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   1733篇
  免费   127篇
  国内免费   1篇
电工技术   20篇
综合类   2篇
化学工业   465篇
金属工艺   15篇
机械仪表   31篇
建筑科学   66篇
矿业工程   1篇
能源动力   95篇
轻工业   178篇
水利工程   6篇
石油天然气   5篇
无线电   139篇
一般工业技术   288篇
冶金工业   47篇
原子能技术   28篇
自动化技术   475篇
  2024年   4篇
  2023年   13篇
  2022年   55篇
  2021年   105篇
  2020年   49篇
  2019年   91篇
  2018年   69篇
  2017年   68篇
  2016年   85篇
  2015年   68篇
  2014年   85篇
  2013年   131篇
  2012年   130篇
  2011年   141篇
  2010年   115篇
  2009年   107篇
  2008年   91篇
  2007年   68篇
  2006年   65篇
  2005年   50篇
  2004年   53篇
  2003年   27篇
  2002年   15篇
  2001年   17篇
  2000年   20篇
  1999年   12篇
  1998年   12篇
  1997年   22篇
  1996年   11篇
  1995年   8篇
  1994年   4篇
  1993年   7篇
  1992年   3篇
  1991年   7篇
  1990年   6篇
  1988年   4篇
  1985年   8篇
  1984年   1篇
  1983年   6篇
  1982年   1篇
  1981年   2篇
  1980年   7篇
  1979年   3篇
  1978年   4篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
  1974年   3篇
  1973年   1篇
  1972年   1篇
排序方式: 共有1861条查询结果,搜索用时 109 毫秒
991.
The development of a divertor concept for fusion power plants that is able to grant efficient recovery and conversion of the considerable fraction (~15%) of the total fusion thermal power incident is deemed to be an urgent task to meet in the EU Fast Track scenario. The He-cooled conceptual divertor design is one of the possible candidates. Helium cooling offers several advantages including chemical and neutronic inertness and the ability to operate at higher temperatures and lower pressures than those required for water cooling. The HETS (high-efficiency thermal shield) concept, initially developed by ENEA for water, has been adapted for use with He as coolant. This DEMO divertor concept is based on elements joined in series and protected by a hemispheric dome; it allows an increase of thermal exchange coefficient both for high speed of gas and for “jet impingement” effects of gas coming out from the internal side of hemispheric dome. It has been calculated to be capable of sustaining an incident heat flux of 10 MW/m2 when operating at 10 MPa, an inlet He temperature of 600 °C, and an outlet temperature of 800 °C. The presented activity, performed in the frame of EFDA-TW5TRP-001 task, was focused on the manufacturing of a single HETS module and on its thermal–hydraulic testing. The materials used for the HETS module manufacturing were all DEMO-compatible: W for the armor material and the hemispherical-dome, DENSIMET for the exchanger body. The testing is performed by connecting the module to HEFUS3 He loop system that is a facility able to supply the He flow to the required testing conditions: 400 °C, 4–8 MPa and 20–40 g/s. The needed incident heat flux is obtained by RF inducting equipment coupled to an inductor coil installed just over the HETS module. A CFD analysis by ANSYS-CFX was performed in order to predict the thermal–mechanical behavior of the module and a final comparison with the experimental data is required to validate the CFD results. All parameters are monitored and recorded by data acquisition system.  相似文献   
992.
BACKGROUND: The enrichment of fruit juices with concentrated polyphenolic extracts is an expedient strategy to compensate possible phenolic loss through gastrointestinal processing. Pycnogenol®, a standardised procyanidin‐rich extract from pine bark, has been proposed as a potential candidate for polyphenol enrichment of foods. In this study the effects of in vitro digestion on the phenolic profile of fruit juices enriched with Pycnogenol® were investigated. RESULTS: After in vitro digestion the level of detectable total phenolic compounds (expressed as gallic acid equivalent) was higher in both pineapple and red fruit juices enriched with Pycnogenol® than in non‐enriched commercial juices. Five phenolic monomeric compounds were identified by high‐performance liquid chromatography, namely chlorogenic acid, caffeic acid, ferulic acid, gallic acid and taxifolin, the last two being predominant. In vitro digestion of both Pycnogenol®‐enriched pineapple and red fruit juices led to a significant (P < 0.05) increase in detectable chlorogenic and ferulic acids, indicating that hydrolysis of more complex molecules occurs. On the other hand, in vitro digestion of non‐enriched juices was associated with a decrease in gallic and caffeic acids in pineapple juice and with a decrease in ferulic acid in red fruit juice. In no case did in vitro digestion increase the amount of detectable phenolic compounds in non‐enriched juices. CONCLUSION: The stability of Pycnogenol® after in vitro gastrointestinal digestion makes it a good choice for phenolic enrichment of fruit juices. Copyright © 2010 Society of Chemical Industry  相似文献   
993.
The development of fluorophores emitting in the near-infrared spectral window has gained increased attention given their suitable features for biological imaging.In this work,we have optimised a general and straightforward synthetic approach to prepare a small library of near-infrared-emitting C-bridged nitrobenzodiazoles using commercial precursors.C-bridged benzodiazoles have low molecular weight and neutral character as important features that are not common in most nearinfrared dyes.We have investigated their fluorescence response in the presence of a wide array of 60 different biomolecules and identified compound 3i as a potential chemosensor to discriminate between Fe2+and Fe3+ions in aqueous media.  相似文献   
994.
This paper presents a lifetime reliability-based approach to the optimization of reinforced concrete (RC) cross-sections in an aggressive environment. The lifetime structural performance is evaluated by using a general methodology for time-variant analysis of RC structures subjected to diffusive attacks from aggressive agents with corrosion of the reinforcement. The lifetime probabilistic optimization is formulated at the cross-sectional level and is aimed to minimize the material cost under a time-dependent constraint on the structural reliability. The optimization problem is solved by combining a discrete gradient-based optimization method with a Monte Carlo simulation. The obtained results demonstrate that in a lifetime-oriented design the amount and location of the steel reinforcement and the value of the concrete cover play a crucial role for the optimal achievement of the desired lifetime structural performance.  相似文献   
995.
A radical shift in our approach to crop production is needed to ensure food security and to address the problems of soil degradation, loss of biodiversity, polluted and restricted water supplies, coupled with a future of fossil fuel limitations and increasingly variable climatic conditions. An interdisciplinary network of European scientists put forward visions for future crop production embracing the complexity of our socio‐ecological system by applying the principle of diversity at all levels from soil micro‐organisms to plant varieties and cropping systems. This approach, integrated with careful deployment of our finite global resources and implementation of appropriate sustainable technology, appears to be the only way to ensure the scale of system resilience needed to cope with many of our concerns. We discuss some of the most important tools such as (i) building soil fertility by recycling of nutrients and sustainable use of other natural and physical resources, (ii) enhancing biological diversity by breeding of crops resilient to climate change and (iii) reconnecting all stakeholders in crop production. Finally, we emphasise some of the changes in agricultural and environmental regulation and policy needed in order to implement the visions. Copyright © 2009 Society of Chemical Industry  相似文献   
996.
The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels (Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers (300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions.  相似文献   
997.
998.
Sideritis species have been used in folk medicine for their antimicrobial, antiulcerogenic, digestive and anti‐inflammatory properties. Over the years, the phytochemistry of the genus Sideritis has been studied, and various terpenoids, sterols, coumarins and especially flavonoid aglycones and glycosides have been identified. In particular, species from the Balkan Peninsula have been studied and were found to be rich in flavonoids, with valuable antioxidant activity. In the folk medicine of the Balkan countries, Sideritis raeseri is used as a herbal tea in the treatment of inflammation, gastrointestinal disorders and coughs, and also as a tonic, whereas extracts are used as a component of dietary supplements for anaemia. Its dried inflorescences are used to prepare a beverage called ‘mountain tea’. In light of the considerable interest generated in the chemistry, pharmacological properties and commercial value of S. raeseri Boiss. & Heldr., we review and summarise the available literature on these plants. The review details the chemical composition of the essential oil, its mineral and polyphenol contents, the naming of these plants and their physicochemical characterisation, and the nuclear magnetic resonance spectral data and biological properties associated with the plant extracts, with a focus on their potential chemotherapeutic applications. © 2016 Society of Chemical Industry  相似文献   
999.
Regeneration is the most efficient way of managing used oil. It saves money by preventing costly cleanups and liabilities that are associated with mismanagement of used oil, it helps to protect the environment and it produces a technically renewable resource by enabling an indefinite recycling potential. There are a variety of processes and licensors currently offering ways to deal with used oils. Selecting a regeneration technology for used oil involves "cross-matching" key criteria. Therefore, the first prototype of spent oil regeneration (SPORE), a decision support tool, has been developed to help decision-makers to assess the available technologies and select the preferred used oil regeneration options. The analysis is based on technical, economical and environmental criteria. These criteria are ranked to determine their relative importance for a particular used oil regeneration project. The multi-criteria decision analysis (MCDA) is the core of the SPORE using the PROMETHEE II algorithm.  相似文献   
1000.
A therapy-specific worsening of cardiovascular stability during bicarbonate dialysis (BD) with respect to acetate-free biofiltration (AFB) have been previously reported. We further investigated the impact of the 2 therapies on electrocardiographic parameters in order to gain novel insight into the cardiac responses. Holter ECG acquired during hypotension-free sessions (12 BD + 12 AFB) were retrospectively analyzed. R-R intervals were extracted from ECG recordings. An autoregressive spectral technique was used to compute low- and high-frequency (LF and HF) components of heart rate variability (HRV). QT interval duration was measured with a computer-assisted technique and corrected for HR. In BD the LF component of HRV after an initial increase was slowly depressed with respect to AFB (p < 0.05). QT duration showed a significant (p < 0.01) hemodialysis-induced reduction. QT shortening was more pronounced (p < 0.05) in BD than in AFB (-31 vs. -10 ms), even after correction for HR (p < 0.05). Cardiac electrical activity is significantly affected by the hemodialysis technique. The decrease in the LF component of HRV and the QT shortening are coherent with the worse cardiovascular tolerance observed in BD and with the hypothesis of an enhanced production of endogenous nitric oxide.  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