全文获取类型
收费全文 | 1158篇 |
免费 | 153篇 |
国内免费 | 101篇 |
专业分类
电工技术 | 37篇 |
综合类 | 91篇 |
化学工业 | 15篇 |
金属工艺 | 14篇 |
机械仪表 | 61篇 |
建筑科学 | 60篇 |
矿业工程 | 12篇 |
能源动力 | 6篇 |
轻工业 | 24篇 |
水利工程 | 15篇 |
石油天然气 | 22篇 |
武器工业 | 9篇 |
无线电 | 289篇 |
一般工业技术 | 77篇 |
冶金工业 | 12篇 |
原子能技术 | 59篇 |
自动化技术 | 609篇 |
出版年
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 22篇 |
2020年 | 29篇 |
2019年 | 12篇 |
2018年 | 29篇 |
2017年 | 39篇 |
2016年 | 53篇 |
2015年 | 68篇 |
2014年 | 69篇 |
2013年 | 92篇 |
2012年 | 98篇 |
2011年 | 119篇 |
2010年 | 83篇 |
2009年 | 70篇 |
2008年 | 106篇 |
2007年 | 92篇 |
2006年 | 87篇 |
2005年 | 67篇 |
2004年 | 47篇 |
2003年 | 42篇 |
2002年 | 26篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1412条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
5.
城市背景建筑的质量决定着城市空间的整体品质,中国城市背景建筑的质量有待提高,这取决于建筑师的城市整体意识、建构意识、过程意识和大众意识的提高。 相似文献
6.
Background concentrations of nitrogen dioxide (NO2) are not constant but vary temporally and spatially. The current paper presents a powerful tool for the quantification of the effects of wind direction and wind speed on background NO2 concentrations, particularly in cases where monitoring data are limited. In contrast to previous studies which applied similar methods to sites directly affected by local pollution sources, the current study focuses on background sites with the aim of improving methods for predicting background concentrations adopted in air quality modelling studies. The relationship between measured NO2 concentration in air at three such sites in Ireland and locally measured wind direction has been quantified using nonparametric regression methods. The major aim was to analyse a method for quantifying the effects of local wind direction on background levels of NO2 in Ireland. The method was expanded to include wind speed as an added predictor variable. A Gaussian kernel function is used in the analysis and circular statistics employed for the wind direction variable. Wind direction and wind speed were both found to have a statistically significant effect on background levels of NO2 at all three sites. Frequently environmental impact assessments are based on short term baseline monitoring producing a limited dataset. The presented non-parametric regression methods, in contrast to the frequently used methods such as binning of the data, allow concentrations for missing data pairs to be estimated and distinction between spurious and true peaks in concentrations to be made. The methods were found to provide a realistic estimation of long term concentration variation with wind direction and speed, even for cases where the data set is limited. Accurate identification of the actual variation at each location and causative factors could be made, thus supporting the improved definition of background concentrations for use in air quality modelling studies. 相似文献
7.
针对在钻削加工噪声背景下振动信号微弱特征识别和提取困难的问题,提出了一种基于小波包分频谱减的钻削振动信号特征增强方法。首先,在经典谱减法原理的基础上,将钻削前机床空转信号视为监测信号的"加性噪声";其次,根据钻削过程振动信号的特点,采用小波包分解方法将"加性噪声"和监测信号分成多个子频带;最后,对每个子频带内"加性噪声"的相应频带进行谱减处理后,重构钻削振动信号。仿真和实验结果表明,该方法能有效降低环境噪声对钻削过程特征提取的影响,从而达到增强监测信号特征的目的,同时建立了钻削过程与监测信号之间很好的映射关系模型。 相似文献
8.
C.R.L. Bauwens J.M. Bergthorson S.B. Dorofeev 《International Journal of Hydrogen Energy》2017,42(11):7691-7697
Large-scale experiments examining spherical-flame acceleration in lean hydrogen-air mixtures were performed in a 64 m3 constant-pressure enclosure. Equivalence ratios ranging from 0.33 to 0.57 were examined using detailed front tracking for flame diameters up to 1.2 m through the use of a Background Oriented Schlieren (BOS) technique. From these measurements, the critical radii for onset of instability for these mixtures, on the order of 2–3 cm, were obtained. In addition, the laminar burning velocity and rate of flame acceleration as a function of radius were also measured. 相似文献
9.
Multiple visual target tracking is a challenging problem due to various uncertainties including occlusion, miss-detection and noisy measurement. Most tracking approaches utilize an object-specific detector, pre-trained on many labeled images, to provide suitable measurements for their tracking system. In this paper, we use a simple background subtraction detector which only needs the background image to localize targets independent of their shape or type. In order to cope with the uncertainties resulted by the detector, we propose an adaptive appearance model and develop an incremental appearance learning algorithm to learn the target appearances in time. The proposed method employs the background information and our defined keypoints’ miss-matched history to adapt the target appearances within different frames. Furthermore, we combine Refined Gaussian Mixture Probability Hypothesis Density (RGM-PHD) tracker with the detectors to keep target trajectories and handle uncertainties. The experiments conducted on several video datasets show the effectiveness of our proposed method. 相似文献
10.
This paper presents a novel framework for detecting abandoned objects by introducing a fully-automatic GrabCut object segmentation. GrabCut seed initialization is treated as a background (BG) modelling problem that focuses only on unhanded objects and objects that become immobile. The BG distribution is constructed with dual Gaussian mixtures that are comprised of high and low learning rate models. We propose a primitive BG model-based removed object validation and Haar feature-based cascade classifier for still-people detection once a candidate for a released object has been detected. Our system can obtain more robust and accurate results for real environments based on evaluations of realistic scenes from CAVIAR, PETS2006, CDnet 2014, and our own datasets. 相似文献