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   573759篇
  免费   6322篇
  国内免费   1012篇
电工技术   10584篇
综合类   467篇
化学工业   90829篇
金属工艺   23411篇
机械仪表   18725篇
建筑科学   12738篇
矿业工程   4335篇
能源动力   14557篇
轻工业   46411篇
水利工程   7019篇
石油天然气   14975篇
武器工业   39篇
无线电   60843篇
一般工业技术   117017篇
冶金工业   98337篇
原子能技术   14751篇
自动化技术   46055篇
  2021年   5555篇
  2019年   5321篇
  2018年   9249篇
  2017年   9475篇
  2016年   9900篇
  2015年   6072篇
  2014年   10340篇
  2013年   26389篇
  2012年   15911篇
  2011年   21278篇
  2010年   17145篇
  2009年   19011篇
  2008年   19289篇
  2007年   18962篇
  2006年   16462篇
  2005年   14908篇
  2004年   14130篇
  2003年   13819篇
  2002年   13392篇
  2001年   12968篇
  2000年   12438篇
  1999年   12157篇
  1998年   28310篇
  1997年   20453篇
  1996年   15979篇
  1995年   12259篇
  1994年   11069篇
  1993年   10807篇
  1992年   8419篇
  1991年   8192篇
  1990年   8097篇
  1989年   7863篇
  1988年   7590篇
  1987年   6849篇
  1986年   6625篇
  1985年   7499篇
  1984年   6770篇
  1983年   6504篇
  1982年   5835篇
  1981年   5974篇
  1980年   5689篇
  1979年   5793篇
  1978年   5717篇
  1977年   6273篇
  1976年   7862篇
  1975年   5171篇
  1974年   4960篇
  1973年   5028篇
  1972年   4317篇
  1971年   4062篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Carboxyl-terminated butadiene-acrylonitrile-rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber-modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.  相似文献   
72.
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described.  相似文献   
73.
Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed.  相似文献   
74.
Many current implementations of protocols such as the Transmission Control Protocol/Internet Protocol (TCP/IP) are inefficient because data are often accessed more frequently than necessary. Three techniques that reduce the need for memory bandwidth are proposed. The techniques are copy-on-write, page remapping, and single-copy. Afterburner, a network-independent card that provides the services that are necessary for a single-copy protocol stack, is described. The card has 1 MByte of local buffers and provides a simple interface to a variety of network link adapters, including HIPPI and asynchronous transfer mode (ATM). Afterburner can support transfers to and from the link adapter card at rates up to 1 Gbit/s. An implementation of TCP/IP that uses the features provided by Afterburner to reduce the movement of data to a single copy is discussed. Measurements of the end-to-end performance of Afterburner and the single-copy implementation of TCP/IP are presented  相似文献   
75.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 423–424, June, 1989.  相似文献   
76.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
77.
An apparent decrease in total phosphorus concentrations of approximately 4.l μgP/L has been reported recently for the spring values of 1977 and 1978 in Lake Ontario. Investigation of the loading reduction for this period independent of sedimentation factors can account for only 10% of the change. The results indicate that changes in the sedimentation rate of total phosphorus during this period offer an explanation for the majority of the change in concentration.  相似文献   
78.
A fast algorithm is proposed for estimating the auto- and cross-correlation functions of a large signal. The algorithm is based on the sectioning method by the fast Fourier transform. We determine the optimal length of the portion of data read from external memory into RAM which achieves Tmin—a minimum processing time. An estimate of Tmin is obtained.Translated from Kibernetika, No. 3, pp. 78–81, May–June, 1991.  相似文献   
79.
80.
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