全文获取类型
收费全文 | 184篇 |
免费 | 8篇 |
专业分类
化学 | 161篇 |
晶体学 | 2篇 |
数学 | 7篇 |
物理学 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1944年 | 2篇 |
1939年 | 1篇 |
1938年 | 1篇 |
1933年 | 1篇 |
1932年 | 2篇 |
1928年 | 1篇 |
1906年 | 1篇 |
排序方式: 共有192条查询结果,搜索用时 62 毫秒
131.
132.
Effect of chemical structure on combustion and thermal behaviour of polyurethane elastomer layered silicate nanocomposites 总被引:1,自引:0,他引:1
The effect of polyol molecular weight and functionality on nanodispersion of clay in PU/clay nanocomposites and the investigation of their thermal and combustion properties are reported and discussed. Lamellar elastomer polyurethane nanocomposites were synthesized using polyols with different molecular weight and functionality and according to these parameters they show several degrees of dispersion which affect their thermal and combustion behaviour. A barrier effect of clay layer is shown in TGA experiments by a delay of thermal degradation products release in nanocomposite materials compared to the virgin polymer; this barrier effect also leads to formation of char during combustion which lowers the peak of rate of heat release in cone calorimeter tests and eliminates fire-induced dripping of the nanocomposite sample during UL 94 test. However, in order to achieve non-burning behaviour nanocomposite technology must be combined with conventional flame retardant technology. 相似文献
133.
134.
Holló Berta Barta Petruševski Vladimir M. Kovács Gréta Bettina Franguelli Fernanda Paiva Farkas Attila Menyhárd Alfréd Lendvay György Sajó István E. Nagy-Bereczki Laura Pawar R. P. Szilágyi Imre Miklós Bódis Eszter Kótai László 《Journal of Thermal Analysis and Calorimetry》2019,138(2):1193-1205
Journal of Thermal Analysis and Calorimetry - A simple synthetic method was developed to prepare 4[Agpy2ClO4]·[Agpy4]ClO4 in a low-temperature decomposition process of [Agpy4]ClO4. A detailed... 相似文献
135.
Martinelli MJ Vaidyanathan R Pawlak JM Nayyar NK Dhokte UP Doecke CW Zollars LM Moher ED Khau VV Kosmrlj B 《Journal of the American Chemical Society》2002,124(14):3578-3585
This paper describes a convenient protocol for the regioselective sulfonylation of alpha-chelatable alcohols. Typically, the reaction of alpha-heterosubstituted alcohols with 1 equiv of p-TsCl and 1 equiv of Et(3)N in the presence of 2 mol % of Bu(2)SnO leads to rapid, regioselective, and exclusive monotosylation. The pK(a) of the amine was correlated to the reaction rate. A plausible mechanism for this reaction has been proposed on the basis of (119)Sn NMR studies. 相似文献
136.
The reactions between alizarin yellow G and six different bases B (including OH?) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature-jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion-controlled reaction between the base and that fraction which is present in the “open” non-hydrogen-bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge. The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method. 相似文献
137.
1,2-Epithiocyclohexane was obtained selectively by irradiation of a mixture of cyclohexene and sulphur with a pulsed laser (266 nm). 相似文献
138.
Cagide Fajín JL Fernández B Felker PM 《The journal of physical chemistry. A》2005,109(50):11602-11608
The ground state intermolecular potential energy surface for the p-difluorobenzene-Ar van der Waals complex is evaluated using the coupled cluster singles and doubles including connected triple excitations [CCSD(T)] model and the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface minima are characterized by the Ar atom located above and below the difluorobenzene center of mass at a distance of 3.5290 A. The corresponding binding energy is -398.856 cm(-1). The surface is used in the evaluation of the intermolecular level structure of the complex. The results clearly improve previously available data and show the importance of using a good correlation method and basis set when dealing with van der Waals complexes. 相似文献
139.
A Catalyst Designed for the Enantioselective Construction of Methyl‐ and Alkyl‐Substituted Tertiary Stereocenters
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Aurélie Claraz Dr. Gokarneswar Sahoo Dénes Berta Dr. Ádám Madarász Dr. Imre Pápai Prof. Dr. Petri M. Pihko 《Angewandte Chemie (International ed. in English)》2016,55(2):669-673
Tertiary methyl‐substituted stereocenters are present in numerous biologically active natural products. Reported herein is a catalytic enantioselective method for accessing these chiral building blocks using the Mukaiyama–Michael reaction between silyl ketene thioacetals and acrolein. To enable remote enantioface control on the nucleophile, a new iminium catalyst, optimized by three‐parameter tuning and by identifying substituent effects on enantioselectivity, was designed. The catalytic process allows rapid access to chiral thioesters, amides, aldehydes, and ketones bearing an α‐methyl stereocenter with excellent enantioselectivities, and allowed rapid access to the C4–C13 segment of (?)‐bistramide A. DFT calculations rationalized the observed sense and level of enantioselectivity. 相似文献
140.
Chuanrui Chen Xiaocong Chang Hazhir Teymourian Doris E. Ramírez‐Herrera Berta Esteban‐Fernández de Ávila Xiaolong Lu Jinxing Li Sha He Chengcheng Fang Yuyan Liang Fangzhi Mou Jianguo Guan Prof. Joseph Wang 《Angewandte Chemie (International ed. in English)》2018,57(1):241-245
While chemical communication plays a key role in diverse natural processes, the intelligent chemical communication between synthetic nanomotors remains unexplored. The design and operation of bioinspired synthetic nanomotors is presented. Chemical communication between nanomotors is possible and has an influence on propulsion behavior. A chemical “message” is sent from a moving activator motor to a nearby activated (receiver) motor by release of Ag+ ions from a Janus polystyrene/Ni/Au/Ag activator motor to the activated Janus SiO2/Pt nanomotor. The transmitted silver signal is translated rapidly into a dramatic speed change associated with the enhanced catalytic activity of activated motors. Selective and successive activation of multiple nanomotors is achieved by sequential localized chemical communications. The concept of establishing chemical communication between different synthetic nanomotors paves the way to intelligent nanoscale robotic systems that are capable of cooperating with each other. 相似文献