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   119861篇
  免费   9090篇
  国内免费   4704篇
电工技术   6547篇
技术理论   11篇
综合类   7250篇
化学工业   20137篇
金属工艺   6252篇
机械仪表   7206篇
建筑科学   9320篇
矿业工程   3347篇
能源动力   3304篇
轻工业   7233篇
水利工程   1973篇
石油天然气   6496篇
武器工业   806篇
无线电   14818篇
一般工业技术   15023篇
冶金工业   6320篇
原子能技术   1322篇
自动化技术   16290篇
  2024年   492篇
  2023年   1936篇
  2022年   3267篇
  2021年   4474篇
  2020年   3402篇
  2019年   2857篇
  2018年   3274篇
  2017年   3669篇
  2016年   3191篇
  2015年   4247篇
  2014年   5360篇
  2013年   6816篇
  2012年   7188篇
  2011年   7802篇
  2010年   6779篇
  2009年   6659篇
  2008年   6655篇
  2007年   6204篇
  2006年   6440篇
  2005年   5755篇
  2004年   3947篇
  2003年   3406篇
  2002年   3113篇
  2001年   2977篇
  2000年   3010篇
  1999年   3474篇
  1998年   2974篇
  1997年   2627篇
  1996年   2337篇
  1995年   1953篇
  1994年   1582篇
  1993年   1246篇
  1992年   987篇
  1991年   754篇
  1990年   607篇
  1989年   508篇
  1988年   403篇
  1987年   303篇
  1986年   207篇
  1985年   181篇
  1984年   110篇
  1983年   82篇
  1982年   89篇
  1981年   58篇
  1980年   46篇
  1979年   32篇
  1978年   25篇
  1977年   25篇
  1976年   41篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Based on vectorial formulations which combine the surface integral equation method and the finite-element method, a novel numerical approach is proposed for calculating the dispersion coefficients of dual-mode elliptical-core fibers with arbitrary refractive index profiles. By differentiating the original formulations involving the propagation constant β and the guided mode fields Hx and Hy once and twice with respect to the normalized frequency V, the new formulations for {dβ/dV, dHx/dV, dHy/dV} and for {d2β/dV2, d2 Hx/dV2, d2Hy/dV2 } are obtained respectively. Once {β, Hx, Hy } is solved through the eigenvalue procedure which dominates the computing time, only a few matrix manipulations are required to obtain {dβ/dV, dHx/dV, dHy/dV} and {d2β/dV2, d2Hx/dV2 , d2Hy/dV2}. Some numerical examples are examined to see the influence of different refractive index distributions with dips on the dispersions of the four nondegenerate LP 11 modes for elliptical-core fibers  相似文献   
22.
本文实验研究了BHP的浓度对产生O2(1△)的影响。实验结果表明:当BHP浓度大于3.5M时,Cl2利用率以及O2(1△)的产率将不依赖于BHP浓度的变化而变化,同时,实验结果表明,使用低浓度的BHP对COIL的操作是可行的。  相似文献   
23.
通过几个典型事例的分析、判断和处理,介绍了该厂怎样利用91l型数采器对2D12—100/8型空压机运行状态进行监测,以预报早期故障,为设备检修提供指导.  相似文献   
24.
The temperature dependence characteristics of hydrogenated amorphous silicon thin-film transistors were investigated. The results indicate that as the temperature was increased, the threshold voltage and the field-effect mobility were first increased, and then decreased, which may be controlled by different mechanisms at low and high temperatures. In addition, if the temperature was higher than 420 K, the Fermi level was promoted to the degenerate-like states, the current channel always existed due to the temperature effect, and the threshold voltage became negative.  相似文献   
25.
Double-step generation of ellipses   总被引:4,自引:0,他引:4  
The principle of double-step incremental generation of nonparametric curves on a discrete plane is used to develop a double-step algorithm for scan converting ellipses in sixteen separate segments. The algorithm iterates only half as many times as current algorithms, while each iteration demands the same number of operations or slightly fewer operations than M. Pitteway's (1967, 1985) algorithm (previously the fastest one). This marked gain in the speed of scan conversion is due to the fact that the middle pixel in a two-step increment is obtained without computation  相似文献   
26.
本文介绍β放射性气体浓度计的一种新的分度方法——泄漏元件排气法。其特点是一只元件可分度放射性气体浓度计的许多读出数(甚至是几个量程),操作方便。  相似文献   
27.
28.
The mode of fuel management of the HTR-10 was studied, including the simulation of the fuel shuffling process and the measurement of the burnup of a fuel element. The prior consideration was the design of the equilibrium state. Based on this the fuel loading of the initial core and the fuel shuffling mode from the initial core through the running-in phase into the equilibrium state were studied. The code system VSOP was used for the physical layout of the HTR-10 at the equilibrium state and in the running-in phase. For the equilibrium state, in order to lessen the difference between the peak and the average burnup, 5-fuel-passage-through-the-core was chosen for the fuel management. The average burnup of the spent fuel for the equilibrium core is 80 000 MWd t−1, and the peak value of it is less than 100 000 MWd t−1 when the burnup of the recycled fuel element is under 72 000 MWd t−1. The mixture of fuel element and graphite element was used for the initial core loading, the volume fractions of the fuel and the graphite elements were 0.57 and 0.43, respectively. During the running-in phase, the volume fraction of graphite will decrease with the fresh fuel elements being loaded from the top of the core and the graphite elements discharged from the bottom of the core. The fuel shuffling mode is similar to that of the equilibrium state. The burnup limit of recycled fuel element is also 72 000 MWd t−1 and the peak burnup is less than 100 000 MWd t−1. Finally the core will be full of fuel elements with a certain profile of burnup and reaches the equilibrium state. According to the characteristics of the pebble-bed high temperature gas-cooled reactor, a calibrating method of concentration of 137Cs was proposed for the measurement of fuel burnup.  相似文献   
29.
The tool portfolio of a plant refers to the makeup, in quantity and type, of processing machines in the plant. It is determined by taking into consideration the future trends of process and machine technologies and the forecasts of product evolution and product demands. Portfolio planning is also a multicriteria decision-making task involving tradeoffs among, investment cost, throughput, cycle time, and risk. Tool portfolio planning is a complex task that has strong bearing on manufacturing efficiency. In the first part of this paper, a multicriteria economic decision model is presented for optimal configuration. of the portfolio and to determine the optimal factory loading. The second and third parts of the paper contain applications of the model. If plants are closely located or have a twin-plant design, portfolio planning at multiple plants can be integrated to enhance the overall effectiveness of portfolios. In the second part, a novel methodology for arbitrating capacity backup between plants is described. Because the economic model is constructed upon a valuation of both cycle time and throughput, it is a suitable method for the evaluation of cycle time reduction projects. The application procedure is outlined in the third part.  相似文献   
30.
STUDYONRESIDUESOF~(14)C-FENITROTHIONINMODELRICE-FISHECOSYSTEMANDFIELDRICE-FISHECOSYSTEMZhangZhongliang(张仲良);WangHuaxin(王化新);G?..  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