全文获取类型
收费全文 | 232篇 |
免费 | 3篇 |
专业分类
化学 | 85篇 |
晶体学 | 2篇 |
力学 | 9篇 |
数学 | 15篇 |
物理学 | 105篇 |
无线电 | 19篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 21篇 |
2011年 | 16篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1938年 | 2篇 |
1937年 | 3篇 |
1936年 | 2篇 |
1935年 | 1篇 |
排序方式: 共有235条查询结果,搜索用时 156 毫秒
131.
132.
A. G. Page S. V. Godbole Madhuri J. Kulkarni S. S. Shelar B. D. Joshi 《Fresenius' Journal of Analytical Chemistry》1979,296(1):40-44
Summary An atomic absorption spectrometric method has been developed for the determination of chromium, cobalt, copper, manganese and nickel in U3O8 by electrothermal atomization of 5 mg powder samples. Nanogram amounts of all the elements can be estimated with a precision ranging between 7–12%. The non-specific absorption due to U3O8 for these measurements is negligible. The use of graphite powder with U3O8 in equal or double the sample amount improves sensitivity for the analyte element and prolongs the life of the atomizer.
Direkte AAS-Bestimmung von Co, Cr, Cu, Mn und Ni in U3O8 durch elektrothermische Atomisierung
Zusammenfassung Das entwickelte AAS-Verfahren geht von pulverförmigen 5mg-Proben aus. Nanogramm-Mengen der genannten Elemente können mit einer Genauigkeit im Bereich von 7–12% bestimmt werden. Die durch U3O8 verursachte unspezifische Absorption ist zu vernachlässigen. Durch Graphitzusatz (in der gleichen oder doppelten Menge der Probe) wird die Empfindlichkeit der Bestimmung verbessert und die Lebensdauer des Atomizers verlängert.相似文献
133.
We derive an effective Hamiltonian for Ga(1-x)Mn(x)As in the dilute limit, where Ga(1-x)Mn(x)As can be described in terms of spin F=3/2 polarons hopping between the Mn sites and coupled to the local Mn spins. We determine the parameters of our model from microscopic calculations. Our approach treats the large Coulomb interaction in a nonperturbative way, captures the effects of spin-orbit coupling and disorder, and is appropriate for other p-doped magnetic semiconductors. 相似文献
134.
Arijit Roy Cher Ming Tan Sean J. OShea Kedar Hippalgaonkar Wulf Hofbauer 《Microelectronics Reliability》2007,47(9-11):1580
In this work, we apply thermovoltage imaging using scanning tunneling microscope to observe atomic scale surface imperfections at room temperature. Thermovoltage mapping can provide high resolution (down to 1 nm) images of standing waves in metal at room temperature, thus avoiding the need for low temperature scanning tunneling microscopy for the investigation of the standing waves. In order to generate a thermovoltage between the sample and tip, the sample (Au(1 1 1)) is heated to about 40 °C above the room temperature and surface scanning is performed. Heating the sample is simpler than heating the tip by laser irradiation. The thermovoltage technique can be applied to estimate surface defect density and the severity of the surface defects in materials, which can be a useful tool for the reliability study of nano-scale materials and devices. 相似文献
135.
Covering arrays for words of length over a ‐letter alphabet are arrays with entries from the alphabet so that for each choice of columns, each of the ‐letter words appears at least once among the rows of the selected columns. We study two schemes in which all words are not considered to be different. In the first case known as partitioning hash families, words are equivalent if they induce the same partition of a element set. In the second case, words of the same weight are equivalent. In both cases, we produce logarithmic upper bounds on the minimum size of a covering array. Definitive results for , as well as general results, are provided. 相似文献
136.
137.
138.
S.K. Sharma P.K. Pujari K. Sudarshan D. Dutta M. Mahapatra S.V. Godbole O.D. Jayakumar A.K. Tyagi 《Solid State Communications》2009,149(13-14):550-554
We report results on positron annihilation spectroscopic (PAS) studies using lifetime and coincidence Doppler broadening techniques in zinc oxide (ZnO) nanoparticles (4 to 40 nm) synthesized by solid state pyrolytic reaction followed by annealing in the temperature range of 200 °C to 800 °C. Positron lifetime in the nanoparticles are observed to be higher than bulk lifetime in all the cases. Theoretical calculation of lifetime indicates the presence of either Zn or (Zn, O) vacancy clusters which migrate and anneal out at high temperature. Comparison of ratio spectra from coincidence Doppler broadening measurement and calculated electron momentum distribution indicates the presence of either Zn or (Zn, O) vacancies. In addition, photoluminescence (PL) measurements have been carried out to examine the role of defects on the intensity of emission in the visible region. 相似文献
139.
S.K. Gupta M. Mohapatra S. Kaity V. Natarajan S.V. Godbole 《Journal of luminescence》2012,132(6):1329-1338
Strontium silicate (Sr2SiO4) samples doped with varying Eu3+content were prepared via sol–gel route and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS) and photoluminescence (PL) techniques. The synthesis temperature could be brought down to 600 °C for formation of a singe phase sample. The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Eu3+ ions was evaluated based on which the quenching mechanism was verified to be a multipole–multipole interaction. Based on the time-resolved emission data (TRES), it was inferred that, two different types of Eu3+ ions were present in the matrix. The first type was a long lived species (τ=4.7 ms) present at 10-coordinated ‘Sr’sites and the other was a short lived species (τ=1.2 ms) present at the 9-coordinated ‘Sr’sites which gets selectively excited at 296 nm. Judd–Ofelt (J–O) intensity parameters for both the species were evaluated. The trend observed for the two species in the J–O parameters, Ω2 and Ω4 were different confirming their existence in two different environments. The color coordinates of the system were evaluated and plotted on a CIE index diagram. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. 相似文献
140.
Bi2Te3 nanoparticles (NPs) have been synthesized at 50?°C by a low-cost wet chemical route. The structural properties of product sample were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy. Thermal properties of product sample were investigated by differential scanning calorimetry (DSC), thermogravimetric (TG), and transient plane source techniques. The XRD and selected area electron diffraction of Bi2Te3 NPs result showed the polycrystalline nature with a rhombohedral (R3m) structure of the nanocrystallites. The average grain size of Bi2Te3 NPs was found to be about 30?nm by XRD and TEM measurements. DSC result shows one endothermic peak and one exothermic peak. TG result shows that only 48?% mass loss has occurred in Bi2Te3 sample. The obtained lower thermal conductivity of Bi2Te3 NPs is about 0.3?W m?1 K?1 at room temperature, which is caused by considering the crystalline nature of this material. 相似文献