全文获取类型
收费全文 | 16984篇 |
免费 | 2253篇 |
国内免费 | 1531篇 |
专业分类
电工技术 | 1793篇 |
综合类 | 1702篇 |
化学工业 | 628篇 |
金属工艺 | 440篇 |
机械仪表 | 1530篇 |
建筑科学 | 742篇 |
矿业工程 | 284篇 |
能源动力 | 427篇 |
轻工业 | 707篇 |
水利工程 | 199篇 |
石油天然气 | 713篇 |
武器工业 | 300篇 |
无线电 | 5323篇 |
一般工业技术 | 2224篇 |
冶金工业 | 229篇 |
原子能技术 | 284篇 |
自动化技术 | 3243篇 |
出版年
2024年 | 101篇 |
2023年 | 236篇 |
2022年 | 361篇 |
2021年 | 470篇 |
2020年 | 520篇 |
2019年 | 482篇 |
2018年 | 455篇 |
2017年 | 615篇 |
2016年 | 674篇 |
2015年 | 744篇 |
2014年 | 1134篇 |
2013年 | 1154篇 |
2012年 | 1345篇 |
2011年 | 1409篇 |
2010年 | 1132篇 |
2009年 | 1175篇 |
2008年 | 1018篇 |
2007年 | 1269篇 |
2006年 | 1167篇 |
2005年 | 906篇 |
2004年 | 759篇 |
2003年 | 738篇 |
2002年 | 522篇 |
2001年 | 445篇 |
2000年 | 375篇 |
1999年 | 293篇 |
1998年 | 194篇 |
1997年 | 225篇 |
1996年 | 136篇 |
1995年 | 168篇 |
1994年 | 100篇 |
1993年 | 91篇 |
1992年 | 64篇 |
1991年 | 64篇 |
1990年 | 51篇 |
1989年 | 42篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 6篇 |
1962年 | 2篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Conventional ultra‐wideband low‐noise amplifiers require a flat gain over the entire 3.1–10.6 GHz bandwidth, which severely restraints the trade‐off spaces in low noise amplifier design. This article proposes a relaxed gain‐flatness requirement based on system level investigations. Considering the wireless transceiver front‐end with antenna and propagation channel, the unflat‐gain low‐noise amplifier with an incremental gain characteristic does not degrade the performance of overall system. As an alternative to its flat‐gain counterpart, the proposed unflat gain requirement tolerates gain ripple as large as 10 dB, which greatly eases the design challenges to low‐noise amplifier for ultra‐wideband wireless receivers. Two low‐noise amplifier examples are given to demonstrate the feasibility and design flexibility under the proposed gain‐flatness requirement. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. 相似文献
993.
A new fast adaptive high-performance filter (FAHPF) has been proposed to remove salt-and-pepper noise in images. ‘Maximize the speed without compromising denoising performance’ is the fundamental intention to build up the FAHPF algorithm. Among diverse phases of filtering employed in the FAHPF, overlapping medians (OM) is our newly proposed frame-based filtering concept which is the basis for speed of FAHPF and running averages embedded with OM is an idea behind excellent denoising performance of FAHPF at the same pace. Simulation experiments have been conducted and denoising results of FAHPF has been investigated against very recently developed filtering methods. It is proved that the FAHPF excellently outperforms many of state-of-the-art filters considered for comparison, in terms of peak signal to noise ratio, structural similarity index, and visual representation and requires the extremely shortest execution time among all, which could make it as a real time filter. 相似文献
994.
There is little information about occupational noise exposure of fishermen working on small and medium-scale fishing vessels, mainly because of the difficulty of conducting noise exposure surveillance in such occupations. The objective of the current study was to evaluate the exposure of this group of workers to occupational noise using a combined measurement and questionnaire approach. Sound pressure levels were measured aboard 24 fishing vessels at all working or resting locations and during speeding and slow-down moods of the engine. The average existence times of the crew at such locations were collected using a questionnaire. The average daily noise exposure levels (LEP,d,8h) for engine mechanics in all vessel types (91.2–94.3 dBA) and the tiller operators in gill/trammel and purse seining vessels (84.7–88.4 dBA) exceeded the NIOSH recommended exposure limit of 85 dBA. Other crew members were found to be exposed, on average, to daily noise exposure levels slightly lower than the recommended one (81.6–83.5 dBA). However, direct personal dosimetry for five crew members revealed daily noise exposure levels 1.1–5.1 dBA higher than the calculated averages, which might be attributed, partly, to sources of uncertainty. The results of this study suggest that small and medium-scale vessels fishermen are at high risk of NIHL, calling for development and enforcement of suitable interventions for hearing protection of the workforce of this sector. 相似文献
995.
996.
997.
为了实现对车牌区域的精确定位,提出了一种基于三次定位过程的车牌定位算法,综合改进了数学形态学和纹理分析等方法.对自然环境下摄像头采集的车辆图像进行预处理后,使用像素统计法对车牌进行粗略定位,使用纹理分析法去除车牌上下边框和干扰,使用阈值法去除车牌左右边框和干扰,得到精确的车牌区域.另外还对图像的预处理进行简化,保证实时性要求.实验结果表明,改进后的算法能够对车牌进行实时、精确定位,满足了系统的要求. 相似文献
998.
This paper investigates the observer-based H∞ fuzzy control problem for a class of discrete-time fuzzy mixed delay systems with random communication packet losses and multiplicative noises, where the mixed delays comprise both discrete time-varying and distributed delays. The random packet losses are described by a Bernoulli distributed white sequence that obeys a conditional probability distribution, and the multiplicative disturbances are in the form of a scalar Gaussian white noise with unit variance. In the presence of mixed delays, random packet losses and multiplicative noises, sufficient conditions for the existence of an observer-based fuzzy feedback controller are derived, such that the closed-loop control system is asymptotically mean-square stable and preserves a guaranteed H∞ performance. Then a linear matrix inequality approach for designing such an observer-based H∞ fuzzy controller is presented. Finally, a numerical example is provided to illustrate the effectiveness of the developed theoretical results. 相似文献
999.
‘Model-free control’and the corresponding ‘intelligent’ PID controllers (iPIDs), which already had many successful concrete applications, are presented here for the first time in an unified manner, where the new advances are taken into account. The basics of model-free control is now employing some old functional analysis and some elementary differential algebra. The estimation techniques become quite straightforward via a recent online parameter identification approach. The importance of iPIs and especially of iPs is deduced from the presence of friction. The strange industrial ubiquity of classic PIDs and the great difficulty for tuning them in complex situations is deduced, via an elementary sampling, from their connections with iPIDs. Several numerical simulations are presented which include some infinite-dimensional systems. They demonstrate not only the power of our intelligent controllers but also the great simplicity for tuning them. 相似文献
1000.
Using the delta operator, the strengthened discrete-time optimal projection equations for optimal reduced-order compensation of systems with white stochastic parameters are formulated in the delta domain. The delta domain unifies discrete time and continuous time. Moreover, when formulated in this domain, the efficiency and numerical conditioning of algorithms improves when the sampling rate is high. Exploiting the unification, important theoretical results, algorithms and compensatability tests concerning finite and infinite horizon optimal compensation of systems with white stochastic parameters are carried over from discrete time to continuous time. Among others, we consider the finite-horizon time-varying compensation problem for systems with white stochastic parameters and the property mean-square compensatability (ms-compensatability) that determines whether a system with white stochastic parameters can be stabilised by means of a compensator. In continuous time, both of these appear to be new. This also holds for the associated numerical algorithms and tests to verify ms-compensatability. They are illustrated with three numerical examples that reveal several interesting theoretical and numerical issues. A fourth example illustrates the improvement of both the efficiency and numerical conditioning of the algorithms. This is of vital practical importance for digital control system design when the sampling rate is high. 相似文献