首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   51172篇
  免费   15105篇
  国内免费   46篇
电工技术   909篇
综合类   21篇
化学工业   19961篇
金属工艺   850篇
机械仪表   1784篇
建筑科学   1933篇
矿业工程   4篇
能源动力   1373篇
轻工业   8175篇
水利工程   362篇
石油天然气   61篇
武器工业   2篇
无线电   9072篇
一般工业技术   14118篇
冶金工业   1525篇
原子能技术   224篇
自动化技术   5949篇
  2024年   9篇
  2023年   188篇
  2022年   206篇
  2021年   695篇
  2020年   1699篇
  2019年   3408篇
  2018年   3403篇
  2017年   3742篇
  2016年   4285篇
  2015年   4252篇
  2014年   4401篇
  2013年   5805篇
  2012年   3606篇
  2011年   3491篇
  2010年   3429篇
  2009年   3365篇
  2008年   2853篇
  2007年   2510篇
  2006年   2185篇
  2005年   1868篇
  2004年   1779篇
  2003年   1725篇
  2002年   1653篇
  2001年   1425篇
  2000年   1353篇
  1999年   739篇
  1998年   508篇
  1997年   364篇
  1996年   265篇
  1995年   181篇
  1994年   148篇
  1993年   140篇
  1992年   90篇
  1991年   91篇
  1990年   80篇
  1989年   73篇
  1988年   46篇
  1987年   51篇
  1986年   28篇
  1985年   38篇
  1984年   22篇
  1983年   16篇
  1982年   10篇
  1981年   16篇
  1980年   8篇
  1978年   9篇
  1977年   10篇
  1976年   15篇
  1975年   8篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
This paper is concerned with the problem of finite‐time asynchronous filtering for a class of discrete‐time Markov jump systems. The communication links between the system and filter are assumed to be unreliable, which lead to the simultaneous occurrences of packet dropouts, time delays, sensor nonlinearity and nonsynchronous modes. The objective is to design a filter that ensures not only the mean‐square stochastic finite‐time bounded but also a prescribed level of performance for the underlying error system over a lossy network. With the help of the Lyapunov–Krasovskii approach and stochastic analysis theory, sufficient conditions are established for the existence of an admissible filter. By using a novel simple matrix decoupling approach, a desired asynchronous filter can be constructed. Finally, a numerical example is presented and a pulse‐width‐modulation‐driven boost converter model is employed to demonstrate the effectiveness of the proposed approach. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
992.
The impression of quality of images can be enhanced on a high dynamic range (HDR) displays. Generally, a conventional 8‐bit image can be processed to an HDR image by inverse tone mapping operators. Among the operators, brightness discrimination mapping by applying brightness adaptation model attempted to mimic the human visual system. In this paper, we use a brightness adaptation model to derive a brightness discrimination mapping algorithm for HDR displays. The proposed algorithm maximizes a function, which represents the local and global brightness discrimination range by exploiting characteristics of the human visual system. Enhancement of details is verified by visualizing HDR images from dark to bright regions. Improvement of dynamic range is quantified by measuring increased discrimination ratio.  相似文献   
993.
We propose a high optical efficiency three‐dimensional (3D)/two‐dimensional (2D) convertible integral imaging display by using a pinhole array on a reflective polarizer. The 3D mode is realized by adopting a pinhole array on a reflective polarizer to generate a point light source array. Three‐dimensional/2D convertible feature is realized by electrically controlling a polarization switcher. The reflective polarizer can reflect the light that has the orthogonal polarization direction with the reflective polarizer and transmit the light that has the same polarization direction with the reflective polarizer. The reflected light is recycled, so the optical efficiencies for both 3D and 2D modes are enhanced. In the practical experiments, the optical efficiencies of the proposed integral imaging display increase by 8.04 times and 1.65 times in 3D and 2D modes comparing with the conventional integral imaging display that has no light recycle, respectively.  相似文献   
994.
This paper studies the partial consensus problem for identical feedforward dynamic systems with input saturations. We construct two consensus protocols using the partial‐state information and full‐state information, respectively. Applying a change of coordinates, feedforward system is transformed into the block diagonal form. Then, by utilizing the bounded real lemma and small gain theorem, we solve the partial consensus problem, and the existence of each protocol is derived. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
995.
Display technologies are used in various industries. However, few studies on color vision testing using self‐luminous displays are reported. In this study, a screen‐based color vision test, termed the digital color vision test (DCVT), is developed on a color‐calibrated monitor. A control bar is adjusted by the observer to build just noticeable chromatic difference ellipses in CIE u′v′ chromaticity diagram, which indicate the capabilities of subjects' color visions. Ten color‐normal observers and 13 deutan observers participated in the psychophysical experiments. The observers also performed the other two typical diagnostic tests (D‐15 and anomaloscope). Results from the experiment using the adjustment psychophysical method for digital quantification of deutan color vision defects are presented. It is found that the diagnosis accuracy of the DCVT is approximately equivalent to those of D‐15 and anomaloscope tests.  相似文献   
996.
Chatter is an unstable nonlinear dynamical phenomenon often encountered in machining operations because of the self‐excitation mechanism, which may lead to overcut or rapid tool wear, and hence, greatly influence the surface quality and productivity in milling operations. Recent years have witnessed an increasing industrial demand of high quality and high efficiency machining. This paper hereby develops a constrained active adaptive control method to mitigate the chatter dynamics with input saturations. To guarantee the feasibility of the proposed approach, moderate stable conditions of the closed‐loop system are afterwards derived by using the LaSalle–Yoshizawa theorem as well. Finally, numerical simulations are conducted to show the substantially enlarged stable region in the Lobe Diagram. Thus, the method can be expected to improve the efficiency of milling processes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
997.
The current landscape of communication technologies is characterized by a wide variety of choices. As each medium provides different affordances, each may occupy a different niche and be used in different relationships. Drawing on the theory of the niche, we did a meta‐analysis involving 27 effect sizes from 22 independent samples to test the correlation between media selection/use and friendship closeness. Results showed that the 5 communication channels filled 2 different friendship closeness niches. Mobile phone calls and texting had stronger positive correlations with friendship closeness than instant messaging, social network sites, and online gaming. Culture, but not gender, moderated some of these correlations: Friendship closeness had a stronger positive association with SNS use and online gaming in collectivist cultures.  相似文献   
998.
In this article, the design and test of both a K‐band dual‐mode bandpass filter (BPF) pair and a K‐band triple‐mode BPF are presented based on N‐mode temporal coupled‐mode theory (CMT). The expressions of transmission and reflection responses are analytically derived. All the parameters in the expressions have clear physical meanings and are easily optimized to reach the required filter performance. Aided by eigenmode simulations, concrete structures of the three integrated BPFs are designed and optimized to approach the calculated physical parameters. After the fabrications and measurements of the three BPFs, extended upper/lower stopband with high stopband rejections are achieved, and by increasing the number of resonant modes, improved frequency selectivity and better passband flatness are obtained. The analytical analysis well predicts the simulation and measurement results, which provides an efficient way for BPF designs. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:609–622, 2016.  相似文献   
999.
A microstrip‐fed conventional annular ring slot (ARS) antenna with linear polarization (LP) is initially studied. To generate two orthogonal degenerate modes for circular polarization (CP) radiations, two identical meandering perturbation slots (MPS) are symmetrically loaded into the ARS. By further incorporating a PIN diode switch across each MPS, the proposed antenna can switch between left‐hand CP (LHCP), right‐hand CP (RHCP), and LP. All three polarizations have shown good impedance bandwidth and broad CP bandwidth that can satisfy the wireless local area network (WLAN) 2.4‐GHz operating band (2400–2480 MHz). Furthermore, desirable gains of 1.8–2.0 dBi and 2.40–2.84 dBic are also exhibited at LP and LHCP/RHCP, respectively. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:110–120, 2016.  相似文献   
1000.
The purpose of this study was to investigate the relationships among job characteristics, organizational commitment, and job satisfaction of foreign workers in Taiwan. Overall, 440 Thailand foreign workers were recruited and structural equation modeling was used to test the research hypotheses. The results of this study supported all proposed hypotheses. Job characteristics had a positive effect on job satisfaction of foreign workers. However, the results showed an indirect effect of job characteristics on job satisfaction via organizational commitment. Moreover, the findings suggested that job autonomy is better compared to other job characteristics. This study contributes to the existing literature by stressing the importance of such relationships in the cross‐cultural management enterprises, particularly those concerning foreign workers.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号