全文获取类型
收费全文 | 2274篇 |
免费 | 33篇 |
国内免费 | 50篇 |
专业分类
电工技术 | 37篇 |
综合类 | 34篇 |
化学工业 | 217篇 |
金属工艺 | 374篇 |
机械仪表 | 115篇 |
建筑科学 | 23篇 |
矿业工程 | 10篇 |
能源动力 | 88篇 |
轻工业 | 722篇 |
水利工程 | 7篇 |
石油天然气 | 23篇 |
武器工业 | 3篇 |
无线电 | 182篇 |
一般工业技术 | 230篇 |
冶金工业 | 42篇 |
原子能技术 | 48篇 |
自动化技术 | 202篇 |
出版年
2024年 | 2篇 |
2023年 | 41篇 |
2022年 | 40篇 |
2021年 | 57篇 |
2020年 | 48篇 |
2019年 | 34篇 |
2018年 | 25篇 |
2017年 | 52篇 |
2016年 | 33篇 |
2015年 | 87篇 |
2014年 | 85篇 |
2013年 | 92篇 |
2012年 | 125篇 |
2011年 | 166篇 |
2010年 | 89篇 |
2009年 | 140篇 |
2008年 | 104篇 |
2007年 | 169篇 |
2006年 | 170篇 |
2005年 | 154篇 |
2004年 | 98篇 |
2003年 | 91篇 |
2002年 | 77篇 |
2001年 | 75篇 |
2000年 | 70篇 |
1999年 | 59篇 |
1998年 | 41篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有2357条查询结果,搜索用时 46 毫秒
71.
《International Journal of Hydrogen Energy》2019,44(21):10732-10743
In this work, microstructure and defect evolution at a temperature and activation treatment of the TiCr2 intermetallic compound of Laves phase C36-type synthesized in the abnormal glow discharge plasma were investigated. The crystalline structure of the C36TiCr2 powder crushed by hydrogenation-dehydrogenation (HD) method is characterized by the following lattice parameters: a = 4.932 Å and c = 16.059 Å. The dilatation of the crystal lattice under the hydrogenation at the HD crushing process leads to the formation of partial dislocations. For the first time ever the experimental value of the positron lifetime of the synthesized compound of the C36TiCr2 Laves phase, this amounted to (141 ± 2) ps, established by the positron spectroscopy. The optimal activation parameters of the HD-crushing C36TiCr2 powder were established: the temperature should be in the range from 450 to 500 °C, the exposure time in a hydrogen atmosphere at a pressure of (1–8) atm. must be at least 10 min. 相似文献
72.
73.
The impact of defect concentration and current density on the effective singlet exciton diffusion length in 4’-bis(carbazol-9-yl)biphenyl (CBP) is quantified by analyzing the electroluminescent characteristics of several sets of OLEDs. The defect concentration and effective diffusion length are determined through fitting of the defect and CBP emission bands in the electroluminescence spectra under constant current operation using an analytical model derived based on the competition between exciton diffusion and energy transfer to defects. Defect concentrations of 3 ± 1 × 1018 cm−3, 2 ± 1 × 1018 cm−3 and 0.3 ± 0.7 × 1018 cm−3 are calculated in three sets of OLEDs, in which the effective diffusion length decreases as the defect concentration increases. Modelling the dependence of the effective diffusion length on defect concentration a “defect free” diffusion length of 4.5 ± 0.3 nm is obtained for CBP singlet excitons in these devices operated under low current density. We also show that the driving voltage scales linearly with the defect concentration. 相似文献
74.
Fang Xu Wang-lin Li Zhan-lei Liu Bo-fan Zhang Bing-yu Zhang 《Geotextiles and Geomembranes》2017,45(3):178-183
In studies on the geomembrane air expansion in plain reservoirs, the forced deformation of a geomembrane is generally simplified as geomembrane air expansion deformation under ring-restrained conditions. In this study, a test apparatus was developed to measure geomembrane air expansion deformation, and a number of factors that can affect geomembrane air expansion deformation were investigated, including the test apparatus diameter, loading rate, and geomembrane defects. The results of this study show that under ring-restrained conditions, as the test apparatus diameter increases, the burst pressure decreases, and the burst crown height increases. Moreover, the burst pressure and the burst crown height gradually increase as the loading rate increases. Geomembrane defects, such as holes, folds, and scratches, decrease both the burst pressure and the burst crown height. 相似文献
75.
Fang Wang Shukun Le Fanyue Song Yiguo Su 《International Journal of Hydrogen Energy》2021,46(2):2103-2116
The appropriate interfacial contact and charges transfer mode of heterojunction photocatalysts were critical for high-efficiency hydrogen production. Inter-step mode heterojunction composite had advantages of enhanced visible-light response, improved charge space separation rate, increased electron utilization, which could also protect catalyst anode from photocorrosion. Zinc-vacancy-rich ZnS decorated CdS heterojunction photocatalyst with inter-step mode was constructed in order to fundamentally enhance photocatalytic performance and overcome photocorrosion of CdS. The charge transfer mode was modulated from pervasive type-II to bran-new inter-step mode by defect engineering. Zinc vacancies functioned as acceptor level for charge separation and up-shifted conduction and valance band energy of ZnS. The defective engineered CdS/ZnS heterojunction displayed a reduced over-potential and enhanced photocatalytic activity. The optimal photocatalytic hydrogen production rate for CdS/ZnS reached 42.1 mmol?g?1 under visible light without any co-catalyst. An apparent quantum yield (AQY) of 38.75% at 450 nm was achieved, which was 269.3 and 71.9 times higher than pristine zinc-vacancy-rich ZnS and CdS, respectively. Meanwhile, holes aggregated on the surface of CdS were blocked and the oxidation corrosion process was suppressed. The charge transfer mechanism and kinetics of charge transfer and separation in inter-step mode heterojunction photocatalysts were investigated and discussed. This work will accelerate practical applications of photocatalysis with inter-step mode and give deep insights into understanding how inherent acceptor levels play a role in designing defect-engineered semiconductor with enhanced photocatalytic performance. 相似文献
76.
Changbai Long Huiqing Fan Wei Ren Jinyan Zhao 《Journal of the European Ceramic Society》2019,39(14):4103-4112
This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi4Ti3O12 (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi4Ti2.97Nb0.03O12.015 (BiT-0.03Nb) shows high remnant polarization (Pr = 12.5 μC/cm2) and large field-induced strain (S33 = 5.6 × 10?4). In addition, this doping results in bulk conductivity (σb) of BiT decreasing dramatically and associated activity energy (Ea) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg2+ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ?0.65 × 10?2 S cm?1 in the bulk. 相似文献
77.
《Ceramics International》2022,48(2):1765-1770
Perovskite lattice was tailored by introducing site vacancies and mixed anion composition, to produce Sr0.83Li0.17Ta0.83O1.88N0.74 (Li02N). Further, Li02N was converted to a defect oxide Sr0.83Li0.17Ta0.83O3 (Li02O) by applying an optimized treatment: heating in air at 1173 K for 2 h. According to the neutron Rietveld refinement, Li02N and Li02O are tetragonal and orthorhombic, respectively, where the lattice volume of Li02O is significantly smaller than that of Li02N. The ionic conductivity (σion) of Li02N and Li02O was evaluated by the ac impedance spectroscopy and the equivalent circuit analysis. Both Li02N (σion = 10?5.5 S/cm at 671 K) and Li02O (σion = 10?6.2 S/cm at 667 K) exhibited an Arrhenius behavior of ionic conductivity with activation energies of 0.87 eV and 0.75 eV, respectively. It is interpreted that the nitride component enhances the ionic conduction of Li02N, while the vacancy of the anion lattice makes an opposite effect. 相似文献
78.
《International Journal of Hydrogen Energy》2019,44(54):28556-28565
NiFe layered double hydroxides (LDHs) is considered to be one of the LDHs electrocatalyst materials with the best electrocatalytic oxygen evolution properties. However, its poor conductivity and inherently poor electrocatalytic activity are considered to be the limiting factors inhibiting the electrocatalytic properties for oxygen evolution reaction (OER). The amorphous NiFeAl-LDHs electrocatalysts were prepared by electrodeposition with nickel foam as the support, and the D-NiFeAl-LDHs electrocatalyst with defect sites was then obtained by alkali etching. The mechanism of catalysts with defect sites in OER was analyzed. The ingenious defects can selectively accelerate the adsorption of OH−, thus enhancing the electrochemical activity. The D-NiFeAl-LDHs electrocatalyst had higher OER electrocatalytic activity than NiFe-LDHs electrocatalyst: its accelerated OER kinetics were mainly due to the introduction of iron and nickel defects in NiFeAl-LDHs nanosheets, which effectively adjusted the surface electronic structure and improved OER electrocatalytic performance. There was only a low overpotential of 262 mV with the current density of 10 mA cm−2, and the Tafel slope was as low as 41.67 mV dec−1. The OER electrocatalytic performance of D-NiFeAl-LDHs was even better than those of most of the reported NiFe-LDHs electrocatalysts. 相似文献
79.
A novel approach using stationary wavelet transform (SWT) is proposed for automatically detecting low-contrast defects under various light conditions in magnetic tile images. In this method, the uneven background was removed by Sobel operation. Then the index low-pass filtering and the nonlinear enhancement were respectively used to eliminate the interference and enhance the target in subbands produced by SWT. To verify the validity of the proposed algorithm, extensive experiments were conducted in a novel machine vision based system. As the result shows, the proposed method achieves an accuracy rate of 92.86% in detecting various defects in magnetic tile surfaces with the average operation time of 0.5190 s, and is superior to traditional methods in terms of the high reliability and accuracy. 相似文献
80.
Tiny defects may escape from in-line defect scan and pass WAT (Wafer Acceptance Test), CP (Chip Probing), FT (Final Test) and SLT (System Level Test). Chips with such kind of defects will cause reliability problem and impact revenue significantly. It is important to catch the defects and derive the prevention strategy earlier in the technology development stage. In this paper, we investigate an SRAM with tiny defects which passed in-line defect scan, WAT, CP and FT but failed in HTOL (High Temperature Operation Life) test, one of the product reliability qualification items. FA (Failure Analysis) reveals gate oxide missing defect is the root cause. The goal is to pass reliability qualification and release product into production on schedule. The failure mechanism, optimization of gate oxide process, enhancement of defect scan and testing methodology will be introduced. Experiment results show very good HTOL performance by the combination of process and testing optimization. 相似文献