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   46687篇
  免费   8024篇
  国内免费   5144篇
电工技术   6153篇
综合类   5587篇
化学工业   2392篇
金属工艺   687篇
机械仪表   3023篇
建筑科学   1565篇
矿业工程   730篇
能源动力   1182篇
轻工业   804篇
水利工程   1249篇
石油天然气   703篇
武器工业   1066篇
无线电   9048篇
一般工业技术   3870篇
冶金工业   818篇
原子能技术   799篇
自动化技术   20179篇
  2024年   337篇
  2023年   1096篇
  2022年   1847篇
  2021年   2096篇
  2020年   2030篇
  2019年   1745篇
  2018年   1510篇
  2017年   1989篇
  2016年   2170篇
  2015年   2273篇
  2014年   3105篇
  2013年   3507篇
  2012年   3412篇
  2011年   3776篇
  2010年   2789篇
  2009年   2967篇
  2008年   3079篇
  2007年   3471篇
  2006年   2719篇
  2005年   2388篇
  2004年   1876篇
  2003年   1625篇
  2002年   1265篇
  2001年   1037篇
  2000年   864篇
  1999年   756篇
  1998年   583篇
  1997年   559篇
  1996年   437篇
  1995年   399篇
  1994年   351篇
  1993年   251篇
  1992年   266篇
  1991年   205篇
  1990年   218篇
  1989年   143篇
  1988年   107篇
  1987年   70篇
  1986年   56篇
  1985年   50篇
  1984年   74篇
  1983年   39篇
  1982年   76篇
  1981年   67篇
  1980年   45篇
  1979年   38篇
  1978年   24篇
  1977年   27篇
  1959年   7篇
  1951年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
辨识时变系统遗忘因子算法的收敛性分析   总被引:7,自引:5,他引:2  
著名的递推遗忘因子算法(RFFA)可以用辨识时变系统参数,具有良好的跟踪性能,本文借助于随机过程理论分析了RFFA的收敛性和稳定性,给出了参数跟踪误差的上下界。  相似文献   
142.
作者根据自身体会,全面、系统地总结了编制一份高质量的概算文件必须注意的问题.  相似文献   
143.
As apparent from the title, this author feels that civilization faces a real threat, one which will become obvious and serious within the lifetimes of many readers of this article. This threat is not global warming, but lack of affordable energy. We take for granted turning on a light, or adjusting our thermostats in winter or summer, or filling our cars gas tank; and lose sight of the fact that there are huge and complicated industrial systems which make this possible. But as we run out of petroleum and natural gas, and worry about the environmental and climatic effects of burning coal on the required scale, how can this continue? This paper makes the case that breeding nuclear fuel, by both fusion and fission, is the only way our civilization as we know it, can continue beyond the next half century or so.  相似文献   
144.
Predictive Maintenance can provide an increase in safety, quality and availability in industrial plants. However, the setting up of a Predictive Maintenance Programme is a strategic decision that until now has lacked analysis of questions related to its setting up, management and control. In this paper, an evaluation system is proposed that carries out the decision making in relation to the feasibility of the setting up. The evaluation system uses a combination of tools belonging to operational research such as: Analytic Hierarchy Process, decision rules and Bayesian tools. This system is a help tool available to the managers of Predictive Maintenance Programmes which can both increase the number of Predictive Maintenance Programmes set up and avoid the failure of these programmes. The Evaluation System has been tested in a petrochemical plant and in a food industry.  相似文献   
145.
为提高声呐对目标航迹的检测性能,从单部声呐时间融合的角度出发,提出了一种基于Hough变换的声呐信号检测算法。该算法把航迹上的观测点变换为参数空间的对应曲线,充分利用一段时间内的目标观测数据,在低信噪比下也能从背景噪声中提取目标的航迹特征,提高了声呐的检测概率,且对部分信息和数据的缺失不敏感。仿真试验证明了该算法的有效性。  相似文献   
146.
Until now, in many forensic reports, the failure cause assessments are usually carried out by a deterministic approach so far. However, it may be possible for the forensic investigation to lead to unreasonable results far from the real collapse scenario, because the deterministic approach does not systematically take into account any information on the uncertainties involved in the failures of structures.Reliability-based failure cause assessment (reliability-based forensic engineering) methodology is developed which can incorporate the uncertainties involved in structural failures and structures, and to apply them to the collapsed bridge in order to identify the most critical failure scenario and find the cause that triggered the bridge collapse. Moreover, to save the time and cost of evaluation, an algorithm of automated event tree analysis (ETA) is proposed and possible to automatically calculate the failure probabilities of the failure events and the occurrence probabilities of failure scenarios. Also, for reliability analysis, uncertainties are estimated more reasonably by using the Bayesian approach based on the experimental laboratory testing data in the forensic report. For the applicability, the proposed approach is applied to the Hang-ju Grand Bridge, which collapsed during construction, and compared with deterministic approach.  相似文献   
147.
张家凡 《振动与冲击》2002,21(1):73-74,82
本文讨论机械振动系统线性二次型状态调节器(LQR)问题,直接针对系统二阶运动微分方程,性能指标为一个依赖于二阶导数的泛函。由欧拉-拉格朗日方程得出一个系统矩阵增广的二阶线性微分方程,指出该方程稳定的特征对就是最优控制振动系统闭环特征对,并给出求解最优控制状态反馈矩阵的方法,另外,由本文方法还可得出基于速度和加速度反馈的最优控制反馈矩阵。这里不涉及求解代数矩阵Riccati方程。  相似文献   
148.
Assuming significant technical success in the ITER project by the year 2015, it is likely that governments will want to develop a more comprehensive plan for DT tokamak fusion power commercialization. To provide a glimpse into many of the related issues, we construct conversations between the director of the U.S. fusion program and three specialists key to commercial fusion success: an environment and safety regulator, an environmentalist, and an electric generation investor. The insights from these imagined conversations will hopefully be of value as tokamak fusion power proponents plan beyond ITER.  相似文献   
149.
调谐质量阻尼器参数设计中的两个问题   总被引:4,自引:0,他引:4  
本文以单自由度系统安装一个调谐质量阻尼器(简称TMD)为例,对抗风和抗震两类不同激励工况下TMD的参数设计问题进行了理论研究与对比分析。通过给出相对误差系数的概念,定量评价了不同的参数方法对TMD减振性能的影响程度。本文的研究为TMD的参数设计提供了理论指导。  相似文献   
150.
This paper introduces and evaluates a new class of knowledge model, the recursive Bayesian multinet (RBMN), which encodes the joint probability distribution of a given database. RBMNs extend Bayesian networks (BNs) as well as partitional clustering systems. Briefly, a RBMN is a decision tree with component BNs at the leaves. A RBMN is learnt using a greedy, heuristic approach akin to that used by many supervised decision tree learners, but where BNs are learnt at leaves using constructive induction. A key idea is to treat expected data as real data. This allows us to complete the database and to take advantage of a closed form for the marginal likelihood of the expected complete data that factorizes into separate marginal likelihoods for each family (a node and its parents). Our approach is evaluated on synthetic and real-world databases.  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