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   96829篇
  免费   18045篇
  国内免费   3206篇
电工技术   4013篇
技术理论   1篇
综合类   3996篇
化学工业   26426篇
金属工艺   3560篇
机械仪表   4438篇
建筑科学   5402篇
矿业工程   1342篇
能源动力   2342篇
轻工业   13158篇
水利工程   1446篇
石油天然气   2164篇
武器工业   471篇
无线电   13258篇
一般工业技术   18154篇
冶金工业   3907篇
原子能技术   727篇
自动化技术   13275篇
  2024年   321篇
  2023年   975篇
  2022年   1913篇
  2021年   2658篇
  2020年   3137篇
  2019年   4548篇
  2018年   4718篇
  2017年   5174篇
  2016年   5532篇
  2015年   6176篇
  2014年   6730篇
  2013年   8676篇
  2012年   6828篇
  2011年   7087篇
  2010年   6769篇
  2009年   6546篇
  2008年   6000篇
  2007年   5535篇
  2006年   4966篇
  2005年   4124篇
  2004年   3377篇
  2003年   2908篇
  2002年   2741篇
  2001年   2361篇
  2000年   2042篇
  1999年   1260篇
  1998年   891篇
  1997年   691篇
  1996年   492篇
  1995年   379篇
  1994年   354篇
  1993年   330篇
  1992年   232篇
  1991年   197篇
  1990年   162篇
  1989年   142篇
  1988年   101篇
  1987年   91篇
  1986年   86篇
  1985年   90篇
  1984年   80篇
  1983年   57篇
  1982年   59篇
  1981年   45篇
  1980年   49篇
  1979年   49篇
  1978年   42篇
  1977年   62篇
  1976年   91篇
  1975年   49篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
We define the very rich language of composed conditionals on a three‐valued logic and use this language as the communication tool between man and machine. Communication takes place for three reasons: knowledge acquisition, query, and response. Learning, thinking, and answering questions are of a pure information theoretical nature. The pivot of this knowledge processing concept is the amount of information (bit) we receive if a conditional becomes true. We follow an axiomatic approach to information theory rather than the classical probabilistic approach of Shannon; information comes first, and then comes probability. In the light of this philosophy, query and response experience new interpretations. Both, acquisition and response are realized by maximizing entropy and minimizing relative entropy, respectively. The iterative solution of these mathematical optimization problems gives new insights into the adaptation of prior knowledge to new information. Our expert system shell SPIRIT supports this kind of knowledge processing, which will be established by suitable examples. © 2003 Wiley Periodicals, Inc.  相似文献   
72.
Wood has long traditions as a building material, and is often used in construction elements, and as interior and exterior surfaces in the Nordic countries. In most applications, there are reaction to fire requirements to products used as surfaces, e.g. in escape routes and larger public spaces. Most wood products will therefore have to be treated with fire retardant (FR) agents to fulfil the strict requirements to properties connected to heat release and flame spread. Unfortunately, FR agents usually also increase the smoke production, as they cause a more incomplete combustion of the wood. The wood product manufacturers seek to find the optimal amount of FR additives where both heat release and smoke production in the classifying test are within the requirements given in the building regulations. This paper describes models for prediction of the European reaction to fire classes of wood products. The models are based on multivariate statistical analysis, and use test results from the cone calorimeter test as input. The presented models are, with very good precision, able to predict which Euroclass and additional smoke class a wood based product would obtain if it were to be tested in the single burning item test. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
73.
This paper presents a method for multi-area power system total transfer capability (TTC) computation. This computation takes into account the limits on the line flows, bus voltage magnitude, generator reactive power, voltage stability, as well as the loss of line contingencies. The multi-area TTC problem is solved by using a network decomposition approach based on REI-type network equivalents. Each area uses REI equivalents of external areas to compute its TTC via the continuation power flow (CPF). The choice and updating procedure for the continuation parameter employed by the CPF is implemented in a distributed but coordinated manner. The proposed method leads to potential gains in the computational efficiency with limited data exchanges between areas. The developed procedure is successfully applied to the three-area IEEE 118-bus test system. Numerical comparisons between the integrated and the proposed multi-area solutions are presented for validation.  相似文献   
74.
75.
76.
77.
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   
78.
Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement.  相似文献   
79.
80.
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry.  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