首页 | 本学科首页   官方微博 | 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   387篇
  免费   13篇
电工技术   3篇
化学工业   76篇
金属工艺   2篇
机械仪表   11篇
建筑科学   10篇
矿业工程   1篇
能源动力   7篇
轻工业   93篇
水利工程   2篇
无线电   36篇
一般工业技术   62篇
冶金工业   12篇
原子能技术   9篇
自动化技术   76篇
  2021年   3篇
  2020年   4篇
  2019年   8篇
  2018年   6篇
  2017年   7篇
  2016年   8篇
  2015年   6篇
  2014年   13篇
  2013年   21篇
  2012年   12篇
  2011年   26篇
  2010年   14篇
  2009年   16篇
  2008年   19篇
  2007年   15篇
  2006年   19篇
  2005年   20篇
  2004年   16篇
  2003年   18篇
  2002年   13篇
  2001年   4篇
  2000年   4篇
  1999年   9篇
  1998年   6篇
  1997年   6篇
  1996年   2篇
  1995年   8篇
  1994年   3篇
  1993年   7篇
  1992年   10篇
  1991年   2篇
  1990年   3篇
  1989年   3篇
  1988年   4篇
  1986年   5篇
  1985年   5篇
  1983年   4篇
  1982年   6篇
  1981年   2篇
  1980年   3篇
  1978年   5篇
  1977年   3篇
  1976年   6篇
  1973年   4篇
  1967年   3篇
  1966年   2篇
  1962年   2篇
  1958年   2篇
  1956年   1篇
  1955年   2篇
排序方式: 共有400条查询结果,搜索用时 31 毫秒
1.
Aqueous solutions of poly(vinyl pyrrolidone)-fullerene complexes (PVP-C70) have been studied using static and dynamic light scattering methods. Two diffusive processes were detected. The slow diffusion was interpreted as dynamics of large intermolecular PVP-C70 complexes while the fast diffusion was associated with the presence of individual PVP molecules in solution. It was also shown that the molecular weights and dimensions of PVP-C70 complexes are smaller than for PVP-C60 by a factor of 2.5-3. In aqueous solutions of PVP-C70 complex the depolarization and dissymmetry of scattered light were observed in contrast to PVP-C60 solutions. It reveals the existence of anisotropic structures in PVP-C70 solutions. Intermolecular interactions within PVP-C70 complexes are weak and a hydrodynamic field can destroy complexes.  相似文献   
2.
The radiation patterns of simple rectangular waveguide feeds have been measured at V band. A low-cost test arrangement, operating in the far field but without any absorbers, is shown to give better than 0.5 dB repeatability and more than 30 dB of dynamic range. The general rules of waveguide-feed design for reflector antennas are applicable, but the tendency of narrow feed patterns is somewhat emphasized compared to observations in earlier work at C or X band. For horizontal polarization, the difference is 5 dB at 90/spl deg/ between WR-28 and WR-90 hardware. This is partly caused by an increase in the relative guide material thickness at shorter wavelengths. No clear connection between pattern widths of the two linear polarizations was observed if the guide height was increased, the largest momentary deviation being 3 dB for a rectangular 7.1 by 7.1 millimeter feed. Changes in the guide width had a monotone effect up to 3 dB at 90/spl deg/ offset. Very small feed aperture sizes, around /spl lambda//4 or less, did not show respective widening of 1 dB patterns, although such expected effects were visible at lower amplitude levels.  相似文献   
3.
Selective antagonists to the Type 3 serotonin receptor (5HT3) in combination with corticosteroids are now considered the standard of care for the prevention of emesis from moderately to highly emetogenic chemotherapy. Here we address issues of optimal dose, schedule and route of administration of four currently available selectable 5HT3 antagonists. This paper utilizes an evidence based medicine approach to the literature regarding this class of drugs, emphasizing the results large, randomized, controlled trials to make formal recommendations concerning optimal use of this important new class of anti-emetic agents. We conclude that for each drug there is a plateau in therapeutic efficacy at a definable dose level above which further dose escalation does not improve outcome. Furthermore, a single dose is as effective as multiple doses or continuous infusion, and finally, emerging data demonstrate that the oral route is equally efficacious as the intravenous route of administration, even with highly emetogenic chemotherapy.  相似文献   
4.
Flexible integration of distributed design and manufacturing activities is one of the key issues in applying just-in-time principles along the logistics chain. The potential of AI based approaches in this field is clear, but the inherent asynchrony, concurrency, and inconsistency of distributed operations has reduced enthusiasm so far.This paper discusses coordination in the context of geographically distributed manufacturing of one-of-a-kind products. Cooperation of partners is based on semi-automated user agents which operate as an integrative layer between more dedicated tools and systems. The management of order changes in elevator manufacture is used as a case example.The work reported here is part of the DIMUN project (DIMUN, 1989) in the RACE program.  相似文献   
5.
Zusammenfassung Es wird über ein Verfahren zur Abtrennung der in gegrillten und geräucherten Lebensmitteln enthaltenen mutagenen polycyclischen organischen Stoffe in einzelne Klassen berichtet. Das Verfahren umfaßt eine erste Extraktion mit Aceton, das Abscheiden von Fett und Proteinen durch Ausfällung bei –55 °C und eine Säure-Base-Extraktion. Die weitere Fraktionierung erfolgte durch Gelfiltration und Silicagel-Chromatographie. Bei vier Proben von gegrillten Würsten waren 80 bis 90% der extrahierten Mutagenität (TA98 + S9) in den basischen Fraktionen enthalten. Die in der Flamme gegrillten Würste hatten eine höhere Mutagenität als die auf Holzkohle gegrillten. Bei den geräucherten Fischen war die Mutagenität gering und verteilte sich gleichmäßig auf die basischen und die neutralen/sauren Fraktionen. Einige Proben zeigten schwache Direktmutagenität in den neutralen/sauren Fraktionen. Die Anwesenheit von Nitrit in den gegrillten Würsten hatte keinen erheblichen Einfluß auf die Mutagenität. Die Gaschromatographie, Selektive Ionregistrierung-Technik, wurde erfolgreich zur Identifizierung mehrerer PAH-Verbindungen eingesetzt, und mit ihr konnten mehrere Nitro-PAH und oxydierte Verbindungen vorläufig identifiziert werden. Der Nachweis der Mutagene in den basischen Fraktionen gestaltete sich jedoch wegen Peak-Schweifbildung und mit-eluierenden Materials kompliziert.Summary A method for class separation of mutagenic polycyclic organic material in grilled and smoked foods is described. The procedure involves an initial extraction with acetone, removal of fat and proteins by precipitation at –55 °C, and an acid-base extraction. Further fractionation was carried out by gel filtration and silica gel chromatography. In four samples of grilled sausages, 80%–90% of the extracted mutagenicity (TA98 + S9) was contained in the basic fractions. Flame-grilled sausages showed higher mutagenicity than charcoal-grilled ones. In a smoked fish sample, the mutagenicity was low and evenly distributed between the basic and the neutral/acidic fractions. A few samples showed a weak direct-acting mutagenicity in the neutral/acidic fractions. The presence of nitrite in grilled sausages did not influence the mutagenicity markedly. Gas chromatography-selected ion monitoring was used to successfully identify a number of polycyclic aromatic hydrocarbons (PAHs) and tentatively identify several nitro-PAHs and oxygenated compounds. However, the identification of mutagens in the basic fractions was complicated by peak tailing and the presence of co-eluting material.
Abtrennung mutagenen polycyclischen organischen Materials in gegrillten und geräucherten Lebensmitteln
  相似文献   
6.
This study demonstrates the usefulness of capillary supercritical fluid chromatography (SFC) for the characterization of triacylglycerols of edible oils and fats. Triacylglycerols were separated according to the acyl carbon number and the degree of unsaturation on a 25% cyanopropyl/25% phenyl/50% methylpolysiloxane stationary phase. Valuable information concerning the triacylglycerol composition of berry oils was obtained, despite the overlapping of certain triacylglycerol peaks. Simultaneous analysis of fat-soluble vitamins and triacylglycerols is not practical by capillary SFC with flame-ionization detection because of the low concentration of naturally-occurring fat-soluble vitamins in edible oils. Therefore, higher loading of the sample, which led to overloading of triacylglycerols, was required to get reasonable peaks for fat-soluble vitamins. The method was applied to the characterization of triacylglycerols and tocopherols in sea buckthorn pulp and seed oil, and cloudberry seed oil without any sample purification prior to SFC. In addition, the stationary phase proved useful for separating the more complex mixtures of triacylglycerols found in milk fat and in fish oil.  相似文献   
7.
It is relatively stress-free to write about computer games as nothing too much has been said yet, and almost anything goes. The situation is pretty much the same when it comes to writing about games and gaming in general. The sad fact with alarming cumulative consequences is that they are under-theorized; there are Huizinga, Caillois and Ehrmann of course, and libraries full of board game studies,in addition to game theory and bits and pieces of philosophy – most notably those of Wittgenstein – but they won't get us very far with computer games. So if there already is or soon will be a legitimate field for computer game studies, this field is also very open to intrusions and colonisations from the already organized scholarly tribes. Resisting and beating them is the goal of our first survival game in this paper, as what these emerging studies need is independence, or at least relative independence.  相似文献   
8.
Human movement in virtual environments (VEs) is a largely unstudied area, and there are no well-established methods of measuring it in VEs. Consequently, it is unclear how movement affects the experiential side of VEs. We introduce a novel method of measuring and modelling human movement. A specific information entropy-based modelling method enabled us to identify different movement patterns and analyse the experiential components related to them. The data was collected by registering the movement patterns of 68 participants who were in a virtual house doing a search task. The experiential side of the VE was measured with the Experimental Virtual Environment Questionnaire (EVEQ). Four movement patterns were identified. In addition, fluent movement in VEs was related to a high sense of presence. Moreover, the participants who moved fluently in the environment assessed their skills high. The results show how movement is related the way in which people experience the VE. The movement analysis method introduced here is applicable to other related research areas as well.  相似文献   
9.
We extracted a collection of eye movement signals employed for almost two decades in clinical otoneurological tests at a balance laboratory. During those years we designed and programmed signal analysis methods to analyse their features in detail and to compute medically important attributes. In the present study, using such attributes and their results computed we classified test cases into groups of healthy subjects and patients with multilayer perceptron neural networks. Classification succeeded in total accuracies from 60% to 90% depending on the type of eye movements, which were saccades, nystagmus, sinusoidal movements and vestibulo-ocular reflex stimulated in two different ways; these are the chief eye movement tests applied in otoneurology.  相似文献   
10.
The prevalent visions of ambient intelligence emphasise natural interaction between user and functions and services embedded in the environment or available through mobile devices. In these scenarios the physical and virtual worlds seamlessly gear into each other, making crossing the border between these worlds natural or even invisible to the user. The bottleneck in reaching these scenarios appear in the natural mapping between the physical objects and their virtual counterparts. The emergence of local connectivity in mobile devices opens possibilities for implementing novel user interface paradigms to enhance this mapping. We present physical selection paradigm for implementing an intuitive human technology interaction for mobile devices. In order to demonstrate the feasibility of the paradigm we implemented two experimental set-ups using commercially available smart phones with IrDA connectivity. The experiments involved selecting a website by physically pointing at its symbol and making a phone call by pointing at an icon representing the person to be called. In tentative user experiments the physical selection method was more time-efficient and it was perceived more positively by the users than a conventional method.
Heikki AilistoEmail:
  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