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   645064篇
  免费   7135篇
  国内免费   1403篇
电工技术   11236篇
综合类   2767篇
化学工业   100216篇
金属工艺   27811篇
机械仪表   21410篇
建筑科学   14591篇
矿业工程   4851篇
能源动力   15487篇
轻工业   49071篇
水利工程   8119篇
石油天然气   15281篇
武器工业   39篇
无线电   69014篇
一般工业技术   131048篇
冶金工业   98053篇
原子能技术   14915篇
自动化技术   69693篇
  2021年   5482篇
  2019年   5273篇
  2018年   22835篇
  2017年   21970篇
  2016年   19274篇
  2015年   6594篇
  2014年   10439篇
  2013年   26247篇
  2012年   18665篇
  2011年   29810篇
  2010年   24651篇
  2009年   23987篇
  2008年   25410篇
  2007年   25990篇
  2006年   16401篇
  2005年   15824篇
  2004年   15033篇
  2003年   14775篇
  2002年   13736篇
  2001年   12943篇
  2000年   12491篇
  1999年   12064篇
  1998年   27734篇
  1997年   20088篇
  1996年   15683篇
  1995年   12017篇
  1994年   10870篇
  1993年   10630篇
  1992年   8343篇
  1991年   8127篇
  1990年   7990篇
  1989年   7766篇
  1988年   7491篇
  1987年   6751篇
  1986年   6539篇
  1985年   7397篇
  1984年   6704篇
  1983年   6441篇
  1982年   5777篇
  1981年   5900篇
  1980年   5631篇
  1979年   5735篇
  1978年   5664篇
  1977年   6179篇
  1976年   7691篇
  1975年   5110篇
  1974年   4904篇
  1973年   4981篇
  1972年   4279篇
  1971年   4039篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
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   
73.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 423–424, June, 1989.  相似文献   
74.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
75.
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   
76.
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   
77.
78.
79.
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures  相似文献   
80.
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs  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