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   242篇
  免费   15篇
  国内免费   1篇
电工技术   6篇
化学工业   63篇
金属工艺   1篇
机械仪表   2篇
建筑科学   2篇
能源动力   6篇
轻工业   20篇
石油天然气   1篇
无线电   43篇
一般工业技术   41篇
冶金工业   35篇
自动化技术   38篇
  2024年   2篇
  2023年   3篇
  2022年   5篇
  2021年   10篇
  2020年   8篇
  2019年   4篇
  2018年   7篇
  2017年   9篇
  2016年   8篇
  2015年   8篇
  2014年   11篇
  2013年   15篇
  2012年   19篇
  2011年   13篇
  2010年   9篇
  2009年   8篇
  2008年   14篇
  2007年   6篇
  2006年   10篇
  2005年   7篇
  2004年   10篇
  2003年   2篇
  2002年   5篇
  2001年   4篇
  2000年   1篇
  1999年   2篇
  1998年   5篇
  1997年   14篇
  1996年   9篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1985年   1篇
  1984年   1篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1976年   4篇
  1974年   1篇
  1971年   1篇
  1960年   1篇
  1959年   1篇
  1942年   1篇
排序方式: 共有258条查询结果,搜索用时 15 毫秒
1.
Equipment was developed to measure the time for complete gelling of sodium alginate fibres in calcium chloride solution, taken as the time to achieve maximum tensile strength. The effects of fibre diameter, alginate concentration, alginate composition and calcium chloride concentration on gelling time were investigated. A diffusional model, developed to predict the gelling time, agreed with experimental results except for the effect of calcium ion concentration which was modelled empirically.  相似文献   
2.
General-base catalysis in the active site of serine proteasesis carried out by the imidazole side chain of a histidine. Duringformation of the transition state, an adjacent carboxylic acidgroup stabilizes the positive charge that forms on the general-basecatalyst and as a result contributes several orders of magnitudeto the catalytic efficiency of these enzymes. In the recentlydiscovered family of self-cleaving proteins exemplified by theLexA repressor of Escherichia coli, instead of the imidazoleof a histidine, the active-site general-base catalyst was foundto be the -amino of a lysine. The considerably higher capacityof the lysine side chain for proton acceptance raises interestingquestions concerning the role of electrostatic interactionsin the mechanism of proton transfer by this highly basic group.The negative charge elimination studies described here and theireffects on the kmax and pK of LexA self-cleavage are consistentwith a model in which electrostatic interactions between anacidic side chain and the general-base catalyst form a barrierto proton transfer. The implications are that the -amino group,unlike the imidazole group, is capable of effecting proton transferwithout the intervention of a countercharge.  相似文献   
3.
This paper presents the Region Splitting and Merging-Fuzzy C-means Hybrid Algorithm (RFHA), an adaptive unsupervised clustering approach for color image segmentation, which is important in image analysis and in understanding pattern recognition and computer vision field. Histogram thresholding technique is applied in the formation of all possible cells, used to split the image into multiple homogeneous regions. The merging technique is applied to merge perceptually close homogeneous regions and obtain better initialization for the Fuzzy C-means clustering approach. Experimental results have demonstrated that the proposed scheme could obtain promising segmentation results, with 12% average improvement in clustering quality and 63% reduction in classification error compared with other existing segmentation approaches.  相似文献   
4.
Thresholding techniques for image segmentation is one of the most popular approaches in Computational Vision systems. Recently, M. Albuquerque has proposed a thresholding method (Albuquerque et al. in Pattern Recognit Lett 25:1059–1065, 2004) based on the Tsallis entropy, which is a generalization of the traditional Shannon entropy through the introduction of an entropic parameter q. However, the solution may be very dependent on the q value and the development of an automatic approach to compute a suitable value for q remains also an open problem. In this paper, we propose a generalization of the Tsallis theory in order to improve the non-extensive segmentation method. Specifically, we work out over a suitable property of Tsallis theory, named the pseudo-additive property, which states the formalism to compute the whole entropy from two probability distributions given an unique q value. Our idea is to use the original M. Albuquerque’s algorithm to compute an initial threshold and then update the q value using the ratio of the areas observed in the image histogram for the background and foreground. The proposed technique is less sensitive to the q value and overcomes the M. Albuquerque and k-means algorithms, as we will demonstrate for both ultrasound breast cancer images and synthetic data.  相似文献   
5.
This paper presents a real-time framework that combines depth data and infrared laser speckle pattern (ILSP) images, captured from a Kinect device, for static hand gesture recognition to interact with CAVE applications. At the startup of the system, background removal and hand position detection are performed using only the depth map. After that, tracking is started using the hand positions of the previous frames in order to seek for the hand centroid of the current one. The obtained point is used as a seed for a region growing algorithm to perform hand segmentation in the depth map. The result is a mask that will be used for hand segmentation in the ILSP frame sequence. Next, we apply motion restrictions for gesture spotting in order to mark each image as a ‘Gesture’ or ‘Non-Gesture’. The ILSP counterparts of the frames labeled as “Gesture” are enhanced by using mask subtraction, contrast stretching, median filter, and histogram equalization. The result is used as the input for the feature extraction using a scale invariant feature transform algorithm (SIFT), bag-of-visual-words construction and classification through a multi-class support vector machine (SVM) classifier. Finally, we build a grammar based on the hand gesture classes to convert the classification results in control commands for the CAVE application. The performed tests and comparisons show that the implemented plugin is an efficient solution. We achieve state-of-the-art recognition accuracy as well as efficient object manipulation in a virtual scene visualized in the CAVE.  相似文献   
6.
SARS-CoV-2 variants raise concern because of their high transmissibility and their ability to evade neutralizing antibodies elicited by prior infection or by vaccination. Here, we compared the neutralizing abilities of sera from 70 unvaccinated COVID-19 patients infected before the emergence of variants of concern (VOCs) and of 16 vaccine breakthrough infection (BTI) cases infected with Gamma or Delta against the ancestral B.1 strain, the Gamma, Delta and Omicron BA.1 VOCs using live virus. We further determined antibody levels against the Nucleocapsid (N) and full Spike proteins, the receptor-binding domain (RBD) and the N-terminal domain (NTD) of the Spike protein. Convalescent sera featured considerable variability in the neutralization of B.1 and in the cross-neutralization of different strains. Their neutralizing capacity moderately correlated with antibody levels against the Spike protein and the RBD. All but one convalescent serum failed to neutralize Omicron BA.1. Overall, convalescent sera from patients with moderate disease had higher antibody levels and displayed a higher neutralizing ability against all strains than patients with mild or severe forms of the disease. The sera from BTI cases fell into one of two categories: half the sera had a high neutralizing activity against the ancestral B.1 strain as well as against the infecting strain, while the other half had no or a very low neutralizing activity against all strains. Although antibody levels against the spike protein and the RBD were lower in BTI sera than in unvaccinated convalescent sera, most neutralizing sera also retained partial neutralizing activity against Omicron BA.1, suggestive of a better cross-neutralization and higher affinity of vaccine-elicited antibodies over virus-induced antibodies. Accordingly, the IC50: antibody level ratios were comparable for BTI and convalescent sera, but remained lower in the neutralizing convalescent sera from patients with moderate disease than in BTI sera. The neutralizing activity of BTI sera was strongly correlated with antibodies against the Spike protein and the RBD. Together, these findings highlight qualitative differences in antibody responses elicited by infection in vaccinated and unvaccinated individuals. They further indicate that breakthrough infection with a pre-Omicron variant boosts immunity and induces cross-neutralizing antibodies against different strains, including Omicron BA.1.  相似文献   
7.
Hydrogen peroxide (H2O2) is one of essential oxygen metabolites in living organisms, but is generated in large amounts during inflammatory responses. Therefore, H2O2 has great potential as diagnostic and therapeutic markers of several inflammatory and life‐threatening diseases. Here, chemiluminescent and antioxidant micelles are reported as novel theranostic agents for H2O2‐associated inflammatory diseases. The chemiluminescent micelles composed of amphiphilic block copolymer Pluronic F‐127, hydroxybenzyl alcohol‐incorporated copolyoxalate (HPOX) and fluorescent dyes perform peroxalate chemiluminescence reactions to detect H2O2 as low as 100 nM and image H2O2 generated in inflamed mouse ankles. The micelles encapsulating HPOX reduce the generation of reactive oxygen species in lipopolysaccharide (LPS)‐activated macrophages by scavenging overproduced H2O2 and releasing antioxidant hydroxybenzyl alcohol (HBA). They also exert inhibitory effects on H2O2‐induced apoptosis. HPOX‐based chemiluminescent and antioxidant micelles have great potential as a theranostic agent for H2O2‐associated inflammatory diseases.  相似文献   
8.
Portable and implantable device applications require low supply voltage reference circuits due to increasing trend for lower power requirements. Voltage references have been proposed for operation below 1 V for CMOS and a comprehensive analysis of the behavior of the different topologies is needed for ultra-low power designs, in order to select the right circuit topology for a given requirement. This work compares two major classes of voltage reference topologies: threshold voltage (VT0)-based and (VG0) bandgap voltage-based reference circuits. Four different topologies of voltage-reference designs with 1-V supply were designed and fabricated in 130 nm CMOS process. Monte Carlo analysis shows the variability of the references and of their temperature coefficients (TC), and the results are compared to measured samples. Simulations and measurements show that the threshold voltage-based references are more susceptible to the variations in the CMOS fabrication process.  相似文献   
9.
Flaxseed oil is an alpha linolenic acid source important in the growth and body development stage; furthermore, this acid acts on adipose tissue and bone health. The aim of this study was to evaluate body composition, fatty acid composition, hormone profile, retroperitoneal adipocyte area and femur structure of pups at weaning, whose mothers were fed a diet containing flaxseed oil during lactation. After birth, pups were randomly assigned: control (C, n = 12) and flaxseed oil (FO, n = 12), rats whose mothers were treated with diet containing soybean or flaxseed oil. At 21 days, the pups were weaned and body mass, length, body composition, biochemical parameter, leptin, osteoprotegerin, osteocalcin, fatty acids composition, intra‐abdominal fat mass and femur structure were analyzed. FO showed (p < 0.05): higher body mass (+12 %) and length (+9 %); body fat mass (g, +45 %); bone mineral density (+8 %), bone mineral content (+55 %) and bone area (+35 %), osteocalcin (+173 %) and osteoprotegerin (+183 %). Arachidonic acid was lower (p < 0.0001), alpha‐linolenic and eicosapentaenoic were higher (p < 0.0001). Intra‐abdominal fat mass was higher (+25 %), however, the retroperitoneal adipocytes area was lower (?44 %). Femur mass (+10 %), distance between epiphyses (+4 %) and bone mineral density (+13 %) were higher. The study demonstrates that adequate flaxseed oil content during a lactation diet plays an important role in the development of pups.  相似文献   
10.
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