全文获取类型
收费全文 | 39371篇 |
免费 | 3586篇 |
国内免费 | 1859篇 |
专业分类
电工技术 | 2488篇 |
技术理论 | 6篇 |
综合类 | 2747篇 |
化学工业 | 6204篇 |
金属工艺 | 2380篇 |
机械仪表 | 2600篇 |
建筑科学 | 3027篇 |
矿业工程 | 1184篇 |
能源动力 | 1207篇 |
轻工业 | 3140篇 |
水利工程 | 760篇 |
石油天然气 | 2430篇 |
武器工业 | 344篇 |
无线电 | 4458篇 |
一般工业技术 | 4524篇 |
冶金工业 | 1860篇 |
原子能技术 | 386篇 |
自动化技术 | 5071篇 |
出版年
2024年 | 227篇 |
2023年 | 758篇 |
2022年 | 1441篇 |
2021年 | 1856篇 |
2020年 | 1506篇 |
2019年 | 1142篇 |
2018年 | 1269篇 |
2017年 | 1429篇 |
2016年 | 1271篇 |
2015年 | 1731篇 |
2014年 | 2047篇 |
2013年 | 2321篇 |
2012年 | 2553篇 |
2011年 | 2688篇 |
2010年 | 2358篇 |
2009年 | 2217篇 |
2008年 | 2217篇 |
2007年 | 2108篇 |
2006年 | 2017篇 |
2005年 | 1714篇 |
2004年 | 1211篇 |
2003年 | 1142篇 |
2002年 | 1298篇 |
2001年 | 1131篇 |
2000年 | 896篇 |
1999年 | 924篇 |
1998年 | 642篇 |
1997年 | 523篇 |
1996年 | 483篇 |
1995年 | 414篇 |
1994年 | 342篇 |
1993年 | 224篇 |
1992年 | 172篇 |
1991年 | 115篇 |
1990年 | 105篇 |
1989年 | 81篇 |
1988年 | 51篇 |
1987年 | 50篇 |
1986年 | 34篇 |
1985年 | 26篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 5篇 |
1969年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Yu-Li Hsueh Jaedon Kim Ching-Fong Su Rabbat R. Hamada T. Tian C. Kazovsky L.G. 《Lightwave Technology, Journal of》2006,24(1):44-53
A sublambda traffic-grooming scheme on wavelength-division-multiplexed (WDM) rings, which is called optical burst transport (OBT), is proposed. The network protocol and architecture allow increased flexibility to tailor the transport network behavior for efficient delivery of bursty data traffic. Using different network parameters, its performance is analyzed via simulation, and the implementation issues including the media-access-control (MAC) protocol, tunable-filter controller, and burst-mode receiver are addressed. Finally, the feasibility of the OBT with an experimental testbed built by the authors is demonstrated and a streaming-video application is used to present its overall functionality. 相似文献
12.
13.
Wei-Cheng Tian Pang S.W. Chia-Jung Lu Zellers E.T. 《Journal of microelectromechanical systems》2003,12(3):264-272
The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 /spl mu/m (h)/spl times/50 /spl mu/m (w)/spl times/3000 /spl mu/m (l), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, /spl sim/200 /spl mu/m in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly. 相似文献
14.
15.
16.
Yufei Tao Xiaokui Xiao Jian Pei 《Knowledge and Data Engineering, IEEE Transactions on》2007,19(8):1072-1088
Skyline and top-k queries are two popular operations for preference retrieval. In practice, applications that require these operations usually provide numerous candidate attributes, whereas, depending on their interests, users may issue queries regarding different subsets of the dimensions. The existing algorithms are inadequate for subspace skyline/top-k search because they have at least one of the following defects: 1) they require scanning the entire database at least once, 2) they are optimized for one subspace but incur significant overhead for other subspaces, or 3) they demand expensive maintenance cost or space consumption. In this paper, we propose a technique SUBSKY, which settles both types of queries by using purely relational technologies. The core of SUBSKY is a transformation that converts multidimensional data to one-dimensional (1D) values. These values are indexed by a simple B-tree, which allows us to answer subspace queries by accessing a fraction of the database. SUBSKY entails low maintenance overhead, which equals the cost of updating a traditional B-tree. Extensive experiments with real data confirm that our technique outperforms alternative solutions significantly in both efficiency and scalability. 相似文献
17.
18.
19.
本文介绍了模糊技术的发展和现状,以及在相关领域中的应用情况,并且讨论了模糊技术在我国的产业化方向等问题。 相似文献
20.
Identifying the key factors of the disaster-related information propagation process can provide decision support for disaster management. This study characterizes the effects of content types, location, and social capital of social media users on the virality of disaster-related information. We found through the Weibo dataset of the Yiliang earthquake that the virality of different types of information can vary on the basis of the social capital of users who post the information. This study fills the current research gaps by examining the individual and joint effects of the content and creator characteristics on the virality of disaster-related information. 相似文献