全文获取类型
收费全文 | 617篇 |
免费 | 24篇 |
国内免费 | 2篇 |
专业分类
化学 | 465篇 |
晶体学 | 3篇 |
力学 | 40篇 |
数学 | 36篇 |
物理学 | 99篇 |
出版年
2023年 | 6篇 |
2022年 | 44篇 |
2021年 | 35篇 |
2020年 | 25篇 |
2019年 | 15篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 28篇 |
2015年 | 21篇 |
2014年 | 29篇 |
2013年 | 61篇 |
2012年 | 31篇 |
2011年 | 36篇 |
2010年 | 18篇 |
2009年 | 22篇 |
2008年 | 17篇 |
2007年 | 29篇 |
2006年 | 16篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1961年 | 2篇 |
1960年 | 2篇 |
排序方式: 共有643条查询结果,搜索用时 46 毫秒
11.
M. Y. El-Sheikh A. M. Habib A. K. Abou-Seif A. B. Zaki 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(4):359-367
The kinetics of the decomposition of hydrogen peroxide was studied in aqueous medium in the temperature range 25–40°C in the presence of Wofatit KPS-resin in the form of Cu(II)-ammine complex ions. The rate constant was deduced at various degrees of resin cross-linkage and different concentrations of hydrogen peroxide. The order of the decomposition reaction varied from first order to half order, i.e., the order of the reaction decreased with increasing the concentration of H2O2. The decomposition process was found to be a catalytic reaction which was controlled by the chemical reaction of H2O2 molecules with the active species inside the resin particles. The mechanism of the reaction can be summarized by the equation
in which the subsequent reactions of the probable active complex are discussed. 相似文献
12.
Mohamed Zaki Barakat Mohamed Fathy Abdel-Wahab 《Monatshefte für Chemie / Chemical Monthly》1961,92(5):1061-1065
Zusammenfassung Die Reaktionen von Natrium-1,2-naphthochino-4-sulfonat mit -Aminosäuren, primären aliphatischen Aminen, Dicarbonsäuren, aliphatischen -Hydroxysäuren und primären Alkoholen werden beschrieben. In allen diesen Fällen reagiert Natrium-1,2-naphtochinon-4-sulfonat als Oxydationsmittel und wird zu dem entsprechenden Diphenol reduziert. 相似文献
13.
V. V. Berentsveig Zaki A. Hasan P. B. Fabrichnyi T. M. Ivanova A. P. Rudenko 《Reaction Kinetics and Catalysis Letters》1980,15(2):239-243
The state of mixed iron-tin oxide catalysts with a variable ratio of their metallic components has been studied by Mössbauer and ESCA spectroscopy. The results are compared with the activity of these catalysts in cyclohexane oxidation.
- . .相似文献
14.
Mohamed Y. El-Sheikh Abdel-Fattah M. Habib Fathy M. Ashmawy Ali H. Gemeay Ahmed B. Zaki 《Transition Metal Chemistry》1989,14(2):95-99
Summary The slow decomposition of H2O2 in the presence of Dowex-50 W resin in the form of an ethylenediaminecopper(II) complex ion in water is accompanied by an induction period. The reaction is first order with respect to [H2O2] and the rate constant (perg of dry resin) was deduced. Autocatalytic behaviour was found for the H2O2 decomposition with 2% crosslinked divinylbenzene. The induction period disappeared and the reaction rate increased when the decomposition was carried out with a resin in the form of a peroxo-copper complex, which proves that the formation of an intermediate (active species) retards the reaction rate. The precursor of the active species, formed during the induction period, was not the amine-copper(II) complex ion but a product of the latter with H2O2. It proved impossible to carry out the decomposition in acid or buffer solutions, in which the resin is regenerated. 相似文献
15.
E. Hallaba A. Al-Suhybani M. E. Abdullah F. S. Zaki 《Journal of Radioanalytical and Nuclear Chemistry》1985,89(1):97-107
The labelling of castor oil, hydrolyzed castor oil and oleic acid by iodine monochloride and chloramine-T has been investigated. The effect of iodinating agent and concentration of castor oil on labelling yield has been studied. A comparative pharmacological study with analogous aliphatic fatty acids was caried out. Castor oil labelled with iodine monochloride concentrates in heart and liver in good proportion, better than other natural fatty acids and nearly equal to analogous fatty acids. Infrared study revealed that the OH group in ricinoleic acid may protect the125I added across the double bond with minor changes in biochemical properties and better extraction by the muscle of the heart. 相似文献
16.
Alfy Badie Sakla Nabil Khalil Masoud Zaki Sawiris Wagih Sadik Ebaid 《Helvetica chimica acta》1974,57(2):481-487
Aryldiazophenyl sulfides prepared from diazotised arylamines and thiophenol at controlled pH, are coupled with β-naphthol yielding the corresponding azo dye. A kinetic study of the diazo coupling reaction of p-nitrobenzenediazo phenyl sulfide with β-naphthol under various conditions revealed that the reaction is of first order kinetics with respect to the diazo phenyl sulfide, and that the rate of coupling measured colorimetrically is influenced by the hydrogen ion concentration and by the ionising power of the medium. 相似文献
17.
Summary The effect of some surfactants and protective colloids on the absorbance of the iron(III)-phenylfluorone complex has been investigated. The binary complex formed at pH 9.0 show a molar absorptivity of 7.5×104 l · mol–1 · cm–1 at 530 nm. In the presence of 2% Triton X-100, at the same pH, the molar absorptivity of the sensitized complex was 1.19×105 l · mo–1 · cm–1 at 555 nm. Full colour development of the sensitized complex occurred within 25 min and Beer's law was followed up to 0.53 ppm of iron. The molar ratio and continuous variation methods indicated a 13 metal-ligand ratio for the sensitized complex. The effect of various amounts of different ions has been studied under the experimental conditions and some masking agents were recommended. The method has been applied to the determination of iron in copper and nickel metals and some non-ferrous alloys.
Spektralphotometrische Bestimmung von Eisen als Phenylfluoronkomplex sensibilisiert mit Triton X-100相似文献
18.
A method for the simultaneous determination of aldehydes in dialdehyde fragments, obtained from carbohydrate samples by periodate oxidation, is proposed. Reaction mixtures obtained from the periodate oxidation of carbohydrate samples are deionized by resins, and evaporated to dryness. The syrupy residues are treated with 2,4-dinitrophenylhydrazine hydrochloride in 1.2-dimethoxyethane at 25°C for 3 h. The resultant mixtures of hydrazones are separated by t.l.c. or l.c., and individual hydrazones are determined by spectrophotometric measurement. Reliable analyses of carbohydrate linkages are possible with 50–250-μg samples. 相似文献
19.
The stability constants of the complexes formed between the anion of 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid and some transition and non-transition metal ions have been measured potentiometrically at a temperature of 25 degrees and an ionic strength of 0.1M (KNO(3)). The acid dissociation constants of the ligand and stability constants of the protonated complexes are also reported. Comparisons are made with the acid dissociation constants of the analogous compounds EDTA, ENTMP and HDTA, and possible structural formulae are given. 相似文献
20.
A potentiometric investigation of the acid dissociation constants of the octabasic ENTMP [N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid] is reported. The stability constants of protonated MH(n)L (n = 1, 2, 3 and 4) and unprotonated ML metal chelates of Mg, Ca, Ba and Cd with ENTMP have been measured. The stabilities are in the order Mg < Ca < Ba < Cd. 相似文献