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   563683篇
  免费   12479篇
  国内免费   5554篇
电工技术   13880篇
技术理论   5篇
综合类   6122篇
化学工业   82820篇
金属工艺   25361篇
机械仪表   21029篇
建筑科学   17710篇
矿业工程   4860篇
能源动力   15917篇
轻工业   38080篇
水利工程   6282篇
石油天然气   13632篇
武器工业   715篇
无线电   69413篇
一般工业技术   108033篇
冶金工业   96750篇
原子能技术   11123篇
自动化技术   49984篇
  2022年   5278篇
  2021年   7712篇
  2020年   5927篇
  2019年   6425篇
  2018年   9781篇
  2017年   10090篇
  2016年   10152篇
  2015年   8222篇
  2014年   12225篇
  2013年   28303篇
  2012年   18552篇
  2011年   23700篇
  2010年   19180篇
  2009年   21148篇
  2008年   21358篇
  2007年   21083篇
  2006年   19661篇
  2005年   17600篇
  2004年   15484篇
  2003年   14875篇
  2002年   13933篇
  2001年   13740篇
  2000年   13209篇
  1999年   14325篇
  1998年   32689篇
  1997年   22650篇
  1996年   17934篇
  1995年   13209篇
  1994年   11526篇
  1993年   11201篇
  1992年   7975篇
  1991年   7454篇
  1990年   7248篇
  1989年   6656篇
  1988年   6214篇
  1987年   5264篇
  1986年   5090篇
  1985年   5605篇
  1984年   5075篇
  1983年   4566篇
  1982年   4245篇
  1981年   4274篇
  1980年   3912篇
  1979年   3707篇
  1978年   3672篇
  1977年   4177篇
  1976年   5622篇
  1975年   3102篇
  1974年   2890篇
  1973年   2937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.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized  相似文献   
73.
This paper analyzes probability of bit-error (Pe) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of Pe analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low Pe (< 10-3) or a prohibitively large computational complexity. The paper presents an alternate method of Pe analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P e performance, user capacity and the accuracy of the proposed method  相似文献   
74.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
75.
76.
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.
79.
Elasticity is discussed as an aspect of viscoelasticity, which is described by the tube model. The effects of both crosslinks and entanglements contribute to this model and a discussion of how these effects can be quantified is given. At high enough concentration, entanglements ensure the existence of elastic effects even without crosslinks, and a theory is presented on how this dynamical phase change comes about.  相似文献   
80.
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   
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