全文获取类型
收费全文 | 81768篇 |
免费 | 10173篇 |
国内免费 | 4359篇 |
专业分类
电工技术 | 6840篇 |
技术理论 | 6篇 |
综合类 | 9504篇 |
化学工业 | 5170篇 |
金属工艺 | 2790篇 |
机械仪表 | 7496篇 |
建筑科学 | 15075篇 |
矿业工程 | 5264篇 |
能源动力 | 3711篇 |
轻工业 | 4823篇 |
水利工程 | 4564篇 |
石油天然气 | 4101篇 |
武器工业 | 1150篇 |
无线电 | 4998篇 |
一般工业技术 | 9839篇 |
冶金工业 | 3402篇 |
原子能技术 | 644篇 |
自动化技术 | 6923篇 |
出版年
2024年 | 512篇 |
2023年 | 1393篇 |
2022年 | 2791篇 |
2021年 | 3015篇 |
2020年 | 3307篇 |
2019年 | 2406篇 |
2018年 | 2249篇 |
2017年 | 2839篇 |
2016年 | 3084篇 |
2015年 | 3247篇 |
2014年 | 5169篇 |
2013年 | 4499篇 |
2012年 | 5927篇 |
2011年 | 6353篇 |
2010年 | 4969篇 |
2009年 | 5035篇 |
2008年 | 4428篇 |
2007年 | 5544篇 |
2006年 | 4902篇 |
2005年 | 4184篇 |
2004年 | 3418篇 |
2003年 | 3088篇 |
2002年 | 2520篇 |
2001年 | 2134篇 |
2000年 | 1915篇 |
1999年 | 1506篇 |
1998年 | 1100篇 |
1997年 | 898篇 |
1996年 | 754篇 |
1995年 | 639篇 |
1994年 | 555篇 |
1993年 | 399篇 |
1992年 | 303篇 |
1991年 | 250篇 |
1990年 | 206篇 |
1989年 | 188篇 |
1988年 | 137篇 |
1987年 | 89篇 |
1986年 | 47篇 |
1985年 | 34篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1966年 | 10篇 |
1964年 | 15篇 |
1962年 | 9篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(94):40099-40115
In order to reveal the mechanism of water fog explosion suppression and research the combined effect of water fog and obstacle on hydrogen/air deflagration, multiple sets of experiments were set up. The results show that the instability of thermal diffusion under lean combustion conditions is the main influencing factor of hydrogen/air flame surface instability, and the existence of water fog will aggravate the hydrogen/air flame surface instability. When obstacle is not considered, 8 μm, 15 μm, 30 μm water fog can significantly reduce the flame velocity and explosion overpressure of hydrogen/air, 45 μm fine water fog plays the opposite role. When considering the relative position of the water fog release position and the obstacle, the 8 μm, 15 μm, 30 μm water fog has almost no suppression effect when released near the obstacle, but a significant suppression effect occur, when using the 45 μm water fog. In the field of theoretical research, the research results not only provide an experimental basis for the fine water fog to reduce the consequences of hydrogen explosion accidents, and the optimal diameter range used by the water fog, but also provide experimental reference for the numerical simulation of hydrogen/air explosion suppression in semi-open space, and promote the development of hydrogen explosion suppression theory. In terms of engineering applications, this study can provide a theoretical basis for the layout of fire fighting equipment in the engine room of nuclear power plants or hydrogen-powered ships. 相似文献
3.
4.
《Ceramics International》2022,48(12):16808-16812
Flash sintering has been reported in various ceramics. Nevertheless, anion and cation conductors exhibit different flash-sintering behaviors, and the interaction mechanism between the conductive species and the sintering environment has remained unclear. Herein, we report the flash-sintering phenomena of a typical cation conductor, Na3Zr2(SiO4)2(PO4) with anode region surrounded by air and NaNO3 environments. The results prove that the ionic behavior and joule heating distribution can be controlled by changing the electrode environment. Four possible scenarios describing the ion migration behavior and interaction with the environment are proposed for providing a guidance for controlling the ion interaction behavior during flash sintering. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(3):2040-2049
The motion trajectory of hydrogen leakage is an essential safe issue for the application of hydrogen energy. A dimensionless fast-running motion trajectory prediction model is proposed to predict the dispersion characteristics of the buoyant jet of hydrogen leakage for the accident. The impact of different leakage angles, leakage velocity and thermal stratification of ambient air on hydrogen leakage behavior was analyzed. The new developed model was verified by experimental results in literatures. Leakage hydrogen can flow upwards freely in a uniform environment. However, it shows an oscillating trajectory at a certain height in a thermally stratified environment, which is so called “locking phenomenon”. The trajectory of hydrogen leakage is upward and hydrogen gathers at the top of the space to form stratification in a uniform environment, while the hydrogen leakage shows an oscillating trajectory at a certain height in a thermal stratification environment. With the increase of Froude number Fr, it shows that the stable height and maximum height of the leakage airflow have a trend of rising first and then falling in a thermally stratified environment. The findings are expected to give guidance in real-world situations, for example, a larger Fr value and a larger temperature gradient can lead to a decrease in the stable height in the thermally stratified environment. It is found that the fitting of the stable height with different temperature gradients satisfies the power function relationship. This work is expected to be helpful for reducing hydrogen leakage accumulation and explosion risk. 相似文献
6.
《Ceramics International》2022,48(24):36860-36870
For the advantages of high-temperature resistance, corrosion resistance and ultra-high hardness, SiCf/SiC composite is becoming a preferred material for manufacturing aero-engine parts. However, the anisotropy and heterogeneity bring great challenges to the processing technology. In this study, a nanosecond pulsed laser is applied to process SiCf/SiC composite, where the influence of the scanning speed and laser scanning direction to the SiC fibers on the morphology of ablated grooves is investigated. The surface characteristics after ablation and the involved chemical reaction of SiCf/SiC are explored. The results show that the increased laser scanning speed, accompanied by the decreasing spot overlap rate, leads to the less accumulation of energy on the material surface, so the ablation effect drops. In addition, for the anisotropy of the SiCf/SiC material, the obtained surface characteristics are closely dependent on the laser scanning direction to the SiC fibers, resulting in different groove morphology. The element composition and phase analysis of the machined surface indicate that the main deposited product is SiO2 and the carbon substance. The results can provide preliminary technical support for controlling the machining quality of ceramic matrix composites. 相似文献
7.
To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration. 相似文献
8.
9.