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   24268篇
  免费   1570篇
  国内免费   62篇
电工技术   356篇
综合类   30篇
化学工业   5686篇
金属工艺   960篇
机械仪表   1432篇
建筑科学   474篇
矿业工程   17篇
能源动力   983篇
轻工业   2136篇
水利工程   102篇
石油天然气   19篇
无线电   4012篇
一般工业技术   5151篇
冶金工业   1615篇
原子能技术   331篇
自动化技术   2596篇
  2024年   34篇
  2023年   305篇
  2022年   440篇
  2021年   754篇
  2020年   544篇
  2019年   569篇
  2018年   794篇
  2017年   747篇
  2016年   869篇
  2015年   725篇
  2014年   1093篇
  2013年   1554篇
  2012年   1641篇
  2011年   1994篇
  2010年   1454篇
  2009年   1485篇
  2008年   1347篇
  2007年   1032篇
  2006年   907篇
  2005年   779篇
  2004年   720篇
  2003年   671篇
  2002年   661篇
  2001年   564篇
  2000年   483篇
  1999年   473篇
  1998年   746篇
  1997年   450篇
  1996年   434篇
  1995年   293篇
  1994年   185篇
  1993年   162篇
  1992年   128篇
  1991年   119篇
  1990年   80篇
  1989年   102篇
  1988年   82篇
  1987年   67篇
  1986年   60篇
  1985年   50篇
  1984年   40篇
  1983年   30篇
  1982年   32篇
  1981年   27篇
  1980年   33篇
  1979年   14篇
  1977年   23篇
  1976年   34篇
  1975年   17篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A. D. Baddeley, N. Thomson, and M. Buchanan (1975) suggested that articulatory rehearsal rate determines the amount of verbal material that can be maintained in working memory. In the current study, 12 children with spastic diplegic cerebral palsy (SDCP) and 38 normal children were tested on measures of articulation rate and memory span for 1-, 2-, and 3-syllable words. Across all conditions, articulation rate for the SDCP group was significantly slower than for the normal group; nonetheless, memory span was equivalent for both groups. This finding implies that covert rehearsal proceeded normally for the SDCP group, in spite of decrements in speech rate. Thus, the relationship between overt and covert rehearsal rates differs for children with SDCP compared with normal children. Findings from the current study further suggest that normal speech rates are not necessary for development of normal covert rehearsal rates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
103.
A new controller for a digital audio amplifier with bit stream input is proposed. The proposed controller has excellent features such as wide error correction range and no limitation on the modulation index. The controller is implemented in the half-bridge class-D amplifier and performance is verified through experiments.  相似文献   
104.
介绍了高频等参数感应的基本原理。以胜利油田比较典型的 3口井为例 ,详细分析了高频感应资料在划分薄夹层、确定储层流体饱和类型、评价储层电阻率空间分布等方面的应用。研究结果表明 ,高频感应具有极高的纵向分辨率和较好的径向探测特性 ,能够准确计算地层真电阻率、侵入带电阻率及侵入半径 ,通过与常规感应及薄层测井资料的对比 ,论证了高频等参数感应在测井技术应用上的优越性  相似文献   
105.
Park  Ken T.  Kong  Jie 《Topics in Catalysis》2002,18(3-4):175-181
The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS2, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H2, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct observation of electron transfer from alkali metals to a model single crystal MoS2 and the capture of the supra-valence electrons in the subsequent oxidation reactions.  相似文献   
106.
107.
This paper deals with the pricing and investment decision problem of multi-modal transportation systems in which the congestion is a significant factor in the assessment of system costs. This study approaches this congestion pricing problem with a number of social welfare maximization problems, all of which have the identical structure except financial constraints. One welfare maximization problem examined in this study yields the pricing and investment decision, which can attain the first-best social optimality for multi-modal transportation systems. Other welfare maximization problems show he second-best optimal solutions that can address two policy questions in transportation economics, namely, the cross-subsidy between competing modes and peak-period congestion charges on a single highway link. Received: February 2001/Accepted: December 2001 This work was supported in part by funds from BK21 Research Division of Seoul National University for Social Infrastructure and Construction Technology.  相似文献   
108.
 A recursive method based on the Kalman filtering is developed to solve inverse natural convection problems of estimating the unsteady nonuniform wall heat flux from temperature measurements in the flow. By employing the Karhunen–Loève Galerkin procedure that reduces the Boussinesq equation to a small set of ordinary differential equations, the computational difficulties associated with the Kalman filtering for the partial differential equations are overcome. The present method is assessed through several numerical experiments, and is found to yield satisfactory results. Received 20 January 2001 / Accepted 31 May 2001  相似文献   
109.
110.
Choung  Jae-Yong  Min  Hong-Ghi  Park  Myeong-Cheol 《Scientometrics》2003,58(1):115-128
In recent years, the topic of knowledge production has been widely investigated in the advanced countries. However, the process by which knowledge is produced in the developing countries has not been fully explored or characterized. In Korea, the science and engineering fields strongly reflect systems of knowledge production in the universities and demonstrate the dynamics of systems of innovation for knowledge production. Through using a case study including data for knowledge production, in the field of information and telecommunication, the following general trends were observed. Firstly, there has been a trend towards increasing the capabilities for knowledge production, via domestic and foreign collaboration. Secondly, there has been an increasing trend towards the diversification of knowledge sources such as university-industry, and university-public research institutes. Finally, the establishment of a nation's knowledge base is influenced by governmental research and development policies. This revised version was published online in August 2006 with corrections to the Cover Date.  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