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41.
S. J. Pearton D. P. Norton Y. W. Heo L. C. Tien M. P. Ivill Y. Li B. S. Kang F. Ren J. Kelly A. F. Hebard 《Journal of Electronic Materials》2006,35(5):862-868
ZnO is a very promising material for spintronics applications, with many groups reporting room-temperature ferromagnetism
in films doped with transition metals during growth or by ion implantation. In films doped with Mn during pulsed laser deposition
(PLD), we find an inverse correlation between magnetization and electron density as controlled by Sn-doping. The saturation
magnetization and coercivity of the implanted single-phase films were both strong functions of the initial anneal temperature,
suggesting that carrier concentration alone cannot account for the magnetic properties of ZnO:Mn and factors such as crystalline
quality and residual defects play a role. Plausible mechanisms for ferromagnetism include the bound magnetic polaron model
or exchange that is mediated by carriers in a spin-split impurity band derived from extended donor orbitals. The progress
in ZnO nanowires is also reviewed. The large surface area of nanorods makes them attractive for gas and chemical sensing,
and the ability to control their nucleation sites makes them candidates for microlasers or memory arrays. Single ZnO nanowire
depletion-mode metal-oxide semiconductor field effect transistors exhibit good saturation behavior, threshold voltage of ∼−3
V, and a maximum transconductance of 0.3 mS/mm. Under ultraviolet (UV) illumination, the drain-source current increased by
approximately a factor of 5 and the maximum transconductance was ∼5 mS/mm. The channel mobility is estimated to be ∼3 cm2/Vss, comparable to that for thin film ZnO enhancement mode metal-oxide semiconductor field effect transistors (MOSFETs),
and the on/off ratio was ∼25 in the dark and ∼125 under UV illumination. The Pt Schottky diodes exhibit excellent ideality
factors of 1.1 at 25°C, very low reverse currents, and a strong photoresponse, with only a minor component with long decay
times thought to originate from surface states. In the temperature range from 25°C to 150°C, the resistivity of nanorods treated
in H2 at 400°C prior to measurement showed an activation energy of 0.089 eV and was insensitive to ambient used. By contrast, the
conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential
as gas sensors. Sensitive pH sensors using single ZnO nanowires have also been fabricated. 相似文献
42.
X-ray diffraction was utilized to follow the transformation from -SiC (3C) to the various -SiC polytypes in the presence of AlN and Al2O3 additives after hot pressing from 1700 to 2100°C. The 2H- and 6H-polytypes of -SiC were the predominate polytypes with additions of only AlN or Al2O3, respectively. The amount of 2H- and 6H-polytypes, and subsequently the microstructural morphology of the SiC materials, were found to be controlled by varying the amount of AlN and Al2O3. Improvements in fracture toughness to 9 MPa-m were achieved with flexural strengths ranging from 600 to 900 MPa. These results suggest that accurate control of the polytypic make-up of SiC-based materials, along with their mechanical properties, can be achieved through AlN and Al2O3 additions. 相似文献
43.
Tien Huynh Catherine Lassez Jean-Louis Lassez 《Annals of Mathematics and Artificial Intelligence》1992,6(4):295-315
Projection of polyhedral sets is a fundamental operation in both geometry and symbolic computation. In most cases, however, it is not practically feasible to generate projections as the size of the output can be exponential in the size of the input. Even when the size of the output is manageable, we still face two serious problems: overwhelming redundancy and degeneracy. Here, we address these problems from a practical point of view. We discuss three algorithms based on algebraic and geometric techniques and we compare their performance in order to assess the feasibility of these approaches. 相似文献
44.
Angela M. Gyurko Gregory E. Vignoul John K. Tien Juan M. Sanchez 《Metallurgical and Materials Transactions A》1992,23(11):3073-3076
Engineering, University of Texas at Austin, Austin, TX 78712 While much of the high-temperature intermetallics research has
centered around Ni3Al and other aluminum-based systems, the present study focuses on the Engel-Brewer Ll2 intermetallic Ir3Zr, which has a melting temperature approaching that of ceramics (2280 °C). Due to limited material availability, the technique
of microindentation was used to study both the temperature and time dependence of strength. Because of the widely held belief
that certain mechanical properties of intermetallics scale roughly with temperature, Ir3Zr was expected to exhibit high strength. The microhardness was observed to vary from 225 MPa at room temperature to 75 MPa
at 1400 °C, which is significantly lower than the behavior of Ni3Al. The activation energy for creep was determined to be 467 kJ/mole, and the stress exponent was found to be 18.2. The ordering
energy of this system was calculated to be 0.114 eV. If it can be assumed that high ordering energy correlates to a high antiphase
boundary (APB) energy, then the behavior of this system is consistent with a model that predicts highly glissile dislocation
cores. 相似文献
45.
46.
In the present paper, both nongray and nonisothermal behaviors of an infrared emittingabsorbing gas have been taken into account in radiative transfer analyses through the use of the nonisothermal band absorptance. Consideration is given specifically to a simple system consisting of a radiating medium bounded by two infinite parallel black surfaces of different temperatures. Solutions are presented for the cases of radiative equilibrium and combined conduction and radiation. Results based on different methods of evaluating the nonisothermal band absorptance are also compared among themselves. Differences in several fundamental features are exhibited in the nongray nonisothermal solutions as compared to those with nongray but isothermal properties. 相似文献
47.
Factors affecting adhesion of oxide scales on alloys 总被引:1,自引:0,他引:1
C. S. Giggins B. H. Kear F. S. Pettit J. K. Tien 《Metallurgical and Materials Transactions B》1974,5(7):1685-1688
48.
49.
50.
Kurt R Bogner HR Straton JB Tien AY Gallo JJ 《Computer methods and programs in biomedicine》2004,73(2):165-171
We wanted to test the psychometric reliability and validity of self-reported information on psychological and functional status gathered by computer in a sample of primary care outpatients. Persons aged 65 years and older visiting a primary care medical practice in Baltimore (n=240) were approached. Complete baseline data were obtained for 54 patients and 34 patients completed 1-week retest follow-up. Standard instruments were administered by computer and also given as paper and pencil tests. Test-retest reliability estimates were calculated and comparisons across mode of administration were made. Separately, an interviewer administered a questionnaire to gauge patient attitudes and feelings after using the computer. Most participants (72%) reported no previous computer use. Nevertheless, inter-method reliability of the GDS15 at baseline (0.719, n=47), intra-method reliability of the computer in time (0.797, n=31), inter-method reliability of the CESDR20 at baseline (0.740, n=53), and the correlation between the CESDR20 computer version at baseline and follow-up (0.849, n=34) were all excellent. The inter-method reliability of the CESDR20 at follow-up (0.615, n=37) was lower but still acceptable. Although 28% were anxious prior to using the computer testing system, that percent decreased to 19% while using the system. The efficiency and reliability in comparison to the paper instruments were good or better. Even though most participants had not ever used a computer prior to participating in the study, they had generally favorable attitudes toward the use of computers, and also reported having favorable experience with the computer testing system. 相似文献