全文获取类型
收费全文 | 370篇 |
免费 | 19篇 |
专业分类
化学 | 257篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 10篇 |
物理学 | 111篇 |
出版年
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 24篇 |
2012年 | 12篇 |
2011年 | 25篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 13篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1997年 | 5篇 |
1995年 | 5篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1969年 | 6篇 |
1968年 | 7篇 |
1967年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有389条查询结果,搜索用时 437 毫秒
291.
M. Arshad A. H. Qureshi S. Rehman K. Masud 《Journal of Thermal Analysis and Calorimetry》2007,89(2):561-566
The iodide complexes of transition metals with 1,2-diimidazoloethane (DIE) of the general formula MLI2, (M=Cu(II), Hg(II), Cd(II); L=1,2-diimidazoloethane) were prepared and studied by means of thermogravimetry (TG/DTG) and differential thermal analysis
(DTA) techniques. Their compositions were investigated by elemental analysis in order to ensure their purity and structural
elucidations were based on conductivity measurements, room temperature magnetic measurements, proton NMR, XRD and IR spectra.
Thermal decomposition of these distorted tetrahedral complexes and the ligand took place in two distinct steps upon heating
up to 800°C, with the loss of inorganic and organic fragments. The thermal degradation of all the complexes (except for cadmium
complex) in static air atmosphere started at temperatures lower than those observed for the free ligand pyrolysis. The composition
of intermediates formed during degradation was confirmed by microanalysis and IR spectroscopy. The residues after heating
above 740°C corresponded to metal oxide except for Hg(II) complex, which behaved differently. It was found on the basis of
thermal analysis that thermal stability of the complexes increased in the following sequence: Hg(II)<Cu(II)<Cd(II). 相似文献
292.
M. Mufazzal Saeed Munir Ahmed M. N. Cheema I. H. Qureshi 《Journal of Radioanalytical and Nuclear Chemistry》1987,108(4):203-215
Synergic extraction of Ni/II/ at pH 1 to 10 was studied using a mixture of 2-thenoyltrifluoroacetone /HTTA/ and tribenzylamine /TBA/ in chloroform. The synergist TBA enhances the extraction of Ni/II/ by an order of 5 from pH 3 to 5 having ionic strength 0.1M /H+, ClO
4
–
/. The synergic adduct was found to be Ni/TTA/2.2TBA. The equilibrium constants K2,0 and K2,2 and stability constant 2,2 have been ascertained radiometrically. The influence of various cations and anions on the extraction of Ni/II/ has been examined under optimal conditions. Back extraction of the adduct species in different acids of varying concentrations has been studied. 相似文献
293.
Summary A spectrophotometric method for the micro-determination of bromate ions has been described. A red colored complex is obtained when 3 ml of 5% antipyrine, 3 ml of 60% perchloric acid and 1 ml of 0.1M sodium nitrite solution are added in a solution containing bromate ions. The maximum absorbance occurs at 525 nm. Beer's law is obeyed for solutions containing 25.0–140.0/ml of bromate ions. Sensitivity has been found to be 0.029g BrO3
–/cm2 for logI
0/I=0.04 with a molar absorptivity of 2·103 moles–1, cm–1. liter. As(III), Ce(IV), Fe(III), CrO4
2–, Cr2O7
2–, and Cl– interfere in the determination.
Zusammenfassung Eine spektrophotometrische Methode zur Mikrobestimmung von Bromationen wurde beschrieben. Nach dem Zusatz von 3 ml 5%iger Antipyrinlösung, 3 ml 60% iger Perchlorsäure und lml 0,1 ·m Natriumnitrit zu einer bromathaltigen Lösung erhält man eine rot gefärbte Komplexverbindung. Deren Absorptionsmaximum liegt bei 525 nm. Lösungen mit 25,0 bis 140,0g Bromat/ml entsprechen dem Beerschen Gesetz. Die Empfindlichkeit der Reaktion beträgt 0,029g BrO3 –/cm2 für logI 0/I=0,04 mit einer molaren Absorption von 2 · 103 m–1 · cm–1 · 1. As(III), Ce(IV), Fe(III), CrO4 2–, Cr2O7 2– und Cl– stören die Bestimmung.相似文献
294.
M. S. Bhatti Shamasud Zuha M. A. Qureshi 《Journal of Radioanalytical and Nuclear Chemistry》1984,82(1):45-52
Extraction of Mo(VI) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiocyanate ions has been investigated at room temperature (23±2°C). From mineral acid (HCl, HNO3, and H2SO4) solutions alone Mo(VI) is not extracted quantitatively while the presence of small amounts of KSCN in the system augments the extraction by a large factor. Stoichiometric studies indicate that ion-pair type complexes (NPyH)2·[MoO2(SCN)4] are responsible for the extraction. Separation factors determined at fixed extraction conditions (0.1M Npy/C6H6–0.1M acid +0.2M KSCN) reveal that Ag(I), Cu(II), Co(II), Zn(II), Hg(II) and U(VI) are co-extracted while a clean separation from alkali metals, alkaline earths and some transition metals like Ln(III), Zr(IV), Hf(IV), Cr(III), Cr(VI) and Ir(III) is possible. Some of the complexing anions like oxalate, citrate, acetate, thiosulfate or ascorbate do not affect the degree of extraction of Mo(VI) allowing it to be recovered from diverse matrices. 相似文献
295.
Catechol and o-nitrophenol have been determined successfully in the solid state by means of their solid-state reaction with soda-lime. The glass-wool plug modification has been used with advantage in the determination of o-nitrophenol. The reaction mechanism is postulated on the basis of the reflectance electronic spectra. Some solid-solid kinetic parameters have also been studied. 相似文献
296.
Columns and papers of titanium arsenate have been utilized for chromatographic studies of several alkaloids in aqueous and mixed solvent systems. The results have been compared with those obtained with plain papers. A number of separations have been achieved on papers impregnated with titanium arsenate. Distribution coefficients of these alkaloids have been determined. A number of alkaloids have been separated quantitatively from nicotine on titanium arsenate columns. 相似文献
297.
G. Gordon Cameron M. Younus Qureshi 《Journal of polymer science. Part A, Polymer chemistry》1980,18(11):3149-3161
The radical grafting of methyl methacrylate (MMA) onto polybutadiene (PBD) in benzene solution at 60°C is more efficiently induced by benzoyl peroxide (BP) than by azoisobutyronitrile (AIBN). PBD exerts a pronounced retardation on the polymerization of MMA and the grafting efficiency is governed by the ratio of rubber to monomer in the system. With BP as initiator, a fairly simple kinetic expression, relating grafting efficiency with reactant concentrations, can be derived by making certain approximations, including the neglect of termination grafting. The experimental data are reasonably consistent with this equation and yield acceptable values of several kinetic parameters. With AIBN, termination grafting is more significant. In consequence the relevant kinetic equation can be only qualitatively validated. 相似文献
298.
Summary A reproducible and chemically stable inorganic ion-exchanger, niobium arsenate has been prepared by mixing acidic solutions
of niobium sulphate and sodium aresenate in the ratio 1∶4 under different conditions. Its exchange behaviour after heat treatment
has been studied. The analytical utility of this material is illustrated by its ability to separate quantitatively Ni(II)
from V(V) and Fe(III). Mn(II) from V(V) and Fe(III). 相似文献
299.
S. Ahmad M. S. Chaudhry I. H. Qureshi 《Journal of Radioanalytical and Nuclear Chemistry》1979,54(1-2):331-341
The concentration of 15 elements in various brands of cigarette tobacco and cigarette wrapping paper were determined using
instrumental neutron activation analysis. The paper of some of the brands contains higher concentrations of toxic elements
than the tobacco. The cigarette filter and the ash were also analyzed to determine the adsorption of toxic elements on the
filter and their transference in smoke. The toxic effects of some of the elements have been briefly discussed. 相似文献
300.
A simple and reproducible procedure has been developed for the dissolution of tantalum pentoxide. The oxide is fused with potassium nitrate and potassium carbonate in the ratio of 2:5:5. The cooled melt is dissolved in concentrated sulphuric acid. If a tartaric acid solution is desired the sulphuric acid is evaporated and the residue dissolved in 20% tartaric acid solution. 相似文献