全文获取类型
收费全文 | 2415篇 |
免费 | 253篇 |
国内免费 | 217篇 |
专业分类
电工技术 | 60篇 |
技术理论 | 1篇 |
综合类 | 132篇 |
化学工业 | 71篇 |
金属工艺 | 41篇 |
机械仪表 | 84篇 |
建筑科学 | 54篇 |
矿业工程 | 11篇 |
能源动力 | 96篇 |
轻工业 | 32篇 |
水利工程 | 108篇 |
石油天然气 | 33篇 |
武器工业 | 10篇 |
无线电 | 899篇 |
一般工业技术 | 114篇 |
冶金工业 | 130篇 |
原子能技术 | 32篇 |
自动化技术 | 977篇 |
出版年
2024年 | 6篇 |
2023年 | 50篇 |
2022年 | 76篇 |
2021年 | 87篇 |
2020年 | 65篇 |
2019年 | 51篇 |
2018年 | 75篇 |
2017年 | 84篇 |
2016年 | 102篇 |
2015年 | 88篇 |
2014年 | 150篇 |
2013年 | 149篇 |
2012年 | 168篇 |
2011年 | 199篇 |
2010年 | 149篇 |
2009年 | 135篇 |
2008年 | 196篇 |
2007年 | 164篇 |
2006年 | 144篇 |
2005年 | 149篇 |
2004年 | 116篇 |
2003年 | 74篇 |
2002年 | 84篇 |
2001年 | 47篇 |
2000年 | 38篇 |
1999年 | 28篇 |
1998年 | 37篇 |
1997年 | 23篇 |
1996年 | 16篇 |
1995年 | 23篇 |
1994年 | 11篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2885条查询结果,搜索用时 0 毫秒
41.
The advent of wireless networks has brought a new set of security issues with it. One of the most feared of these is the jamming-based attacks. In this paper, we propose a pre-emptive detection strategy using honeynodes and a response mechanism based on the existing Channel Surfing Algorithm [Xu W, Trappe W, Zhang Y, Wood T. Channel surfing and spatial retreats: defenses against wireless denial of service. ACM Wireless Security 2004;80-9] to protect wireless nodes from a jammer. Honeynodes generate dummy communication at a frequency close to the actual frequency of operation, and pre-emptively alert authentic nodes of imminent attacks, so that the authentic nodes can jump to another frequency even before a jammer starts scanning that frequency. The next frequency is selected using a novel approach which uses a hybrid of reactive and proactive channel selection procedures. We have simulated the proposed approach using NS-2. The experimental results further prove a marked improvement in the performance of the proposed system over the Channel Surfing Algorithm in terms of the packet delivery ratio, the jammed duration, control message overhead and the number of channel re-configurations. 相似文献
42.
43.
在流形学习的谱方法中, 流形展开被表述为优化问题. 这些优化问题的解是退化的, 即所有的样本将被嵌入到同一个点. 为了避免退化解, 谱方法对嵌入坐标人为地强加了一个单位协方差矩阵约束. 然而, 该约束往往导致流形展开的失真非常明显. 本文提出一种新的流形学习方法, 彻底抛弃了人为的单位协方差矩阵约束. 主要思路是先对流形边界进行嵌入, 然后再求流形内部的嵌入; 流形边界的嵌入位置被确定后, 流形内部样本的嵌入位置将被边界拉开, 使得它们不会都收缩到一个点上, 从而避免了退化解的出现. 将流形边界的嵌入位置作为边界条件, 求解一个线性方程组来得到内部样本的嵌入; 该线性方程组反映了尽量保持邻近样本间距离不变的要求. 流形边界的嵌入由简化流形的嵌入求出; 为此, 本文还设计了一种流形边界检测算法以及一种流形简化算法. 与目前代表性的几种流形学习方法进行了比较实验, 结果表明了本文方法的有效性, 其展开失真比谱方法明显要小. 相似文献
44.
现有基于边信息的半监督维数约减算法大都是直接将保留边信息和数据拓扑结构的目标函数相加,因此数据拓扑结构中的错误连接不会因已知的边信息而得到修正.提出通过边信息传播及修正机制将边信息融入到数据拓扑结构图中的方法,从而在保留边信息的同时保留更为真实的数据拓扑结构信息.实验结果表明本文所提出的算法较之其它算法,对数据降维后用于分类时可取得较高的准确率,且算法对创建的KNN图中的参数K最具鲁棒性. 相似文献
45.
46.
47.
48.
The Multi-Carrier Code Division Multiple Access (MC-CDMA) is becoming a very attractive multiple access technique for high-rate data transmission in the future wireless communication systems. This paper is focused on the joint channel and power allocation in the downlink transmission of multi-user MC-CDMA systems and considers the throughput maximization problem as a mixed integer optimization problem. For simple analysis, the problem is divided into two less complex sub-problems: power allocation and channel allocation, which can be solved by a suboptimal Adaptive Power Allocation (APA) algorithm and an optimal Adaptive Channel Allocation (ACA) algorithm, respectively. By combining APA and ACA algorithms, an adaptive channel and power allocation scheme is proposed. The numerical results show that the proposed APA algorithm is more suitable for MC-CDMA systems than the conventional equal power allocation algorithm, and the proposed channel and power allocation scheme can significantly improve the system throughput performance. 相似文献
49.
The role of spectral resolution and classifier complexity in the analysis of hyperspectral images of forest areas 总被引:1,自引:0,他引:1
Michele Dalponte Lorenzo Bruzzone Loris Vescovo 《Remote sensing of environment》2009,113(11):2345-2355
Remote sensing hyperspectral sensors are important and powerful instruments for addressing classification problems in complex forest scenarios, as they allow one a detailed characterization of the spectral behavior of the considered information classes. However, the processing of hyperspectral data is particularly complex both from a theoretical viewpoint [e.g. problems related to the Hughes phenomenon (Hughes, 1968) and from a computational perspective. Despite many previous investigations that have been presented in the literature on feature reduction and feature extraction in hyperspectral data, only a few studies have analyzed the role of spectral resolution on the classification accuracy in different application domains. In this paper, we present an empirical study aimed at understanding the relationship among spectral resolution, classifier complexity, and classification accuracy obtained with hyperspectral sensors for the classification of forest areas. We considered two different test sets characterized by images acquired by an AISA Eagle sensor over 126 bands with a spectral resolution of 4.6 nm, and we subsequently degraded its spectral resolution to 9.2, 13.8, 18.4, 23, 27.6, 32.2 and 36.8 nm. A series of classification experiments were carried out with bands at each of the degraded spectral resolutions, and bands selected with a feature selection algorithm at the highest spectral resolution (4.6 nm). The classification experiments were carried out with three different classifiers: Support Vector Machine, Gaussian Maximum Likelihood with Leave-One-Out-Covariance estimator, and Linear Discriminant Analysis. From the experimental results, important conclusions can be made about the choice of the spectral resolution of hyperspectral sensors as applied to forest areas, also in relation to the complexity of the adopted classification methodology. The outcome of these experiments are also applicable in terms of directing the user towards a more efficient use of the current instruments (e.g. programming of the spectral channels to be acquired) and classification techniques in forest applications, as well as in the design of future hyperspectral sensors. 相似文献
50.