全文获取类型
收费全文 | 314篇 |
免费 | 6篇 |
国内免费 | 4篇 |
专业分类
化学 | 181篇 |
晶体学 | 12篇 |
力学 | 4篇 |
数学 | 19篇 |
物理学 | 108篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 14篇 |
2014年 | 16篇 |
2013年 | 18篇 |
2012年 | 27篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 7篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有324条查询结果,搜索用时 46 毫秒
1.
Summary Th(IV) was quantitatively extracted from 1 . 10-3M HNO3 using 1 . 10-3M Cyanex302 in xylene and was stripped from the organic phase with 5M HCl. The effect of different parameters affecting the
extraction was systematically studied to achieve optimum conditions for the extraction of thorium. Based on the data some
separations of thorium from binary and complex mixtures and its recovery from monazite sand were achieved. The method is reproducible
with a relative standard deviation of 0.4%. 相似文献
2.
The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents. 相似文献
3.
The malonate, succinate, glutarate and adipate complexes of lead have been examined polarographically and the overall stability constants evaluated. The values found are log beta(1) = 2.60, 2.40, 2.48, 2.38; log beta(2) = 3.62, 3.73, 3.45, 3.20; log beta(3) = 4.32, 4.11, 3.90, 3.69, for the malonate, succinate, glutarate and adipate complexes respectively. 相似文献
4.
Previous work in the application of chronopotentiometry in aqueous and fused salt media has been reviewed. This investigation describes the application of this principle to the reduction of cadmium, cobalt, lead and thallium ions in a fused eutectic mixture of potassium, chloride and lithium. chloride at 450°C. Platinum microelectrodes of different areas and geometry were used. The transition time was limited to the order of 0.2 to 0.7 sec using oscillographic recording.It was found that so long as the dimensions of the electrode were considerably greater than the thickness of the diffusion, layer, linear diffusion theory was obeyed. The transition time constants for cadmium, cobalt, lead and thallium ions were found to be 0.83± 0.02, 0.90 ± 0.03, 0.95 ± 0.04, and 0.59 ± 0.02.103 amp cm sec per mole, respectively. The diffusion coefficients of these ions were calculated to be 2.08, 2.42, 2.18 and 3.88.IO-5 cm2 sec-1, respectively. 相似文献
5.
R. C. Bopp U. Gaur R. P. Kambour B. Wunderlich 《Journal of Thermal Analysis and Calorimetry》1982,25(2):243-258
The thermal behavior of poly(2,6-dimethyl-1,4-phenyiene oxide) (PPO R resin), poly(3-bromo-2,6-dimethyl-1,4-phenylene oxide), and a series of their statistical copolymers with identical average molecular lengths has been characterized by thermogravimetry and computer-interfaced differential scanning calorimetry. The heat capacities are found to be additive with respect to the concentrations of the two components. The change in heat capacity at the glass transition ( C
p) is independent of composition for bromination of up to 75% of the repeat units. At higher bromine levels C
p decreases abruptly. This behavior is attributed to the temperature dependence of C
p for the two components. The glass transition temperature (T
g) of the copolymers varies nearly linearly with composition. A comparison of the experimental values ofT
g is made with various equations derived for statistical copolymers and homogeneous polymer blends. A modification of the Couchman equation is presented taking into account the temperature dependence ofC
p.
This work was supported by the National Science Foundation, Polymers Program (DMR 78-15279) and the General Electric Corporate Research and Development Center. The authors are indebted to the following individuals at General Electric CRD for their experimental assistance: S. R. Weissman and P. E. Gundlach (molecular weight characterizations); D. W. Marsh (X-ray analysis); V. H. Watkins and E. L. Hall (electron microscopy); and N. A. Marotta (thermogravimetry). P. E. Donahue and E. A. Williams are gratefully acknowledged for carrying out and interpreting the NMR experiments.
One of the authors (R. C. Bopp) would like to thank A. R. Shultz, J. T. Bendler, and D. M. White at General Electric CRD for their helpful discussions of this work and express his sincere appreciation to Professor P. R. Couchman (Rutgers University) for his illuminating discussions of the thermodynamic basis of his equation. 相似文献
Zusammenfassung Das thermische Verhalten von Poly(2.6-dimethyl-1.4-phenylenoxyd) (PPO R-Harz), Poly(3-brom-2.6-dimethyl-1.4-phenylenoxyd) und einer Reihe von statistischen Copolymeren dieser Verbindungen mit gleicher durchschnittlicher Moleküllänge wurde durch Thermogravimetrie und Differential-Scanning-Kalorimetrie mit Computerinterface charakterisiert. Die Wärmekapazitäten sind hinsichtlich der Konzentrationen der beiden Komponenten additiv. Die Veränderung in der Wärmekapazität beim Übergang zum Glas (Cp) ist unabhängig von der Zusammensetzung bei Bromierung bis zu 75% der wiederho-lungseinheiten. Bei höheren Bromierungsgraden nimmtC p abrupt ab. Dieses Verhalten wird der Temperaturabhängigkeit vonC p der beiden Komponenten zugeschrieben. Die Glasübergangstemperatur (Tg) der Copolymeren verändert sich nahezu linear mit der Zusammensetzung. Ein Vergleich der experimentellen Werte von Tg wird mit verschiedenen für statistische Copolymere und Mischungen homogener Polymere abgeleiteten Gleichungen ausgeführt. Eine die Temperaturabhängigkeit vonC p berücksichtigende Modifikation der Gleichung von Couchman wird angegeben.
, , (2,6- -1,4), (3--2,6--1,4- ) . , ë . ë (C ) 75%. C . C . T . . T . , . , C .
This work was supported by the National Science Foundation, Polymers Program (DMR 78-15279) and the General Electric Corporate Research and Development Center. The authors are indebted to the following individuals at General Electric CRD for their experimental assistance: S. R. Weissman and P. E. Gundlach (molecular weight characterizations); D. W. Marsh (X-ray analysis); V. H. Watkins and E. L. Hall (electron microscopy); and N. A. Marotta (thermogravimetry). P. E. Donahue and E. A. Williams are gratefully acknowledged for carrying out and interpreting the NMR experiments.
One of the authors (R. C. Bopp) would like to thank A. R. Shultz, J. T. Bendler, and D. M. White at General Electric CRD for their helpful discussions of this work and express his sincere appreciation to Professor P. R. Couchman (Rutgers University) for his illuminating discussions of the thermodynamic basis of his equation. 相似文献
6.
Laxman Khatal Ashwani Gaur Ashish Naphade Vishwottam Kandikere Kasim Mookhtiar 《Biomedical chromatography : BMC》2016,30(10):1676-1685
Measurement of test article concentration in tissue samples has been an important part of pharmacokinetic study and has helped to co‐relate pharmacokinetic/pharmacodynamic relationships since the 1950s. Bioanalysis of tissue samples using LC–MS/MS comes with unique challenges in terms of sample handling and inconsistent analyte response owing to nonvolatile matrix components. Matrix effect is a phenomenon where the target analyte response is either suppressed or enhanced in the presence of matrix components. Based on previous reports electrospray ionization (ESI) mode of ionization is believed to be more affected by matrix components than atmospheric pressure chemical ionization (APCI) or atmospheric pressure photoionization. To explore the impact of ionization source with respect to bioanalysis of tissue samples, five structurally diverse compounds – atenolol, verapamil, diclofenac, propranolol and flufenamic acid – were selected. Quality control standards were spiked into 10 different biological matrices like whole blood, liver, heart, brain, spleen, kidney, skeletal muscle, eye and skin tissue and were quantified against calibration standards prepared in rat plasma. Quantitative bioanalysis was performed utilizing both APCI and ESI mode and results were compared. Quality control standards when analyzed with APCI mode were found to be more consistent in terms of accuracy and precision as compared with ESI mode. Additionally, for some instances, up to 20‐fold broader dynamic linearity range was observed with APCI mode as compared with ESI mode. As phospholid interferences have poor response in APCI mode, protein precipitation extraction technique can be used for multimatrix quantitation, which is more amenable to automation. The approach of multiple biological matrix quantitation against a single calibration curve helps bioanalysts to reduce turnaround time. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
A. K. Maheshwari Dr. D. S. Jain J. N. Gaur 《Monatshefte für Chemie / Chemical Monthly》1977,108(2):279-283
The reduction of Cd(II) in propylenediamine was found to be reversible and diffusion controlled. The complexes of Cd(II) with propylenediamine in 25%, 50%, and 75% dimethylformamide have been studied polarographically using theDeFord andHume's treatment as extended byIrving. Increase in the stability constants was observed with increase in dimethylformamide percentage. The percentage composition of the various complexed and uncomplexed species in 25% and 50% dimethylformamide are presented. 相似文献
8.
Madhukar N. Jachak Sandeep M. Bagul Bhausaheb K. Ghotekar Raghunath B. Toche 《Monatshefte für Chemie / Chemical Monthly》2009,20(5):655-662
Abstract
A series of (2E)-3-(1-chloro-6-methoxy-3,4-dihydronaphthalen-2-yl)-1-(4-aryl)prop-2-en-1-ones (chalcones) have been synthesized by a new synthetic route. The 3-pyridinecarbonitrile derivatives were synthesized by the Michael reaction of malononitrile (in base) and aroylacetonitriles (in acid) with chalcones in one pot. The fluorescent properties and quantum yields of these compounds were studied. 相似文献9.
J. N. Gaur S. C. Baghel Rajaya Shree Sharma 《Monatshefte für Chemie / Chemical Monthly》1981,112(4):439-443
Polarographic study of Pd(II) reveals that it reduces quasireversibly at d.m.e. in 0.2M-pyridine+0.1N-HCl medium. Kinetic parameters of Pd(II) in various concentrations of -resorcyclic acid were calculated usingGellings method and thus the effect of concentration of -resorcyclic acid on the kinetics of the reduction of Pd(II) has been explained.DeFord/Hume graphical extrapolation method and the mathematical method ofMihailov have been employed for the evaluation of overall formation constants of the complexes formed with -resorcyclic acid. The logarithmic values of overall formation constants 1, 2 and 3 obtained by the two methods are 7.47, 8.60, 9.66 (DeFord andHume Method) and 7.44, 8.64, 9.66 (Mihailov Method) at 298 K. Thermodynamic parameters of these complexes are reported.
Elektrodenkinetik und thermodynamische Untersuchungen an Pd(II)-Komplexen mittels polarographie
Zusammenfassung Pd(II) zeigt eine quasireversible Reduktion in 0,2M-Pyridin/0,1N-HCl. Kinetische Parameter wurden mittels der Methode vonGelling ermittelt und damit der Effekt verschiedener -Resorcylsäurekonzentrationen erklärt. Bildungskonstanten der entsperechenden Komplexe wurden nachDeFord/Hume und nachMihailov ermittelt. Die logarithmischen Werte der Gesamtbildungskonstanten 1, 2 und 3 bei 298 K betragen nach derDe Ford/Hume-Methode 7,47, 8,60 und 9,66, nach derMihailov-Methode 7,44. 8,64 und 9,66. Die thermodynamischen Parameter der Komplexbildung werden angegeben.相似文献
10.
Madhukar N. Jachak Maruti G. Ghagare Dilip R. Birari Ramhari V. Rote Muddassar A. Kazi Sanjay M. Jachak Raghunath B. Toche 《Monatshefte für Chemie / Chemical Monthly》2010,46(3):569-576