全文获取类型
收费全文 | 4419篇 |
免费 | 66篇 |
国内免费 | 138篇 |
学科分类
工业技术 | 4623篇 |
出版年
2024年 | 1篇 |
2023年 | 47篇 |
2022年 | 78篇 |
2021年 | 88篇 |
2020年 | 92篇 |
2019年 | 93篇 |
2018年 | 79篇 |
2017年 | 117篇 |
2016年 | 63篇 |
2015年 | 67篇 |
2014年 | 169篇 |
2013年 | 190篇 |
2012年 | 204篇 |
2011年 | 409篇 |
2010年 | 237篇 |
2009年 | 271篇 |
2008年 | 277篇 |
2007年 | 265篇 |
2006年 | 246篇 |
2005年 | 171篇 |
2004年 | 159篇 |
2003年 | 161篇 |
2002年 | 157篇 |
2001年 | 123篇 |
2000年 | 100篇 |
1999年 | 111篇 |
1998年 | 117篇 |
1997年 | 101篇 |
1996年 | 85篇 |
1995年 | 84篇 |
1994年 | 68篇 |
1993年 | 39篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 25篇 |
1988年 | 27篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有4623条查询结果,搜索用时 15 毫秒
71.
《Current Opinion in Solid State & Materials Science》2015,19(1):49-67
This review provides an overview of the current status of ion-implantation research in silicon, germanium and the compound semiconductors SiC, GaN and ZnO. The discussion of silicon includes recent developments in metrology and device simulation, as well as a brief discussion of emerging applications in photovoltaics and quantum electronics. That of Ge includes a more detailed overview of doping, radiation damage and annealing processes due to the renewed research interest in this material. Finally, the discussion of compound semiconductors focuses on the newer wide bandgap materials where there are remaining implantation issues to be solved and potentially new implantation applications emerging. 相似文献
72.
The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×1015 cm−3 has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×1014 electrons-cm−2. For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×1015 to 6.8×1015 cm−3 after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm−2 K−2 for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area. 相似文献
73.
《Journal of the European Ceramic Society》2020,40(10):3499-3508
Oxidation behavior of boron-containing HfC/SiC nanocomposites (SHBC) at temperatures up to 1500 °C and with exposure time up to 100 h was investigated. Two strategies to improve the oxidation resistance of the HfC/SiC ceramics are proposed. First concept involves the incorporation of a small amount of boron (ca. 0.6 wt.%) into the nanocomposite via a single-source-precursor approach, which contributes significantly to the enhancement of its oxidation resistance. Parabolic oxidation rate constants of 10−3 to 10-4 mg2/(cm4 h) at 1300−1500 °C were measured for SHBC and were several orders of magnitude lower than those recorded for boron-free HfC/SiC. The second improvement concept is realized via passivation of the samples upon short-term oxidation at 1400 °C, providing an excellent oxidation resistance over a wide temperature range. This is a crucial step especially when considering the poor oxidation behavior of HfC and the sluggish formation of protective silica scale at moderate temperatures. 相似文献
74.
《Ceramics International》2020,46(2):2063-2071
Photocurable gray-colored Si3N4 ceramic slurry with high solid loading, suitable viscosity and high curing depth is critical to fabricate dense ceramic parts with complex shape and high surface precision by stereolithography technology. In the present study, Si3N4 ceramic slurry with suitable viscosity, high solid loading (45 vol %) and curing depth of 50 μm was prepared successfully when surface modifier KH560 (1 wt%) and dispersant Darvan (1 wt%) were used. The slurry exhibits the shear thinning behavior. Based on the Beer-Lambert formula, Dp (the attenuation length) and Ec (the critical energy dose) of Si3N4 ceramic slurry with solid loading of 45 vol % were derived as 0.032 mm and 0.177 mJ/mm2, respectively. Si3N4 ceramic green parts with complex shape and high surface precision were successfully fabricated by stereolithography technology. After optimizing the debinding and sintering process for green parts, dense Si3N4 ceramics with 3.28 g/cm3 sintering density were fabricated. The microhardness and fracture toughness of as-sintered Si3N4 ceramics are ~14.63 GPa and ~5.82 MPa m1/2, respectively, which are comparable to those of the samples by traditional dry-pressed and pressureless sintering technology. These results show that ceramic stereolithography technology could be promising to fabricate high performance ceramics, especially for gray-colored monolithic Si3N4 ceramics. 相似文献
75.
《International Journal of Hydrogen Energy》2019,44(23):11817-11823
Extremely low content of Ruthenium (Ru) nanoparticles were loaded on the carbon black (Ru/C) via reducing Ru ions with silicon monoxide. The obtained Ru/C nanocomposites exhibit an exciting electrochemical catalytic activity for hydrogen evolution reaction (HER) in the oxygen-free 0.5 M H2SO4 medium. The optical one (Ru/C-2) with a low Ru amount of 2.34% shows higher activity than previously reported Ru-based catalysts. The overpotential at 10 mA cm−2 is 114 mV and the Tafel slope is 67 mV·dec−1. Ru/C-2 catalyst also has good stability. The overpotential that afford the current density of 10 mA cm−2 of 20 wt% Pt/C increased 92 mV while that of Ru/C-2 only increased 50 mV after a 30,000 s chronopotentiometry test. Furthermore, the mass activity of Ru/C-2 catalyst is even better than that of the commercial 20 wt% Pt/C when the overpotential is larger than 0.18 V. This silicon monoxide-mediated strategy may open a new way for the fabrication of high performance electrocatalysts. 相似文献
76.
Kathy Lu Donald Erb Kaustubh Bawane Ni Yang 《Journal of the European Ceramic Society》2019,39(10):3035-3041
This study is to understand the effect of carbon content on the pyrolysis behaviors and phase contents of silicon oxycarbides (SiOCs). Flash pyrolysis conditions, evolution of different SiOC phases, and free carbon types/amounts are compared for C-rich and less C-rich precursors. The C-rich system experiences the flash event at a much lower pyrolysis temperature with a much higher current density even though the internal temperatures at flash are very similar. SiC formation is more obvious for the C-rich samples along with a much higher carbon content under both flash and traditional pyrolysis conditions. The phase contents of SiO2, SiC, and other SiOC intermediates can be calculated using a Gibbs energy minimization method, showing that the C-rich sample has more C-rich SiOC intermediates while the less C-rich sample has more Si-rich intermediates. This research provides a general framework in assessing the pyrolysis behaviors of different SiOC materials. 相似文献
77.
Guandong Liang Guoxun Sun Jianqiang Bi Weili Wang Xiangning Yang Yonghan Li 《Ceramics International》2021,47(2):2058-2067
Uniformly dispersed boron nitride nanosheets (BNNSs) reinforced silicon nitride (Si3N4) composites were prepared by surface modification assisted flocculation combined with SPS sintering. In order to improve the dispersibility of the BNNSs in the composites, the liquid phase stripped BNNSs are surface functionalized by a two-step covalently modification. The amino-modified BNNSs (NH2-BNNSs) and Si3N4 powders have opposite surface potential, mixed evenly by electrostatic interaction during flocculation. The results showed that mechanical properties of Si3N4 composites were obviously enhanced by adding NH2-BNNSs. The fracture toughness and bending strength of Si3N4 composites added 0.75 wt% NH2-BNNSs were increased by 34% and 28%, respectively, compared with monolithic Si3N4. Toughening mechanisms are synergistic action of the torn, pull-out or bridging of BNNSs and crack deflection mechanisms with microstructural analyzes. The dielectric properties of the Si3N4 ceramics are also improved after the addition of NH2-BNNSs. 相似文献
78.
《Journal of the European Ceramic Society》2019,39(13):3627-3633
We performed in-situ X-ray diffraction measurements of polycrystalline cubic silicon nitride samples at high temperatures under atmospheric pressure and at simultaneous high-pressure-temperature conditions. In air, cubic silicon nitride survives metastably up to 1733 K without oxidation. The temperature dependence of the thermal expansion coefficient was determined to be α(T) = a1 + a2T – a3T−2 where a1 = 1.34(6) × 10−5 K−1, a2 = 5.06(44) × 10−9 K−2, and a3 = 0.20(10) K. Using all the experimental data obtained under atmospheric and high pressures, a complete set of parameters of the high-temperature third-order Birch Murnaghan equation of state was obtained: K300,0 = 303(5) GPa, K′300,0 = 5.1(8), and (∂KT,0/∂T)P = –0.017(1) GPa K−1, where K0, K′0, and (∂KT,0/∂T)P are the isothermal bulk modulus, its pressure derivative, and its temperature derivative, respectively. These parameters are necessary to calculate the equilibrium phase boundary between the β and cubic phases in silicon nitride. 相似文献
79.
Naveen Kosar Sajida Munsif Khurshid Ayub Tariq Mahmood 《International Journal of Hydrogen Energy》2021,46(13):9163-9173
The barriers for the encapsulation and decapsulation of hydrogen ions (cationic hydrogen and hydride), atom, and molecule through silicon carbide nanotube are thoroughly studied. DFT method is selected to measure the kinetic barriers for the passage of hydrogen atom, ions and molecule through nanotube via scanning potential energy surface. The kinetic barriers for the passage (encapsulation and decapsulation) of hydrogen are very important to understand the mechanism of hydrogen storage and release. The barriers for the permeation of H, H+ and H? across SiC nanosheet are lower compared to hydrogen molecule (H2). The exohedral and endohedral adsorption of hydrogen ions (cation and anion), atom and exohedral hydrogen molecule on silicon carbide are exothermic in nature. Whereas the encapsulation of hydrogen molecule in silicon carbide is endothermic. Electronic properties are analyzed through measurement of energy gap between highest occupied and lowest unoccupied molecular orbitals gap (GH-L) and the density of state (DOS) spectra. The GH-L analysis reveals that endohedral complexes have more pronounced effect on electronic properties compared to exohedral complexes. The SiC nanotube has highly favorable properties for storage and release of hydrogen ions, and atom. 相似文献
80.
A. Baux S. Jacques A. Allemand G.L. Vignoles P. David T. Piquero M.-P. Stempin G. Chollon 《Journal of the European Ceramic Society》2021,41(6):3274-3284
We present here an original route for the manufacturing of SiC ceramics based on 3D printing, polymer impregnation and pyrolysis and chemical vapor deposition (CVD). The green porous elastomer structures were first prepared by fused deposition modeling (FDM) 3D-printing with a composite polyvinyl alcohol/elastomer wire and soaking in water, then impregnated with an allylhydridopolycarbosilane preceramic polymer. After crosslinking and pyrolysis, the polymer-derived ceramics were reinforced by CVD of SiC using CH3SiCl3/H2 as precursor. The multiscale structure of the SiC porous specimens was examined by X-ray tomography and scanning electron microscopy analyses. Their oxidation resistance was also studied. The pure and dense CVD-SiC coating considerably improves the oxidation resistance. 相似文献