全文获取类型
收费全文 | 1780篇 |
免费 | 97篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 38篇 |
综合类 | 12篇 |
化学工业 | 556篇 |
金属工艺 | 45篇 |
机械仪表 | 40篇 |
建筑科学 | 127篇 |
矿业工程 | 2篇 |
能源动力 | 52篇 |
轻工业 | 136篇 |
水利工程 | 3篇 |
石油天然气 | 3篇 |
无线电 | 128篇 |
一般工业技术 | 342篇 |
冶金工业 | 126篇 |
原子能技术 | 18篇 |
自动化技术 | 255篇 |
出版年
2023年 | 18篇 |
2022年 | 34篇 |
2021年 | 45篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 41篇 |
2017年 | 32篇 |
2016年 | 56篇 |
2015年 | 66篇 |
2014年 | 69篇 |
2013年 | 81篇 |
2012年 | 84篇 |
2011年 | 137篇 |
2010年 | 93篇 |
2009年 | 100篇 |
2008年 | 84篇 |
2007年 | 89篇 |
2006年 | 58篇 |
2005年 | 64篇 |
2004年 | 54篇 |
2003年 | 43篇 |
2002年 | 46篇 |
2001年 | 24篇 |
2000年 | 30篇 |
1999年 | 39篇 |
1998年 | 45篇 |
1997年 | 28篇 |
1996年 | 31篇 |
1995年 | 23篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1969年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有1883条查询结果,搜索用时 0 毫秒
21.
Prof. Dr. phil. nat. W. Gerlach Dr.-Ing. N. Qu 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(6):433-444
Contents A fine structured GTO thyristor, abbreviated FGTO, has been developed to improve the switching characteristics. The new device has a cathode finger width of only 20 m and can be turned off without a negative gate bias at an anode current level of more than 200 A/cm2. The turn-off time can be shortened down tot
off
500 ns by increasing the negative gate current. A snubber circuit is not necessary to turn off the FGTO's. The maximum rate of rise of anode voltage du/dl reaches more than 10 kV/s. Analytical models are developed to describe the turn-off transients of the FGTO's. Good agreement between the theoretical and experimental results could be achieved.
FGTO — Ein feinstrukturierter GTO-Thyristor mit verbessertem Schaltverhalten
Übersicht Zur Verbesserung des Schaltverhaltens ist ein feinstrukturierter GTO-Thyristor, abgekürzt FGTO, entwickelt worden. Dieses neue Bauelement hat eine Kathoden-streifenbreite von nur 20 m und kann ohne negative Gatevorspannung bei einer Anodenstromdichte von mehr als 200 A/cm2 abgeschaltet werden. Die Abschaltzeit läßt sich durch Erhöhung des negativen Gatestroms bis zut off 500 ns verkürzen. Beim Abschalten von FGTOs ist keine RC-Beschaltung erforderlich. Der maximale du/dl-Wert erreicht mehr als 10 kV/s. Zur Beschreibung des Abschalt-verhaltens von FGTOs werden analytische Modelle entwickelt, die eine gute Übereinstimmung mit den Meßergebnissen liefern.相似文献
22.
We have investigated the surface of thin films (thickness 2 µm) of solid H2 between 1.5 and 4.2 K by measuring the ac conductivity of surface-state electrons (SSE). The films were prepared on a glass substrate by quench condensation at 1.5 K and were therefore initially strongly disordered. In fact the surface of the virgin films before any heat treatment was so rough that no current due to SSE could be observed. Annealing the films decreased the surface roughness and gave rise to a thermal-activation-type temperature dependence of the SSE conductivity. By proper heat treatment up to 8 K the activation energy could be reduced to 10k
B.On leave from the Hyogo University of Teacher Education, Shimokume 942-1, Yashiro, 673-14, Japan. 相似文献
23.
Christoph Windmeier Felix Flegiel Alexander Döß Ronald Franz Eckhard Schleicher Michael Wiezorek Markus Schubert Uwe Hampel 《化学,工程师,技术》2021,93(7):1119-1125
An optimized equipment design for natural gas processing and liquefaction plants becomes increasingly difficult with changing process conditions: Particularly low values of surface tension create rising challenges on the design of phase separators and column internals. The TERESA test rig at HZDR was designed to allow the investigation of multiphase thermohydraulics and phase separator performance under critical fluid properties in industrial dimensions. A versatile pipe test section is available in DN200 and equipment internals may be tested in a sectional DN300/DN500 test separator. The applied test fluid shows a high vapor-liquid density difference between 1470 and 940 kg m−3, viscosity as low as 0.12 mm2s−1, and surface tension down to 1.3 mN m−1. Volumetric liquid and vapor flow rates may be varied up to 9 and 530 m3h−1 in the test rig, respectively. 相似文献
24.
Andrei Tchernykh Luz Lozano Uwe Schwiegelshohn Pascal Bouvry Johnatan E. Pecero Sergio Nesmachnow Alexander Yu. Drozdov 《Journal of Grid Computing》2016,14(1):5-22
This paper focuses on a bi-objective experimental evaluation of online scheduling in the Infrastructure as a Service model of Cloud computing regarding income and power consumption objectives. In this model, customers have the choice between different service levels. Each service level is associated with a price per unit of job execution time, and a slack factor that determines the maximal time span to deliver the requested amount of computing resources. The system, via the scheduling algorithms, is responsible to guarantee the corresponding quality of service for all accepted jobs. Since we do not consider any optimistic scheduling approach, a job cannot be accepted if its service guarantee will not be observed assuming that all accepted jobs receive the requested resources. In this article, we analyze several scheduling algorithms with different cloud configurations and workloads, considering the maximization of the provider income and minimization of the total power consumption of a schedule. We distinguish algorithms depending on the type and amount of information they require: knowledge free, energy-aware, and speed-aware. First, to provide effective guidance in choosing a good strategy, we present a joint analysis of two conflicting goals based on the degradation in performance. The study addresses the behavior of each strategy under each metric. We assess the performance of different scheduling algorithms by determining a set of non-dominated solutions that approximate the Pareto optimal set. We use a set coverage metric to compare the scheduling algorithms in terms of Pareto dominance. We claim that a rather simple scheduling approach can provide the best energy and income trade-offs. This scheduling algorithm performs well in different scenarios with a variety of workloads and cloud configurations. 相似文献
25.
Uwe Neumann 《Journal of population ageing》2013,6(3):189-209
Among the highly developed countries, demographic ageing is particularly advanced in Germany. Accentuated by migration, there is great regional variation in the progress of demographic change. Within urban areas, residential neighbourhoods differ considerably in their demographic composition and perspectives. Based on municipal data, this paper examines regional variability in the diversity and pace of neighbourhood-level ageing. Focusing on the Rhine-Ruhr conurbation in North Rhine-Westphalia, the analysis outlines at what pace ageing proceeds in a variety of neighbourhoods, which attract no constant influx of working-age migrants. After decades of suburbanisation, in the period from 1998 to 2008 regional migration concentrated on the central districts of large cities. More profoundly in the most prosperous cities growing in population than in other cities, childless working-age adults separate from other age groups and family types in selected central city quarters. The findings suggest that spatial differentials in ageing are likely to affect future location decisions and, thereby, regional and local prosperity. 相似文献
26.
Leonid B. Freidovich Pedro La Hera Uwe Mettin Anders Robertsson Anton S. Shiriaev Rolf Johansson 《Asian journal of control》2009,11(5):548-556
We consider an underactuated two‐link robot called the inertia wheel pendulum. The system consists of a free planar rotational pendulum and a symmetric disk attached to its end, which is directly controlled by a DC‐motor. The goal is to create stable oscillations of the pendulum, which is not directly actuated. We exploit a recently proposed feedback‐control design strategy based on motion planning via virtual holonomic constraints. This strategy is shown to be useful for design of regulators for achieving orbitally exponentially stable oscillatory motions. The main contribution is a step‐by‐step procedure on how to achieve oscillations with pre‐specified amplitude from a given range and an arbitrary independently chosen period. The theoretical results are verified via experiments with a real hardware setup. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society 相似文献
27.
28.
Biologically-inspired methods such as evolutionary algorithms and neural networks are proving useful in the field of information fusion. Artificial immune systems (AISs) are a biologically-inspired approach which take inspiration from the biological immune system. Interestingly, recent research has shown how AISs which use multi-level information sources as input data can be used to build effective algorithms for realtime computer intrusion detection. This research is based on biological information fusion mechanisms used by the human immune system and as such might be of interest to the information fusion community. The aim of this paper is to present a summary of some of the biological information fusion mechanisms seen in the human immune system, and of how these mechanisms have been implemented as AISs. 相似文献
29.
Peter Coschurba Joachim Baumann Uwe Kubach Alexander Leonhardi 《Personal and Ubiquitous Computing》2001,5(1):16-19
Metaphors are often used to provide the user with a mental model to ease the use of computers. An example of such a metaphor
is the commonly used “Desktop Metaphor”. Metaphors also can be used to ease context-aware information access for the users
of mobile information systems. In this paper we present a taxonomy that allows the categorisation of such metaphors. Furthermore,
we give an overview of existing metaphors and their implementations. After introducing some new metaphors we conclude our
considerations with a classification of new and existing metaphors using our taxonomy. 相似文献
30.
Metrics for shot boundary detection in digital video sequences 总被引:5,自引:0,他引:5
The detection of shot boundaries in video sequences is an important task for generating indexed video databases. This paper
provides a comprehensive quantitative comparison of the metrics that have been applied to shot boundary detection. In addition,
several standardized statistical tests that have not been applied to this problem, as well as three new metrics, are considered.
A mathematical framework for quantitatively comparing metrics is supplied. Experimental results based on a video database
containing 39,000 frames are included. 相似文献