全文获取类型
收费全文 | 123篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 113篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 8篇 |
物理学 | 7篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 11篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有130条查询结果,搜索用时 421 毫秒
41.
An innovative soft chemical approach was applied, using ionic liquids as an alternative reaction medium for the synthesis of tellurium polycationic cluster compounds at room temperature. [Mo2Te12]I6, Te6[WOCl4]2, and Te4[AlCl4]2 were isolated from the ionic liquid [BMIM]Cl/AlCl3 ([BMIM]+: 1‐n‐butyl‐3‐methylimidazolium) and characterized. Black, cube‐shaped crystals of [Mo2Te12]I6, which is not accessible by conventional chemical transport reaction, were obtained by reaction of the elements at room temperature in [BMIM]Cl/AlCl3. The monoclinic structure (P21/n, a = 1138.92(2) pm, b = 1628.13(2) pm, c = 1611.05(2) pm, β = 105.88(1) °) is homeotypic to the triclinic bromide [Mo2Te12]Br6. In the binulear complex [Mo2Te12]6+, the molybdenum(III) atoms are η4‐coordinated by terminal Te42+ rings and two bridging η2‐Te22– dumbbells. Despite the short Mo···Mo distance of 297.16(5) pm, coupling of the magnetic moments is not observed. The paramagnetic moment of 3.53 μB per molybdenum(III) atom corresponds to an electron count of seventeen. Black crystals of monoclinic Te6[WOCl4]2 are obtained by the oxidation of tellurium with WOCl4 in [BMIM]Cl/AlCl3. Tellurium and tellurium(IV) synproportionate in the ionic liquid at room temperature yielding violet crystals of orthorhombic Te4[AlCl4]2. 相似文献
42.
Khan SB Afza N Malik A Azhar-Ul-Haq Perveen S Ahmad I Ejaz A Choudhary MI 《Natural product research》2006,20(4):335-339
A new flavonol glycoside (1) has been isolated from the ethyl acetate soluble fraction of Amberboa ramosa and assigned the structure 5,7,4'-trihydroxy-3,8-dimethoxylflavone 5-O-beta-D-gluco-pyranoside (1). In addition, 6,4'-dihydroxy-3,5,7-trimethoxyflavone (2), 5,7-dihydroxy-4'-methoxyflavone (3) and (23R)-5alpha-cycloart-24-ene-3beta,21,23-triol (4) have also been reported for the first time from this species. The structures were deduced on the basis of 1D and 2D NMR techniques. The compounds 1-3 displayed weak to moderate inhibition against the xanthine oxidase enzyme. 相似文献
43.
44.
Azhar-Ul-Haq Malik A Anis I Khan SB Ahmed E Ahmed Z Nawaz SA Choudhary MI 《Chemical & pharmaceutical bulletin》2004,52(11):1269-1272
Two new lignans trivially named negundins A (1) and B (2), were isolated along with (+)-diasyringaresinol (3), (+)-lyoniresinol (4), vitrofolal E (5) and vitrofolal F (6), reported for the first time from this species. The structures of the new compounds were established through spectral studies. Compound 2 showed potent inhibitory activity against lipoxygenase enzyme, while 5 showed moderate activity against butyryl-cholinesterase. 相似文献
45.
Ali Rusheed Suhail Ahmed M. Ejaz 《Journal of Radioanalytical and Nuclear Chemistry》1979,49(2):205-211
A new method is introduced to estimate uranium(VI) spectrophotometrically by extraction of its ferron (7-iodo-8-hydroxyquinoline-5-sulfonic
acid) complex with 1% tridodecylamine in chloroform at pH 4.5. The optimum absorption wavelength is 380 nm. The stoichiometry
of the uranium-ferron complex as indicated by a mole ratio plot is 1:2 and its dissociation constant is 3.24·10−9. The effects of various parameters on the absorption are studied. This method has a sensitivity of 0.028 ppm on Sandell's
scale. Interferences are described. 相似文献
46.
The distribution of chromium(VI) between 5-(4-pyridyl)nonane in benzene and hydrochloric acid media has been studied as a function of the concentration of the acid, extractant, chromium(VI), chloride and a few other ions. The extraction mechanism and the composition of the extracted complexes of Cr(VI) have been proposed. The separation of Cr(VI) from uranium, thorium and fission products in 3M hydrochloric acid has been achieved. 相似文献
47.
Technetium-99m, separated from fission molybdenum-99, has been studied as a component of liquid-liquid phase distribution equilibria. 5-(4-Pyridyl)nonane in a carrier diluent, benzene, has been used to study the distribution of the nuclide from thermodynamically suitable aqueous phases of electrolytes with and without sterically receptive thiocyanate ions. Efficient extraction of the metal can be accomplished in a variety of aqueous phase compositions. The separation factors with respect to molybdenum, under certain experimental conditions, are fairly high. The data have been utilized to effect clean separations of technetium from molybdenum. 相似文献
48.
Muhammad Abdul Hamid Ejaz Ur Rehman Muhammad Fuzail Riffat Naheed Amin-Uddin Ahmed 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(1):37-50
The oxidation-reduction reaction between U(VI) and Ti(III) in HCl solution was studied spectrophotometrically. The reaction is second-order at all concentrations of reactants, HCl, ferrous chloride and mannitol used in this work. In 5M HCl the rate constantk increases with increasing Ti(III) concentration, whereas it decreases with increasing U(VI) concentration, with increasing HCl concentration from 1.00M to 7.17M and increases thereafter from 7.17M to 11.79M. The addition of mannitol causes a consistent decrease in the rate of reaction, whereas ferrous chloride has no effect. The activation energy for this oxidation-reduction reaction was 47.90±0.11 kJ·mol–1. The values of H
, G
and S
were 45.40±0.11 kJ·mol–1, 72.50±0.17 kJ·mol–1 and –91.10±0.22J·k–1·mol–1, respectively. The mode of reaction is discussed in the light of kinetic results. 相似文献
49.
M. Ejaz Shamasud-Zuha Shujaat Ahmad M. Saeed Chaudhary M. Rashid 《Mikrochimica acta》1980,73(1-2):7-16
Summary Tracer (10–8
M) zinc can be quantitatively extracted with 0.1M diphenyl(2-pyridyl)methane (DPPM) in benzene from neutral and acidic aqueous thiocyanate solutions in a single extraction. In all cases, extraction times of 1–5 min are sufficient for equilibration. The effects of the concentration of the mineral acids, the reagent, complexing and salting-out agents and phase-volume ratios on the metal extraction are reported. The metal is predominantly extracted through solvation, and the extraction of the metal as Zn(SCN)2(DPPM)2 is indicated. Among the common salts only sodium chloride exerts a slight depressing effect on extraction when present in high concentration. The metal can be stripped from the organic phase with aqueous oxalate, citrate or acetate solutions in a single operation. Distribution coefficients and separation factors for a number of metal ions, relative to zinc, are reported for 0.2M potassium thiocyanate media that contain the optimal concentration of mineral acid. The method can be employed for the simultaneous preconcentration of toxic metals such as zinc, copper and mercury from neutral aqueous solution in water pollution studies.
Diphenyl(2-pyridyl)methan als Lösungsmittel für Zink-Rhodanidkomplexe in wäßrigen Mineralsäuren
Zusammenfassung Zinkspuren (10–8 M) lassen sich mit einer benzolischen, 0,1 M Lösung von Diphenyl(2-pyridyl)methan (DPPM) aus neutralen oder sauren, wäßrigen Rhodanidlösungen durch eine einzige Extraktion ausschütteln. Jedenfalls sind 1–5 min hinreichend für die Einstellung des Gleichgewichtes. Der Einfluß der Konzentration der Mineralsäure, des Reagens, des Komplexbildners und des Aussalzmittels sowie des Volumenverhältnisses der Phasen auf die Metallextraktion wurde beschrieben. Die Extraktion erfolgt vorherrschend durch Solvatation und zwar als Zn(SCN)2(DPPM)2. Unter den gewöhnlichen Salzen beeinträchtigt nur NaCl in hoher Konzentration die Extraktion in geringem Maß. Das Metall kann aus der organischen Phase mit wäßrigen Oxalat-, Citrat- oder Acetatlösungen in einem Arbeitsgang rückextrahiert werden. Die Verteilungskoeffizienten und Trennungsfaktoren für einige Metallionen in bezug auf Zink in 0,2M Kaliumrhodanid bei optimaler Mineralsäurekonzentration wurden angegeben. Das Verfahren eignet sich für die gleichzeitige Anreicherung toxischer Metalle, wie Zn, Cu und Hg aus neutraler Lösung bei der Untersuchung der Gewässerverunreinigung.相似文献
50.
5-(4-Pyridyl)nonane dissolved in benzene has been applied to the extraction of zinc, down to very low concentration (< 10(-6)M), from aqueous thiocyanate solutions. The metal can be quantitatively extracted from neutral and acidic thiocyanate solutions (up to 5M HCl, 0.25M HNO(3) or 0.25M H(2)SO(4)) in a single extraction. Equilibration times of 5 min are sufficient for almost complete extraction. The optimum thiocyanate concentration range is 0.05-0.5M. Among the common anions chloride exerts a slight depressing effect on extraction from neutral solution when present in high concentration. The extraction mechanism and the composition of the extracted complexes of zinc are discussed. The metal is predominantly extracted by means of a solvate mechanism. The effect of chloride, nitrate, sulphate, acetate, citrate, oxalate and ascorbate ions on the extraction of zinc is described. Several elements, including those of interest in separation of zinc, have been tested for extraction from O.1M KSCN at the optimal concentrations of the mineral acids, and the separation factors estimated. 相似文献