全文获取类型
收费全文 | 156篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 104篇 |
力学 | 6篇 |
数学 | 10篇 |
物理学 | 46篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 9篇 |
2014年 | 1篇 |
2013年 | 10篇 |
2011年 | 5篇 |
2010年 | 2篇 |
2009年 | 4篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1967年 | 4篇 |
1957年 | 1篇 |
排序方式: 共有166条查询结果,搜索用时 15 毫秒
51.
Comtois D. Pepin H. Vidal F. Rizk F.A.M. Ching-Yuan Chien Johnston T.W. Kieffer J.-C. La Fontaine B. Martin F. Potvin C. Couture P. Mercure H.P. Bondiou-Clergerie A. Lalande P. Gallimberti I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2003,31(3):377-386
Using a plasma channel produced by an ultrashort laser pulse, we have studied the laser triggering and guiding of a positive leader from the tip of a 2-m vertical rod standing on the bottom plane of a 7-m plane-plane gap. The purpose of this setup was to reproduce in the laboratory the electric field conditions leading to the onset of a positive upward leader from a ground rod as a downward negative leader is approaching during a thunderstorm, in order to demonstrate the working principle of a possible future laser lightning rod. The leader triggering properties of the laser-created plasma channel have been studied as a function of the synchronization of the laser pulse with the voltage impulse applied to the gap. We show that the laser pulse reduces the inception voltage of the leader compared to its normal value and that the laser plasma channel guides the propagation of the upward leader at a velocity ten times higher than that of an ordinary leader, with a significantly lower charge per unit length. We show that laser guiding of the leader significantly reduces the breakdown voltage of the gap and that the effect of the laser channel at the end of a lightning rod can be compared quite favorably with the effect of an additional metal rod of the same length. 相似文献
52.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
53.
C.?Ternon C.?Dufour F.?GourbilleauEmail author R.?Rizk 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,41(3):325-332
The increasing interest in photonics in the field of communication has led to intense research work on silicon based nanostructures showing efficient photoluminescence. The present paper reports photoluminescence measurements obtained at room temperature in silicon-rich-silica-silica multilayers grown by reactive magnetron sputtering. The silicon nanograin size is controlled via the silicon layer thickness which can be monitored with high accuracy. We aim to develop a comprehensive understanding of the combined roles played by the quantum confinement effect through the silicon grain size and the existence of an interfacial region between the grain and the surrounding silica matrix. Two bands of photoluminescence are displayed in the 600 nm-900 nm range and correspond to the bands previously observed at 2 K. Their origin is demonstrated through a model based on the solution of the Schrödinger equation of the exciton wavefunction in a one-dimension geometry corresponding to the growth direction of the multilayers. The silicon layer as well as the Si-SiO2 interface thicknesses are the key parameters of the photoluminescence features.Received: 6 April 2004, Published online: 21 October 2004PACS:
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures - 73.21.Ac Multilayers - 71.23.An Theories and models; localized states 相似文献
54.
R. A. M. Rizk 《Journal of Radioanalytical and Nuclear Chemistry》1998,231(1-2):69-76
Prompt gamma-ray energy spectrum following the capture of thermal neutrons by the atomic nuclei in an alumina ore sample was
measured using a HPGe detector in a borehole environment. Based on the in formation obtained from the spectrum and nuclear
data the nuclear ratio that compares the content of an unknown element with an estimate of aluminium in the ore can be determined.
The work aimed to explore the applicability of this technique for quality control measurements in the aluminium industry of
Egypt. 相似文献
55.
56.
57.
58.
59.
Rizk E. Khidre Ibrahim Ali M. Radini Diaa A. Ibrahim 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):1040-1047
AbstractThe reaction of 3-oxopropanenitriles with phenyl isothiocyanate in DMF containing KOH afforded the corresponding potassium salts. The latter salts were converted into ketene N,S-acetals upon acidification with hydrogen chloride. The reaction of the ketene N,S-acetals with 2-bromo-1-[5-methyl-1-(p-tolyl)-1H-1,2,3-triazol-4-yl]ethan-1-one or 3-(2-bromoacetyl)-2H-chromen-2-one gave novel thiophenes in good yields. Treatment of the ketene N,S-acetals with hydrazonyl halides afforded 1,3,4-thiadiazoles in good yields. The stereochemistry of the synthesized compounds was studied. 相似文献
60.
R. A. M. Rizk 《Journal of Radioanalytical and Nuclear Chemistry》1998,231(1-2):25-35
Grain-size effects on γ-ray absorptiometry in non-destructive assay of rainy solid materials with uniform grain radii are
widely investigated. In many applications the grain radii are not uniform, but follow more or less a distribution function.
The present work offers a Monte Carlo model for γ-ray attenuation in materials with grain-size distributions. Suitable correction
functions for grain-size effects have been derived. A comparison between the Monte Carlo results and those from analytical
calculations shows a good agreement when the grain sizes are uniform, but a disagreement appears when grain sizes are statistically
distributed. This disagreement between the two results may be due to the several approximations introduced in the analytical
calculations. 相似文献