全文获取类型
收费全文 | 1741篇 |
免费 | 210篇 |
国内免费 | 72篇 |
专业分类
电工技术 | 183篇 |
综合类 | 310篇 |
化学工业 | 46篇 |
金属工艺 | 25篇 |
机械仪表 | 130篇 |
建筑科学 | 229篇 |
矿业工程 | 23篇 |
能源动力 | 37篇 |
轻工业 | 28篇 |
水利工程 | 5篇 |
石油天然气 | 30篇 |
武器工业 | 9篇 |
无线电 | 172篇 |
一般工业技术 | 159篇 |
冶金工业 | 8篇 |
原子能技术 | 5篇 |
自动化技术 | 624篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 24篇 |
2021年 | 38篇 |
2020年 | 51篇 |
2019年 | 40篇 |
2018年 | 43篇 |
2017年 | 60篇 |
2016年 | 69篇 |
2015年 | 64篇 |
2014年 | 103篇 |
2013年 | 101篇 |
2012年 | 124篇 |
2011年 | 120篇 |
2010年 | 99篇 |
2009年 | 123篇 |
2008年 | 122篇 |
2007年 | 139篇 |
2006年 | 96篇 |
2005年 | 79篇 |
2004年 | 70篇 |
2003年 | 56篇 |
2002年 | 43篇 |
2001年 | 43篇 |
2000年 | 38篇 |
1999年 | 39篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 28篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2023条查询结果,搜索用时 15 毫秒
21.
22.
We extend extreme learning machine (ELM) classifiers to complex Reproducing Kernel Hilbert Spaces (RKHS) where the input/output variables as well as the optimization variables are complex-valued. A new family of classifiers, called complex-valued ELM (CELM) suitable for complex-valued multiple-input–multiple-output processing is introduced. In the proposed method, the associated Lagrangian is computed using induced RKHS kernels, adopting a Wirtinger calculus approach formulated as a constrained optimization problem similarly to the conventional ELM classifier formulation. When training the CELM, the Karush–Khun–Tuker (KKT) theorem is used to solve the dual optimization problem that consists of satisfying simultaneously smallest training error as well as smallest norm of output weights criteria. The proposed formulation also addresses aspects of quaternary classification within a Clifford algebra context. For 2D complex-valued inputs, user-defined complex-coupled hyper-planes divide the classifier input space into four partitions. For 3D complex-valued inputs, the formulation generates three pairs of complex-coupled hyper-planes through orthogonal projections. The six hyper-planes then divide the 3D space into eight partitions. It is shown that the CELM problem formulation is equivalent to solving six real-valued ELM tasks, which are induced by projecting the chosen complex kernel across the different user-defined coordinate planes. A classification example of powdered samples on the basis of their terahertz spectral signatures is used to demonstrate the advantages of the CELM classifiers compared to their SVM counterparts. The proposed classifiers retain the advantages of their ELM counterparts, in that they can perform multiclass classification with lower computational complexity than SVM classifiers. Furthermore, because of their ability to perform classification tasks fast, the proposed formulations are of interest to real-time applications. 相似文献
23.
24.
This paper proposes the use of speech-specific features for speech / music classification. Features representing the excitation source, vocal tract system and syllabic rate of speech are explored. The normalized autocorrelation peak strength of zero frequency filtered signal, and peak-to-sidelobe ratio of the Hilbert envelope of linear prediction residual are the two source features. The log mel energy feature represents the vocal tract information. The modulation spectrum represents the slowly-varying temporal envelope corresponding to the speech syllabic rate. The novelty of the present work is in analyzing the behavior of these features for the discrimination of speech and music regions. These features are non-linearly mapped and combined to perform the classification task using a threshold based approach. Further, the performance of speech-specific features is evaluated using classifiers such as Gaussian mixture models, and support vector machines. It is observed that the performance of the speech-specific features is better compared to existing features. Additional improvement for speech / music classification is achieved when speech-specific features are combined with the existing ones, indicating different aspects of information exploited by the former. 相似文献
25.
This paper introduces a new algorithm for Boolean operations on rasterized geometric shapes that are represented with chain codes. The algorithm works in three steps. Firstly, the chain code symbols are transformed in the Hilbert space, where the overlaid chain code symbols are recognised. After that, a suitable starting cell is determined. Finally, the walk-about through the sequence of the initial chain code symbols is performed to obtain the sequence of chain code symbols representing the shape of the required Boolean operation. The algorithm is demonstrated on Freeman chain code in four directions. The time and space complexity of the proposed algorithm is linear, which was proven theoretically and confirmed by experiments. 相似文献
26.
27.
Based on theories of scientific discovery learning (SDL) and conceptual change, this study explores students' preconceptions in the domain of torques in physics and the development of these conceptions while learning with a computer-based SDL task. As a framework we used a three-space theory of SDL and focused on model space, which is supposed to contain the current conceptualization/model of the learning domain, and on its change through hypothesis testing and experimenting. Three questions were addressed: (1) What are students' preconceptions of torques before learning about this domain? To do this a multiple-choice test for assessing students' models of torques was developed and given to secondary school students (N = 47) who learned about torques using computer simulations. (2) How do students' models of torques develop during SDL? Working with simulations led to replacement of some misconceptions with physically correct conceptions. (3) Are there differential patterns of model development and if so, how do they relate to students’ use of the simulations? By analyzing individual differences in model development, we found that an intensive use of the simulations was associated with the acquisition of correct conceptions. Thus, the three-space theory provided a useful framework for understanding conceptual change in SDL. 相似文献
28.
《Measurement》2016
The Hilbert–Huang transform (HHT) has proven to be a promising tool for the analysis of non-stationary signals commonly occurred in industrial machines. However, in practice, multi-frequency intrinsic mode functions (IMFs) and pseudo IMFs are likely generated and lead to grossly erroneous or even completely meaningless instantaneous frequencies, which raise difficulties in interpreting signal features by the HHT spectrum. To enhance the time–frequency resolution of the traditional HHT, an improved HHT is proposed in this study. By constructing a bank of partially overlapping bandpass filters, a series of filtered signals are obtained at first. Then a subset of filtered signals, each associated with certain energy-dominated components, are selected based on the maximal-spectral kurtosis–minimal-redundancy criterion and the information-related coefficient, and further decomposed by empirical mode decomposition to extract sets of IMFs. Furthermore, IMF selection scheme is applied to select the relevant IMFs on which the HHT spectrum is constructed. The novelty of this method is that the HHT spectrum is just constructed with the relevant, almost monochromatic IMFs rather than with the IMFs possibly with multiple frequency components or with pseudo components. The results on the simulated data, test rig data, and industrial gearbox data show that the proposed method is superior to the traditional HHT in feature extraction and can produce a more accurate time–frequency distribution for the inspected signal. 相似文献
29.
针对控制棒驱动机构滚轮振动信号采集过程受到噪声干扰的问题,提出了小波半软阈值(SWT)和Hilbert变换法相结合的去噪方法。该方法首先利用小波半软阈值算法在时频域对滚轮振动信号进行降噪处理,然后进行Hilbert变换求出其包络谱,分析寿命试验与缺陷验证试验中不同的滚轮振动信号。试验结果表明,该方法可有效消除噪声对振动信号的干扰,证明了小波半软阈值与Hilbert变换相结合的方法在驱动机构滚轮状态识别和故障诊断中的有效性,为驱动机构的状态判别提供了理论支持。 相似文献
30.
Human recognition of the actions of other humans is very efficient and is based on patterns of movements. Our theoretical starting point is that the dynamics of the joint movements is important to action categorization. On the basis of this theory, we present a novel action recognition system that employs a hierarchy of Self-Organizing Maps together with a custom supervised neural network that learns to categorize actions. The system preprocesses the input from a Kinect like 3D camera to exploit the information not only about joint positions, but also their first and second order dynamics. We evaluate our system in two experiments with publicly available datasets, and compare its performance to the performance with less sophisticated preprocessing of the input. The results show that including the dynamics of the actions improves the performance. We also apply an attention mechanism that focuses on the parts of the body that are the most involved in performing the actions. 相似文献