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   46101篇
  免费   3946篇
  国内免费   2148篇
电工技术   2524篇
技术理论   3篇
综合类   3173篇
化学工业   6223篇
金属工艺   2422篇
机械仪表   2433篇
建筑科学   2786篇
矿业工程   1339篇
能源动力   1150篇
轻工业   2871篇
水利工程   743篇
石油天然气   1603篇
武器工业   296篇
无线电   4550篇
一般工业技术   4579篇
冶金工业   1828篇
原子能技术   549篇
自动化技术   13123篇
  2024年   154篇
  2023年   593篇
  2022年   1055篇
  2021年   1484篇
  2020年   1148篇
  2019年   1033篇
  2018年   1110篇
  2017年   1221篇
  2016年   1145篇
  2015年   1553篇
  2014年   2108篇
  2013年   2517篇
  2012年   3213篇
  2011年   4728篇
  2010年   3436篇
  2009年   3073篇
  2008年   2761篇
  2007年   2516篇
  2006年   2365篇
  2005年   2234篇
  2004年   1792篇
  2003年   2081篇
  2002年   2270篇
  2001年   1750篇
  2000年   1089篇
  1999年   859篇
  1998年   560篇
  1997年   456篇
  1996年   373篇
  1995年   344篇
  1994年   271篇
  1993年   176篇
  1992年   165篇
  1991年   143篇
  1990年   91篇
  1989年   76篇
  1988年   59篇
  1987年   34篇
  1986年   27篇
  1985年   21篇
  1984年   10篇
  1982年   15篇
  1981年   9篇
  1980年   23篇
  1979年   9篇
  1978年   5篇
  1977年   6篇
  1974年   4篇
  1959年   6篇
  1951年   4篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
81.
提出了一种考虑分布电容的故障测距新算法。该算法基于微分方程描述的线路数学模型,利用单端信息对高压输电线路进行故障测距,保留了解微分方程算法的简单可靠、现实可行、不必考虑衰减直流分量和谐波及电网频率波动影响的特点,同时考虑过渡电阻和分布电容的影响,克服了传统解微分方程法中在经高阻接地故障时测距误差过大和忽略分布电容引起的故障定位不准确的缺点。为了检验算法的精度,进行了大量的动模实验。结果表明,算法原理正确并具有较高的测距精度。  相似文献   
82.
This paper presents a distributed adaptive coordinated control method for multiple robot arms grasping a common object. The cases of rigid contact and rolling contact are analyzed. In the proposed controller, the dynamic parameters of both object and robot arms are estimated adaptively. The desired motions of the robot arms are generated by an estimated object reference model. The control method requires only the measurements of the positions and velocities of the object and robot arms, but not the measurements of forces and moments at contact points. The asymptotic convergence of trajectory is proven by the Lyapunov-like Lemma. Experiments involving two robot arms handling a common object are shown.  相似文献   
83.
The paper is devoted to the first order delayed linear system with relay output controlled by the proportional-integral (PI) regulator. The deterministic system exhibits stable oscillations, and, since the system itself is stable, it can be suitable to switch off the controller if there are no disturbances during a long time interval. In the present work, the random disturbances are modelled by a Poisson stream of impulses, and the goal is to determine the instants of switching on (off) of the PI controller. After several assumptions and quantization of the time axis, we construct the new optimal control problem which is successfully solved with the help of the dynamic programming approach.  相似文献   
84.
一文 《园林》2005,(11):51-51
鸟笼艺术装饰 鸟笼中是薜荔,能攀援、匍匐成下垂生长,所以在此构成了一幅活的 笼中艺术画。  相似文献   
85.
The goal of face recognition is to distinguish persons via their facial images. Each person's images form a cluster, and a new image is recognized by assigning it to the correct cluster. Since the images are very high-dimensional, it is necessary to reduce their dimension. Linear discriminant analysis (LDA) has been shown to be effective at dimension reduction while preserving the cluster structure of the data. It is classically defined as an optimization problem involving covariance matrices that represent the scatter within and between clusters. The requirement that one of these matrices be nonsingular restricts its application to datasets in which the dimension of the data does not exceed the sample size. For face recognition, however, the dimension typically exceeds the number of images in the database, resulting in what is referred to as the small sample size problem. Recently, the applicability of LDA has been extended by using the generalized singular value decomposition (GSVD) to circumvent the nonsingularity requirement, thus making LDA directly applicable to face recognition data. Our experiments confirm that LDA/GSVD solves the small sample size problem very effectively as compared with other current methods.  相似文献   
86.
87.
A stochastic realization problem of a stationary stochastic process is re-visited, and a new stochastically balanced realization algorithm is derived in a Hilbert space generated by second-order stationary processes. The present algorithm computes a stochastically balanced realization by means of the singular value decomposition of a weighted block Hankel matrix derived by a “block LQ decomposition”. Extension to a stochastic subspace identification method explains how the proposed abstract algorithm is implemented in system identification.  相似文献   
88.
白文 《山西建筑》2004,30(20):79-80
结合工程实例,论述了露天栈桥产生裂缝和腐蚀的原因,对栈桥结构进行了评价,提出了加固方案及加固施工中应注意的事项,经使用证明,加固效果良好。  相似文献   
89.
Reset controllers are linear controllers that reset some of their states to zero when their input is zero. We are interested in their feedback connection with linear plants, and in this paper we establish fundamental closed-loop properties including stability and asymptotic tracking. This paper considers more general reset structures than previously considered, allowing for higher-order controllers and partial-state resetting. It gives a testable necessary and sufficient condition for quadratic stability and links it to both uniform bounded-input bounded-state stability and steady-state performance. Unlike previous related research, which includes the study of impulsive differential equations, our stability results require no assumptions on the evolution of reset times.  相似文献   
90.
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