全文获取类型
收费全文 | 125篇 |
免费 | 4篇 |
专业分类
化学 | 92篇 |
晶体学 | 3篇 |
数学 | 2篇 |
物理学 | 32篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 14篇 |
2013年 | 16篇 |
2012年 | 13篇 |
2011年 | 9篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有129条查询结果,搜索用时 46 毫秒
121.
Proton nuclear magnetic resonance longitudinal relaxation rates are reported at 100MHz for CH4 and CHD3 in deuterium oxide solutions. The results demonstrate that methane reorients with a correlation time on the order of 0.1 psec, considerably faster than molecule correlation times in aqueous solutions. 相似文献
122.
Pankaj Hazarika Diganta Kalita Swapnalee Sarmah Ruli Borah Nashreen S. Islam 《Polyhedron》2006,25(18):3501-3508
Two new dinuclear oxo-bridged peroxo complexes of tungsten with coordinated dipeptides of the type, Na2[W2O3(O2)4(glycyl-glycine)2] · 3H2O (1) and Na2[W2O3(O2)4(glycyl-leucine)2] · 3H2O (2) have been synthesized from the reaction of H2WO4, 30% H2O2 and the respective dipeptide at pH ca. 2.5. Synthesis of the compounds, in addition to pH, is sensitive to reaction temperature and concentrations of the components. The compounds were characterized by elemental analysis, spectral and physico-chemical methods including thermal analysis. In the dimeric complexes the two W(VI) centres with edge bound peroxo groups are bridged by an oxo group. The dipeptides occurring as zwitterions bind the metal centers through O (carboxylate) atoms leading to hepta co-ordination around each W(VI). Thermal stability of the compounds as well as their stability in solution were determined. The compounds are highly stable toward decomposition in solutions of acidic as well as physiological pH. These compounds, besides another similar dimeric compound Na2[W2O3(O2)4(cystine)] · 4H2O (3) efficiently oxidized bromide to a bromination competent intermediate in phosphate buffer at physiological pH, a reaction in which only two of the peroxide groups of the complex species were found to be active. The complexes could also mediate bromination of organic substrate in aqueous-organic media. 相似文献
123.
The present paper deals with the room temperature conductivity study of some polymer electrolytes based on polyacrylonitrile,
ammonium tetraflouroborate as dopant, and propylene carbonate (PC) and polyethylene glycols (PEG300 and PEG600) as plasticizers.
The additions of plasticizers having different dielectric constant have been found to modify the conductivity of polymer electrolytes.
The increase in room temperature conductivity with plasticizer addition has been found to depend upon (1) the amount of salt
present and (2) amount of plasticizers added. The polymer electrolytes prepared were characterized by X-ray diffraction, scanning
electron micrographs, infrared, thermogravimetric, and AC impedance measurements. The highest room temperature conductivity
observed in case of these polymer electrolytes was ∼10–13 s/cm. 相似文献
124.
P. J. Bhuyan H. N. Borah K. C. Lekhok J. S. Sandhu 《Journal of heterocyclic chemistry》2001,38(2):491-493
The reaction of 6‐hydrazino uracils 1 and nitrones 2 result in an efficient one‐pot synthesis of pyrazolo[3,4‐d]pyrimidines 3 in excellent yields. The isolation of the by‐product aniline from the reaction mixture supported the plausible mechanism for the formation of pyrazolo[3,4‐d]pyrimidines. 相似文献
125.
The infrared spectra of the hydrogen bonded complex cation (triethylamine H+ pyridine) and of the three similar cations resulting from deuterium substitution in pyridine and at the bridge, have been examined in solution. The bridging proton occupies a potential with a single minimum closer to the triethylamine moiety. The Vs band structure is ascribed to Fermi resonance with triethylamine mode combinations. The N · N stretching mode of this complex, and also of the (trimethylamine H+ pyridine) complex have been observed in the far-infrared range.The present complex is weaker than the corresponding trimethylamine one. 相似文献
126.
Kongkona Gogoi Anindita Dewan Ankur Gogoi Geetika Borah Utpal Bora 《Heteroatom Chemistry》2014,25(2):127-130
A simple, efficient, and environmentally benign boric acid catalyzed methodology for the ipso‐hydroxylation of arylboronic acid to phenol has been developed using aqueous hydrogen peroxide as an oxidizing agent and ethanol as the solvent. The versatility of this protocol is that the reactions were performed at room temperature in short reaction time under metal‐, ligand‐, and base‐free conditions. 相似文献
127.
Silica-supported p-toluene sulfonic acid is found to be an excellent catalyst for the Prins reaction to produce 1,3-dioxanes in good yields from olefins and aliphatic aldehydes in dichloromethane at room temperature and solventless microwave irradiation within a short reaction time. 相似文献
128.
Borah JM Mahiuddin S Sarma N Parsons DF Ninham BW 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8710-8717
Adsorption of organic acid at the mineral oxide-electrolyte interface has been explored. The adsorption of 2,4-dihydroxybenzoic acid onto α-alumina illustrates that specific ion effects show up at very low salt concentration (<0.05 mM). These surprising Hofmeister effects occur at salt concentrations an order of magnitude lower than in a previous study ( J. Colloid Interface Sci. 2010, 344, 482 ). Salts enhance adsorption and specifically at ≤0.05 mM. With increasing concentration of ion, the adsorption density decreases. The results are accounted for by incorporating the ion size and dispersion forces in the theoretical modeling based on ab initio calculations of polarizabilities. The order appears to be governed by ion size, determining the maximum concentration that ions can attain near the surface due to close packing. 相似文献
129.
Dipu Borah 《Applied Surface Science》2008,254(10):3049-3056
A commercial grade carbon black was chemically modified using mineral acids (either with HNO3 or H2SO4 or mixture) and the sorption performance of the virgin and modified forms were investigated. Chemical modification resulted in the creation of surface acidic functional groups (COOH, SO2OH) and was verified by FTIR spectra. This was further verified by TGA analysis revealing higher weight loss characteristics of the modified carbons in comparison to virgin carbon black. Morphological changes were observed from BET surface area measurements and SEM analysis. XRD study revealed the change of graphitic crystallite size as a result of modification. The suspension pH of the materials in deionized water and the point of zero charge (pHpzc) in inert electrolyte were determined. The measured values of suspension pH and pHpzc for all the carbons were found to be acidic with more acidic character in the modified carbons. These materials were used as sorbents for the removal of arsenic from aqueous medium and showed excellent adsorption performance. 相似文献