全文获取类型
收费全文 | 2646篇 |
免费 | 103篇 |
国内免费 | 23篇 |
专业分类
化学 | 1464篇 |
晶体学 | 7篇 |
力学 | 42篇 |
数学 | 399篇 |
物理学 | 565篇 |
无线电 | 295篇 |
出版年
2023年 | 11篇 |
2022年 | 22篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 35篇 |
2018年 | 34篇 |
2017年 | 48篇 |
2016年 | 68篇 |
2015年 | 64篇 |
2014年 | 72篇 |
2013年 | 135篇 |
2012年 | 198篇 |
2011年 | 194篇 |
2010年 | 156篇 |
2009年 | 133篇 |
2008年 | 175篇 |
2007年 | 180篇 |
2006年 | 185篇 |
2005年 | 216篇 |
2004年 | 155篇 |
2003年 | 134篇 |
2002年 | 123篇 |
2001年 | 23篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 37篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1932年 | 4篇 |
排序方式: 共有2772条查询结果,搜索用时 156 毫秒
11.
Panos M. Pardalos Wanpracha Chaovalitwongse Leonidas D. Iasemidis J. Chris Sackellares Deng-Shan Shiau Paul R. Carney Oleg A. Prokopyev Vitaliy A. Yatsenko 《Mathematical Programming》2004,101(2):365-385
There is growing evidence that temporal lobe seizures are preceded by a preictal transition, characterized by a gradual dynamical change from asymptomatic interictal state to seizure. We herein report the first prospective analysis of the online automated algorithm for detecting the preictal transition in ongoing EEG signals. Such, the algorithm constitutes a seizure warning system. The algorithm estimates STLmax, a measure of the order or disorder of the signal, of EEG signals recorded from individual electrode sites. The optimization techniques were employed to select critical brain electrode sites that exhibit the preictal transition for the warning of epileptic seizures. Specifically, a quadratically constrained quadratic 0-1 programming problem is formulated to identify critical electrode sites. The automated seizure warning algorithm was tested in continuous, long-term EEG recordings obtained from 5 patients with temporal lobe epilepsy. For individual patient, we use the first half of seizures to train the parameter settings, which is evaluated by ROC (Receiver Operating Characteristic) curve analysis. With the best parameter setting, the algorithm applied to all cases predicted an average of 91.7% of seizures with an average false prediction rate of 0.196 per hour. These results indicate that it may be possible to develop automated seizure warning devices for diagnostic and therapeutic purposes.Mathematics Subject Classification (1991):20E28, 20G40, 20C20 相似文献
12.
13.
Chris Bergen 《电子测试》2005,(4):56-58
背板互连特性 背板是位于机架内的互连装置,它可能具备或不具备智能功能,通常其上可以有各种插卡和电路板插在插槽上.被动式背板电路可能需要使用电阻、处理器或一些控制驱动器电路.过去,背板互连一直是附加的物理端口如插头、插座或无线端口,如发射器、接收器等装置.大部分情况下,背板上都会为交换卡保留1~2个插槽作为背板的基础架构和逻辑层. 相似文献
14.
Editorial: Metal-Enhanced Fluorescence 总被引:1,自引:0,他引:1
15.
16.
Sanghoon Lee Chris Podilchuk Vidhya Krishnan Alan C. Bovik 《The Journal of VLSI Signal Processing》2003,34(1-2):149-166
By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protection; (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB. 相似文献
17.
Chris Rasmussen Michelle Zandieh Karen King Anne Teppo 《Mathematical Thinking and Learning》2005,7(1):51-73
The purpose of this article is to contribute to the dialogue about the notion of advanced mathematical thinking by offering an alternative characterization for this idea, namely advancing mathematical activity. We use the term advancing (versus advanced) because we emphasize the progression and evolution of students' reasoning in relation to their previous activity. We also use the term activity, rather than thinking. This shift in language reflects our characterization of progression in mathematical thinking as acts of participation in a variety of different socially or culturally situated mathematical practices. For these practices, we emphasize the changing nature of students' mathematical activity and frame the process of progression in terms of multiple layers of horizontal and vertical mathematizing. 相似文献
18.
Chris Quigg 《EPJ direct》2002,4(1):1-15
We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ− in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ− are promising. 相似文献
19.
20.
Chris Good 《Topology and its Applications》2007,154(3):734-740
One possible natural monotone version of countable paracompactness, MCP, turns out to have some interesting properties. We investigate various other possible monotone versions of countable paracompactness and how they are related. 相似文献