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   61991篇
  免费   6857篇
  国内免费   3729篇
电工技术   14783篇
技术理论   7篇
综合类   7373篇
化学工业   3799篇
金属工艺   1533篇
机械仪表   5840篇
建筑科学   4549篇
矿业工程   2149篇
能源动力   1764篇
轻工业   1285篇
水利工程   1065篇
石油天然气   1378篇
武器工业   1916篇
无线电   6219篇
一般工业技术   3289篇
冶金工业   2610篇
原子能技术   261篇
自动化技术   12757篇
  2024年   213篇
  2023年   736篇
  2022年   1369篇
  2021年   1814篇
  2020年   1981篇
  2019年   1539篇
  2018年   1423篇
  2017年   2093篇
  2016年   2189篇
  2015年   2509篇
  2014年   4109篇
  2013年   3392篇
  2012年   4772篇
  2011年   5194篇
  2010年   3757篇
  2009年   3841篇
  2008年   3752篇
  2007年   4656篇
  2006年   4002篇
  2005年   3434篇
  2004年   2599篇
  2003年   2376篇
  2002年   1901篇
  2001年   1689篇
  2000年   1311篇
  1999年   984篇
  1998年   670篇
  1997年   622篇
  1996年   465篇
  1995年   401篇
  1994年   353篇
  1993年   202篇
  1992年   165篇
  1991年   136篇
  1990年   128篇
  1989年   73篇
  1988年   72篇
  1987年   58篇
  1986年   45篇
  1985年   145篇
  1984年   245篇
  1983年   290篇
  1982年   205篇
  1981年   314篇
  1980年   116篇
  1979年   39篇
  1978年   40篇
  1977年   15篇
  1975年   21篇
  1974年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Fumio Negoro 《Knowledge》2003,16(7-8):383-397
The purpose of our study is to build up relationships between requirement and source programs with our originally thought-out rules. When other rules to be derived from these original rules are applied to software development, even a single instruction in a programming language could be determined, and the program would satisfy the requirement. More specifically speaking, these rules will turn into a formula or a prototype of software programs. Hence, when the variables in the requirement are placed in the formula, we can get a required program in an automatic way.  相似文献   
162.
简要介绍了自复中电/机调速器的机械和电气原理,并就使用该调速器的机组在生产运行中容易出现的停机后导叶开度漂移、停机时导叶不能完全关闭和显示开度与实际开度不一致等主要问题,通过修改可编程逻辑控制器(PLC)程序、调节调零杆位置、修改PLC程序参数等方法进行解决,这些方法对同类水电厂处理类似问题有借鉴作用。  相似文献   
163.
外转子电机关键技术及解决措施   总被引:1,自引:0,他引:1  
赵伽敏  刘金泽 《微电机》2004,37(2):51-52,62
对外转子电机的关键技术和主要工艺问题进行了探讨分析,并提出了解决措施。  相似文献   
164.
Technological determinism has become a kind of religion for many people since it appears to offer solutions for societal problems as never before in history. Transport is one of the fascinating technology branches developed during the last 200 years. Effortless movement over long distances has become possible for car users as long as cheap fossil energy is available. However, the effect of fast transport on urban structures and society was not taken into account when developing these technical means. Technologists and economists have used indicators for expected benefits of these fast transport modes without taking into account the real system effects on society and urban structures. Plausible assumptions and hopes instead of scientific understanding of the complex system are used in practice. In contradiction to widely held beliefs of transportation planners, there is actually no growth of mobility if counted in number of trips per person per day, no time saving by increasing speed in the system, and no real freedom of modal choice. Modal choice is dependent on physical and other structures, the artificial environment built by urban planners, transport experts and political decisions. The core hypothesis of traditional urban and transport planning ‘growth of mobility’, ‘travel time saving by increasing speed’ and ‘freedom of modal choice’ are myths and do not exist in the real urban and transport system. This is the reason why urban planning and transport planning based on traditional non-scientific assumptions is creating continuously not only more transport problems, but also environmental and social as well as economic problems all over the world, where these principals are applied. Urban transport planning in Europe, understanding the transport system and the solutions are presented in this paper.  相似文献   
165.
Mobile robots can be used in many applications, such as exploration, search and rescue, reconnaissance, security, and cleaning. Mobile robots usually carry batteries as their energy source and their operational time is restricted by the finite energy available from the batteries. Therefore, energy constraints are critical to the service time of mobile robots. This paper investigates the minimum-energy control problem for translational trajectory generation, which minimizes the energy drawn from the batteries. Optimal control theory is used to find the optimal velocity trajectory in analytic form. To demonstrate energy efficiency obtainable, we performed simulations of minimum-energy velocity control and compared the results with loss-minimization control and energy-optimal trapezoidal velocity profiles. Simulation results showed that significant energy savings can be achieved, of up to 9% compared with loss-minimization control and up to 10% compared with energy-optimal trapezoidal velocity profile. We also performed an actual robot experiment using Pioneer 3-AT platform to show the validity of the proposed minimum-energy velocity control. The experimental results revealed that the proposed minimum-energy velocity control can save the battery energy up to 10% compared with loss-minimization control. Categories (3): Robot control, (5): RobotMotion Planning  相似文献   
166.
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
167.
城市化进程中的小城镇交通初探   总被引:4,自引:0,他引:4  
通过对小城镇城市结构、路网结构、交通结构和交通管理特征进行详细分析,得出小城镇交通问题症结所在,并初步提出小城镇交通规划和交通治理的对策。  相似文献   
168.
简述了铅锌选厂废水回用小型试验及工业试验情况,在基本上不改变工艺结构基础上改变药剂制度达到废水回用的目的,使选矿废水回用率达到80%,实现尾矿库废水零排放。  相似文献   
169.
介绍了热力厂4^#锅炉电气系统与微机联络控制的方式。系统分别采用变频器485接口式电动机保护测控单元或接触器与微机连接,实现4^#锅炉电气控制过程。  相似文献   
170.
中压电动机传统起动方式的危害性   总被引:17,自引:1,他引:16  
本通过对中压电动机的几种传统起动方式的探讨分析,阐述了使用这些方法对电网和周围其他用电设备产生的不利影响,提出了改进措施。  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