全文获取类型
收费全文 | 43742篇 |
免费 | 6934篇 |
国内免费 | 5759篇 |
专业分类
化学 | 24520篇 |
晶体学 | 569篇 |
力学 | 1785篇 |
综合类 | 419篇 |
数学 | 3399篇 |
物理学 | 11810篇 |
无线电 | 13933篇 |
出版年
2024年 | 112篇 |
2023年 | 980篇 |
2022年 | 1177篇 |
2021年 | 1583篇 |
2020年 | 1599篇 |
2019年 | 1565篇 |
2018年 | 1366篇 |
2017年 | 1413篇 |
2016年 | 1832篇 |
2015年 | 2074篇 |
2014年 | 2453篇 |
2013年 | 3122篇 |
2012年 | 3753篇 |
2011年 | 3902篇 |
2010年 | 3022篇 |
2009年 | 2874篇 |
2008年 | 3140篇 |
2007年 | 2994篇 |
2006年 | 2671篇 |
2005年 | 2265篇 |
2004年 | 1659篇 |
2003年 | 1464篇 |
2002年 | 1395篇 |
2001年 | 1165篇 |
2000年 | 1017篇 |
1999年 | 903篇 |
1998年 | 693篇 |
1997年 | 635篇 |
1996年 | 586篇 |
1995年 | 535篇 |
1994年 | 495篇 |
1993年 | 363篇 |
1992年 | 306篇 |
1991年 | 295篇 |
1990年 | 248篇 |
1989年 | 166篇 |
1988年 | 124篇 |
1987年 | 119篇 |
1986年 | 83篇 |
1985年 | 69篇 |
1984年 | 58篇 |
1983年 | 37篇 |
1982年 | 36篇 |
1981年 | 23篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
41.
用CPLD实现SRAM工艺FPGA的安全应用 总被引:1,自引:0,他引:1
提出了一种利用CPLD产生的伪随机码来加密SRAM工艺FPGA的方法,并详细介绍了具体的电路和VHDL代码。 相似文献
42.
43.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
44.
Design of 5.9 ghz dsrc-based vehicular safety communication 总被引:3,自引:0,他引:3
Daniel Jiang Vikas Taliwal Andreas Meier Wieland Holfelder Ralf Herrtwich 《Wireless Communications, IEEE》2006,13(5):36-43
The automotive industry is moving aggressively in the direction of advanced active safety. Dedicated short-range communication (DSRC) is a key enabling technology for the next generation of communication-based safety applications. One aspect of vehicular safety communication is the routine broadcast of messages among all equipped vehicles. Therefore, channel congestion control and broadcast performance improvement are of particular concern and need to be addressed in the overall protocol design. Furthermore, the explicit multichannel nature of DSRC necessitates a concurrent multichannel operational scheme for safety and non-safety applications. This article provides an overview of DSRC based vehicular safety communications and proposes a coherent set of protocols to address these requirements 相似文献
45.
在探讨了Web查询服务的典型模型后,论文阐述了服务器端会话追踪机制的实现方式,设计了基于服务器端会话追踪的Web查询服务的典型解决方案。该设计方案可以较为安全地保存和维护客户的上下文信息,可靠地跟踪用户查询所处的状态,有效地实现有状态的Web查询服务。 相似文献
46.
姜浩 《信息安全与通信保密》2006,(10):49-50
论文详细描述并分析了从RC5到RC6的演化设计过程,在详细研究了RC6性能的同时,指出了应该如何从一个旧的密码设计出好的新密码。最后对RC6和Rijndael作了一些比较,指出各自在性能上的优缺点。 相似文献
47.
48.
Hui Luo Wei Hao David H Foos Craig W Cornelius 《IEEE transactions on information technology in biomedicine》2006,10(2):302-311
Chest radiography is one of the most widely used techniques in diagnostic imaging. It comprises at least one-third of all diagnostic radiographic procedures in hospitals. However, in the picture archive and communication system, images are often stored with the projection and orientation unknown or mislabeled, which causes inefficiency for radiologists' interpretation. To address this problem, an automatic hanging protocol for chest radiographs is presented. The method targets the most effective region in a chest radiograph, and extracts a set of size-, rotation-, and translation-invariant features from it. Then, a well-trained classifier is used to recognize the projection. The orientation of the radiograph is later identified by locating the neck, heart, and abdomen positions in the radiographs. Initial experiments are performed on the radiographs collected from daily routine chest exams in hospitals and show promising results. Using the presented protocol, 98.2% of all cases could be hung correctly on projection view (without protocol, 62%), and 96.1% had correct orientation (without protocol, 75%). A workflow study on the protocol also demonstrates a significant improvement in efficiency for image display. 相似文献
49.
The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment. 相似文献
50.