全文获取类型
收费全文 | 102925篇 |
免费 | 10931篇 |
国内免费 | 6141篇 |
专业分类
电工技术 | 7582篇 |
技术理论 | 2篇 |
综合类 | 8033篇 |
化学工业 | 15473篇 |
金属工艺 | 6354篇 |
机械仪表 | 6905篇 |
建筑科学 | 8502篇 |
矿业工程 | 3370篇 |
能源动力 | 2761篇 |
轻工业 | 7150篇 |
水利工程 | 2262篇 |
石油天然气 | 5223篇 |
武器工业 | 1100篇 |
无线电 | 12608篇 |
一般工业技术 | 11752篇 |
冶金工业 | 4240篇 |
原子能技术 | 1221篇 |
自动化技术 | 15459篇 |
出版年
2024年 | 545篇 |
2023年 | 1634篇 |
2022年 | 3373篇 |
2021年 | 4402篇 |
2020年 | 3365篇 |
2019年 | 2748篇 |
2018年 | 3019篇 |
2017年 | 3398篇 |
2016年 | 3135篇 |
2015年 | 4609篇 |
2014年 | 5507篇 |
2013年 | 6563篇 |
2012年 | 7423篇 |
2011年 | 7865篇 |
2010年 | 7264篇 |
2009年 | 7118篇 |
2008年 | 6771篇 |
2007年 | 6595篇 |
2006年 | 6088篇 |
2005年 | 5098篇 |
2004年 | 3470篇 |
2003年 | 3002篇 |
2002年 | 3013篇 |
2001年 | 2644篇 |
2000年 | 2082篇 |
1999年 | 1983篇 |
1998年 | 1314篇 |
1997年 | 1166篇 |
1996年 | 1015篇 |
1995年 | 826篇 |
1994年 | 668篇 |
1993年 | 520篇 |
1992年 | 416篇 |
1991年 | 309篇 |
1990年 | 249篇 |
1989年 | 208篇 |
1988年 | 156篇 |
1987年 | 104篇 |
1986年 | 88篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 16篇 |
1980年 | 23篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1959年 | 7篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
介绍了对大桥的风向、风力和交通流量的测试依据和内容,分析了风向、风力的测试结果以及梁体在风力及交通流量等作用下的受力情况,指出钢箱梁体主要受到的力是风力。 相似文献
92.
93.
94.
802.22 工作组的主要任务是开发和建立一套基于认知无线电(CR)技术, 在现有电视频段利用暂时空闲的频道进行无线通信的区域网空中接口标准。由于基于802.22 协议的无线区域网(WRAN)工作在现有电视频段中 , 要求不能对正在广播的电视频道产生干扰 , 所以WRAN采用了认知无线电技术 , 对电视频段进行感知和测量 , 利用动态频谱管理技术找到空闲频道进行再分配。认知无线电技术将是未来无线通信的发展方向之一。本讲座分3 期对无线区域网和认知无线电技术进行介绍, 第1 讲已经介绍无线区域网络和IEEE 802.22工作组情况 , 包括WRAN背景、802.22 系统、802.22空中接口等;第2讲已经介绍认知无线电技术和实现其的基础软件无线电(SDR)技术 , 包括无线电知识描述语言(RKRL)和认知循环、无线电频谱礼仪等;本讲介绍802.22 WRAN频谱共存问题和认知无线电技术的应用。 相似文献
95.
96.
The structure and properties of high density polyethylene (HDPE) functionalized by ultraviolet irradiation at different light intensities in air were studied by electron analysis, FTIR spectroscopy, contact angle with water, differential scanning calorimetry and mechanical properties measurement. The results show that oxygen‐containing groups such as C?O, C—O and C(?O)O were introduced onto the molecular chain of HDPE following irradiation, and the rate and efficiency of HDPE functionalization increased with enhancement of irradiation intensity. After irradiation, the melting temperature, contact angle with water and notched impact strength of HDPE decreased, the degree of crystallinity increased, and their variation amplitude increased with irradiation intensity. Compared with HDPE, the yield strength of HDPE irradiated at lower light intensity (32 W m?2 and 45 W m?2) increases monotonically with irradiation time, and the yield strength of HDPE irradiated at higher light intensity (78 W m?2) increases up to 48 h and then decreased with further increase in irradiation time. The irradiated HDPE behaved as a compatibilizer in HDPE/polycarbonate (PC) blends, and the interface bonding between HDPE and PC was ameliorated. After adding 20 wt% HDPE irradiated at 78 W m?2 irradiation intensity for 24 h to HDPE/PC blends, the tensile yield strength and notched Izod impact strength of the blend were increased from 26.3 MPa and 51 J m?1 to 30.2 MPa and 158 J m?1, respectively. Copyright © 2003 Society of Chemical Industry 相似文献
97.
Jinman Kim Weidong Cai Dagan Feng Hao Wu 《IEEE transactions on information technology in biomedicine》2006,10(3):598-607
The advances in digital medical imaging and storage in integrated databases are resulting in growing demands for efficient image retrieval and management. Content-based image retrieval (CBIR) refers to the retrieval of images from a database, using the visual features derived from the information in the image, and has become an attractive approach to managing large medical image archives. In conventional CBIR systems for medical images, images are often segmented into regions which are used to derive two-dimensional visual features for region-based queries. Although such approach has the advantage of including only relevant regions in the formulation of a query, medical images that are inherently multidimensional can potentially benefit from the multidimensional feature extraction which could open up new opportunities in visual feature extraction and retrieval. In this study, we present a volume of interest (VOI) based content-based retrieval of four-dimensional (three spatial and one temporal) dynamic PET images. By segmenting the images into VOIs consisting of functionally similar voxels (e.g., a tumor structure), multidimensional visual and functional features were extracted and used as region-based query features. A prototype VOI-based functional image retrieval system (VOI-FIRS) has been designed to demonstrate the proposed multidimensional feature extraction and retrieval. Experimental results show that the proposed system allows for the retrieval of related images that constitute similar visual and functional VOI features, and can find potential applications in medical data management, such as to aid in education, diagnosis, and statistical analysis. 相似文献
98.
99.
Supermedia-enhanced Internet-based telerobotics 总被引:4,自引:0,他引:4
Elhajj I. Ning Xi Wai Keung Fung Yun-Hui Liu Hasegawa Y. Fukuda T. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2003,91(3):396-421
This paper introduces new planning and control methods for supermedia-enhanced real-time telerobotic operations via the Internet. Supermedia is the collection of video, audio, haptic information, temperature, and other sensory feedback. However, when the communication medium used, such as the Internet, introduces random communication time delay, several challenges and difficulties arise. Most importantly, random communication delay causes instability, loss of transparency, and desynchronization in real-time closed-loop telerobotic systems. Due to the complexity and diversity of such systems, the first challenge is to develop a general and efficient modeling and analysis tool. This paper proposes the use of Petri net modeling to capture the concurrency and complexity of Internet-based teleoperation. Combined with the event-based planning and control method, it also provides an efficient analysis and design tool to study the stability, transparency, and synchronization of such systems. In addition, the concepts of event transparency and event synchronization are introduced and analyzed. This modeling and control method has been applied to the design of several supermedia-enhanced Internet-based telerobotic systems, including the bilateral control of mobile robots and mobile manipulators. These systems have been experimentally implemented in three sites test bed consisting of robotic laboratories in the USA, Hong Kong, and Japan. The experimental results have verified the theoretical development and further demonstrated the stability, event transparency, and event synchronization of the systems. 相似文献
100.