全文获取类型
收费全文 | 166篇 |
免费 | 3篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 26篇 |
金属工艺 | 3篇 |
机械仪表 | 5篇 |
建筑科学 | 12篇 |
能源动力 | 5篇 |
轻工业 | 22篇 |
石油天然气 | 1篇 |
无线电 | 8篇 |
一般工业技术 | 53篇 |
冶金工业 | 7篇 |
原子能技术 | 2篇 |
自动化技术 | 24篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 7篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1974年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有169条查询结果,搜索用时 15 毫秒
61.
Lawrence T. Clark Terje Gloerstad Robert O. Grondin Sandwip K. Dey 《Integrated ferroelectrics》2013,141(4):309-320
Abstract In digital memory applications, metal ferroelectric metal (MFM) capacitors are typically fully switched from one polarization state to the other, with the difference in displacement current allowing determination of the cell state. However, by applying a pulse of insufficient amplitude and/or duration to fully switch the ferroelectric, such a device may be partially polarized. Here, the measurement of partial switching in sol-gel derived PZT MFM capacitors due to applied voltage pulses is reported. SPICE, a commonly used circuit simulation program, has been modified to incorporate a ferroelectric capacitor device model. The MFM device model added to SPICE is reviewed, and the simulation of partial switching is demonstrated. Simulation results modeling the PE hysteresis loops and switching transients due to applied voltage steps closely match those measured in the laboratory. We conclude with the modeling of incomplete switching due to applied pulses of insufficient amplitude to cause polarization saturation, which is attributed to the polycrystalline nature of the thin-films. 相似文献
62.
Tanaka K Berntsen T Fuglestvedt JS Rypdal K 《Environmental science & technology》2012,46(9):5205-5213
Passenger transport affects climate through various mechanisms involving both long-lived and short-lived climate forcers. Because diesel cars generally emit less CO(2) than gasoline cars, CO(2) emission taxes for vehicle registrations and fuels enhance the consumer preference for diesel cars over gasoline cars. However, with the non-CO(2) components, which have been changed and will be changed under the previous and upcoming vehicle emission standards, what does the shift from gasoline to diesel cars mean for the climate mitigation? By using a simple climate model, we demonstrate that, under the earlier emissions standards (EURO 3 and 4), a diesel car causes a larger warming up to a decade after the emissions than a similar gasoline car due to the higher emissions of black carbon and NO(X) (enhancing the O(3) production). Beyond a decade, the warming caused by a diesel car becomes, however, weaker because of the lower CO(2) emissions. As the latter emissions standards (EURO 5 and 6) are phased in, the short-term warming due to a diesel car becomes smaller primarily due to the lower black carbon emissions. Thus, although results are subject to restrictive assumptions and uncertainties, the switch from gasoline to diesel cars encouraged by CO(2) taxes does not contradict with the climate mitigation focusing on long-term consequences. 相似文献
63.
Antonina M. Araszkiewicz Eduarda P. Oliveira Terje Svendsen Katarzyna Drela Piotr Rogujski Izabela Malysz-Cymborska Michal Fiedorowicz Rui L. Reis Joaquim Miguel Oliveira Piotr Walczak Miroslaw Janowski Barbara Lukomska Luiza Stanaszek 《International journal of molecular sciences》2022,23(5)
Cell transplantation has been studied extensively as a therapeutic strategy for neurological disorders. However, to date, its effectiveness remains unsatisfactory due to low precision and efficacy of cell delivery; poor survival of transplanted cells; and inadequate monitoring of their fate in vivo. Fortunately, different bio-scaffolds have been proposed as cell carriers to improve the accuracy of cell delivery, survival, differentiation, and controlled release of embedded stem cells. The goal of our study was to establish hydrogel scaffolds suitable for stem cell delivery that also allow non-invasive magnetic resonance imaging (MRI). We focused on alginate-based hydrogels due to their natural origin, biocompatibility, resemblance to the extracellular matrix, and easy manipulation of gelation processes. We optimized the properties of alginate-based hydrogels, turning them into suitable carriers for transplanted cells. Human adipose-derived stem cells embedded in these hydrogels survived for at least 14 days in vitro. Alginate-based hydrogels were also modified successfully to allow their injectability via a needle. Finally, supplementing alginate hydrogels with Mn ions or Mn nanoparticles allowed for their visualization in vivo using manganese-enhanced MRI. We demonstrated that modified alginate-based hydrogels can support therapeutic cells as MRI-detectable matrices. 相似文献
64.
Kadrin Mereme Priit Elias Terje Tamme Toomas Kramarenko Merike Lillenberg Avo Karus Marja-Liisa Hnninen Mati Roasto 《Food Control》2010,21(3):272-275
The aim of the present study was to monitor the occurrence of Campylobacter spp. in broiler chicken production in Estonia from 2002 to 2007. Campylobacter spp. was isolated in 163 (12.3%) of 1320 broiler chicken meat samples form 2002 to 2007 and in 115 (6.3%) of 1819 cecal samples in 2005–2007. Campylobacter jejuni was the most commonly isolated species (98.2%), followed by Campylobacter coli (1.4%) and Campylobacter lari (0.4%). The seasonal peak of Campylobacter contamination was from July to September. Our findings showed that Campylobacter contamination at all levels of broiler chicken production in Estonia was low. 相似文献
65.
Although there exist several alternative frameworks and standards for describing the digital competencies expected from teachers, there is a lack of Web-based assessment tools that allow authentic, reliable and valid assessment of these competencies. This paper addresses the design challenges related to a software solution for self- and peer-assessment of teachers’ digital competencies. The empirical part of the paper describes the participatory design process and results from the first user testing of a Web-based self- and peer-assessment tool DigiMina, which supports teachers in building and sharing a personal competency profile. In DigiMina, the competencies are assessed by a teacher herself or by her peers using the performance indicators that are based on the competency model NETS for Teachers created by the International Society of Technology in Education. 相似文献
66.
Naresh B. Muddada Terje Fuglerud Carlo Lamberti Unni Olsbye 《Topics in Catalysis》2014,57(6-9):741-756
CuCl2/γ-Al2O3 catalysts with and without promoter metal chlorides (Cu5.0, K3.1Cu5.0, La10.9Cu5.0, Li0.5Cu5.0, Cs10.4Cu5.0, Mg1.9Cu5.0, Ce5.5La5.45Cu5.0, and K1.55La5.45Cu5.0) were studied for the ethene oxychlorination reaction in a fixed-bed reactor at 503 and 573 K, with C2H4:HCl:O2:He = 1.0:1.1:0.38:14.4 (mole ratio), P(tot) = 1 atm and weight hourly space velocity (WHSV) = 1.5 g g?1 h?1 (based on ethene). It was found that all promoter metals enhanced the activity of the catalyst, as well as its selectivity towards the target product 1,2-dichloroethane (1,2-EDC). Co-promoted catalysts (K1.55La5.45Cu5.0 and Ce5.5La5.45Cu5.0) gave even higher activity and product selectivity than the single metal promoted catalysts. The activity of the CuCl2/γ-Al2O3 catalyst, as well as the γ-Al2O3 support, both with and without metal chloride promoter(s), were further tested for 1,2-EDC conversion to byproducts in a fixed-bed reactor at 503 K, under a feed stream of 1,2-EDC:Ar = 1:11.5 (mole ratio), at P(tot) = 1 atm and WHSV = 1.5 g g?1 h?1 (based on 1,2-EDC). Prior to testing, the catalysts were pretreated in flowing ethene, HCl and/or O2. It was observed that Lewis and Brønsted acid sites on the alumina surface were main reaction sites for conversion of 1,2-EDC to chlorinated byproducts: vinyl chloride monomer (VCM), 1,1-EDC, 1,2-dichloroethene (1,2-DCE) and ethyl chloride (EC) as well as dimerisation (butadiene) and aromatisation reactions (toluene), both with and without the presence of the Cu phase. The Cu phase was shown to contribute mainly to CO2 and trichloroethane formation from 1,2-EDC via VCM. Co-promotion (K1.55La5.45Cu5.0) was found to enhance the activity of the Cu phase, and to mask acid sites on the alumina surface, thereby promoting ethene oxychlorination while at the same time hindering undesired conversion of the target product 1,2-EDC. 相似文献
67.
Simulation and prediction of eigenfrequencies and mode shapes for active flexible multibody systems is an important task in disciplines such as robotics and aerospace engineering. A challenge is to accurately include both controller effects and flexible body dynamics in a multidisciplinary system model appropriate for modal analysis. A method for performing modal analyses of such systems in a finite element environment was recently developed by the authors. On issue is, however, that for engineers working in a finite element environment, the controller properties are not always explicitly available prior to modal analyses. The authors encountered this problem when working with the design of a particular offshore windmill. The controller for the windmill was delivered in the form of a dynamic link library (dll) from a third party provider, and when performing virtual testing of the windmill design, it was of great importance to use the “real” controller in the form of the provided dll, rather than re-model it in for instance Simulink or EASY5. This paper presents a method for estimating the controller parameters of PID-type controllers when solving the closed-loop eigenvalue problem for active flexible multibody systems in a finite element environment. The method is based on applying incremental changes, perturbations, to relevant system variables while recording reactions from other system variables. In this work, the theory of the method is derived and the method is tested through several numerical examples. 相似文献
68.
Terje Tande Harald Breivik Terje Aasoldsen 《Journal of the American Oil Chemists' Society》1992,69(11):1124-1130
A gas chromatographic method for the determination of all-cis-5,8,11,14,17-eicosapentaenoic acid (EPA) and all-cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) as active ingredients in medicinal products was developed and validated. In accordance
with the rules governing medicinal products in the European Community, the method establishes relations between label claims
of active ingredients and known reference standards. A routine for examining instrument status is proposed. The relative standard
deviation was 1% (n=26) for determination of the empirical response factors of EPA ethyl ester and DHA ethyl ester relative
to the internal standard, C23:0 methyl ester. This experiment included two columns and EPA and DHA standards from two different
suppliers and was carried out over a five-month period. Repeatability (n=6) for low and medium concentrates of glycerides
and high concentrates of ethyl esters, expressed as coefficient of variation, was 4, 0.7 and 0.7%, respectively. Accuracy
(n=6) determined as percent recovery was better than 98% for all sample types. Analytical results from a twelve-month stability
study of the high concentrate are shown.
Presented at the AOCS Annual Meeting in Chicago, IL, May 1991. 相似文献
69.
Gjerde H Normann PT Pettersen BS Assum T Aldrin M Johansen U Kristoffersen L Øiestad EL Christophersen AS Mørland J 《Accident; analysis and prevention》2008,40(5):1765-1772
The objective of the study was to determine the prevalence of alcohol, psychoactive medicinal drugs and illegal drugs among drivers in Norwegian road traffic. Drivers of motor vehicles were selected from April 2005 to April 2006 in the south-eastern part of Norway, surrounding, but not including the capital, Oslo. A stratified two-stage cluster sampling procedure was used. In the first stage, random road sites and time intervals were selected, and in the second stage, drivers were stopped by random at those sites and time intervals. Altogether about 12,000 drivers were asked to provide a sample of oral fluid (saliva) and answer a few questions. Samples of oral fluid were obtained from 88% of the drivers, of whom 30% were females and 70% males. The prevalence of each drug was estimated by a weighted average using weights adjusted for under- or over-sampling compared to traffic statistics. Alcohol or drugs were found in oral fluid samples of 4.5% of the drivers; alcohol in 0.4%, psychoactive medicinal drugs in 3.4%, and illegal drugs in 1.0%. Illegal drugs were found more frequently in samples from younger drivers, while psychoactive medicinal drugs were more frequently found in samples from older drivers. Psychoactive medicinal drugs were more prevalent among females than males, among drivers stopped on working days rather than weekends, and among those who reported annual driving distances less than 16,000km. The drugs found most frequently were zopiclone (1.4%), benzodiazepines (1.4%), codeine (0.8%), tetrahydrocannabinol (0.6%) and amphetamines (0.3%). Two or more drugs were found in 0.6% of the samples, corresponding to 15% of the drug-positive drivers. 相似文献
70.
The influence of meteorological parameters on soil radon concentrations in a permeable ice-marginal deposit in Kinsarvik, Norway, was investigated based on continuous measurements of soil radon concentrations, temperature, precipitation, wind speed, wind direction, air pressure and soil moisture content over a period of 10 months. The results show that the soil radon concentrations exhibit distinct seasonal and diurnal variations that predominantly are caused by changes in air temperature. Air flows between areas of different elevation occur in the ice-marginal deposit due to temperature differences between soil air and atmospheric air, and instantaneous changes in air flow direction were recorded when the atmospheric air temperature reached the average annual air temperature. Air pressure was found to be the second most important parameter influencing soil radon concentrations, while no apparent effect of precipitation, wind speed, wind direction or soil moisture was observed. Seasonal variations in indoor and soil radon levels were also investigated in a glaciofluvial deposit located 40 km southwest of Kinsarvik, and the close correlation between the seasonal variation patterns observed in the two areas suggests that the results of the Kinsarvik study also might be applicable to other areas of highly permeable building grounds where differences in terrain elevation exist. 相似文献