全文获取类型
收费全文 | 51538篇 |
免费 | 5512篇 |
国内免费 | 4777篇 |
专业分类
电工技术 | 3920篇 |
技术理论 | 5篇 |
综合类 | 4040篇 |
化学工业 | 3446篇 |
金属工艺 | 1035篇 |
机械仪表 | 2284篇 |
建筑科学 | 2479篇 |
矿业工程 | 549篇 |
能源动力 | 1759篇 |
轻工业 | 1326篇 |
水利工程 | 600篇 |
石油天然气 | 532篇 |
武器工业 | 306篇 |
无线电 | 4580篇 |
一般工业技术 | 4840篇 |
冶金工业 | 1956篇 |
原子能技术 | 440篇 |
自动化技术 | 27730篇 |
出版年
2024年 | 254篇 |
2023年 | 923篇 |
2022年 | 953篇 |
2021年 | 1373篇 |
2020年 | 1675篇 |
2019年 | 1714篇 |
2018年 | 1613篇 |
2017年 | 2020篇 |
2016年 | 2183篇 |
2015年 | 2052篇 |
2014年 | 3238篇 |
2013年 | 4491篇 |
2012年 | 2844篇 |
2011年 | 3379篇 |
2010年 | 2506篇 |
2009年 | 3048篇 |
2008年 | 3017篇 |
2007年 | 3000篇 |
2006年 | 2654篇 |
2005年 | 2292篇 |
2004年 | 1946篇 |
2003年 | 1776篇 |
2002年 | 1583篇 |
2001年 | 1264篇 |
2000年 | 1276篇 |
1999年 | 1102篇 |
1998年 | 982篇 |
1997年 | 858篇 |
1996年 | 755篇 |
1995年 | 673篇 |
1994年 | 593篇 |
1993年 | 548篇 |
1992年 | 431篇 |
1991年 | 412篇 |
1990年 | 335篇 |
1989年 | 253篇 |
1988年 | 222篇 |
1987年 | 179篇 |
1986年 | 155篇 |
1985年 | 188篇 |
1984年 | 198篇 |
1983年 | 175篇 |
1982年 | 177篇 |
1981年 | 118篇 |
1980年 | 78篇 |
1979年 | 88篇 |
1978年 | 65篇 |
1977年 | 70篇 |
1976年 | 20篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
41.
This paper presents the Navigation Maps Modeling approach (NMM), which provides platform independent models for characterizing navigation maps of web applications. The NMM approach is conceived to obtain a trade off between high and low-level design notations. As high-level design notations, NMM models permit architectural details that may hinder the overall understanding of the web application to be left out. As low-level design notations, NMM models can easily be transformed into detailed architectural designs, which are very valuable at coding and maintenance stages. 相似文献
42.
The paper presents a case study of the development of an expert decision support system which uses simple heuristic methods for fast determination of routes for simultaneous signals in a transmission network of limited capacity. It illustrates how heuristic solutions can be embodied in a model-based DSS and how the standard decision support literature, although intuitively appealing, provides little practical assistance in system construction or classification 相似文献
43.
T. R. Black 《Journal of Computer Assisted Learning》1987,3(4):204-213
Abstract In the past, authoring systems have been used to generate computer-assisted learning materials that have often followed the rather restrictive programmed learning format. A number of innovative ways of using recently developed systems to develop CAL packages that include a wider range of learning activities (access to data bases, simulations, interactive video, etc.) are described. Analogous to the concept of a media selection model, a computer delivery mode selection model is presented as an aid to decision making for designers. This increase in flexibility should broaden the applicability of computerassisted learning (CAL) to a wider range of educational objectives and raise the level of the cognitive emphasis in learning packages, as well as facilitate the implementation of visually appealing materials. The paper also implies a standard of acceptability for authoring systems. 相似文献
44.
John W. Reeder 《国际能源研究杂志》1985,9(3):229-239
This paper examines in a very broad fashion the formation of geothermal resources at lithospheric subduction zones. Regions of highly silicic calc-alkaline Quaternary volcanoes and/or plutons have been identified as prime candidates for having high-temperature hydrothermal systems. Regions of large tholeiitic Quaternary volcanoes have been identified as prime candidates for having large moderate-temperature hydrothermal systems. In addition, active magmatic, phreatomagnetic, and/or tectonic fracturing must be occurring in order to keep any moderate to high temperature hydrothermal system from chemically sealing. Connate, meteoric and/or oceanic water sources must also be present. Owing to tectonic and magmatic processes, volcanic arcs of subduction zones represent regions of the crust that have anomalously high mechanical and heat energy. Such arc regions are expected to contain significantly more moderate to high temperature hydrothermal systems than what is presently known. Many of these arcs are briefly discussed with respect to their potential for containing such resources. 相似文献
45.
46.
On formalism and stability of switched systems 总被引:1,自引:1,他引:0
In this paper,we formulate a uniform mathematical framework for studying switched systems with piecewise linear partitioned state space and state dependent switching.Based on known results from the the... 相似文献
47.
This paper investigates the stability analysis and antiwindup design problem for a class of discrete-time switched linear systems with time-varying norm-bounded uncertainties and saturating actuators by using the switched Lyapunov function approach.Supposing that a set of linear dynamic output controllers have been designed to stabilize the switched system without considering its input saturation,we design antiwindup compensation gains in order to enlarge the domain of attraction of the closed-loop system in the presence of saturation.Then,in terms of a sector condition,the antiwindup compensation gains which aim to maximize the estimation of domain of attraction of the closed-loop system are presented by solving a convex optimization problem with linear matrix inequality(LMI)constraints.A numerical example is given to demonstrate the effectiveness of the proposed design method. 相似文献
48.
This paper is concerned with the problem of positive observer synthesis for positive systems with both interval parameter uncertainties and time delay. Conventional observers may no longer be applicable for such kind of systems due to the positivity constraint on the observers, and they only provide an estimate of the system state in an asymptotic way. A pair of positive observers with state‐bounding feature is proposed to estimate the state of positive systems at all times in this paper. A necessary and sufficient condition for the existence of desired observers is first established, and the observer matrices can be obtained easily through the solutions of a set of linear matrix inequalities (LMIs). Then, to reduce the error signal between the system state and its estimates, an iterative LMI algorithm is developed to compute the optimized state‐bounding observer matrices. Finally, a numerical example is presented to show the effectiveness and applicability of the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
49.
Stephen O. Dean 《Journal of Fusion Energy》1988,7(1):25-47
Fusion is an essentially inexhaustible source of energy that has the potential for economically attractive commercial applications with excellent safety and environmental characteristics. The primary focus for the fusion-energy development program is the generation of centralstation electricity. Fusion has the potential, however, for many other applications. The fact that a large fraction of the energy released in a DT fusion reaction is carried by high-energy neutrons suggests potentially unique applications. These include breeding of fissile fuels, production of hydrogen and other chemical products, transmutation or burning of various nuclear or chemical wastes, radiation processing of materials, production of radioisotopes, food preservation, medical diagnosis and medical treatment, and space power and space propulsion. In addition, fusion R&D will lead to new products and new markets.Each fusion application must meet certain standards of economic and safety and environmental attractiveness. For this reason, economics on the one hand, and safety and environment and licensing on the other hand, are the two primary criteria for setting long-range commercial fusion objectives. A major function of systems analysis is to evaluate the potential of fusion against these objectives and to help guide the fusion R&D program toward practical applications. The transfer of fusion technology and skills from the national laboratories and universities to industry is the key to achieving the long-range objective of commercial fusion applications. 相似文献
50.
A network of powerful personal computers, linked by a high-speed local area network, is being seen increasingly as an alternative to a traditional centralized time-sharing operating system. The PULSE project is investigating how such a system may be constructed to give the benefits of a self-sufficient personal computer to each user without losing the facilities for communication and sharing of data inherent in centralized systems. In particular, a distributed file system has been built which provides a single global UNIX 1 UNIX is a trademark of Bell Laboratories. -like hierarchy, with a consistent appearance when accessed from any machine. Replicated copies of files are maintained to improve reliability, increase performance, and enable each machine to run stand-alone, albeit with reduced facilities. 相似文献