全文获取类型
收费全文 | 292788篇 |
免费 | 32346篇 |
国内免费 | 23377篇 |
专业分类
电工技术 | 39063篇 |
技术理论 | 15篇 |
综合类 | 32501篇 |
化学工业 | 19118篇 |
金属工艺 | 10557篇 |
机械仪表 | 24792篇 |
建筑科学 | 27422篇 |
矿业工程 | 11124篇 |
能源动力 | 10352篇 |
轻工业 | 8551篇 |
水利工程 | 13612篇 |
石油天然气 | 12507篇 |
武器工业 | 4455篇 |
无线电 | 23008篇 |
一般工业技术 | 18678篇 |
冶金工业 | 11387篇 |
原子能技术 | 2451篇 |
自动化技术 | 78918篇 |
出版年
2024年 | 541篇 |
2023年 | 3600篇 |
2022年 | 6478篇 |
2021年 | 8021篇 |
2020年 | 9038篇 |
2019年 | 7470篇 |
2018年 | 6940篇 |
2017年 | 9366篇 |
2016年 | 10749篇 |
2015年 | 11620篇 |
2014年 | 19062篇 |
2013年 | 17875篇 |
2012年 | 21674篇 |
2011年 | 23246篇 |
2010年 | 17950篇 |
2009年 | 18483篇 |
2008年 | 18486篇 |
2007年 | 21932篇 |
2006年 | 19385篇 |
2005年 | 17029篇 |
2004年 | 13920篇 |
2003年 | 12257篇 |
2002年 | 9751篇 |
2001年 | 8027篇 |
2000年 | 6827篇 |
1999年 | 5346篇 |
1998年 | 4247篇 |
1997年 | 3621篇 |
1996年 | 3086篇 |
1995年 | 2650篇 |
1994年 | 2228篇 |
1993年 | 1583篇 |
1992年 | 1295篇 |
1991年 | 981篇 |
1990年 | 769篇 |
1989年 | 660篇 |
1988年 | 446篇 |
1987年 | 268篇 |
1986年 | 206篇 |
1985年 | 204篇 |
1984年 | 249篇 |
1983年 | 161篇 |
1982年 | 176篇 |
1981年 | 109篇 |
1980年 | 98篇 |
1979年 | 110篇 |
1978年 | 64篇 |
1977年 | 53篇 |
1959年 | 29篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
A multiphase dc‐dc converter is effective for miniaturization and achieving high‐power density in a switching power supply. However, its mathematical modeling becomes complex as the phase number of the circuit increases. This study proposes a new modeling method to derive a reduced‐order method in a simple manner. The frequency characteristics of the reduced‐order model are fit to those of the original mathematical model of the multiphase dc‐dc converter. Therefore, the efficacy of the proposed method is validated. 相似文献
92.
Yaghoub Azizi Alireza Yazdizadeh 《International Journal of Adaptive Control and Signal Processing》2019,33(3):512-526
Mechanical systems are always suffering from the effects of temperature dependent friction forces where the system is operated in a wide range of temperature. Temperature and its variation play an important role in friction force in mechanical systems. If it is not compensated, it will tend to unwanted consequences, including steady‐state errors, limit cycling, and hunting. Therefore, it is necessary to take the temperature effects into account. This has been a strong motivation for the researchers to work on temperature effects on joint friction. In this paper, an adaptive compensation (control) scheme is proposed and applied to a 2‐degree‐of‐freedom serial robot manipulator by taking the temperature effects into account on the joints friction. In the proposed control scheme, the temperature is not required to be sensed. In this paper, joint friction is described by LuGre dynamic model with temperature dependent parameters. These parameters are described by some functions with unknown temperature dependent terms. According to the mathematical and practical concepts, the temperature dependent friction is decomposed into a viscous term and a disturbance term. An adaptive controller is designed to compensate the friction effect and it is shown that the proposed controller relaxes the condition for a priori knowledge about the environment characteristics, including the upper and lower bounds of the environment temperature and the parameters of the functions, describing the temperature dependent joint frictions. The stability and convergence of the joint position and velocity are proved in the sense of Lyapunov and then the proposed method is confirmed by the simulations. 相似文献
93.
To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses. 相似文献
94.
Miroslav Kárný Marko Ruman 《International Journal of Adaptive Control and Signal Processing》2021,35(5):660-675
Any knowledge extraction relies (possibly implicitly) on a hypothesis about the modelled-data dependence. The extracted knowledge ultimately serves to a decision-making (DM). DM always faces uncertainty and this makes probabilistic modelling adequate. The inspected black-box modeling deals with “universal” approximators of the relevant probabilistic model. Finite mixtures with components in the exponential family are often exploited. Their attractiveness stems from their flexibility, the cluster interpretability of components and the existence of algorithms for processing high-dimensional data streams. They are even used in dynamic cases with mutually dependent data records while regression and auto-regression mixture components serve to the dependence modeling. These dynamic models, however, mostly assume data-independent component weights, that is, memoryless transitions between dynamic mixture components. Such mixtures are not universal approximators of dynamic probabilistic models. Formally, this follows from the fact that the set of finite probabilistic mixtures is not closed with respect to the conditioning, which is the key estimation and predictive operation. The paper overcomes this drawback by using ratios of finite mixtures as universally approximating dynamic parametric models. The paper motivates them, elaborates their approximate Bayesian recursive estimation and reveals their application potential. 相似文献
95.
96.
Sayan Basu Roy Shubhendu Bhasin 《International Journal of Adaptive Control and Signal Processing》2019,33(12):1759-1774
This paper is a generalization of the recently developed techniques of initial excitation (IE)–based adaptive control with an introduction to the definition of semi‐initial excitation (semi‐IE), a still more relaxed notion than IE. Classical adaptive controllers typically ensure Lyapunov stability of the extended error dynamics (tracking error + parameter estimation error) and asymptotic tracking, while requiring a stringent condition of persistence of excitation (PE) for parameter convergence. Of late, the authors have proposed a new adaptive control architecture, which guarantees parameter convergence under the online‐verifiable IE condition leading to exponential stability of the extended error dynamics. In earlier works, it has been established that the IE condition is significantly milder than the classical PE condition. The current work further slackens the excitation condition by proposing the concept of semi‐IE. The proposed adaptive controller is proved to ensure convergence of the parameter estimation error to a lower‐dimensional manifold under the weaker semi‐IE condition, while the stronger condition of IE guarantees convergence of the parameter estimation error to zero. The designed algorithm is shown to improve transient response of tracking error sufficiently in contrast to conventional adaptive controllers. 相似文献
97.
仲春华 《皮革制作与环保科技》2021,(5):34-35
社会经济的快速发展对生态环境造成了较大破坏,并产生了一系列连锁反应,不利于我国可持续发展目标的实现。为此,必须要切实做好环境监测工作。本文从环境监测的概念出发,就现阶段的环境监测现状进行了分析,并在此基础上阐述了环境监测工作未来发展及优化对策,以供参考。 相似文献
98.
Xin-Yu Zhang Li Tang Yan-Jun Liu 《International Journal of Adaptive Control and Signal Processing》2021,35(7):1404-1416
In this article, based on partial differential equations (PDEs), the flexible manipulator system with both dead-zone input and state constraints is studied. The dynamic model of the flexible manipulator system is described by PDEs. The parameters of the dead-zone input are unknown, and the state constraint problem is also considered. An adaptive approach is proposed to offset the effects caused by dead-zone input. Thus, to guarantee that all states remain within their respective constraint regions, the boundary control law based on the barrier Lyapunov function is given, and an adaptive controller is designed. According to the Lyapunov analysis method, the control method is given to ensure that all signals of the closed-loop system are bounded and all states satisfy the constraint conditions. Finally, simulation results show the effectiveness of the proposed control method in this article. 相似文献
99.
100.
Jun Yang Jing Na Guanbin Gao 《International Journal of Adaptive Control and Signal Processing》2019,33(12):1868-1884
This paper provides a modified model reference adaptive control (MRAC) scheme to achieve better transient control performance for systems with unknown unmatched dynamics, where an adaptive law with guaranteed convergence is introduced. We first revisit the standard MRAC system and analyze the tracking error bound by using L2‐norm and Cauchy‐Schwartz inequality. Based on this analysis, we suggest a feasible way to compensate the undesired transient dynamics induced by the gradient descent–based adaptive laws subject to sluggish convergence or even parameter drift. Then, a modified adaptive law with an alternative leakage term containing the parameter estimation error is developed. With this adaptive law, the convergence of both the estimation error and tracking error can be proved simultaneously. This enhanced convergence property can contribute to deriving smoother control signal and improved control response. Moreover, this paper provides a simple and numerically feasible approach to online verify the well‐known persistent excitation condition by testing the positive definiteness of an introduced auxiliary matrix. Comparative simulations based on a benchmark 3‐DOF helicopter model are given to validate the effectiveness of the proposed MRAC approach and show the improved performance over several other MRAC schemes. 相似文献