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   703篇
  免费   134篇
  国内免费   115篇
电工技术   136篇
综合类   126篇
化学工业   18篇
金属工艺   11篇
机械仪表   36篇
建筑科学   14篇
矿业工程   6篇
能源动力   13篇
轻工业   11篇
水利工程   9篇
石油天然气   10篇
武器工业   6篇
无线电   96篇
一般工业技术   91篇
冶金工业   2篇
原子能技术   3篇
自动化技术   364篇
  2024年   8篇
  2023年   11篇
  2022年   20篇
  2021年   27篇
  2020年   37篇
  2019年   32篇
  2018年   31篇
  2017年   38篇
  2016年   54篇
  2015年   42篇
  2014年   61篇
  2013年   64篇
  2012年   57篇
  2011年   63篇
  2010年   59篇
  2009年   53篇
  2008年   33篇
  2007年   40篇
  2006年   42篇
  2005年   28篇
  2004年   20篇
  2003年   14篇
  2002年   14篇
  2001年   16篇
  2000年   18篇
  1999年   8篇
  1998年   11篇
  1997年   8篇
  1996年   11篇
  1995年   4篇
  1994年   6篇
  1993年   3篇
  1992年   3篇
  1991年   4篇
  1990年   3篇
  1987年   1篇
  1986年   1篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1981年   1篇
排序方式: 共有952条查询结果,搜索用时 0 毫秒
1.
Let us consider n data measurements of a univariate process that have been altered by random errors. We assume that an underlying model function has a substantially smaller number of turning points than the observed ones. We propose algorithms that make least the sum of the moduli of the errors by requiring k monotonic sections, alternately increasing and decreasing, in the sequence of the smoothed values. The main difficulty in this calculation is that the optimal positions of the joins of the monotonic sections have to be found automatically among so many combinations that it is impossible to test each one separately. Moreover, the calculation seems to be very intractable to general optimization techniques because O(nk) local minima can occur. It is shown that dynamic programming can be used for separating the data into optimal disjoint sections of adjacent data, where each section requires a single L1 monotonic calculation. This procedure is highly efficient, requiring at most O(kn2) computer operations and O(n) best L1 monotonic calculations to subranges of data for a global minimum.  相似文献   
2.
本文对代数曲面的几何连续拼接作了研究,给出了多个代数曲面的几何连续过渡方法,同时给出了一种基于分片的曲面过渡方法。  相似文献   
3.
The main preoccupations of research in computer-aided geometric design have been on shape-specification techniques for polynomial curves and surfaces, and on the continuity between segments or patches. When modelling with such techniques, curves and surfaces can be compressed or expanded arbitrarily. There has been relatively little work on interacting with direct spatial properties of curves and surfaces, such as their arc length or surface area. As a first step, we derive families of parametric piecewise polynomial curves that satisfy various positional and tangential constraints together with arc-length constraints. We call these curves isometric curves. A space curve is defined as a sequence of polynomial curve segments, each of which is defined by the familiar Hermite or Bézier constraints for cubic polynomials; as well, each segment is constrained to have a specified arc length. We demonstrate that this class of curves is attractive and stable. We also describe the numerical techniques used that are sufficient for achieving real time interaction with these curves on low-end workstations.  相似文献   
4.
This paper addresses the problem of approximating parameter dependent nonlinear systems in a unified framework. This modeling has been presented for the first time in the form of parameter dependent piecewise affine systems. In this model, the matrices and vectors defining piecewise affine systems are affine functions of parameters. Modeling of the system is done based on distinct spaces of state and parameter, and the operating regions are partitioned into the sections that we call ’multiplied simplices’. It is proven that this method of partitioning leads to less complexity of the approximated model compared with the few existing methods for modeling of parameter dependent nonlinear systems. It is also proven that the approximation is continuous for continuous functions and can be arbitrarily close to the original one. Next, the approximation error is calculated for a special class of parameter dependent nonlinear systems. For this class of systems, by solving an optimization problem, the operating regions can be partitioned into the minimum number of hyper-rectangles such that the modeling error does not exceed a specified value. This modeling method can be the first step towards analyzing the parameter dependent nonlinear systems with a uniform method.  相似文献   
5.
首先,通过引入拟减法算子给出K-积分模定义,并针对广义Mamdani模糊系统实施等距剖分其输入空间. 其次,应用分片线性函数(Piecewise linear function,PLF)的性质构造性地证明了广义Mamdani模糊系统在K-积分模意义下具有泛逼近性,从而将该模糊系统对连续函数空间的逼近能力扩展到一类可积函数类空间上. 最后,通过模拟实例给出该广义Mamdani模糊系统对给定可积函数的泛逼近及实现过程.  相似文献   
6.
This paper deals with the problem of piecewise auto regressive systems with exogenous input(PWARX) model identification based on clustering solution. This problem involves both the estimation of the parameters of the affine sub-models and the hyper planes defining the partitions of the state-input regression. The existing identification methods present three main drawbacks which limit its effectiveness. First, most of them may converge to local minima in the case of poor initializations because they are based on the optimization using nonlinear criteria. Second, they use simple and ineffective techniques to remove outliers. Third, most of them assume that the number of sub-models is known a priori. To overcome these drawbacks, we suggest the use of the density-based spatial clustering of applications with noise(DBSCAN) algorithm. The results presented in this paper illustrate the performance of our methods in comparison with the existing approach. An application of the developed approach to an olive oil esterification reactor is also proposed in order to validate the simulation results.  相似文献   
7.
为提高小生境遗传算法的全局以及局部搜索能力,提出一种多交叉混沌选择反向小生境遗传算法。利用分段线性混沌映射函数生成一组混沌数序列,在每次进行交叉操作前,依据序列中对应元素的数值大小选择不同的交叉算子进行操作,通过小生境遗传算法产生较优的子代种群。针对子代种群,应用反向搜索策略获得反向种群,在子代种群和反向种群中进行精英选择得到最终新种群,以进一步加强算法的局部寻优能力。仿真实验结果表明,该算法在最优解及均值方面好于小生境遗传算法,从而证明其可行性和优越性。  相似文献   
8.
Oxygen consumption is an important index of coal oxidation.In order to explore the coal-oxygen reaction,we developed an experimental system of coal spontaneous combustion and tested oxygen consumption of differently ranked coals at programmed temperatures.The size of coal samples ranged from 0.18~0.42 mm and the system heat-rate was 0.8℃/min.The results show that,for high ranked coals,oxygen consumption rises with coal temperature as a piecewise non-linear process.The critical coal temperature is about 50%.Below this temperature,oxygen consumption decreases with rising coal temperatures and reached a minimum at 50℃,approximately.Subsequently,it begins to increase and the rate of growth clearly increased with temperature.For low ranked coals,this characteristic is inconspicuous or even non-existent.The difference in oxygen consumption at the same temperatures varies for differently ranked coals.The results show the difference in oxygen consumption of the coals tested in our study reached 78.6% at 100 ℃.Based on the theory of coal-oxygen reaction,these phenomena were analyzed from the point of view of physical and chemical characteristics,as well as the appearance of the coal-oxygen complex.From theoretical analyses and our experiments,we conclude that the oxygen consumption at programmed temperatures reflects the oxidation ability of coals perfectly.  相似文献   
9.
利用渐近概周期函数以及序列的定义和基本性质,得出下面离散系统存在正渐近概周期序列解唯一性的充分条件.  相似文献   
10.
以皮尔格LG60轧机轧制304不锈钢管为例,研究皮尔格轧机冷轧不锈钢管回弹预测模型。首先通过单向拉伸试验及数据处理的方法得到材料的分段非线性本构方程;其次根据钢管轧制的塑性变形规律结合增量理论,得到变形过程中各应变分量的计算方法,并把钢管变形过程中的受力状态由三向应力状态转化为单向应力状态,利用材料的卸载定律建立冷轧钢管的回弹预测模型;最后通过大型有限元模拟软件DEFORM-3D进行完整轧制过程的3维有限元模拟仿真,并利用皮尔格轧机进行实际轧制试验验证来检验回弹预测模型的可靠性与正确性。结果表明,本模型精度较高,对皮尔格轧机孔型设计及实际生产中成品管尺寸精度控制有重要指导意义。  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