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1.
Growth experiments with GaN in the system Ga/HCl/NH3/He or H2 were carried out in a reactor with two deposition zones. The extent of the reaction in the first zone, called the predeposition zone, is controlled by the NH3 flow rate. In the second zone GaN is deposited epitaxially onto sapphire substrates. The variation of the carrier concentration of these epilayers indicates the dominating effect of impurities especially oxygen in opposition to the widely accepted vacancy model. Due to the high incorporation ratio of donor impurities into the solid a predeposition reduces the impurity content in the vapour phase. A reduction of the free carrier concentration in the epitaxial layers could be achieved. Different behaviour in the two carrier gas systems could be established. 相似文献
2.
Equilibria between quaternary liquid phases Ga–In–As–Ge(–Sn) and the ternary solid phase Ga–In–As have been calculated by application of the KRUPKOWSKI formalism on the excess free enthalpy. Experimental liquidus data were obtained from solubility experiments in a LPE equipment. Results of calculation and experimental liquidus data are compared. 相似文献
3.
The used liquid-phase epitaxy apparates are described and the experimental conditions of growth on GaP and Ga(AsP) onto GaAs-substrates are reported. The influence of growing conditions (temperature, cooling rate, composition of melt) on the quality of interface and on the inlusion of solvent are discussed. The consequence of varying degrees of substrat-misorientation on the surface morphology has been studied. 相似文献
4.
5.
6.
M. Raffel H. Richard K. Ehrenfried B. Van der Wall C. Burley P. Beaumier K. McAlister K. Pengel 《Experiments in fluids》2004,36(1):146-156
Three-component particle image velocimetry measurements at moderate speeds and observation distances can now be accomplished on a routine basis. This article discusses the experiment performed on a 4 m-diameter model rotor in the 6-m×8-m open test section of the Large Low Speed Facility of the German–Dutch Wind Tunnels. More than half a terabyte of raw data were recorded at various positions on the advancing and retreating sides of the rotor in order to obtain detailed measurements of the trailing vortex in the frame of an international project. This paper addresses measuring techniques and possible sources of errors and presents a limited number of cases for the purpose of illustrating the solutions to numerous technical challenges relating to the acquisition and analysis of vortical flows.List of symbols
C
T
thrust coefficient (T/2
R
4)
-
M
magnification
-
r
c
radius of vortex core (mm)
-
R
rotor radius (m)
-
T
thrust (N)
-
u,v,w
velocity components in x, y and z coordinates (m/s)
- (u,v,w)wt
velocity components in wind tunnel coordinates (m/s)
-
U
max
maximum in-plane velocity component (m/s)
-
W
max
maximum out-of-plane velocity component (m/s)
-
x,y,z
particle image velocimetry (PIV) frame coordinates (m)
- (x,y,z)wt
wind tunnel coordinates (m)
- t
time delay (s)
- Z
light sheet thickness (mm)
- Z
light sheet thickness (mm)
-
rotor rotation frequency (rad/s)
-
rotor azimuth angle during recording (deg) vortex age
-
rotor shaft angle (deg)
-
x
displacement measurement error
-
advance ratio (V/R)
-
air density (kg/m3)
-
circulation (m2/s)
-
z
vorticity (s–1)
Abbreviations AFDD
Aeroflightdynamics Directorate
- BVI
blade–vortex interaction
- DLR
Deutches zentrum für Luft- und Raumfahrt
- DNW
German–Dutch Wind tunnel
- HART
HHC aeroacoustic rotor test
- LLF
large low speed facility
- NASA
National Aeronautics and Space Administration
- ONERA
Office National dEtudes e de Recherches Aerospatiales
- RANS
Reynolds-averaged Navier–Stokes
- SPR
stereo pattern recognition
- 3C-PIV
three-component particle image velocimetry 相似文献
7.
Dr.-Ing. U. Butter 《Archive of Applied Mechanics (Ingenieur Archiv)》1971,40(5):281-303
Übersicht Es wird ein finites Verfahren zur Berechnung der Spannungen in Rotationskörpern unter rotationssymmetrischer Belastung angegeben. Die Spannungen werden als Unbekannte eingeführt. Gleichgewichts- und Verträglichkeitsgleichungen werden mit Hilfe des Prinzips der virtuellen Arbeiten aufgestellt. Durch parabolische Näherung der Spannungsverläufe und Verwendung geeigneter virtueller Verschiebungs- und Gleichgewichtszustände wird eine hohe Genauigkeit erzielt. Es wird eine Verfahrensweise zum Aufstellen virtueller Zustände durch systematischen Fehlerabgleich entwickelt.
Gekürzte Fassung einer Dissertation an der TU Berlin (D 83); Berichterstatter: Prof. Dr.-Ing. E. Giencke, Prof. Dr. rer. nat. J. Albrecht. 相似文献
Summary A finite element method for axisymmetric stress analysis is presented. The stresses are introduced as unknown quantities. Equilibrium and compatibility equations are set up by application of the principle of virtual work. High accuracy is achieved by parabolic approximation of the stress distribution and the use of appropriate displacement and equilibrium states. A procedure for constructing virtual states by systematic error balance is developed.
Gekürzte Fassung einer Dissertation an der TU Berlin (D 83); Berichterstatter: Prof. Dr.-Ing. E. Giencke, Prof. Dr. rer. nat. J. Albrecht. 相似文献
8.
The crystalline perfection and the epitaxial relationships of GaN layers prepared by the reaction of GaCl and NH3 in He carrier gas on {111} and {100} spinel substrates have been determined by RHEED measurements. The epitaxial relationships were found to be The best crystalline perfection could be achieved at growth temperatures of 1000…︁1050°C and growth rates more than 1 μm/min. – The growth direction 〈101 1〉 has been found to be more suitable for rapid growth than the direction 〈0001〉. 相似文献
9.
Some aspects of Ga(CH3)3/AsH3/H2 pyrolysis are described. The quality of the epitaxial GaAs layers on GaAs substrates is examined by chemical etching, X-ray technique and observation of the surface morphology. The investigations show a relation between the quality of the layers and growth conditions (As/Ga-proportion, substrate temperature). 相似文献
10.
In the temperature range from 950 to 1200 K Kp-values result from 5 · 10−5 to 6,9 · 10−3 for the heterogeneous reversible reaction Ge(s) + H2O(g) ⇋ GeO(g) + H2O(g), the average reaction enthalpy being 46,5 ± 05 kcal/mol. Etching rates calculated with these equilibrium constants for closed systems are 20-25% larger than the experimental etching rates for (110)-Ge in the sandwich device. The ratio of the etching rates is for (111)-, (100)- and (110)-Ge 1:1,4:1,8; the average reaction enthalpy calculated experimentally is 46 ± 1 kcal/mol for the temperature range 1000-1200 K. The dependence of transport rate on distance between source and substrate characterizes the sandwich device as a quasi-closed system with the diffusion as the rate controlling step of the material transport. 相似文献