全文获取类型
收费全文 | 148851篇 |
免费 | 16905篇 |
国内免费 | 10292篇 |
专业分类
电工技术 | 12523篇 |
技术理论 | 3篇 |
综合类 | 14328篇 |
化学工业 | 19165篇 |
金属工艺 | 9209篇 |
机械仪表 | 9424篇 |
建筑科学 | 10673篇 |
矿业工程 | 5647篇 |
能源动力 | 4158篇 |
轻工业 | 16465篇 |
水利工程 | 4355篇 |
石油天然气 | 5499篇 |
武器工业 | 2241篇 |
无线电 | 14703篇 |
一般工业技术 | 12324篇 |
冶金工业 | 13004篇 |
原子能技术 | 1953篇 |
自动化技术 | 20374篇 |
出版年
2024年 | 1047篇 |
2023年 | 2933篇 |
2022年 | 6331篇 |
2021年 | 8036篇 |
2020年 | 5714篇 |
2019年 | 4122篇 |
2018年 | 4401篇 |
2017年 | 4885篇 |
2016年 | 4361篇 |
2015年 | 6813篇 |
2014年 | 8248篇 |
2013年 | 9366篇 |
2012年 | 11668篇 |
2011年 | 12025篇 |
2010年 | 11064篇 |
2009年 | 10317篇 |
2008年 | 10255篇 |
2007年 | 9769篇 |
2006年 | 8414篇 |
2005年 | 6642篇 |
2004年 | 4916篇 |
2003年 | 3762篇 |
2002年 | 3685篇 |
2001年 | 3216篇 |
2000年 | 2370篇 |
1999年 | 1392篇 |
1998年 | 3095篇 |
1997年 | 1881篇 |
1996年 | 1250篇 |
1995年 | 801篇 |
1994年 | 665篇 |
1993年 | 682篇 |
1992年 | 212篇 |
1991年 | 189篇 |
1990年 | 172篇 |
1989年 | 149篇 |
1988年 | 128篇 |
1987年 | 109篇 |
1986年 | 100篇 |
1985年 | 64篇 |
1983年 | 22篇 |
1982年 | 57篇 |
1981年 | 50篇 |
1980年 | 92篇 |
1979年 | 26篇 |
1977年 | 158篇 |
1976年 | 283篇 |
1975年 | 13篇 |
1959年 | 37篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
Ferrous ion was transformed into feroxyhyte (δ-FeOOH) by oxidation. Then, manganese sulfate and zinc sulfate in some ratio were added to the feroxyhyte solution. The co-precipitation was boiling reflux conditions sometime under constant stirring. The nanosize MnZn ferrite powder was formed. The mechanism of preparation of the nanosize MnZn ferrite was discussed, and the formation of feroxyhyte which was playing a key role during the process was mentioned. The properties of powder was tested by means of X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results show that the samples of spherical particles about 20 nm, which have characteristics of ferrimagnetism, has larger saturation magnetization, but the remanent magnetization and coercivity are comparatively smaller. The spinel MnZn ferrite nanosize powder was successfully prepared from δ-FeOOH at low temperature, with low-carbon steel and peroxide as main material. 相似文献
75.
76.
77.
A set of Co promoted 10% Mo/Al2O3 samples have been characterized by means of Raman spectroscopy under ambient as well as in situ dehydrated conditions. Under ambient conditions, the degree of the polymerization of surface molybdenum oxide species decreases with increasing Co loading. Under dehydrated conditions, the polymeric molybdenum oxide species is absent with the addition of only 0.2% Co. At low Co loadings (2%), before the formation of CoMoO4 compound, the spectral features are very similar under ambient conditions. Dehydration causes the upward shift of the Mo=O symmetric stretching mode. A broad band around 920–930 cm–1 was thus observed. This band has been suggested to be associated with the Co-Mo interaction species. In contrast to crystalline CoMoO4, this species shows a reversibility on H2 reduction-O2 reoxidation treatments. From the results obtained, it is proposed that cobalt oxide interacts with the most polymerized molybdenum oxide species to form Co-Mo interaction species and/or crystalline CoMoO4; therefore, the amount of the surface molybdenum oxide species decreases with a change in the molecular structure as a function of the Co concentration. 相似文献
78.
79.
80.
The study of collective user behaviours in social networking sites has become an increasing important topic in social media mining. Understanding such behaviours has its potential to extract actionable patterns that can be beneficial to develop effective marketing strategies, optimise user experiences and maximise website revenues. With the rapid development of micro-blogging, Twitter has become a richer source of intelligence that can be used to study collective user behaviour, due to its efficient and meaningful user-to-user interactions. However, the classical statistical methods have some drawbacks in bridging the gap between user-generated data and human analysts who mostly use linguistic terms to analyse data and model/summarise knowledge learned. To address this gap, this work proposes a new approach, which employs the mass assignment theory-based fuzzy association rules algorithm (MASS-FARM), for the first time, to extract useful interaction behaviour of Twitter users. The influential factors (including activity time, number of friends/followers and the number of tweets) are represented as fuzzy granules, and the associations amongst are studied by employing MASS-FARM. The collective user behaviours are analysed in the Reply category and the Non-Reply category, respectively. The applicability and usefulness of the proposed method are demonstrated via an empirical study on a collected Twitter data set. The derived results are also discussed and compared with existing works. 相似文献