promising
ethanol vapour sensor-effect has been observed for PEG-NCC followed by PVAc-NCC and EVA-NCC. 相似文献
206.
Dr. Suresh Moorthy Dr. Hugues Lambert Dr. Neetha Mohan Thomas Schwarzlose Prof. Werner M. Nau Dr. Elina Kalenius Dr. Tung-Chun Lee 《Angewandte Chemie (International ed. in English)》2023,62(32):e202303491
In the gas phase, thermal activation of supramolecular assemblies such as host–guest complexes leads commonly to noncovalent dissociation into the individual components. Chemical reactions, for example of encapsulated guest molecules, are only found in exceptional cases. As observed by mass spectrometry, when 1-amino-methyl-2,3-diazabicyclo[2.2.2]oct-2-ene (DBOA) is complexed by the macrocycle β-cyclodextrin, its protonated complex undergoes collision-induced dissociation into its components, the conventional reaction pathway. Inside the macrocyclic cavity of cucurbit[7]uril (CB7), a competitive chemical reaction of monoprotonated DBOA takes place upon thermal activation, namely a stepwise homolytic covalent bond cleavage with the elimination of N2, while the doubly protonated CB7⋅DBOA complex undergoes an inner-phase elimination of ethylene, a concerted, electrocyclic ring-opening reaction. These chemical reaction pathways stand in contrast to the gas-phase chemistry of uncomplexed monoprotonated DBOA, for which an elimination of NH3 predominates upon collision-induced activation, as a heterolytic bond cleavage reaction. The combined results, which can be rationalized in terms of organic-chemical reaction mechanisms and density-function theoretical calculations, demonstrate that chemical reactions in the gas phase can be steered chemoselectively through noncovalent interactions. 相似文献