全文获取类型
收费全文 | 182篇 |
免费 | 14篇 |
专业分类
化学 | 155篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 9篇 |
物理学 | 27篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 21篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 11篇 |
2012年 | 15篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 10篇 |
2008年 | 5篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 3篇 |
1996年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有196条查询结果,搜索用时 390 毫秒
1.
Ewelina Minta 《Tetrahedron letters》2005,46(11):1795-1797
Alkali metal trimethylsilanolates, TMSO−, M+, has been used for efficient conversion of methyl esters into their corresponding anhydrous acid salts under mild non-aqueous conditions. This strategy has been applied to SPPS for the preparation of neurotoxin cyclic analogues and in (S)-5-hydroxynorvaline synthesis. 相似文献
2.
3.
The title phase was synthesized by direct fusion of a stoichiometric amount of the elements followed by annealing at 650 degrees C for 3 weeks. The compound crystallizes in the orthorhombic space group Pnma (No. 62), Z = 4, with a = 19.451(6) A, b = 12.164(3) A, c = 6.581(1) A. The compound is made up of As(3)Pb(3)(5-) crown clusters that can be likened geometrically and electronically to 6-atom hypho-clusters derived from a tricapped trigonal prismatic closo parent. These crowns are interconnected via intercluster Pb-Pb bonds to form infinite chains along the b axis, which means the compound contains an extra two cations and two electrons per formula unit. Extended Hückel calculations indicate that the two additional electrons per cluster are accommodated in pi states on the cluster and predict that the phase should be semiconducting. The latter is confirmed by microwave resistivity measurements, rho(298) = 1.0 x 10(2) microOmega.cm; (deltarho/deltaT)/rho = -0.14(3) K(-)(1). 相似文献
4.
The title compound, the Tl-richest in the K-Tl system, has been synthesized in Ta containers via direct reaction of the elements at 400 degrees C followed by quenching to room temperature and subsequent annealing at 150 degrees C for 4 weeks. It crystallizes in the orthorhombic space group Cccm (No. 66) with a = 16.625(1) A, b = 23.594(2) A, c = 15.369(2) A (22 degrees C), and Z = 8. Two different Tl(12) units consisting of augmented tetrahedral stars are condensed into layers of such tetrahedra, and further Tl(2) dumbbells and the potassium cations also interconnect the stars and layers into a three-dimensional network. The former anionic Tl(8) subunits clearly resemble those in the heteroatomic 3-D structure of cubic Cr(3)Si before their augmentation with bridging atoms. The compound is metallic (rho(270) = 22.6 micro omega x cm, alpha = 0.0023 K(-)(1)) and shows Pauli-like paramagnetic susceptibility (chi(296) = 1.1 x 10(-4) emu/mol). EHTB calculations illustrate the importance of Tl p-orbital bonding, the positive Tl-Tl overlap populations up to E(F), and greater strengths of the Tl-Tl bonding between and about the surface of the augmented Tl(12) units. Cations between the thallium layers play specific and important roles in the structure. 相似文献
5.
Ewelina Nawrot 《Journal of fluorine chemistry》2006,127(7):943-947
N-Aryl substituted amides react with chlorodifluoromethane in the presence of concentrated aqueous sodium hydroxide and benzyltriethylammonium chloride (TEBAC) as a catalyst in benzene (phase-transfer catalysis, PTC), affording mixtures of N- and O-difluoromethyl substituted derivatives. Amide anions are involved in this process. The reaction carried out with oximes gives O-difluoromethyl oxime ethers. 相似文献
6.
7.
8.
Ewelina Ciecierska Anna Boczkowska Krzysztof Jan Kurzydlowski Iosif Daniel Rosca Suong Van Hoa 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1019-1024
The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (T g) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in T g was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity. 相似文献
9.
Antoni W. Morawski Ewelina Kusiak-Nejman Jacek Przepiórski Roksana Kordala Juliusz Pernak 《Cellulose (London, England)》2013,20(3):1293-1300
TiO2/N-cellulose nanocomposite was successfully prepared in the (cyclohexyl)hexyl-dimethylammonium acetate–dimethyl sulfoxide solution. The obtained composite was characterized with various techniques like UV–Vis/DR, FTIR/DRS, X-ray diffraction, thermogravimetric analysis, DLS method and BET SSA measurements. TiO2/N-cellulose nanocomposite exhibited high UV–Vis light absorption with energy gap shifted to the visible region. Additive of TiO2/N photocatalyst to cellulose-IL-DMSO solution leads to obtaining the material with higher thermostability and limited photoactivity. 相似文献
10.
Prof. Dr. Antoni W. Morawski Dr. Ewelina Kusiak-Nejman Dr. Iwona Pełech Katarzyna Ćmielewska Dr. Daniel Sibera Piotr Staciwa Dr. Agnieszka Wanag Marcin Gano Dr. Ewa Ekiert Dr. Joanna Kapica-Kozar Kordian Witkowski Prof. Dr. Urszula Narkiewicz 《ChemistryOpen》2022,11(4):e202100262
A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7–8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO2 under UV-C, the hydrogen production amounted to 0.6 μmol h−1 during 24 h of radiation. 相似文献