全文获取类型
收费全文 | 1988篇 |
免费 | 268篇 |
国内免费 | 105篇 |
学科分类
工业技术 | 2361篇 |
出版年
2024年 | 14篇 |
2023年 | 42篇 |
2022年 | 39篇 |
2021年 | 47篇 |
2020年 | 67篇 |
2019年 | 34篇 |
2018年 | 41篇 |
2017年 | 62篇 |
2016年 | 73篇 |
2015年 | 77篇 |
2014年 | 125篇 |
2013年 | 129篇 |
2012年 | 130篇 |
2011年 | 173篇 |
2010年 | 142篇 |
2009年 | 121篇 |
2008年 | 137篇 |
2007年 | 147篇 |
2006年 | 135篇 |
2005年 | 95篇 |
2004年 | 87篇 |
2003年 | 62篇 |
2002年 | 59篇 |
2001年 | 40篇 |
2000年 | 48篇 |
1999年 | 40篇 |
1998年 | 31篇 |
1997年 | 32篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2361条查询结果,搜索用时 0 毫秒
1.
相干源二维波达方向估计 总被引:4,自引:0,他引:4
本文分析了平面阵接收信号的协方差矩阵,发现它可分解为一个广义对称矩阵与一个非广义对称矩阵之和,利用信号协方差矩阵的这一结构特征,重点研究了相干源二维波达方向(DOA)估计.该方法通过构造一个差矩阵,求出其本特征值对应的任一特征向量,利用谱函数估计相干源二维DOA.简要分析了二维DOA估计的分维处理。 相似文献
2.
Guangyan Li W. Ian Hamilton Ged Morrisroe Theresa Clarke 《Cognition, Technology & Work》2006,8(1):30-40
A study was carried out using simulation to investigate driver responses to lineside signals and signs at various approach
speeds. The objectives of the study were: (1) to find out whether train speed would significantly affect signal/sign reading;
(2) to examine at which point certain types of signs or signals could be detected or recognised, and (3) to determine a speed
cut-off level above which certain types of signs or signals are no longer recognisable or detectable. Fifty-seven train drivers
from 12 Train Operating Companies in the UK participated in the trials. Twenty different types of lineside signs and ten types
of signals were tested under six different approach speeds ranging from 100 to 350 km/h (62–218 mph). Driver performance measures
were ‘time remaining to the signal/sign’ at the point of detection or recognition, and reading error rate. The results showed
a significant influence of train speed on driver responses to lineside signals/signs and demonstrated a non-linear relationship
between driver responses to signals/signs and approach speed. This has been used to estimate a maximum approach speed limit
within which a specific signal or sign can be correctly detected or recognised. The findings and implications of the study
are discussed in the paper. 相似文献
3.
Time‐domain waveform measurements of wideband modulated signals, although attractive for communication systems modeling applications, have until now lacked the required accuracy for quantitative analysis. New developments described here enhance the accuracy of these measurements, enabling their application to communication system characterization and modeling. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 32–39, 2003. 相似文献
4.
飞机交流发电机是飞机关键部件之一,监测其健康状况具有重要意义。通过设计实验数据获取平台采集交流发电机在转速上升(从6000转/分到8500转/分)、平稳运行(7500转/分)及转速下降(8500转/分到6000转/分)三个阶段的振动信号,利用符号序列Shannon熵的计算方法以及符号化方法设定合适参数对振动信号进行了处理,得出了交流发电机在三个阶段的振动信号的Shannon熵;通过初步的分析表明,交流发电机在正常状态下三个阶段的Shannon熵都比较有规律的在一定范围内变化,一旦发生振动异常将会引起Shannon熵突变;经过分析讨论,Shannon熵的突变与否是可以用来反映交流发电机在机械方面是否存在故障隐患的。 相似文献
5.
《Expert systems with applications》2014,41(16):7161-7170
The features extracted from the cardiac sound signals are commonly used for detection and identification of heart valve disorders. In this paper, we present a new method for classification of cardiac sound signals using constrained tunable-Q wavelet transform (TQWT). The proposed method begins with a constrained TQWT based segmentation of cardiac sound signals into heart beat cycles. The features obtained from heart beat cycles of separately reconstructed heart sounds and murmur can better represent the various types of cardiac sound signals than that from containing both. Therefore, heart sounds and murmur have been separated using constrained TQWT. Then the proposed novel raw feature set has been created by the parameters that have been optimized while constraining the output of TQWT together with that of extracted by using time-domain representation and Fourier–Bessel (FB) expansion of separated heart sounds and murmur. However, the adaptively selected features have been used to obtain the final feature set for subsequent classification of cardiac sound signals using least squares support vector machine (LS-SVM) with various kernel functions. The performance of the proposed method has been validated with publicly available datasets and the results have been compared with the existing short-time Fourier transform (STFT) based method. The proposed method shows higher percentage classification accuracy of 94.01 as compared to 93.53 of STFT based method. In comparison with STFT based method, it is noteworthy that the proposed method uses well defined and lower dimensionality of feature vector that can reduce the computational complexity. 相似文献
6.
7.
8.
全变分原理在地震数据去噪中的应用 总被引:1,自引:0,他引:1
公成敏 《计算机与数字工程》2014,(7):1271-1274
地震图像资料的解释和后续处理中的重点环节是如何有效地降除地震资料记录中的噪声。高效的地震资料降噪算法在较好降除噪声的同时可以将图像的边缘信息予以较好的保留。论文首先全面地介绍了全变分去噪模型,同时详细介绍了参数的选取方法,最后进行实验和模型验证。结合小波阈值降噪方法进行比较,实验结果表明全变分降噪方法在很好地消除地震信号图像中的噪声,大面积提高信号剖面质量的同时,可以有效提高地震资料的信噪比。 相似文献
9.
10.
In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish. 相似文献