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   34571篇
  免费   2419篇
  国内免费   1276篇
电工技术   1649篇
综合类   2000篇
化学工业   6114篇
金属工艺   1632篇
机械仪表   1975篇
建筑科学   3097篇
矿业工程   651篇
能源动力   1107篇
轻工业   2075篇
水利工程   518篇
石油天然气   1878篇
武器工业   219篇
无线电   4158篇
一般工业技术   4441篇
冶金工业   1861篇
原子能技术   477篇
自动化技术   4414篇
  2024年   134篇
  2023年   481篇
  2022年   844篇
  2021年   1172篇
  2020年   888篇
  2019年   761篇
  2018年   839篇
  2017年   998篇
  2016年   897篇
  2015年   1164篇
  2014年   1499篇
  2013年   1912篇
  2012年   2027篇
  2011年   2193篇
  2010年   1833篇
  2009年   1836篇
  2008年   1785篇
  2007年   1764篇
  2006年   1833篇
  2005年   1645篇
  2004年   1145篇
  2003年   1010篇
  2002年   1008篇
  2001年   856篇
  2000年   941篇
  1999年   1011篇
  1998年   982篇
  1997年   807篇
  1996年   796篇
  1995年   651篇
  1994年   514篇
  1993年   466篇
  1992年   319篇
  1991年   238篇
  1990年   243篇
  1989年   166篇
  1988年   138篇
  1987年   95篇
  1986年   79篇
  1985年   57篇
  1984年   48篇
  1983年   34篇
  1982年   32篇
  1981年   20篇
  1980年   19篇
  1979年   10篇
  1977年   10篇
  1976年   12篇
  1973年   8篇
  1970年   7篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
82.
Batch Nearest Neighbor Search for Video Retrieval   总被引:2,自引:0,他引:2  
To retrieve similar videos to a query clip from a large database, each video is often represented by a sequence of high- dimensional feature vectors. Typically, given a query video containing m feature vectors, an independent nearest neighbor (NN) search for each feature vector is often first performed. After completing all the NN searches, an overall similarity is then computed, i.e., a single content-based video retrieval usually involves m individual NN searches. Since normally nearby feature vectors in a video are similar, a large number of expensive random disk accesses are expected to repeatedly occur, which crucially affects the overall query performance. Batch nearest neighbor (BNN) search is stated as a batch operation that performs a number of individual NN searches. This paper presents a novel approach towards efficient high-dimensional BNN search called dynamic query ordering (DQO) for advanced optimizations of both I/O and CPU costs. Observing the overlapped candidates (or search space) of a pervious query may help to further reduce the candidate sets of subsequent queries, DQO aims at progressively finding a query order such that the common candidates among queries are fully utilized to maximally reduce the total number of candidates. Modelling the candidate set relationship of queries by a candidate overlapping graph (COG), DQO iteratively selects the next query to be executed based on its estimated pruning power to the rest of queries with the dynamically updated COG. Extensive experiments are conducted on real video datasets and show the significance of our BNN query processing strategy.  相似文献   
83.
A major factor contributing to the total measuring error of coordinate measuring machines (CMMs) is the performance of the probing sub-system. Probing test methods are typically used to detect errors due to the probing sub-system. The probe performance evaluation method specified in the ANSI B89 standard is investigated in this paper. The sampling plan associated in the probe performance evaluation was tested by using experimental probing data from a CMM. Research findings indicate that the performance of touch trigger probes is overestimated due to a systematic bias in the vertical direction of the best-fit reference ball center in the probe performance test. A two-latitude sampling plan synthesis method based on a pretravel model for touch trigger probes is proposed in this paper. The proposed method can be used to accurately identify the reference ball center in the performance test of touch trigger probes.  相似文献   
84.
Tensile tests show that ferroelastic loops always occur at 100–150 K, 200–250 K and room temperature in the Y1–xPrxBa2Cu3Oy samples withx=0 and 0.1 for whichT c is 92 K and 82.5 K respectively, and the shape memory effect is always observed in the compact sample near 130 K, just similar to that of thermal elastic martensitic alloys. The loss fraction (W/W) which is proportional to the area of ferroelastic loop as a function of temperature shows that there always exist static hysteresis (W/W) peaks at 130 K and 110 K which are attributed to the phaselike transition (PLT) characterized by the jump of lattice parameters. No ferroelastic loops and shape memory effect are observed in the range of 100 K to 150 K for the lowerT c samples withx=0.3, 0.4 and 0.6.  相似文献   
85.
水和甲醇存在下MAMS的消失反应动力学研究   总被引:1,自引:0,他引:1  
通过实验研究了甲基丙烯酰胺硫酸盐(MAMS)与甲醇、水进行反应的动力学,并对该反应的机理进行了探讨。  相似文献   
86.
87.
In this paper, Adjusted Rand Index (ARI) is generalized to two new measures based on matrix comparison: (i) Adjusted Rand Index between a similarity matrix and a cluster partition (ARImp), to evaluate the consistency of a set of clustering solutions with their corresponding consensus matrix in a cluster ensemble, and (ii) Adjusted Rand Index between similarity matrices (ARImm), to evaluate the consistency between two similarity matrices. Desirable properties of ARI are preserved in the two new measures, and new properties are discussed. These properties include: (i) detection of uncorrelatedness; (ii) computation of ARImp/ARImm in a distributed environment; and (iii) characterization of the degree of uncertainty of a consensus matrix. All of these properties are investigated from both the perspectives of theoretical analysis and experimental validation. We have also performed a number of experiments to show the usefulness and effectiveness of the two proposed measures in practical applications.  相似文献   
88.
89.
90.
Lijuan Shen  Jitao Sun 《Automatica》2012,48(10):2705-2709
This paper studies the approximate controllability of stochastic impulsive functional system with infinite delay in abstract space. By using the contraction mapping principle, some sufficient conditions are given with no compactness condition imposed on the semigroup generated by the linear part of the system. Then with the help of the Nussbaum fixed point theorem, the restriction of the combination of system parameters is dropped. Finally, an example is shown to illustrate our 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