全文获取类型
收费全文 | 304708篇 |
免费 | 18633篇 |
国内免费 | 9383篇 |
专业分类
电工技术 | 13133篇 |
技术理论 | 24篇 |
综合类 | 16006篇 |
化学工业 | 48924篇 |
金属工艺 | 17482篇 |
机械仪表 | 17272篇 |
建筑科学 | 19445篇 |
矿业工程 | 7912篇 |
能源动力 | 7437篇 |
轻工业 | 16845篇 |
水利工程 | 4773篇 |
石油天然气 | 16686篇 |
武器工业 | 1648篇 |
无线电 | 33537篇 |
一般工业技术 | 42238篇 |
冶金工业 | 15036篇 |
原子能技术 | 2482篇 |
自动化技术 | 51844篇 |
出版年
2024年 | 776篇 |
2023年 | 3600篇 |
2022年 | 5921篇 |
2021年 | 8909篇 |
2020年 | 6879篇 |
2019年 | 5858篇 |
2018年 | 19911篇 |
2017年 | 19772篇 |
2016年 | 15856篇 |
2015年 | 9344篇 |
2014年 | 11418篇 |
2013年 | 13401篇 |
2012年 | 17183篇 |
2011年 | 24310篇 |
2010年 | 21274篇 |
2009年 | 17868篇 |
2008年 | 18770篇 |
2007年 | 19281篇 |
2006年 | 12449篇 |
2005年 | 11900篇 |
2004年 | 8319篇 |
2003年 | 7333篇 |
2002年 | 5982篇 |
2001年 | 4977篇 |
2000年 | 5602篇 |
1999年 | 6464篇 |
1998年 | 5464篇 |
1997年 | 4445篇 |
1996年 | 4203篇 |
1995年 | 3487篇 |
1994年 | 2799篇 |
1993年 | 1953篇 |
1992年 | 1533篇 |
1991年 | 1228篇 |
1990年 | 922篇 |
1989年 | 725篇 |
1988年 | 538篇 |
1987年 | 325篇 |
1986年 | 265篇 |
1985年 | 189篇 |
1984年 | 130篇 |
1983年 | 98篇 |
1982年 | 119篇 |
1981年 | 97篇 |
1980年 | 68篇 |
1968年 | 47篇 |
1966年 | 43篇 |
1965年 | 48篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
181.
182.
Qianglong He Aiyang Wang Chun Liu Weimin Wang Hao Wang Zhengyi Fu 《Journal of the European Ceramic Society》2018,38(7):2832-2840
B4C-TiB2-SiC composites were fabricated via hot pressing using ball milled B4C, TiB2, and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84?GPa, 858?MPa and 8.21?MPa?m1/2, respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B4C-TiB2-SiC composite. 相似文献
183.
Fei Li Xin-Gang Wang Xiao Huang Ji-Xuan Liu Weichao Bao Guo-Jun Zhang Hongzhi Wang 《Journal of the European Ceramic Society》2018,38(14):4806-4813
We present a straightforward method via sol-gel process using polyethylene glycol (PEG) as phase separation inducer to prepare zirconium carbide/silicon carbide (ZrC/SiC) porous monoliths. Organic/inorganic hybrid gels are prepared using zirconium oxychloride, furfuryl alcohol, and tetraethyl orthosilicate as major starting materials. In the presence of PEG, crack-free hybrid monoliths are obtained by drying the wet gels under ambient pressure, whereas in the absence of PEG, the wet gels break into pieces as expected. PEG plays a key role in maintaining the macroscopic shape of the monoliths. After ceramization at 1300–1500?°C, ZrC/SiC porous monoliths are obtained. SEM and mercury intrusion porosimetry data show that PEG also has strong influence on the microstructures of the monoliths. The compressive strengths of the ceramic monoliths are in the range of 0.3 to 0.7?MPa. And their compressive behavior starts to differ due to the changes in their microstructures, especially the pore structure. 相似文献
184.
ABSTRACTImproving the hydration resistance of CaO particle in manufacturing and application of free CaO-containing materials has practical significance. In this study, CaO granules was made from Ca(OH)2 particles, which were fabricated by the granulation method. The results showed that the hydration resistance of the CaO granules which was prepared under 1700?r?min?1 was the best, the CaO granules was sintered well in calcination process, the shell of CaO granules was relatively dense, which improves the hydration resistance of CaO granules, and the rate of hydration weight increment was 0.58% after placed in the air for 20 days under a temperature of 10–14°C and a relative humidity of 57–81%. 相似文献
185.
186.
Understanding semantic word shifts in scientific domains is essential for facilitating interdisciplinary communication. Using a data set of published papers in the field of information retrieval (IR), this paper studies the semantic shifts of words in IR based on mining per-word topic distribution over time. We propose that semantic word shifts not only occur over time, but also over topics. The shifts are examined from two perspectives, the topic-level and the context-level. According to the over-time word-topic distribution, stable words and unstable words are recognized. The diverging and converging trends in the unstable type reveal characteristics of the topic evolution process. The context-level shifts are further detected by similarities between word vectors. Our work associates semantic word shifts with the evolving of topics, which facilitates a better understanding of semantic word shifts from both topics and contexts. 相似文献
187.
Research funding has been seen as one of the most important resource in the reward system of science. And usage of publications denotes an interesting perspective of user behavior in scientific communication. This study aims to address the relationship between funding and Usage Count, which is a new metrics item established on the platform of Web of Science. Full records of 300,010 articles published in 2013 were downloaded in October 2015, and divided into six disciplines, including information science library science, education educational research, economics, computer science, materials science, and chemistry. Seven indicators were proposed to measure the impact, including Funding rate, Citation per paper, Usage rate, Usage per paper, Citation difference, Usage difference, and Conversion rate. It concluded funding has impact on usage and citation, and funded papers attract more usage, but varying in different disciplines. Usage Count can be used in the extension of citation metrics but with limits. This study originally engages with usage metrics and detected that there is positive correlation between usage and funding. 相似文献
188.
189.
Han Yan Gu Yi Chen Lei Li Bing Liu Xiang Ming Chen 《International Journal of Applied Ceramic Technology》2020,17(2):790-796
SrLa[Ga1−x(R0.5Ti0.5)x]O4 (R = Mg, Zn) ceramics were prepared by a standard solid state sintering method. The single-phase ceramics with K2NiF4-type layered perovskite structure and I4/mmm space group were obtained, indicating that SrLa(R0.5Ti0.5) and SrLaGaO4 can form the unlimited solid solutions. With increasing x for R = Mg and Zn, εr increases monotonously, the Qf value first increases and then decreases, while τf increases from a negative to a positive value. The optimized microwave dielectric properties were obtained as following: εr = 23.3, Qf = 89 400 GHz, τf = −0.8 ppm/°C for SrLa[Ga0.6(Mg0.5Ti0.5)0.4]O4 and εr = 23.3, Qf = 76 200 GHz, τf = 0.2 ppm/°C for SrLa[Ga0.7(Zn0.5Ti0.5)0.3]O4, indicating that the present solid solution ceramics are the promising candidates as microwave resonator materials for the telecommunication applications. 相似文献
190.
全息术是一种三维成像技术,它已经被应用于多种实际场景。随着计算机科学与技术的迅猛发展,计算全息由于其方便和灵活的特性,已经成为一种广泛应用的全息成像方法。本文回顾了我们近期基于超表面的太赫兹计算全息研究进展。其中,作为全息板的超表面展示出了超越传统光学器件的独特性能。首先,利用超表面实现了对于全息板每个像素的相位振幅同时且独立的调控,进而实现了高质量全息成像。这种新的电磁波操控能力也带来了新的全息成像效果,如利用介质超表面实现了全息像沿传播方向上的连续变化。其次,对超表面在不同偏振态下的响应进行设计,分别实现了线偏振态与频率复用、圆偏振态复用、以及基于表面波的偏振复用超表面全息术。此外,本文提出了依赖于温度变化而主动可控的超表面全息术,为今后计算全息术的设计与实现提供了新的方案,也推动了超表面在实际应用方面的发展。 相似文献