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   19446篇
  免费   5077篇
  国内免费   765篇
电工技术   400篇
技术理论   8篇
综合类   2722篇
化学工业   1966篇
金属工艺   2095篇
机械仪表   1153篇
建筑科学   515篇
矿业工程   197篇
能源动力   1330篇
轻工业   1011篇
水利工程   152篇
石油天然气   184篇
武器工业   2130篇
无线电   2277篇
一般工业技术   2578篇
冶金工业   2925篇
原子能技术   130篇
自动化技术   3515篇
  2025年   149篇
  2024年   556篇
  2023年   844篇
  2022年   960篇
  2021年   1013篇
  2020年   1069篇
  2019年   848篇
  2018年   602篇
  2017年   800篇
  2016年   908篇
  2015年   937篇
  2014年   1279篇
  2013年   1495篇
  2012年   1822篇
  2011年   1693篇
  2010年   1355篇
  2009年   1488篇
  2008年   939篇
  2007年   1517篇
  2006年   1508篇
  2005年   666篇
  2004年   307篇
  2003年   275篇
  2002年   278篇
  2001年   231篇
  2000年   259篇
  1999年   238篇
  1998年   155篇
  1997年   131篇
  1996年   111篇
  1995年   97篇
  1994年   66篇
  1993年   66篇
  1992年   55篇
  1991年   34篇
  1990年   28篇
  1989年   25篇
  1988年   37篇
  1987年   81篇
  1986年   89篇
  1985年   15篇
  1984年   23篇
  1982年   21篇
  1981年   15篇
  1974年   15篇
  1972年   16篇
  1970年   13篇
  1966年   15篇
  1965年   16篇
  1951年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In this paper, a model-predictive trajectory-tracking control applied to a mobile robot is presented. Linearized tracking-error dynamics is used to predict future system behavior and a control law is derived from a quadratic cost function penalizing the system tracking error and the control effort. Experimental results on a real mobile robot are presented and a comparison of the control obtained with that of a time-varying state-feedback controller is given. The proposed controller includes velocity and acceleration constraints to prevent the mobile robot from slipping and a Smith predictor is used to compensate for the vision-system dead-time. Some ideas for future work are also discussed.  相似文献   
2.
An easy to use method for an approximate creep life prediction for pipe bends was developed within a recent R & D-project in Germany. The new algorithm is based on a Finite-Element parameter study comprising approximately 200 pipe bends. The creep behaviour of the materials primarily used for main steam and hot reheat piping is described using the Graham–Walles creep law. Since the new algorithm considers the time dependent out-of-roundness and stress redistribution of the pipe bend, it yields a more precise creep life prediction, compared to standard piping codes. It is possible to integrate this new calculation into existing online lifetime-monitoring-systems.  相似文献   
3.
4.
5.
Statistical analysis of air mass back trajectories combined with long-term ambient air pollution measurements are useful tools for source identification. Using these methods, the geographic information system (GIS) based software, TrajStat, was developed to view, query, and cluster the trajectories and compute the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) analyses when measurement data are included.  相似文献   
6.
The paper presents an approach to nonlinear buckling fiber angle optimization of laminated composite shell structures. The approach accounts for the geometrically nonlinear behaviour of the structure by utilizing response analysis up until the critical point. Sensitivity information is obtained efficiently by an estimated critical load factor at a precritical state. In the optimization formulation, which is formulated as a mathematical programming problem and solved using gradient-based techniques, a number of the lowest buckling factors are included such that the risk of “mode switching” during optimization is avoided. The presented optimization formulation is compared to the traditional linear buckling formulation and two numerical examples, including a large laminated composite wind turbine main spar, to clearly illustrate the pitfalls of the traditional formulation and the advantage and potential of the presented approach.  相似文献   
7.
In this paper, we design a Z-type microspring, which consists of several “Z” type micromechanical beams within mutual connection. With good mechanical performance and mature LIGA fabrication technology, Ni is chosen as the material of Z-type MEMS microspring. The mechanical properties of electroformed Ni have been tested by the Micro Hardness Tester, and the Young’s modulus is 219 GPa. Different from traditional springs, microsprings can be divided into three application patterns in direction x, y, and z to study. Applying the Castigliano second theorem of energy method in macro theory, the formulas used to calculate the spring constant of Z-type microspring in the directions of the three application patterns were derived, and verified by the ANSYS finite element method. Using the Tytron250 micro force test machine, the experiments of the Z-type microspring deformation properties were carried out. The spring constant, rupture force and rupture strength of Z-type microspring in direction y are 3821 N/m, 1.64 N and 1.61 GPa, respectively. The experimental results agree with the theoretical analysis. Based on the analysis above, the change laws of the spring constant of microspring in the three application patterns are summarized.  相似文献   
8.
The prototype of a CO2 sensor made of CuO–BaTiO3, which has capacitance sensitive effect, is designed based on the pn heterojunctions of CuO and BaTiO3 semiconductors. The preparation of BaTiO3 semiconductor powders is pointed out, using the coprecipitation and semiconducting techniques. The characteristic quantities relating to the capacitance sensitive effect of the sensor are studied systematically with the aid of a gas tester. A reasonable mechanism of the sensor is proposed.  相似文献   
9.
10.
肖乾广  肖岚 《遥感信息》2006,(2):29-30,F0002
主要探索用EOS/MODIS极轨卫星监测闪电的可行性,应用大气和云辐射原理以及云中水滴mie散射的原理,从EOS/MODIS的中红外通道及热红外通道中提取夜间强对流云团产生的闪电信息,并可由强对流卫星云图的云顶温度确定可能出现冰雹的区域,对减灾、预警提供宏观信息。  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