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   471篇
  免费   21篇
电工技术   5篇
化学工业   227篇
金属工艺   5篇
机械仪表   4篇
建筑科学   17篇
矿业工程   2篇
能源动力   4篇
轻工业   68篇
水利工程   1篇
石油天然气   1篇
无线电   16篇
一般工业技术   78篇
冶金工业   13篇
原子能技术   2篇
自动化技术   49篇
  2023年   11篇
  2022年   70篇
  2021年   63篇
  2020年   25篇
  2019年   15篇
  2018年   21篇
  2017年   18篇
  2016年   19篇
  2015年   22篇
  2014年   17篇
  2013年   33篇
  2012年   25篇
  2011年   43篇
  2010年   21篇
  2009年   15篇
  2008年   21篇
  2007年   16篇
  2006年   9篇
  2005年   5篇
  2004年   4篇
  2003年   4篇
  2002年   3篇
  2001年   2篇
  1999年   2篇
  1998年   2篇
  1997年   1篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
排序方式: 共有492条查询结果,搜索用时 15 毫秒
131.
To validate the accuracy of 2 commercially available activity loggers in determining lying, standing, walking, and number of steps in dairy cows, 30 cows were fitted with the CowScout Leg (GEA Farm Technologies, Bönen, Germany) system and the IceTag (IceRobotics Ltd., Edinburgh, Scotland) system. The CowScout Leg logger reports standing and lying in 15-min periods, whereas the IceTag logger reports standing and lying every second. To make data comparable, the IceTag data were therefore also summarized over 15-min periods corresponding to the paired CowScout Leg sensor. These data from the 2 systems were then analyzed (more than 1,000 cow days in total). Video recordings of a total of 29.5 h were used for labeling the behaviors of the selected cows (n = 10) and these labels were used as a gold standard to determine the accuracy with which these 2 loggers can record behavioral states lying, standing, walking, and the behavioral event number of steps. A concordance correlation coefficient analysis showed that both the standing and lying durations obtained with the 2 systems were almost perfectly correlated with the video labeling (IceTag: ρc = 0.999 and 0.999, respectively; CowScout Leg: ρc = 0.995 and 0.996, respectively). However, both loggers performed poorly regarding number of steps (classified as an event; IceTag: ρc = 0.629; CowScout Leg: ρc = 0.678) and CowScout Leg did not detect walking (classified as a state) very accurately (ρc = 0.860). The IceTag system does not measure walking behavior. When comparing the 2 loggers, the correlation between them for standing and lying was substantial (ρc = 0.953 and ρc = 0.953, respectively). The number of steps poorly correlated between the 2 loggers (ρc = 0.593), which might be due to the CowScout Leg logger being attached to the front leg and the IceTag logger being attached to the hind leg. We conclude that both the IceTag and the CowScout Leg logger are able to record standing and lying almost perfectly, but the step counting by both loggers and the walking recording by the CowScout Leg logger are not very accurate.  相似文献   
132.
New Restricted Access Materials—Molecularly Imprinted Polymers (RAM-MIP) were synthesized by using caffeine (CAFF), methacrylic acid (MAA), divinyl benzene (DVB) and glycidil methacrylate (GMA) as model template, functional monomer, crosslinking agent and pro-hydrophilic co-monomer, respectively. Furthermore, a screening of the ratio of functional monomer to template was performed. After the preliminary characterizations of conventional MIP prepared in absence of GMA, different GMA amounts were inserted in the pre-polymerization feeds and different reactions conditions were tested for GMA epoxide ring opening. In particular, perchloric acid, ammonia, lactic acid, glycine and triethylene glycol were chosen for this purpose. In perchloric acid and ammonia cases, a further modification was performed by phosphorylation and methylation procedures, respectively. Imprinting efficiency of all the obtained materials was evaluated by binding experiments using caffeine and its analogue theophylline both in organic and in water media. The increased hydrophilic characteristics of RAM polymers by water absorption measurement and protein binding experiments were performed.  相似文献   
133.
134.
In vitro biomineralization process was investigated on functionalized single wall nanotube (SWNT) films. The films were prepared by solvent casting method by using carboxylated and fluorinated nanotubes. SWNT films were characterized by means of electron microscopy, contact angle measurements and optical absorption. The in vitro assays were performed on cultured human alveolar bone-derived cells (HABDC) to determine the capabilities of carboxylated single-walled nanotubes (SWNTs-COOH) and fluorinated single-walled nanotubes (F-SWNTs) to promote the deposit of mineral-like tissue. The results showed that the cellular response of HABDC in secreting a mineralized extracellular matrix and their consequent mineralization is dependent on the degree of functionalization of the SWNTs. Differences were found related to the kind of sidewall functionalization. Both structures promoted hydroxyapatite formation, however, calcium uptake on SWNTs-COOH increased and it was related to crystal density. From our results, it is possible to infer that CNT functionalization opens a path to future developments in new bone graft materials and techniques.  相似文献   
135.
A new strategy to obtain transparent, thermally stable, and formable photoluminescent materials for LED applications is presented. Starting from commercially available silicon-based polymers, luminescence properties are developed by means of simple heat treatment. Solid polymethylsilsesquioxane MK (Wacker-Besil®PMS MK) and liquid poly(ureamethylvinyl)silazane Ceraset (Kion Ceraset® PUVMS) were thermally treated between 200 and 700 °C for 2 h under Ar atmosphere. Photoluminescence properties were observed in all the samples. The structural rearrangements during thermal annealing were effective in order to red-shift the emission spectra of the untreated polymers to the visible range. The formation of dangling bonds and carbon sp2, associated with the annealing procedure and confirmed by means of Electron Paramagnetic Resonance (EPR) spectroscopy and solid state Magic Angle Spinning NMR (MAS-NMR) contribute to the red-shift of the photoluminescence emissions of the polymers. After heat treatment at low temperatures (200, 300, and 400 °C), both the polymers show fluorescence in the UV range. While the polysiloxane reveals white luminescence after annealing at 500 and 600 °C, the polysilazane heat-treated at 500 °C exhibits emission in the blue-green range and is transparent. At higher temperatures the presence of free carbon counteracts the luminescence properties.  相似文献   
136.
Beyond the nutritional value, legumes and particularly common beans are found in several dietary supplements used to treat diabesity (diabetes and obesity). These products contain not only inhibitors of carbohydrate-hydrolising enzymes (α-amylase, α-glucosidase), but also antinutritional factors that can cause adverse effects on human health. In the present research, twenty-two accessions of grain legumes were screened for bioactive (α-amylase and α-glucosidase inhibitors) and antinutritional (lectins, flatulence-producing sugars, trypsin inhibitors) phytochemicals. Results showed that four accessions had high α-amylase inhibiting activities (AI > 30%), and particularly the common bean ‘Great Northern’ resulted of interest for its high carbo-blocker activity (AI = 42.6 ± 0.5%), absence of lectins, low amounts of flatulence-producing oligosaccharides (2.5 ± 0.2 g/100 g DW) and low anti-trypsin activity (22.5 ± 4.3 trypsin inhibiting unit/mg DW). The knowledge offered from this work provides leads to the ultimate goal of developing new, more effective and safer dietary supplements for diabesity management.  相似文献   
137.
138.
This paper presents an innovative procedure to solve the Connection Admission Control Problem for a telecommunication network. Here, this important problem in the context of Communication Theory and Network Dynamics is dealt with by imbedding it in the framework of System and Control Theory. Highlights of the procedure are technology independence, coordinated and coherent decoupling, optimality and feedback properties, stochastic dynamic control.  相似文献   
139.
The potential migration of genotoxic compounds into mineral water stored in polyethylene terephthalate (PET) bottles was evaluated by an integrated chemical/biological approach using short-term toxicity/genotoxicity tests and chemical analysis. Six commercial brands of still and carbonated mineral water bottled in PET and in glass were stored at 40 °C for 10 days in a stove according to the standard EEC total migration test (82/711/EEC), or at room temperature in the dark. After treatment, the samples were analysed using gas-chromatography/mass spectrometry (GC/MS) to detect volatile and non-volatile compounds, the Microtox® test to evaluate potential toxicity of the samples, and three mutagenicity tests - Tradescantia and Allium cepa micronucleus tests and the Comet assay on human leukocytes - to detect their genotoxic activity.GC/MS analysis did not detect phthalates or acetaldehyde in the water samples. The Microtox® test found no toxic effects. Mutagenicity tests detected genotoxic properties of some samples in both PET and glass bottles. Statistical analyses showed a positive association between mineral content and mutagenicity (micronuclei in A. cepa and DNA damage in human leukocytes). No clear effect of treatment and PET bottle was found. These results suggest the absence of toxic compounds migrating from PET regardless of time and conditions of storage. In conclusion, bottle material and stove treatment were not associated with the genotoxic properties of the water; the genotoxic effects detected in bottled water may be related to the characteristics of the water (minerals and CO2 content).  相似文献   
140.
The formulation of innovative transparent hydrorepellent coatings is strongly motivated in order to satisfy the market request and necessity to improve the cleanability of the sanitarywares. A lot of attention is devoted to the use of cheap precursors, low temperature synthesis process and industrial scalability potentiality. In this framework, in the present paper the set-up of the deposition of modified SiO2 coatings on glazed ceramic supports by spraying technique was reported. Several solutions were formulated using as precursor tetraethylorthosilicate (TEOS) and co-precursor methyltriethoxysilane (MTES) in different molar ratios (i.e. 50:50, 25:75, 75:25), in suitable solvents and mixture of solvents (i.e. H2O, ethanol). The influence of the process parameters (i.e. precursors ratio, solvents, catalyser, annealing temperature) on the properties of the produced coatings was deeply investigated by means of scanning electron microscopy (SEM), simultaneous thermogravimetric and differential analyses (TG–DTA), infrared spectroscopy (FT-IR), X-Ray diffraction (XRD) and Vickers microhardness. Their hydrophobic behaviour was tested by the measurements of the static water contact angles and the chemical and stain resistance by the conformity to some tests of the standard UNI 4543. The obtained coatings were amorphous, homogeneous, uniform, thin (average thickness 300 nm), crack-free, leading to an improved hardness value of the glazed ceramic support (4.47 GPa vs 3.68 GPa for the coated and uncoated substrates, respectively), and allowed to improve both the hydrophobic behaviour and the chemical and stains resistance of the glazed sanitaryware supports, on the basis of the standard UNI 4543. The best hydrophobic performances were revealed in the case of coatings prepared starting from acidic catalysis derived precursor solutions. Moreover, the highest water contact angle values were detected for lower temperatures annealing, due to the methyl groups preservation, in agreement with the FT-IR and TG–DTA findings.  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