全文获取类型
收费全文 | 38358篇 |
免费 | 2135篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 242篇 |
综合类 | 17篇 |
化学工业 | 7156篇 |
金属工艺 | 670篇 |
机械仪表 | 731篇 |
建筑科学 | 969篇 |
矿业工程 | 73篇 |
能源动力 | 734篇 |
轻工业 | 5836篇 |
水利工程 | 318篇 |
石油天然气 | 127篇 |
武器工业 | 5篇 |
无线电 | 1286篇 |
一般工业技术 | 5828篇 |
冶金工业 | 11700篇 |
原子能技术 | 139篇 |
自动化技术 | 4690篇 |
出版年
2024年 | 59篇 |
2023年 | 291篇 |
2022年 | 371篇 |
2021年 | 839篇 |
2020年 | 700篇 |
2019年 | 818篇 |
2018年 | 1348篇 |
2017年 | 1316篇 |
2016年 | 1375篇 |
2015年 | 1054篇 |
2014年 | 1276篇 |
2013年 | 2674篇 |
2012年 | 2015篇 |
2011年 | 1922篇 |
2010年 | 1550篇 |
2009年 | 1410篇 |
2008年 | 1363篇 |
2007年 | 1246篇 |
2006年 | 876篇 |
2005年 | 768篇 |
2004年 | 709篇 |
2003年 | 638篇 |
2002年 | 612篇 |
2001年 | 468篇 |
2000年 | 428篇 |
1999年 | 614篇 |
1998年 | 3630篇 |
1997年 | 2383篇 |
1996年 | 1538篇 |
1995年 | 875篇 |
1994年 | 699篇 |
1993年 | 786篇 |
1992年 | 229篇 |
1991年 | 237篇 |
1990年 | 194篇 |
1989年 | 205篇 |
1988年 | 194篇 |
1987年 | 168篇 |
1986年 | 144篇 |
1985年 | 169篇 |
1984年 | 127篇 |
1983年 | 99篇 |
1982年 | 145篇 |
1981年 | 168篇 |
1980年 | 184篇 |
1979年 | 79篇 |
1978年 | 83篇 |
1977年 | 335篇 |
1976年 | 749篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 38 毫秒
971.
In this paper we present adaptive algorithms for solving the uniform continuous piecewise affine approximation problem (UCPA)
in the case of Lipschitz or convex functions. The algorithms are based on the tree approximation (adaptive splitting) procedure.
The uniform convergence is achieved by means of global optimization techniques for obtaining tight upper bounds of the local
error estimate (splitting criterion). We give numerical results in the case of the function distance to 2D and 3D geometric
bodies. The resulting trees can retrieve the values of the target function in a fast way. 相似文献
972.
973.
974.
975.
Rafael Bárcena Ainhoa Etxebarria 《International Journal of Control, Automation and Systems》2010,8(2):244-249
A study on the convenient tuning of fractional-order hold electronic devices for digital control systems is presented. When certain constraints are fulfilled, this study assures in advance the attainment of inverse stable discrete plants. The main result is based on classic numerical analysis techniques and is applicable when the process to be digitally controlled is described as a second order plant or as a first order plant with time delay. In such cases, by using a conveniently tuned fractional-order hold, the discretization nonminimum-phase zeros emerged when using a common zero-order hold are avoided. In this way, the performance of the digitally controlled system may be improved. 相似文献
976.
J.P. Torreglosa F. Jurado P. García L.M. Fernández 《Control Engineering Practice》2011,19(10):1182-1194
This paper focuses on describing a control strategy for a real surface tramway powered by a hybrid system based on fuel cell and battery. This tramway, called Metro Centro, serves the centre of Seville, a city in Spain. Currently, it operates as catenary-powered tramway.The configuration and modeling of all principal components of the hybrid system are briefly described. The models, implemented in MATLAB-Simulink environment, have been designed from commercially available components. The implemented control is based on an equivalent consumption minimization strategy. It allows a suitable energy management of the hybrid system, minimizing the hydrogen consumption. 相似文献
977.
We present in this paper an analysis of a semi-Lagrangian second order Backward Difference Formula combined with hp-finite
element method to calculate the numerical solution of convection diffusion equations in ℝ2. Using mesh dependent norms, we prove that the a priori error estimate has two components: one corresponds to the approximation
of the exact solution along the characteristic curves, which is
O(Dt2+hm+1(1+\frac\mathopen|logh|Dt))O(\Delta t^{2}+h^{m+1}(1+\frac{\mathopen{|}\log h|}{\Delta t})); and the second, which is O(Dtp+|| [(u)\vec]-[(u)\vec]h||L¥)O(\Delta t^{p}+\| \vec{u}-\vec{u}_{h}\|_{L^{\infty}}), represents the error committed in the calculation of the characteristic curves. Here, m is the degree of the polynomials in the finite element space, [(u)\vec]\vec{u} is the velocity vector, [(u)\vec]h\vec{u}_{h} is the finite element approximation of [(u)\vec]\vec{u} and p denotes the order of the method employed to calculate the characteristics curves. Numerical examples support the validity
of our estimates. 相似文献
978.
979.
Rafael Marín-LópezAuthor Vitae Fernando Pereñíguez Author VitaeGabriel López Author Vitae Alejandro Pérez-Méndez Author Vitae 《Computer Standards & Interfaces》2011,33(5):494-504
Kerberos is a well-known standard protocol which is becoming one of the most widely deployed for authentication and key distribution in application services. However, whereas service providers use the protocol to control their own subscribers, they do not widely deploy Kerberos infrastructures to handle subscribers coming from foreign domains, as happens in network federations. Instead, the deployment of Authentication, Authorization and Accounting (AAA) infrastructures has been preferred for that operation. Thus, the lack of a correct integration between these infrastructures and Kerberos limits the service access only to service provider's subscribers. To avoid this limitation, we design an architecture which integrates a Kerberos pre-authentication mechanism, based on the use of the Extensible Authentication Protocol (EAP), and advanced authorization, based on the standards SAML and XACML, to link the end user authentication and authorization performed through an AAA infrastructure with the delivery of Kerberos tickets in the service provider's domain. We detail the interfaces, protocols, operation and extensions required for our solution. Moreover, we discuss important aspects such as the implications on existing standards. 相似文献
980.
Manuel Silva Jorge Júlvez Cristian Mahulea C. Renato Vázquez 《Discrete Event Dynamic Systems》2011,21(4):427-497
As a preliminary overview, this work provides first a broad tutorial on the fluidization of discrete event dynamic models,
an efficient technique for dealing with the classical state explosion problem. Even if named as continuous or fluid, the relaxed models obtained are frequently hybrid in a technical sense. Thus,
there is plenty of room for using discrete, hybrid and continuous model techniques for logical verification, performance evaluation
and control studies. Moreover, the possibilities for transferring concepts and techniques from one modeling paradigm to others
are very significant, so there is much space for synergy. As a central modeling paradigm for parallel and synchronized discrete
event systems, Petri nets (PNs) are then considered in much more detail. In this sense, this paper is somewhat complementary
to David and Alla (2010). Our presentation of fluid views or approximations of PNs has sometimes a flavor of a survey, but also introduces some new
ideas or techniques. Among the aspects that distinguish the adopted approach are: the focus on the relationships between discrete and continuous PN models, both for untimed, i.e., fully non-deterministic abstractions, and timed versions; the use of structure theory of (discrete) PNs, algebraic and graph based concepts and results; and the bridge to Automatic Control Theory. After discussing
observability and controllability issues, the most technical part in this work, the paper concludes with some remarks and
possible directions for future research. 相似文献