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   3972篇
  免费   547篇
  国内免费   3篇
电工技术   14篇
综合类   1篇
化学工业   1148篇
金属工艺   35篇
机械仪表   72篇
建筑科学   147篇
矿业工程   7篇
能源动力   60篇
轻工业   1579篇
水利工程   40篇
石油天然气   27篇
无线电   134篇
一般工业技术   599篇
冶金工业   262篇
原子能技术   3篇
自动化技术   394篇
  2024年   12篇
  2023年   43篇
  2022年   61篇
  2021年   125篇
  2020年   134篇
  2019年   137篇
  2018年   238篇
  2017年   224篇
  2016年   250篇
  2015年   230篇
  2014年   234篇
  2013年   440篇
  2012年   349篇
  2011年   344篇
  2010年   225篇
  2009年   177篇
  2008年   175篇
  2007年   209篇
  2006年   117篇
  2005年   117篇
  2004年   92篇
  2003年   103篇
  2002年   87篇
  2001年   32篇
  2000年   21篇
  1999年   27篇
  1998年   65篇
  1997年   60篇
  1996年   36篇
  1995年   32篇
  1994年   18篇
  1993年   17篇
  1992年   8篇
  1991年   5篇
  1990年   6篇
  1989年   7篇
  1988年   5篇
  1987年   2篇
  1985年   3篇
  1984年   5篇
  1982年   2篇
  1981年   7篇
  1980年   7篇
  1979年   2篇
  1978年   2篇
  1977年   6篇
  1976年   10篇
  1974年   7篇
  1969年   1篇
  1968年   1篇
排序方式: 共有4522条查询结果,搜索用时 937 毫秒
61.
Beacon-Less Geographic Routing in Real Wireless Sensor Networks   总被引:2,自引:1,他引:1       下载免费PDF全文
Geographic Routing(GR)algorithms require nodes to periodically transmit HELLO messages to allow neigh- bors to know their positions(beaconing mechanism).Beacon-less routing algorithms have recently been proposed to reduce the control overheads due to these messages.However,existing beacon-less algorithms have not considered realistic physical layers.Therefore,those algorithms cannot work properly in realistic scenarios.In this paper we present a new beacon- less routing protocol called BOSS.Its design is based on the conclusions of our open-field experiments using Tmote-sky sensors.BOSS is adapted to error-prone networks and incorporates a new mechanism to reduce collisions and duplicate messages produced during the selection of the next forwarder node.We compare BOSS with Beacon-Less Routing(BLR) and Contention-Based Forwarding(CBF)algorithms through extensive simulations.The results show that our scheme is able to achieve almost perfect packet delivery ratio(like BLR)while having a low bandwidth consumption(even lower than CBF).Additionally,we carried out an empirical evaluation in a real testbed that shows the correctness of our simulation results.  相似文献   
62.
Recently, multi-objective evolutionary algorithms have been applied to improve the difficult tradeoff between interpretability and accuracy of fuzzy rule-based systems. It is known that both requirements are usually contradictory, however, these kinds of algorithms can obtain a set of solutions with different trade-offs. This contribution analyzes different application alternatives in order to attain the desired accuracy/interpr-etability balance by maintaining the improved accuracy that a tuning of membership functions could give but trying to obtain more compact models. In this way, we propose the use of multi-objective evolutionary algorithms as a tool to get almost one improved solution with respect to a classic single objective approach (a solution that could dominate the one obtained by such algorithm in terms of the system error and number of rules). To do that, this work presents and analyzes the application of six different multi-objective evolutionary algorithms to obtain simpler and still accurate linguistic fuzzy models by performing rule selection and a tuning of the membership functions. The results on two different scenarios show that the use of expert knowledge in the algorithm design process significantly improves the search ability of these algorithms and that they are able to improve both objectives together, obtaining more accurate and at the same time simpler models with respect to the single objective based approach.
María José Gacto (Corresponding author)Email:
Rafael AlcaláEmail:
Francisco HerreraEmail:
  相似文献   
63.
International Journal of Control, Automation and Systems - This article presents a fuzzy adaptive control law (FACL) designed for tracking the trajectory of a low-scale unmanned aerial vehicle...  相似文献   
64.

The permanent availability and relative obscurity of blockchains is the perfect ground for using them for malicious purposes. However, the use of blockchains by malwares has not been characterized yet. This paper analyses the current state of the art in this area. One of the lessons learned is that covert communications for malware have received little attention. To foster further defence-oriented research, a novel mechanism (dubbed Smart-Zephyrus) is built leveraging smart contracts written in Solidity. Our results show that it is possible to hide 4 Kb of secret in 41 s. While being expensive (around USD 1.82 per bit), the provided stealthiness might be worth the price for attackers.

  相似文献   
65.
Appropriate plant material at processing and film packaging selection has a strong influence on product quality preservation. This is the first report studying the feasibility for minimal processing of four zucchini cultivars at two maturity stages, immature (MS1) and mature, stored at 6 °C during 10 days under different packaging conditions. The treatments consisted a 4 × 2 × 2 × 3 factorial combination of variety, maturity at processing, film packaging and storage time, including correlation studies between quality parameters. Negative effect on final quality after processing at MS1 was observed as a result of a higher respiration rate (between 15.91 and 20.12% than at mature), CO2 production and soluble solid consumption contributing to loss of firmness, slice discolouration and less overall quality. After 10 days under 25 µm film, cv. ‘Cronos’ showed the highest values in total chlorophylls (9.03 mg/100 g FW), while slices at MS1 suffered a noticeable oxidative stress increasing the total phenolic content (cv. ‘Parador’ > ‘Amalthée’ > ‘Cronos’ > ‘Cassiope’). At the end of storage, the highest vitamin C content was observed in trays sealed with 25 µm film (more evident in cv. ‘Cronos’ at MS1). In conclusion, processing more mature zucchini and 25 µm film packaging were the most effective combination for preserving quality. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
66.
67.
In this work we present a general (mono and multiobjective) optimization framework for the technological improvement of biochemical systems. The starting point of the method is a mathematical model in ordinary differential equations (ODEs) of the investigated system, based on qualitative biological knowledge and quantitative experimental data. In the method we take advantage of the special structural features of a family of ODEs called power-law models to reduce the computational complexity of the optimization program. In this way, the genetic manipulation of a biochemical system to meet a certain biotechnological goal can be expressed as an optimization program with some desired properties such as linearity or convexity.The general method of optimization is presented and discussed in its linear and geometric programming versions. We furthermore illustrate the use of the method by several real case studies. We conclude that the technological improvement of microorganisms can be afforded using the combination of mathematical modelling and optimization. The systematic nature of this approach facilitates the redesign of biochemical systems and makes this a predictive exercise rather than a trial-and-error procedure.  相似文献   
68.
69.
The formalization of engineering processes is necessary for guaranteeing the quality and cost of the products involved. Agent-oriented engineering has already proposed development processes that still need to be further formalized to be applicable by non-researchers. This paper proposes a technique to instantiate processes for specific agent-oriented methodologies. This technique is based on three orthogonal views that are respectively related with lifecycles, disciplines and guidances. In addition, processes are modeled with a tool, which is automatically generated from a process metamodel inspired by the software & systems process engineering metamodel. Accordingly, engineers can choose the methodology–process pair best-suited for the characteristics of their project. The paper illustrates the approach based on the unified development process and the scrum process for the INGENIAS methodology and compares the results with other existing alternatives.  相似文献   
70.
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