首页 | 官方网站   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   2565篇
  免费   257篇
  国内免费   81篇
工业技术   2903篇
  2024年   19篇
  2023年   66篇
  2022年   124篇
  2021年   115篇
  2020年   141篇
  2019年   88篇
  2018年   92篇
  2017年   101篇
  2016年   120篇
  2015年   121篇
  2014年   151篇
  2013年   143篇
  2012年   187篇
  2011年   186篇
  2010年   139篇
  2009年   183篇
  2008年   121篇
  2007年   139篇
  2006年   147篇
  2005年   103篇
  2004年   62篇
  2003年   57篇
  2002年   59篇
  2001年   54篇
  2000年   54篇
  1999年   43篇
  1998年   20篇
  1997年   10篇
  1996年   12篇
  1995年   6篇
  1994年   5篇
  1993年   6篇
  1992年   13篇
  1991年   3篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1982年   3篇
  1962年   1篇
排序方式: 共有2903条查询结果,搜索用时 15 毫秒
21.
In this paper, we present an analysis and synthesis approach for guaranteeing that the phase of a single-input, single-output closed-loop transfer function is contained in the interval [−α,α] for a given α>0 at all frequencies. Specifically, we first derive a sufficient condition involving a frequency domain inequality for guaranteeing a given phase constraint. Next, we use the Kalman–Yakubovich–Popov theorem to derive an equivalent time domain condition. In the case where , we show that frequency and time domain sufficient conditions specialize to the positivity theorem. Furthermore, using linear matrix inequalities, we develop a controller synthesis approach for guaranteeing a phase constraint on the closed-loop transfer function. Finally, we extend this synthesis approach to address mixed gain and phase constraints on the closed-loop transfer function.  相似文献   
22.
In this study, the crack propagation behaviors in the equiaxed and equiaxed-columnar grain regions of a heat-treated laser additive manufacturing (LAM) TC11 alloy with a special bi-modal microstructure are investigated. The results indicate that the alloy presents a special bi-modal microstructure that comprises a fork-like primary α (αp) phase surrounded by a secondary α colony (αs) in the β phase matrix after the heat treatment is completed. The samples demonstrate a fast crack growth rate with larger da/dN values through the equiaxed grain sample versus across the equiaxed-columnar grain sample at low ΔK values (<13.8). The differences that are observed between the crack propagation behaviors (in the crack initiation stage) of the samples can be mostly attributed to the different size and morphology of the αp lamellae and αs colony within the grains in the equiaxed and columnar grain regions rather than the grain boundaries. The cracks prefer to grow along the α/β boundary with a smooth propagation route and a fast propagation rate in the equiaxed grain region, where the αp and α clusters have a large size. However, in the columnar grain region, small and randomly distributed αp lamellae generate a zigzag-shaped propagation path with a reduction in the da/dN value. Additionally, the change in the size of the αp lamellae in the equiaxed grains (heat affected bands, HAB) is also observed to influence the propagation behavior of the crack during the crack initiation stage.  相似文献   
23.
研究了TC11钛合金中α"相和α'相的显微组织转变和显微硬度。金相显微组织观察和X射线衍射分析的结果表明: 随着固溶温度的提高α"相逐渐向α'相的晶体结构转变,α相、α"相和α'相的显微组织演变规律为:α+α",α+α"+α',α+α',α'。显微硬度测试的结果表明:在935~995℃固溶后显微硬度随着温度的提高先增大后减少,在985℃固溶后显微硬度达到峰值。综合分析显微组织影响合金显微硬度的机理:在935~985℃固溶后α'片层的厚度和间距变化的幅度小,β转变组织长大缓慢,在β转变组织中先后析出α"和α'相,随着固溶温度的提高α'片层的含量随之提高产生了相变强度效果,使其显微硬度提高;在985~995℃固溶后α'片层的厚度和间距明显增大,β转变组织变粗大,α"相消失,α'相的含量降低,相变强化的效果减弱,使β转变组织的显微硬度降低。  相似文献   
24.
The p--T relationships have been measured for 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 158 to 400 K for R152a and from 166 to 400 K for R143a, while pressures were up to 35 MPa. Measurements were conducted on compressed liquid samples. Determinations of saturated liquid densities were made by extrapolating each isochore to the vapor pressure, and determining the temperature and density at the intersection. Published p--T data are in good agreement with this study. For the p--T apparatus, the uncertainty of the temperature is ±0.03 K, and for pressure it is ±0.01% at p>3 MPa and ±0.05% at p&#60;3 MPa. The principal source of uncertainty is the cell volume (28.5 cm3), which has a standard uncertainty of ±0.003 cm3. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) of the density measurements is estimated to be ±0.05%.  相似文献   
25.
介绍了台湾凌阳科技公司的16位单片机SPCE061A和Siemens公司TC35系列的TC35i。详细介绍了TC35i的原理、特性和系统的硬件构成。设计并实现了一款有短信收发功能的智能电子锁。  相似文献   
26.
For a positive integer d, an L(d,1)-labeling f of a graph G is an assignment of integers to the vertices of G such that |f(u)−f(v)|?d if uvE(G), and |f(u)−f(v)|?1 if u and u are at distance two. The span of an L(d,1)-labeling f of a graph is the absolute difference between the maximum and minimum integers used by f. The L(d,1)-labeling number of G, denoted by λd,1(G), is the minimum span over all L(d,1)-labelings of G. An L(d,1)-labeling of a graph G is an L(d,1)-labeling of G which assigns different labels to different vertices. Denote by the L(d,1)-labeling number of G. Georges et al. [Discrete Math. 135 (1994) 103-111] established relationship between the L(2,1)-labeling number of a graph G and the path covering number of Gc, the complement of G. In this paper we first generalize the concept of the path covering of a graph to the t-group path covering. Then we establish the relationship between the L(d,1)-labeling number of a graph G and the (d−1)-group path covering number of Gc. Using this result, we prove that and for bipartite graphs G can be computed in polynomial time.  相似文献   
27.
We consider the stochastic input-output properties of a simple non-linear dynamical system, the so-called Page-Hinkley detector, playing a key role in change detection, and also in queuing theory. We show that for L-mixing inputs with negative expectation the output process of this system is L-mixing. The result is applied to get an upper bound for the false alarm rate. The proof is then adapted to get a similar result for the case of random i.i.d. inputs. Possible extensions and open problems are given in the discussion.  相似文献   
28.
应用TC35I模块和DS18B30单总线数字温度传感器模块,利用STC89C52RC微控制器和GSM移动通信网络中的短消息业务,设计一种基于TC35I的汽车空调温控系统,详细阐述了系统的基本组成和相关的软硬件方面的设计.系统具有实时性、操作简单、实用等优点.  相似文献   
29.
Stability of linear systems with uncertain bounded time-varying delays is studied under the assumption that the nominal delay values are not equal to zero. An input-output approach to stability of such systems is known to be based on the bound of the L2-norm of a certain integral operator. There exists a bound on this operator norm in two cases: in the case where the delay derivative is not greater than 1 and in the case without any constraints on the delay derivative. In the present note we fill the gap between the two cases by deriving a tight operator bound which is an increasing and continuous function of the delay derivative upper bound d?1. For d→∞ the new bound corresponds to the second case and improves the existing bound. As a result, for the first time, delay-derivative-dependent frequency domain and time domain stability criteria are derived for systems with the delay derivative greater than 1.  相似文献   
30.
Robert   《Automatica》2006,42(12):2151-2158
This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of lp exogenous disturbances and the robust stabilization of lp unstructured perturbations, for all p[1,∞].  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-23

京公网安备 11010802026262号