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   1851篇
  免费   56篇
  国内免费   6篇
电工技术   33篇
综合类   1篇
化学工业   298篇
金属工艺   41篇
机械仪表   41篇
建筑科学   25篇
矿业工程   1篇
能源动力   76篇
轻工业   41篇
水利工程   4篇
石油天然气   35篇
无线电   453篇
一般工业技术   359篇
冶金工业   179篇
原子能技术   15篇
自动化技术   311篇
  2023年   13篇
  2022年   47篇
  2021年   40篇
  2020年   35篇
  2019年   33篇
  2018年   50篇
  2017年   48篇
  2016年   37篇
  2015年   52篇
  2014年   64篇
  2013年   136篇
  2012年   72篇
  2011年   64篇
  2010年   81篇
  2009年   55篇
  2008年   63篇
  2007年   56篇
  2006年   63篇
  2005年   54篇
  2004年   49篇
  2003年   46篇
  2002年   47篇
  2001年   29篇
  2000年   41篇
  1999年   36篇
  1998年   64篇
  1997年   52篇
  1996年   33篇
  1995年   41篇
  1994年   38篇
  1993年   38篇
  1992年   26篇
  1991年   29篇
  1990年   32篇
  1989年   27篇
  1988年   24篇
  1987年   20篇
  1986年   20篇
  1985年   23篇
  1984年   12篇
  1983年   9篇
  1982年   14篇
  1981年   8篇
  1980年   12篇
  1979年   11篇
  1978年   9篇
  1977年   9篇
  1976年   8篇
  1974年   12篇
  1973年   9篇
排序方式: 共有1913条查询结果,搜索用时 15 毫秒
1.
Water Resources Management - The present study investigates and evaluate the scope and potential of modern computing tools and techniques such as ensembled machine learning methods in estimating...  相似文献   
2.
Wireless Personal Communications - Traffic network is basically a “network of networks” consisting of mainly two types of networks: road network and a travel network. Due to drastic...  相似文献   
3.
Neural Computing and Applications - To obtain the optimal set of features in feature selection problems is the most challenging and prominent problem in machine learning. Very few human-related...  相似文献   
4.
Multimedia Tools and Applications - Emotions are spontaneous feelings that are accompanied by fluctuations in facial muscles, which leads to facial expressions. Categorization of these facial...  相似文献   
5.
Attribute Allocation and Retrieval Scheme for Large-Scale Sensor Networks   总被引:1,自引:0,他引:1  
Wireless sensor network is an emerging technology that enables remote monitoring of large geographical regions. In this paper, we address the problem of distributing attributes over such a large-scale sensor network so that the cost of data retrieval is minimized. The proposed scheme is a data-centric storage scheme where the attributes are distributed over the network depending on the correlations between them. The problem addressed here is similar to the Allocation Problem of distributed databases. In this paper, we have defined the Allocation Problem in the context of sensor networks and have proposed a scheme for finding a good distribution of attributes to the sensor network. We also propose an architecture for query processing given such a distribution of attributes. We analytically determine the conditions under which the proposed architecture is beneficial and present simulation results to demonstrate the same. To the best of our knowledge, this is the first attempt to determine an allocation of attributes over a sensor network based on the correlations between attributes.  相似文献   
6.
Why does it pay to be selfish in a MANET?   总被引:2,自引:0,他引:2  
Routing protocols for a mobile ad hoc network have assumed that all mobile nodes voluntarily participate in forwarding others' packets. This was a reasonable assumption because all MNs in a MANET belonged to a single authority. In the near future, however, a MANET may consist of MNs that belong to many different organizations since numerous civilian applications are expected to crop up. In this situation, some MNs may run independently and purposely decide not to forward packets so as to save their own energy. This could potentially lead to network partitioning and corresponding performance degradation. To minimize such situations in MANETs, many studies have explored the use of both the carrot and the stick approaches by having reputation-based, credit-payment, and game theory schemes. This article summarizes existing schemes, identifies their relative advantages, and projects future directions  相似文献   
7.
8.
A new finite-difference-based method for wide-angle beam propagation   总被引:1,自引:0,他引:1  
A novel split-step finite-difference method for wide-angle beam propagation is presented. The formulation allows solution of the second-order scalar wave equation without having to make the slowly varying envelope and one-way propagation approximations. The method is highly accurate and numerically efficient requiring only simple matrix multiplication for propagation.  相似文献   
9.
Exploring spatial datasets with histograms   总被引:2,自引:0,他引:2  
As online spatial datasets grow both in number and sophistication, it becomes increasingly difficult for users to decide whether a dataset is suitable for their tasks, especially when they do not have prior knowledge of the dataset. In this paper, we propose browsing as an effective and efficient way to explore the content of a spatial dataset. Browsing allows users to view the size of a result set before evaluating the query at the database, thereby avoiding zero-hit/mega-hit queries and saving time and resources. Although the underlying technique supporting browsing is similar to range query aggregation and selectivity estimation, spatial dataset browsing poses some unique challenges. In this paper, we identify a set of spatial relations that need to be supported in browsing applications, namely, the contains, contained and the overlap relations. We prove a lower bound on the storage required to answer queries about the contains relation accurately at a given resolution. We then present three storage-efficient approximation algorithms which we believe to be the first to estimate query results about these spatial relations. We evaluate these algorithms with both synthetic and real world datasets and show that they provide highly accurate estimates for datasets with various characteristics. Recommended by: Sunil Prabhakar Work supported by NSF grants IIS 02-23022 and CNF 04-23336. An earlier version of this paper appeared in the 17th International Conference on Data Engineering (ICDE 2001).  相似文献   
10.
Most of the previous treatments of semiconductor lasers subject to optical feedback from a phase-conjugate mirror (PCM) have assumed that the PCM responds instantaneously. Furthermore, the mechanism responsible for phase conjugation does not usually enter into the analysis. In this paper, we derive the time-dependent reflectivity of a PCM created through nondegenerate four-wave mixing in a Kerr-type nonlinear medium. The resulting laser dynamics are compared with the case of the ideal PCM, as a function of the external-cavity length, the PCM reflectivity, and the PCM interaction depth. The PCM with a significant interaction depth tends to suppress otherwise chaotic output and produces pulses whose repetition rate is tunable by varying PCM reflectivity. At high feedback levels, it stabilizes the laser output. We use the circle-map formalism to explain our numerical results  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