全文获取类型
收费全文 | 4559篇 |
免费 | 768篇 |
国内免费 | 407篇 |
专业分类
电工技术 | 198篇 |
技术理论 | 3篇 |
综合类 | 575篇 |
化学工业 | 31篇 |
金属工艺 | 11篇 |
机械仪表 | 203篇 |
建筑科学 | 160篇 |
矿业工程 | 38篇 |
能源动力 | 47篇 |
轻工业 | 19篇 |
水利工程 | 140篇 |
石油天然气 | 46篇 |
武器工业 | 112篇 |
无线电 | 2333篇 |
一般工业技术 | 269篇 |
冶金工业 | 90篇 |
原子能技术 | 16篇 |
自动化技术 | 1443篇 |
出版年
2024年 | 21篇 |
2023年 | 110篇 |
2022年 | 163篇 |
2021年 | 204篇 |
2020年 | 204篇 |
2019年 | 179篇 |
2018年 | 168篇 |
2017年 | 181篇 |
2016年 | 200篇 |
2015年 | 245篇 |
2014年 | 327篇 |
2013年 | 277篇 |
2012年 | 375篇 |
2011年 | 337篇 |
2010年 | 302篇 |
2009年 | 264篇 |
2008年 | 299篇 |
2007年 | 296篇 |
2006年 | 270篇 |
2005年 | 209篇 |
2004年 | 175篇 |
2003年 | 181篇 |
2002年 | 120篇 |
2001年 | 95篇 |
2000年 | 81篇 |
1999年 | 68篇 |
1998年 | 60篇 |
1997年 | 60篇 |
1996年 | 51篇 |
1995年 | 52篇 |
1994年 | 50篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5734条查询结果,搜索用时 31 毫秒
1.
在干扰条件下,卫星导航抗干扰波束形成算法往往需要卫星信号波达方向(Direction-of-Arrival,DOA)的先验信息。但当存在低信噪比信号或主动干扰源时,常规的DOA估计算法性能急剧下降甚至失效。针对此问题,提出了一种被干扰信号压制的低信噪比“北斗”信号的DOA估计算法。该算法首先通过对接收信号进行子空间投影抑制干扰信号,然后对抑制干扰后的信号进行解扩重构处理,最后通过多重信号分类算法完成对“北斗”信号的DOA估计。仿真结果表明,在干扰信号干信比80 dB条件下,“北斗”信号DOA估计误差在5°以内,为下一步进行波束形成计算提供了高精度的入射角信息。 相似文献
2.
The proposed work involves the multiobjective PSO based adaption of optimal neural network topology for the classification of multispectral satellite images. It is per pixel supervised classification using spectral bands (original feature space). This paper also presents a thorough experimental analysis to investigate the behavior of neural network classifier for given problem. Based on 1050 number of experiments, we conclude that following two critical issues needs to be addressed: (1) selection of most discriminative spectral bands and (2) determination of optimal number of nodes in hidden layer. We propose new methodology based on multiobjective particle swarm optimization (MOPSO) technique to determine discriminative spectral bands and the number of hidden layer node simultaneously. The accuracy with neural network structure thus obtained is compared with that of traditional classifiers like MLC and Euclidean classifier. The performance of proposed classifier is evaluated quantitatively using Xie-Beni and β indexes. The result shows the superiority of the proposed method to the conventional one. 相似文献
3.
针对目前运动想象脑电(EEG)信号识别率较低的问题,考虑到脑电信号蕴含着丰富的时频信息,提出一种基于时频域的卷积神经网络(CNN)运动想象脑电信号识别方法。首先,利用短时傅里叶变换(STFT)对脑电信号的相关频带进行预处理,并将多个电极的时频图组合构造出一种二维时频图;然后,针对二维时频图的时频特性,通过一维卷积的方法设计了一种新颖的CNN结构;最后,通过支持向量机(SVM)对CNN提取的特征进行分类。基于BCI数据集的实验结果表明,所提方法的平均识别率为86.5%,优于其他传统运动想象脑电信号识别方法;同时将该方法应用在智能轮椅上,验证了其有效性。 相似文献
4.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
5.
6.
7.
8.
9.
Navid Ehsan Mingyan Liu Roderick J. Ragland 《International Journal of Communication Systems》2003,16(6):513-534
Performance enhancing proxies (PEPs) are widely used to improve the performance of TCP over high delay‐bandwidth product links and links with high error probability. In this paper we analyse the performance of using TCP connection splitting in combination with web caching via traces obtained from a commercial satellite system. We examine the resulting performance gain under different scenarios, including the effect of caching, congestion, random loss and file sizes. We show, via analysing our measurements, that the performance gain from using splitting is highly sensitive to random losses and the number of simultaneous connections, and that such sensitivity is alleviated by caching. On the other hand, the use of a splitting proxy enhances the value of web caching in that cache hits result in much more significant performance improvement over cache misses when TCP splitting is used. We also compare the performance of using different versions of HTTP in such a system. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
10.
本文从小卫星、星座飞速发展以及对测控通信系统新的要求出发,介绍了综合基带、连续波多波束相控阵天线的功能、特点及工作原理,提出了建立新型多功能智能化测控通信站的设想。 相似文献