全文获取类型
收费全文 | 1006篇 |
免费 | 156篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 135篇 |
综合类 | 82篇 |
化学工业 | 39篇 |
金属工艺 | 96篇 |
机械仪表 | 116篇 |
建筑科学 | 65篇 |
矿业工程 | 14篇 |
能源动力 | 17篇 |
轻工业 | 9篇 |
水利工程 | 16篇 |
石油天然气 | 18篇 |
武器工业 | 10篇 |
无线电 | 121篇 |
一般工业技术 | 360篇 |
冶金工业 | 42篇 |
原子能技术 | 4篇 |
自动化技术 | 84篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 43篇 |
2021年 | 32篇 |
2020年 | 49篇 |
2019年 | 42篇 |
2018年 | 35篇 |
2017年 | 47篇 |
2016年 | 34篇 |
2015年 | 51篇 |
2014年 | 64篇 |
2013年 | 68篇 |
2012年 | 62篇 |
2011年 | 70篇 |
2010年 | 67篇 |
2009年 | 52篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 42篇 |
2005年 | 35篇 |
2004年 | 46篇 |
2003年 | 41篇 |
2002年 | 29篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 29篇 |
1997年 | 21篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1985年 | 2篇 |
排序方式: 共有1228条查询结果,搜索用时 15 毫秒
61.
M. Mojiri Author Vitae 《Automatica》2007,43(3):450-455
Online frequency estimation of a sinusoidal signal is a classical problem and has many practical applications. Recently an adaptive notch filter (ANF) with global convergence property has been developed for frequency estimation of a pure sinusoidal signal. This paper addresses a modified ANF structure that can estimate the fundamental frequency of any periodic signal including pure sinusoidal signals. To prove the stability of the modified ANF, the paper introduces a new theorem that shows for any periodic signal, there exists a locally asymptotically stable periodic orbit of this ANF by which the frequency estimation becomes feasible. This alternative stability proof is simple and uses widely known mathematical tools, and therefore alleviates the problem complexity even when the input signal is a pure sinusoidal signal. A further contribution of this paper is obtaining a necessary and sufficient condition in terms of design parameters for local asymptotical stability of the modified ANF. This condition, obtained from the numerical study of Floquet multipliers of a linear time-varying periodic system, provides a strict stability region in the modified ANF design parameters space. 相似文献
62.
63.
Soon-Ryul Nam Sang-Hee Kang Jin-Man Sohn Jong-Keun Park 《Electrical Engineering (Archiv fur Elektrotechnik)》2007,89(4):311-317
A novel method for estimating the instantaneous phasor of a fault current signal is proposed for high-speed distance protection
immune to a DC-offset. The method uses a modified notch filter in order to eliminate the fundamental frequency component from
the fault current signal. Since the output of the modified notch filter is the delayed DC-offset, delay compensation results
in the same waveform as the original DC-offset. Subtracting the obtained DC-offset from the fault current signal yields a
sinusoidal waveform, which becomes the real part of the instantaneous phasor. The imaginary part of the instantaneous phasor
is based on the first difference of the fault current signal. Since a DC-offset also appears in the first difference, the
DC-offset is removed from the first difference using the results of the delay compensation. The performance of the proposed
method was evaluated for a–phase to ground faults on a 345 kV 100 km overhead transmission line. The Electromagnetic Transient
Program was used to generate fault current signals for different fault locations and fault inception angles. The performance
evaluation showed that the proposed method can estimate the instantaneous phasor of a fault current signal with high speed
and high accuracy. The paper concludes by describing the hardware implementation of the proposed method on a prototype unit
based on a digital signal processor. 相似文献
64.
65.
X. LI T. KASAI S. NAKAO T. ANDO M. SHIKIDA K. SATO 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(12):1172-1181
The influence of notches on the fracture of single crystal silicon thin films was investigated. The tests were conducted on notched and smooth tensile specimens micromachined on a silicon wafer. The specimen geometry was 100 μm long, 50 μm wide and 5 μm thick. For the notched specimen, a V‐shaped sub‐micrometer notch was introduced on one edge of it by using a focused ion beam (FIB) process. The notch lengths ranged from 0.07 to 1.3 μm. Four types of specimens with different surfaces and tensile orientations were tested. The smooth specimens showed scattered fracture strengths and ‘collapsed’ fractures. For the restrictive‐shaped notches, the critical length was 0.5 μm. The short‐notched (<0.5 μm) specimens also showed ‘collapsed’ fractures, and the stress concentrations on notch tips decreased their fracture strengths. For the long‐notched (>0.5 μm) specimens, the notch was equivalent to a crack in the Griffith model and the crack mainly propagated on {111} cleaved planes. 相似文献
66.
介绍了一种新颖的频域陷波算法,以消除窄带干扰对通信的影响,并讨论了这种陷波算法在直接序列扩频通信中的应用。该算法将时域自适应滤波器中复杂的卷积运算转换为频域的相乘运算,从而减少了运算量,节省了资源,使得自适应陷波器更易于工程实现。仿真结果证实,该算法能有效地消除直接序列扩频方式中的窄带干扰。 相似文献
67.
Stress intensity factors for surface cracks in single‐edge notch bend specimen by a three‐dimensional weight function method
下载免费PDF全文
![点击此处可从《Fatigue & Fracture of Engineering Materials & Structures》网站下载免费的PDF全文](/ch/ext_images/free.gif)
X C Zhao X R Wu J C Newman D H Tong 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(11):1407-1418
Stress intensity factors for half‐elliptical surface cracks at a semi‐circular notch in a recently developed single‐edge notch bend specimen are determined for a wide range of geometrical parameters using a three‐dimensional weight function method. Two load cases of pin loading and uniform remote tension are considered. The results are in good agreement with abaqus/franc3d finite element analysis. It is found that the Ziegler–Newman engineering similitude approach (programmed into the Fatigue Crack Growth Structural Analysis life‐prediction code) produces good results for a wide range in a/c ratios. Expressions by multi‐variable curve fitting to the weight function results are presented for easy engineering applications. 相似文献
68.
Brittle fracture assessment of engineering components in the presence of notches: a review
下载免费PDF全文
![点击此处可从《Fatigue & Fracture of Engineering Materials & Structures》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M. R. Ayatollahi A. R. Torabi A. S. Rahimi 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(3):267-291
Brittle fracture of notched components has been widely investigated in recent decades both experimentally and theoretically. This is because of designers' concern about catastrophic failure in notched engineering components made of brittle or quasi‐brittle materials. Up to now, extensive studies have been performed on brittle fracture analysis of engineering components weakened by notches of various features under mode I, mode II, mode III and mixed mode loading conditions. In the present paper, the attempt is made to review the research articles published in the open literature on brittle fracture assessment of notched components by means of notch fracture mechanics concepts. The main focus of this paper is on the stress‐based fracture criteria, which are the basis of authors' experience in recent years. 相似文献
69.
70.