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   216篇
  免费   11篇
电工技术   6篇
综合类   1篇
化学工业   75篇
机械仪表   5篇
建筑科学   9篇
能源动力   21篇
轻工业   16篇
水利工程   3篇
无线电   18篇
一般工业技术   21篇
冶金工业   3篇
原子能技术   6篇
自动化技术   43篇
  2023年   2篇
  2022年   7篇
  2021年   9篇
  2020年   4篇
  2019年   2篇
  2018年   6篇
  2017年   6篇
  2016年   7篇
  2015年   5篇
  2014年   11篇
  2013年   21篇
  2012年   15篇
  2011年   21篇
  2010年   9篇
  2009年   21篇
  2008年   11篇
  2007年   11篇
  2006年   11篇
  2005年   7篇
  2004年   4篇
  2003年   9篇
  2002年   6篇
  2001年   1篇
  2000年   5篇
  1999年   1篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1994年   1篇
  1992年   2篇
  1991年   2篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有227条查询结果,搜索用时 468 毫秒
111.
Fruit seeds are byproducts from fruit processing. Characterisation of the bioactive compounds present in seeds and evaluation of their potential biological properties is therefore of particular importance in view of a possible valorisation of seeds as a source of health beneficial components. In this work, we have analysed the seeds of Sambucus and Rubus species in order to identify their bioactive components and to determine the antioxidant and anti-inflammatory activities of the extracts. We first analysed their oil content, in order to assess the fatty acid profile and tocopherol content. Moreover, the methanolic extracts of the seeds were analysed for their total phenolic contents and antioxidant capacities. Polyphenols were identified by HPLC–ESI–MS/MS analysis. Furthermore, extracts were evaluated for their inhibitory effects on the production of LPS-induced inflammatory mediators (NO, CCL-20) in RAW 264.7 cells.  相似文献   
112.
In this paper we consider a multiple-access scheme in which different users share the same bandwidth and the same pulse, and are discriminated at the receiver on the basis of the received energy using successive decoding. More specifically, we extend the performance analysis from the case of additive white Gaussian noise channels (presented in a previous work Salvo Rossi in Wirel Pers Commun, in press) to the case of fading channels. The presence of channel coefficients introduces a new degree of freedom in the transceiver design: unlike the AWGN case, different ordering among the users provides different transmitted energy, thus different overall system performance. Optimal ordering, in terms of minimum transmitted energy, is derived analytically. Analytical and numerical results, in terms of bit error rate and normalized throughput, are derived for performance evaluation in fading environments with optimal ordering exhibiting significant gains w.r.t. static ordering.  相似文献   
113.
The test campaigns of the ITER conductors in the SULTAN test facility re-started in December 2011 after three months break. The main focus of the activities is about the qualification tests of the Central Solenoid (CS) conductors, with three different samples for a total six variations of strand suppliers and cable layouts. In 2012, five Toroidal Field (TF) conductor samples have also been tested as part of the supplier and process qualification phase of the European, Korean, Chinese and Russian Federation Agencies.A summary of the test results for all the ITER samples tested in the last period is presented, including an updated statistics of the broad transition, the performance degradation and the impact of layout variations.The role of SULTAN test facility during the ITER construction is reviewed, and the load of work for the next three years is anticipated.  相似文献   
114.
Welding processes involve localized heating which in turn give rise to thermal stresses and distortion. Friction stir welding (FSW) is a solid state joining process where temperatures below melting are experienced. Nonetheless, some degree of thermal heating and consequently thermal stresses develop at the joint. This study aims to quantify the stresses developed in friction stir welding of mild steel DH36 plates, through an experimental and numerical investigation. The temperatures and transient strains developed during FSW, are experimentally measured and used to validate thermo-elastoplastic numerical models. These models are used to investigate the evolution of thermal stresses and distortion for different welding parameters.  相似文献   
115.
We examined the extent to which three Fraxinus cultivars and a wild population that vary in their resistance to Emerald Ash Borer (EAB) could be differentiated on the basis of a suite of constitutive chemical defense traits in phloem extracts. The EAB-resistant Manchurian ash (F. mandshurica, cv. Mancana) was characterized by having a rapid rate of wound browning, a high soluble protein concentration, low trypsin inhibitor activities, and intermediate levels of peroxidase activity and total soluble phenolic concentration. The EAB-susceptible white ash (F. americana, cv. Autumn Purple) was characterized by a slow wound browning rate and low levels of peroxidase activity and total soluble phenolic concentrations. An EAB-susceptible green ash cultivar (F. pennsylvanica, cv. Patmore) and a wild accession were similar to each other on the basis of several chemical defense traits, and were characterized by high activities of peroxidase and trypsin inhibitor, a high total soluble phenolic concentration, and an intermediate rate of wound browning. Lignin concentration and polyphenol oxidase activities did not differentiate resistant and susceptible species. Of 33 phenolic compounds separated by HPLC and meeting a minimum criterion for analysis, nine were unique to Manchurian ash, five were shared among all species, and four were found in North American ashes and not in the Manchurian ash. Principal components analysis revealed clear separations between Manchurian, white, and green ashes on the basis of all phenolics, as well as clear separations on the basis of quantities of phenolics that all species shared. Variation in some of these constitutive chemical defense traits may contribute to variation in resistance to EAB in these species.  相似文献   
116.
Here we describe an innovative mechanism for carbon sequestration in soil by in situ photopolymerization of soil organic matter under biomimetic catalysis. Three different Mediterranean soils were added with a synthetic water-soluble iron-porphyrin, irradiated by solar light, and subjected first to 5 days incubation and, then, 15, and 30 wetting and drying (w/d) cycles. The in situ catalyst-assisted photopolymerization of soil organic carbon (SOC) increased water stability of soil aggregates both after 5 days incubation and 15 w/d cycles, but not after 30 w/d cycles. Particle-size distribution of all treated soils confirmed the induced soil physical improvement, by showing a concomitant lower yield of the clay-sized fraction and larger yields of either coarse sand- or fine sand-size fractions, depending on soil texture, though only after 5 days incubation. The gain in soil physical quality was reflected by the shift of OC content from small to large soil aggregates, thereby suggesting that photopolymerization stabilized OC by both chemical and physical processes. A further evidence of the carbon sequestration capacity of the photocatalytic treatment was provided by the significant reduction of CO(2) respired by all soils after both incubation and w/d cycles. Our findings suggest that "green" catalytic technologies may potentially be the bases for future practices to increase soil carbon stabilization and mitigate CO(2) emissions from arable soils.  相似文献   
117.
In this paper we describe a multiple-access protocol in which different users are assumed to share the same bandwidth and the same pulse. Users employ the same modulation (binary-phase shift keying, quadrature-phase shift keying, and rectangular-phase shift keying are considered) with different transmitted magnitude, and are discriminated on the basis of the corresponding magnitude at receiver location. Conditions for user discrimination are analyzed. The proposed receiver uses successive decoding in order to avoid exponential complexity of maximum-likelihood decoding. Such a scheme, compared to orthogonal multiaccess schemes (e.g. time- or frequency-division multiple access) allows to achieve larger normalized throughput for systems operating in large signal-to-noise ratio range, and may be jointly applied with classical protocols in personal-area networks. Analytical and numerical results, in terms of bit error rate and normalized throughput, are derived for performance evaluation on additive white Gaussian noise channels.  相似文献   
118.
119.
Summary: A study of the structure–property relationships for nanocomposites prepared by melt compounding from ethylene–acrylic acid copolymers of varied composition and molecular architecture, and organoclays modified with different ammonium ions has been made by DSC, POM, SEM, TEM, WAXD, and rheological and mechanical tests. Within the series of clays investigated, the best levels of dispersion were displayed by those organically modified with quaternary ammonium ions containing two long alkyl tails. The relevant nanocomposites were shown to possess mixed exfoliated and intercalated morphology. The spacing of the intercalated clay stacks, most of which comprise few silicate layers, was found to be independent of clay loading, in the range of 2–50 phr, and to change with the molecular architecture of the matrix polymer. An indication that the excess surfactant present in some of the clays, and the organic material added in others to expand the interlayer spacing, were expelled from the clay galleries during melt blending and acted as plasticisers for the matrix polymer, was obtained from WAXD and rheological characterisations.

TEM micrograph of the nanocomposite of EAA1 with 11 phr of 15A.  相似文献   

120.
Compost humic acid-like (cHAL) polymeric matter (MW = 15610), isolated in 12% yield from food and green waste compost, exhibits very good surfactant properties in aqueous solution: i.e., critical micelle concentration (cmc) = 403 mg/L and surface tension at cmc = 36.1 mN/m. Values of cmc are confirmed also by conductivity and phenanthrene solubility measurements. These results, compared with those for other major commercial and research surfactants, propose cHAL as a competitive low-cost biosurfactant.  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