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   57561篇
  免费   4803篇
  国内免费   2542篇
电工技术   3574篇
技术理论   3篇
综合类   3964篇
化学工业   9590篇
金属工艺   3327篇
机械仪表   3840篇
建筑科学   4521篇
矿业工程   1805篇
能源动力   1678篇
轻工业   3736篇
水利工程   1033篇
石油天然气   3871篇
武器工业   525篇
无线电   6228篇
一般工业技术   6900篇
冶金工业   2552篇
原子能技术   591篇
自动化技术   7168篇
  2024年   206篇
  2023年   996篇
  2022年   1724篇
  2021年   2381篇
  2020年   1902篇
  2019年   1529篇
  2018年   1703篇
  2017年   1876篇
  2016年   1629篇
  2015年   2262篇
  2014年   2939篇
  2013年   3283篇
  2012年   3597篇
  2011年   4051篇
  2010年   3511篇
  2009年   3283篇
  2008年   3223篇
  2007年   2981篇
  2006年   3079篇
  2005年   2581篇
  2004年   1844篇
  2003年   1636篇
  2002年   1612篇
  2001年   1391篇
  2000年   1296篇
  1999年   1526篇
  1998年   1282篇
  1997年   1115篇
  1996年   1000篇
  1995年   828篇
  1994年   663篇
  1993年   479篇
  1992年   416篇
  1991年   263篇
  1990年   211篇
  1989年   164篇
  1988年   119篇
  1987年   79篇
  1986年   61篇
  1985年   42篇
  1984年   33篇
  1983年   27篇
  1982年   29篇
  1981年   17篇
  1980年   16篇
  1979年   6篇
  1940年   3篇
  1933年   1篇
  1929年   1篇
  1928年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Message forwarding (e.g.,retweeting on Twitter.com) is one of the most popular functions in many existing microblogs,and a large number of users participate in the propagation of information,for any given messages.While this large number can generate notable diversity and not all users have the same ability to diffuse the messages,this also makes it challenging to find the true users with higher spreadability,those generally rated as interesting and authoritative to diffuse the messages.In this paper,a novel method called SpreadRank is proposed to measure the spreadability of users in microblogs,considering both the time interval of retweets and the location of users in information cascades.Experiments were conducted on a real dataset from Twitter containing about 0.26 million users and 10 million tweets,and the results showed that our method is consistently better than the PageRank method with the network of retweets and the method of retweetNum which measures the spreadability according to the number of retweets.Moreover,we find that a user with more tweets or followers does not always have stronger spreadability in microblogs.  相似文献   
992.
The heat treatment of Nb(3)Sn coil with the glass fabric insulation is one of the key and critical processes for the outsert solenoids of the 40 T hybrid magnet, which could be wound with cable-in-conduit conductors using the insulation-wind-and-react technique. The manufacturing of the large vertical type vacuum/Ar atmosphere-protection heat treatment system has been completed and recently installed in the High Magnetic Filed Laboratory, Chinese Academy of Sciences. The heat treatment system composed mainly the furnace, the purging gas supply system, the control system, the gas impurities monitoring system, and so on. At present, the regulation and testing of the heat treatment system has been successfully finished, and all of technical parameters meet or exceed specifications.  相似文献   
993.
This paper proposes an optimal design method based on dynamic isotropy conditions of a generalized natural frequency matrix in task space for a standard Gough-Stewart parallel manipulator (GSPM). Firstly, the dynamic isotropy conditions are discussed and presented. Next, it is proved that standard GSPMs lie on a circular hyperboloid of one sheet. Further, we present a method to use a circular hyperboloid to construct 3-3-, 6-3- and 6-6-type standard GSPMs. Moreover, such novel definition is used to examine various dynamic isotropy conditions as functions of the coefficients of a hyperboloid. An optimal design method is also proposed accordingly. Finally, a numerical example is given to illustrate the design procedures. The results are very close to the complete dynamic isotropy.  相似文献   
994.
本文分析了计算机实验教学现状,并提出了若干计算机实验教学改革的建议,以期提高计算机实验教学的质量,全面提高学生的计算机应用能力.  相似文献   
995.
在网络行为分析与控制系统中,传统的关系数据库在异构数据、海量日志的管理上难以胜任。NoSQL非关系型数据库的出现,对于解决面向文档的超大规模和高并发的问题提供了卓有成效的方案。本文在研究非关系数据库的基础上,着重分析MongoDB的特点和优势,通过性能测试,提出将MongoDB数据库应用于网络行为分析与控制系统,有效提高了大规模日志数据在网络行为分析与控制系统中的存储效率。  相似文献   
996.
Adaptive detection of range-spread targets without secondary data is addressed in a multichannel autoregressive Gaussian disturbance with unknown space–time covariance matrix, by utilizing the Rao test. The proposed Rao test without secondary data is theoretically proved to be asymptotically (large-sample in the number of temporal observations) constant false alarm rate with respect to unknown space–time covariance matrix, thanks to an asymptotic equivalence between the Rao test and the generalized likelihood ratio test. Moreover, the performance loss due to no secondary data can be remedied by appropriately increasing the temporal dimension. The performance assessment conducted by Monte Carlo simulation, also in comparison with the existing detector without secondary data, confirms the effectiveness of the proposed detectors.  相似文献   
997.
We consider a class of stochastic Nash equilibrium problems (SNEP). Under some mild conditions, we reformulate the SNEP as a stochastic mixed complementarity problem (SMCP). We apply the well-known sample average approximation (SAA) method to solve the SMCP. We further introduce a semismooth Newton method to solve the SAA problems. The comprehensive convergence analysis is given as well. In addition, we demonstrate the proposed approach on a stochastic Nash equilibrium model in the wholesale gas–oil markets.  相似文献   
998.
Packet delay (either one-way time or round-trip time) is a very important metric for measuring the performance of networks in a highly dynamic environment such as the Internet. Many network applications are also sensitive to packet delay or delay variation for ensuring an acceptable level of quality in providing network-based services such as VoIP, multimedia streaming, etc. A very important property of packet delay is that it is very dynamic and therefore should be measured frequently with measurement results being updated on a timely basis. Measurement of packet delay has thus generated a great deal of interest in the past years and a lot of research has been performed in the development of measurement architecture as well as specific measurement techniques. However, how to reduce network overhead resulting from measurement while achieving a reasonable level of accuracy still remains a challenge. In this paper, we propose to use delay estimation as an alternative to delay measurement for reducing measurement overhead and, in particular, examine the level of accuracy that delay estimation can achieve. With delay estimation, measurement nodes can be dynamically selected and activated and other nodes can share measurement results by performing delay estimation, thus reducing measurement overhead while supporting the dynamic requirement for delay measurement. Consequently, while measurement overhead can be reduced by activating only a subset of network nodes to perform actual measurement, desired accuracy can be achieved by exploring the correlation between delays as well as by sharing measurement results to do delay estimation based on such a correlation. We illustrate how packet delays of network nodes can correlate to each other based on topological properties and show how delays can be estimated based on such a correlation to meet accuracy requirements, which would make delay measurement in the Internet highly dynamic and adaptable to the accuracy requirements and measurement results highly reliable. We also show how delay estimation can be applied by presenting three application scenarios as well as an example to demonstrate the usefulness and effectiveness of delay estimation in the measurement of packet delays.  相似文献   
999.
This paper presents an improved Euclidean Ricci flow method for spherical parameterization. We subsequently invent a scale space processing built upon Ricci energy to extract robust surface features for accurate surface registration. Since our method is based on the proposed Euclidean Ricci flow, it inherits the properties of Ricci flow such as conformality, robustness and intrinsicalness, facilitating efficient and effective surface mapping. Compared with other surface registration methods using curvature or sulci pattern, our method demonstrates a significant improvement for surface registration. In addition, Ricci energy can capture local differences for surface analysis as shown in the experiments and applications.  相似文献   
1000.
Social media provide an online platform for enterprises to engage existing customers and attract new customers. Although social media can be easily set up at no cost, however, due to limited human and financial resources, many small businesses find it challenging to compete against large enterprises in social media use. While more and more small businesses have jumped on the bandwagon of social media in recent years, few studies investigated the social media strategies that can help small businesses to survive and even thrive against large competitors in the social media arena. Therefore, we studied 32 small pizzerias in a mid-size U.S. city in terms of their social media use for business. Our study found that small pizzerias emphasizing social media use on community relations and social responsibility tend to be more successful in attracting and engaging local customers. This study also sheds light on both effective strategies and successful practices of social media use by small pizzerias. The insights and recommendations identified from this study can help small businesses to enhance their social media competitiveness against large enterprises.  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