全文获取类型
收费全文 | 234712篇 |
免费 | 15766篇 |
国内免费 | 7955篇 |
专业分类
电工技术 | 11934篇 |
技术理论 | 10篇 |
综合类 | 12915篇 |
化学工业 | 34279篇 |
金属工艺 | 13464篇 |
机械仪表 | 12302篇 |
建筑科学 | 14163篇 |
矿业工程 | 4611篇 |
能源动力 | 5672篇 |
轻工业 | 14433篇 |
水利工程 | 4613篇 |
石油天然气 | 7315篇 |
武器工业 | 1453篇 |
无线电 | 28380篇 |
一般工业技术 | 34135篇 |
冶金工业 | 9669篇 |
原子能技术 | 2146篇 |
自动化技术 | 46939篇 |
出版年
2024年 | 607篇 |
2023年 | 2449篇 |
2022年 | 4920篇 |
2021年 | 6955篇 |
2020年 | 4980篇 |
2019年 | 3993篇 |
2018年 | 18455篇 |
2017年 | 17983篇 |
2016年 | 14243篇 |
2015年 | 7084篇 |
2014年 | 8395篇 |
2013年 | 10274篇 |
2012年 | 14141篇 |
2011年 | 21244篇 |
2010年 | 18439篇 |
2009年 | 15281篇 |
2008年 | 16294篇 |
2007年 | 16674篇 |
2006年 | 8763篇 |
2005年 | 8275篇 |
2004年 | 5882篇 |
2003年 | 4903篇 |
2002年 | 4179篇 |
2001年 | 3146篇 |
2000年 | 3060篇 |
1999年 | 2875篇 |
1998年 | 2530篇 |
1997年 | 2126篇 |
1996年 | 1989篇 |
1995年 | 1575篇 |
1994年 | 1259篇 |
1993年 | 1004篇 |
1992年 | 815篇 |
1991年 | 597篇 |
1990年 | 480篇 |
1989年 | 375篇 |
1988年 | 332篇 |
1987年 | 218篇 |
1986年 | 179篇 |
1985年 | 161篇 |
1984年 | 107篇 |
1983年 | 79篇 |
1982年 | 79篇 |
1981年 | 68篇 |
1980年 | 61篇 |
1976年 | 62篇 |
1968年 | 50篇 |
1959年 | 48篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
102.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
103.
104.
105.
106.
The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m3m?2h?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization. 相似文献
107.
由于臭氧的强的氧化性能,使其成为一种强氧化剂和消毒剂;臭氧技术已经广泛用于废水处理行业,臭氧具有较好的的消毒杀菌、脱色、除臭味等作用,文章通过介绍臭氧的一些基本性质,臭氧消毒杀菌、氧化、脱色及除臭味的机理,臭氧的制取方式,现代臭氧技术的研究方向等,为废水处理中臭氧技术的应用提供参考。 相似文献
108.
109.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
110.
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