全文获取类型
收费全文 | 31563篇 |
免费 | 4284篇 |
国内免费 | 1738篇 |
专业分类
化学 | 6720篇 |
晶体学 | 60篇 |
力学 | 880篇 |
综合类 | 286篇 |
数学 | 1454篇 |
物理学 | 7515篇 |
无线电 | 20670篇 |
出版年
2024年 | 133篇 |
2023年 | 458篇 |
2022年 | 876篇 |
2021年 | 1222篇 |
2020年 | 1159篇 |
2019年 | 810篇 |
2018年 | 775篇 |
2017年 | 1230篇 |
2016年 | 1401篇 |
2015年 | 1658篇 |
2014年 | 2509篇 |
2013年 | 2183篇 |
2012年 | 2499篇 |
2011年 | 2269篇 |
2010年 | 1706篇 |
2009年 | 1872篇 |
2008年 | 2082篇 |
2007年 | 2100篇 |
2006年 | 1685篇 |
2005年 | 1560篇 |
2004年 | 1349篇 |
2003年 | 1109篇 |
2002年 | 822篇 |
2001年 | 638篇 |
2000年 | 560篇 |
1999年 | 457篇 |
1998年 | 383篇 |
1997年 | 353篇 |
1996年 | 306篇 |
1995年 | 278篇 |
1994年 | 163篇 |
1993年 | 170篇 |
1992年 | 141篇 |
1991年 | 112篇 |
1990年 | 95篇 |
1989年 | 78篇 |
1988年 | 83篇 |
1987年 | 61篇 |
1986年 | 42篇 |
1985年 | 45篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 19篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
51.
52.
As we approach 100 nm technology the interconnect issues are becoming one of the main concerns in the testing of gigahertz system-on-chips. Voltage distortion (noise) and delay violations (skew) contribute to the signal integrity loss and ultimately functional error, performance degradation and reliability problems. In this paper, we first define a model for integrity faults on the high-speed interconnects. Then, we present a BIST-based test methodology that includes two special cells to detect and measure noise and skew occurring on the interconnects of the gigahertz system-on-chips. Using an inexpensive test architecture the integrity information accumulated by these special cells can be scanned out for final test and reliability analysis. 相似文献
53.
An adaptive antenna array is incorporated into a decorrelatingmulti-user detector to effectively increase the DS-CDMA system capacity.Capacity improvement is due to beamforming gain, spatial diversity gain(assuming large angle spread), and the decorrelating effect. Thereceiver has been analyzed for the cases of sufficiently andinsufficiently spaced receiving antennas. The receiver consists of afront-end beamformer for every user in the cell and has knowledge of allusers' signature sequences. The beamformer estimates the desired userchannel vector, enhancing its signal and reducing the co-channelinterference from other directions. The multi-user detection, exploitingknowledge of other users, rejects those interferers whose arrival anglesare close to that of the desired user. The average uncoded Bit ErrorRate (BER) as a function of the number of in-beam active users, theaverage antenna Signal-to-Noise Ratio (SNR), and the number of receivingantennas is examined in both single-path and multi-path Rayleigh fadingchannels. Analysis shows an increase in system capacity proportional tothe number of receiving antennas. 相似文献
54.
一种新颖的表面等离子谐振效应光波导水质传感技术 总被引:4,自引:0,他引:4
光学表面等离子谐振(SPR)效应是一种很有效的水质检测技术,经过详细的理论推导,同了SPR反射光强的普遍适用公式。在纯水与受污染水两种情况下,根据一些已知参数计算出结果。由计算结果数据一出的曲线比较表明,SPR效应在两种情况下有明显差别,这也正是SPR效应用于水质检测的理论根据。 相似文献
55.
56.
Ying Tan 《The Journal of VLSI Signal Processing》2002,32(1-2):45-54
In this paper, we propose a new approach for signal detection in wireless digital communications based on the neural network with transient chaos and time-varying gain (NNTCTG), and give a concrete model of the signal detector after appropriate transformations and mappings. It is well known that the problem of the maximum likelihood signal detection can be described as a complex optimization problem that has so many local optima that conventional Hopfield-type neural networks fail to solve. By refraining from the serious local optima problem of Hopfield-type neural networks, the NNTCTG makes use of the time-varying parameters of the recurrent neural network to control the evolving behavior of the network so that the network undergoes the transition from chaotic behavior to gradient convergence. It has richer and more flexible dynamics rather than conventional neural networks only with point attractors, so that it can be expected to have much ability to search for globally optimal or near-optimal solutions. After going through a transiently inverse-bifurcation process, the NNTCTG can approach the global optimum or the neighborhood of global optimum of our problem. Simulation experiments have been performed to show the effectiveness and validation of the proposed neural network based method for the signal detection in digital communications. 相似文献
57.
在分析了像增强夜视系统信息传递的基础上,指出像增强器输出端荧光屏至人眼的图像传递过程,构成了像增强夜视系统信息传递量的限制.提出了采用系统信息传递量作为夜视系统设计与评价的方法,利用这种方法可以发现在像增强器增益足以补偿光谱选道衰减的条件下,采用彩色像增强可以大幅度增加夜视系统传输的信息量. 相似文献
58.
在摄像机进行航拍的图像处理系统中,由摄像机运动所引起的视频运动,背景变化是主要特点。在进行图像采集时,每个像素都在变化,采用传统的图像编码方式进行图像压缩,压缩效果比较差。提出了基于块分割的精确运动估计算法,它是一种很好的图像压缩方法。 相似文献
59.
60.