全文获取类型
收费全文 | 64447篇 |
免费 | 6486篇 |
国内免费 | 3693篇 |
专业分类
电工技术 | 4422篇 |
技术理论 | 1篇 |
综合类 | 6359篇 |
化学工业 | 10221篇 |
金属工艺 | 3482篇 |
机械仪表 | 3673篇 |
建筑科学 | 4883篇 |
矿业工程 | 1662篇 |
能源动力 | 1448篇 |
轻工业 | 8207篇 |
水利工程 | 1580篇 |
石油天然气 | 2331篇 |
武器工业 | 647篇 |
无线电 | 7147篇 |
一般工业技术 | 6467篇 |
冶金工业 | 2481篇 |
原子能技术 | 669篇 |
自动化技术 | 8946篇 |
出版年
2024年 | 338篇 |
2023年 | 1066篇 |
2022年 | 2189篇 |
2021年 | 2766篇 |
2020年 | 2144篇 |
2019年 | 1685篇 |
2018年 | 1755篇 |
2017年 | 2022篇 |
2016年 | 1879篇 |
2015年 | 2694篇 |
2014年 | 3603篇 |
2013年 | 4094篇 |
2012年 | 4730篇 |
2011年 | 5206篇 |
2010年 | 4834篇 |
2009年 | 4685篇 |
2008年 | 4709篇 |
2007年 | 4407篇 |
2006年 | 4094篇 |
2005年 | 3275篇 |
2004年 | 2366篇 |
2003年 | 1853篇 |
2002年 | 1903篇 |
2001年 | 1608篇 |
2000年 | 1247篇 |
1999年 | 859篇 |
1998年 | 543篇 |
1997年 | 405篇 |
1996年 | 388篇 |
1995年 | 321篇 |
1994年 | 206篇 |
1993年 | 159篇 |
1992年 | 120篇 |
1991年 | 110篇 |
1990年 | 70篇 |
1989年 | 66篇 |
1988年 | 62篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1959年 | 4篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
12.
Grain refinement is critical for fabricating high-quality Al-Si casting components in the application of automobile and aerospace industries,while the well-known Si-poisoning effect makes it difficult.Nbbased refiners offer an effective method to refine Al-Si casting alloys,but their anti Si-poisoning capability is far from being understood.In this work,the grain refining mechanism and the anti Si-poisoning effect in the Al-10 Si/Al-5 Nb-B system were systematically investigated by combining transmission electron microscope,first-principles calculations,and thermodynamic calculations.It is revealed that NbB2provides the main nucleation site in the Al-10 Si ingot inoculated by 0.1 wt.%Nb Al-5 Nb-B refiner.The exposed Nb atoms on the(0001)NbB2and(1-100)NbB2surface can be substituted by Al to form(Al,Nb)B2intermedia layers.In addition,a layer of NbAl3-like compound(NbAl3')can cover the surface of NbB2with the orientation relation of(1-100)[11-20]NbB2//(110)[110]NbAl3'.Both of the(Al,Nb)B2and NbAl3'intermedia layers contribute to enhancing the nucleation potency of NbB2particles.These discoveries provide fundamental insight to the grain refining mechanism of the Nb-B based refiners for Al-Si casting alloys and are expected to guide the future development of stronger refiners for Al-Si casting alloys. 相似文献
14.
15.
Chuntao Lan Haiyang Zou Longfei Wang Meng Zhang Shuang Pan Ying Ma Yiping Qiu Zhong Lin Wang Zhiqun Lin 《Advanced materials (Deerfield Beach, Fla.)》2020,32(47):2005481
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc. 相似文献
16.
Wireless Personal Communications - The existing long term evolution networks originally designed for human-to-human communications are hard to tackle numerous and bursty random access requests from... 相似文献
17.
Thermoresponsive behavior and rheology of SiO2–hyaluronic acid/poly(N‐isopropylacrylamide) (NaHA/PNIPAm) core–shell structured microparticles 下载免费PDF全文
18.
19.
20.
In this study, 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors. 相似文献