全文获取类型
收费全文 | 1524087篇 |
免费 | 30013篇 |
国内免费 | 8399篇 |
专业分类
电工技术 | 35538篇 |
技术理论 | 2篇 |
综合类 | 8571篇 |
化学工业 | 265593篇 |
金属工艺 | 65705篇 |
机械仪表 | 43583篇 |
建筑科学 | 47920篇 |
矿业工程 | 12213篇 |
能源动力 | 50888篇 |
轻工业 | 111928篇 |
水利工程 | 15828篇 |
石油天然气 | 38839篇 |
武器工业 | 344篇 |
无线电 | 199107篇 |
一般工业技术 | 286090篇 |
冶金工业 | 173835篇 |
原子能技术 | 34099篇 |
自动化技术 | 172416篇 |
出版年
2021年 | 16614篇 |
2020年 | 12780篇 |
2019年 | 15381篇 |
2018年 | 15621篇 |
2017年 | 15029篇 |
2016年 | 21836篇 |
2015年 | 18528篇 |
2014年 | 30255篇 |
2013年 | 89655篇 |
2012年 | 37246篇 |
2011年 | 49510篇 |
2010年 | 43793篇 |
2009年 | 52010篇 |
2008年 | 46065篇 |
2007年 | 43092篇 |
2006年 | 46683篇 |
2005年 | 40729篇 |
2004年 | 42501篇 |
2003年 | 42265篇 |
2002年 | 41248篇 |
2001年 | 38539篇 |
2000年 | 36846篇 |
1999年 | 36372篇 |
1998年 | 50061篇 |
1997年 | 41736篇 |
1996年 | 35003篇 |
1995年 | 31476篇 |
1994年 | 29346篇 |
1993年 | 29036篇 |
1992年 | 25906篇 |
1991年 | 23091篇 |
1990年 | 23433篇 |
1989年 | 22252篇 |
1988年 | 20792篇 |
1987年 | 19025篇 |
1986年 | 18495篇 |
1985年 | 21783篇 |
1984年 | 21991篇 |
1983年 | 19967篇 |
1982年 | 19015篇 |
1981年 | 19082篇 |
1980年 | 17690篇 |
1979年 | 18258篇 |
1978年 | 17493篇 |
1977年 | 17162篇 |
1976年 | 17961篇 |
1975年 | 15746篇 |
1974年 | 15284篇 |
1973年 | 15388篇 |
1972年 | 12896篇 |
排序方式: 共有10000条查询结果,搜索用时 734 毫秒
41.
Telecommunication Systems - Energy saving in User Equipment (UE) is one of the important issues for limited sources of power in the device. It is critical for the UE to maximize its energy... 相似文献
42.
Seredin P. V. Radam Ali Obaid Goloshchapov D. L. Len’shin A. S. Buylov N. S. Barkov K. A. Nesterov D. N. Mizerov A. M. Timoshnev S. N. Nikitina E. V. Arsentyev I. N. Sharafidinov Sh. Kukushkin S. A. Kasatkin I. A. 《Semiconductors》2022,56(4):253-258
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid... 相似文献
43.
Kravchenko V. F. Konovalov Ya. Yu. 《Journal of Communications Technology and Electronics》2022,67(8):952-964
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically... 相似文献
44.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
45.
Boltar K. O. Burlakov I. D. Iakovleva N. I. Vlasov P. V. Lazarev P. S. 《Journal of Communications Technology and Electronics》2022,67(9):1175-1184
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of... 相似文献
46.
Mobile Networks and Applications - Project MindCatcher is an art/research project which has the intention to explore the potential of interactive artistic environments for measuring and a better... 相似文献
47.
In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content. 相似文献
48.
Jiajia Suo Bowen Yang Edoardo Mosconi Hyeon-Seo Choi YeonJu Kim Shaik M. Zakeeruddin Filippo De Angelis Michael Grätzel Hui-Seon Kim Anders Hagfeldt 《Advanced functional materials》2021,31(34):2102902
Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions. 相似文献
49.
Glass and Ceramics - Ceramic bricks based on low-melting clay and ferro-dust from self-disintegrating, low-carbon, ferrochrome slags, graded from M100 to M175, respectively, were obtained in the... 相似文献
50.
针对热液白云岩展布非均质性强的问题,开展基底断裂与茅三段沉积演化关系研究,分析断裂样式与白云岩分布关系,建立沉积演化模式,预测白云岩的分布。研究结果表明:茅三段可划分为5个小层,1~3小层为白云岩发育主要时期,4~5小层为台地均一化时期,不发育白云岩;15-1、15-2和16号基底断裂控制了早期“台-洼”相间的沉积地貌,断裂附近的地貌高部位为生屑滩发育有利部位,为白云岩的发育提供物质基础;15-1、15-2号基底断裂样式为花状,周边生屑滩白云石化程度高,为白云岩发育最有利区;16号基底断裂为直立状,附近白云石化发育程度较低,为白云岩发育较有利区。研究成果可为热液白云岩领域的进一步勘探提供指导依据。 相似文献