全文获取类型
收费全文 | 238篇 |
免费 | 11篇 |
专业分类
化学 | 147篇 |
晶体学 | 7篇 |
力学 | 32篇 |
数学 | 17篇 |
物理学 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 3篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 7篇 |
2009年 | 15篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1962年 | 2篇 |
1961年 | 2篇 |
排序方式: 共有249条查询结果,搜索用时 984 毫秒
21.
Thermal, structural and optical properties of Nd3+ ions in tellurite glass (TeO2-ZnO-Na2O-Li2O-Nb2O5) have been investigated. Differential thermal analysis revealed reasonably good forming tendency of the glass composition. FTIR spectra were used to analyze the functional groups present in the glass. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative lifetime, branching ratio and stimulated emission cross-section of the 4F3/2→4I9/2, 11/2, 13/2 transitions. The quantum efficiency of the 4F3/2 level is comparable as well as higher than the typical value of the other tellurite based glasses. The decay from the 4F3/2 level is found to be single exponential for different concentrations of Nd3+ ions with a shortening of lifetime with increasing concentration. The experimental values of branching ratio and saturation intensity of 4F3/2→4I11/2 transition indicate the favourable lasing action with low threshold power. 相似文献
22.
Miss Ganjam K. Rajeswari Seekote L. Rathna 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1962,13(1):43-57
Zusammenfassung Die Bewegungsgleichungen für die stationären Strömungen einer besonderen Klasse nichtnewtonscher viskoelastischer und viskounelastischer Flüssigkeiten nahe einem Staupunkt sind nach der Kármán-Pohlhausen-Methode integriert worden. Es hat sich gezeigt, dass der Effekt der Querviskosität und Viskoelastizität durch den dimensionslosen ParameterR=a/ beziehungsweiseK=a/ dargestellt werden. Aus der Betrachtung der Dissipationsfunktion folgern wir, dass der ganze Umfang der negativen Werte vonK undR physikalisch zulässig ist. Die zweidimensionalen Grenzschichtgleichungen für viskoelastische Flüssigkeiten sind abgeleitet worden. 相似文献
23.
This paper discusses the availability of a two-unit standby redundant repairable system in which the pdf of the life time of the online unit depends on the time it has spent in the standby state before it is switched online. Explicit expressions for the Laplace transforms of the availability and reliability of the system are obtained by identifying suitable regeneration points.
Zusammenfassung In dieser Arbeit wird die Verfügbarkeit eines redundanten 2-Komponentensystems mit heißer Reserve und Reparatur betrachtet. -Die Lebensdauerverteilung der Betriebskomponente hängt von der Länge der Zeit ab, die sie vorher als Reservekomponente verbracht hat. Es werden explizite Ausdrücke der Laplacetransformierten für die Verfügbarkeit und Zuverlässigkeit des Systems ermittelt, indem geeignete Regenerationspunkte verwendet werden.相似文献
24.
P. B. Janardhan und S. Rajeswari 《Colloid and polymer science》1978,256(8):831
Ohne Zusammenfassung 相似文献
25.
Ebenezer DD Ravichandran K Ramesh R Padmanabhan C 《The Journal of the Acoustical Society of America》2005,117(6):3645-3656
A method is presented to determine the forced responses of piezoelectric cylinders using weighted sums of only certain exact solutions to the equations of motion and the Gauss electrostatic conditions. One infinite set of solutions is chosen such that each field variable is expressed in terms of Bessel functions that form a complete set in the radial direction. Another infinite set of solutions is chosen such that each field variable is expressed in terms of trigonometric functions that form a complete set in the axial direction. Another solution is used to account for the electric field that can exist even when there is no vibration. The weights are determined by using the orthogonal properties of the functions and are used to satisfy specified, arbitrary, axisymmetric boundary conditions on all the surfaces. Special cases including simultaneous mechanical and electrical excitation of cylinders are presented. All numerical results are in excellent agreement with those obtained using the finite element software ATILA. For example, the five lowest frequencies at which the conductance and susceptance of a stress-free cylinder, of length 10 mm and radius 5 mm, reach a local maximum or minimum differ by less than 0.01% from those computed using ATILA. 相似文献
26.
P. Santhana Raman K.G.M. Nair R. Kesavamoorthy B.K. Panigrahi S. Dhara V. Ravichandran 《Applied Physics A: Materials Science & Processing》2007,87(4):709-713
Indium nanoclusters are synthesized in an amorphous silica matrix using an ion-implantation technique. Indium ions (In2+) with energy of 890 keV are implanted on silica to fluences in the range of 3×1016–3×1017 cm-2. The formation of indium nanoclusters is confirmed by optical absorption spectrometry and glancing incidence X-ray diffraction
studies. A low frequency Raman scattering technique is used to study the growth of embedded indium nanoclusters in the silica
matrix as a function of fluence and post-implantation annealing duration. Rutherford backscattering spectrometry studies show
the surface segregation of implanted indium. Photoluminescence studies indicate the formation of a small quantity of indium
oxide phase in the ion-implanted samples.
PACS 85.40.Ry; 78.67.Bf; 73.20.Mf; 82.75.Fq 相似文献
27.
28.
C. Ravichandran G. Srinivasan Craig Lennon S. Sivananthan J. Kumar 《Superlattices and Microstructures》2011
Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (OZn), interstitial zinc (Zni), interstitial oxygen (Oi) and zinc vacancy (VZn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films. 相似文献
29.
N. Rajeswari Yogamalar A. Chandra Bose 《Applied Physics A: Materials Science & Processing》2011,103(1):33-42
Nanopowders of pure and lithium-doped semiconducting ZnO (Zn1−x
Li
x
O, where x= 0, 0.01, 0.03, 0.06, 0.09 and 0.15 in atomic percent (at.%)) are prepared by PEG-assisted low-temperature hydrothermal method.
The average crystallite size is calculated using Debye–Scherrer formula and corrected for strain-induced broadening by Williamson–Hall
(W–H) plot. The peak shift in XRD and the lattice constant of ZnO as a function of unit cell composition are predicted by
Vegard’s law. The evolution of ZnO nanostructures from rod-shaped to particle nature is observed from TEM images and the influence
of dopant on the morphology is investigated. The optical absorption measurement marks an indication that the incorporation
of lithium ion into the lattice of ZnO widens the optical band gap energy from ∼2.60 to ∼3.20 eV. The near band edge (NBE)
emission peak centered at ∼3.10 eV is considered to be the dominant emission peak in the PL spectra. Blue emission peak is
not observed in doped ZnO, thus promoting defect-free nanoparticles. The Burstein–Moss shift serves as a qualitative tool
to analyze the widening of the optical band gap and to study the shape of the NBE luminescence in doped ZnO nanopowders. FT-IR
spectra are used to identify the strong metal–oxide (Zn–O) interaction. 相似文献
30.
G. MurugananthamK. Ravichandran K. SaravanakumarA.T. Ravichandran B. Sakthivel 《Superlattices and Microstructures》2011,50(6):722-733
Undoped and fluorine doped tin oxide films were deposited from starting solutions having different values of solvent volume (10-50 ml) by employing a low cost and simplified spray technique using perfume atomizer. X-ray diffraction studies showed that there was a change in the preferential orientation from (2 1 1) plane to (1 1 0) plane as the volume of the solvent was increased. The sheet resistance (Rsh) of undoped SnO2 film was found to be minimum (13.58 KΩ/□) when the solvent volume was lesser (10 ml) and there was a sharp increase in Rsh for higher values of solvent volume. Interestingly, it was observed that while the Rsh increases sharply with the increase in solvent volume for undoped SnO2 films, it decreases gradually in the case of fluorine doped SnO2 films. The quantitative analysis of EDAX confirmed that the electrical resistivity of the sprayed tin oxide film was mainly governed by the number of oxygen vacancies and the interstitial incorporation of Sn atoms which in turn was governed by the impinging flux on the hot substrate. The films were found to have good optical characteristics suitable for opto-electronic devices. 相似文献