首页 | 官方网站   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   234篇
  免费   15篇
工业技术   249篇
  2024年   1篇
  2023年   10篇
  2022年   14篇
  2021年   28篇
  2020年   5篇
  2019年   14篇
  2018年   23篇
  2017年   17篇
  2016年   21篇
  2015年   8篇
  2014年   8篇
  2013年   27篇
  2012年   8篇
  2011年   9篇
  2010年   7篇
  2009年   10篇
  2008年   8篇
  2007年   6篇
  2006年   5篇
  2005年   2篇
  2004年   3篇
  2003年   1篇
  2002年   1篇
  2001年   1篇
  1998年   2篇
  1997年   1篇
  1995年   1篇
  1992年   1篇
  1991年   1篇
  1986年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   2篇
排序方式: 共有249条查询结果,搜索用时 0 毫秒
101.
The key solution to study birds in their natural habitat is the continuous survey using wireless sensors networks (WSN). The final objective of this study is to conceive a system for monitoring threatened bird species using audio sensor nodes. The principal feature for their recognition is their sound. The main limitations encountered with this process are environmental noise and energy consumption in sensor nodes. Over the years, a variety of birdsong classification methods has been introduced, but very few have focused to find an adequate one for WSN. In this paper, a tonal region detector (TRD) using sigmoid function is proposed. This approach for noise power estimation offers flexibility, since the slope and the mean of the sigmoid function can be adapted autonomously for a better trade-off between noise overvaluation and undervaluation. Once the tonal regions in the noisy bird sound are detected, the features gammatone teager energy cepstral coefficients (GTECC) post-processed by quantile-based cepstral normalization were extracted from the above signals for classification using deep neural network classifier. Experimental results for the identification of 36 bird species from Tonga lake (northeast of Algeria) demonstrate that the proposed TRD–GTECC feature is highly effective and performs satisfactorily compared to popular front-ends considered in this study. Moreover, recognition performance, noise immunity and energy consumption are considerably improved after tonal region detection, indicating that it is a very suitable approach for the acoustic bird recognition in complex environments with wireless sensor nodes.  相似文献   
102.
The fundamental goals of security policy are to allow uninterrupted access to the network resources for authenticated users and to deny access to unauthenticated users. For this purpose, firewalls are frequently deployed in every size network. However, bad configurations may cause serious security breaches and network vulnerabilities. In particular, conflicted filtering rules lead to block legitimate traffic and to accept unwanted packets. This fact troubles administrators who have to insert and delete filtering rules in a huge configuration file. We propose in this paper a quick method for managing a firewall configuration file. We represent the set of filtering rules by a firewall anomaly tree (FAT). Then, an administrator can update the FAT by inserting and deleting some filtering rules. The FAT modification automatically reveals emerged anomalies and helps the administrator to find the adequate position for a new added filtering rule. All the algorithms presented in the paper have been implemented, and computer experiments show the usefulness of updating the FAT data structure in order to quickly detect anomalies when dealing with a huge firewall configuration file.  相似文献   
103.
104.
The development of reliable models for transmission of intramammary infections (IMI) is the subject of extensive research. Such models are useful to enhance the identification and understanding of factors that affect pathogen-specific IMI dynamics. Longitudinal transmission models are valuable for predicting infection outbreak risks, quantifying the effectiveness of response tactics, and performing response planning. In this work, we focused on modeling Corynebacterium spp. by using a compartmental model. Previous investigations have considered modeling the transmission dynamics of several bacterial pathogens, but not Corynebacterium spp. We established a Corynebacterium spp. Susceptible–Infectious–Susceptible (SIS) model. We simulated the model numerically by using parameters that we estimated by a generalized linear model approach, using month of study as the time variable. The data, from which the parameters of the model were estimated, were obtained in a field trial conducted in 2 US dairy herds. Altogether, 786 cows were sampled at least once during the 13-mo study period. The total number of quarter milk cultures and cases of IMI caused by Corynebacterium spp. were 11,744 and 556, respectively, in farm A; the corresponding figures for farm B were 11,804 and 179. Our modeling study included only transmission from persistent IMI caused by Corynebacterium spp. within the lactation pens. The rate of new infections was significantly related to preexisting IMI in both farms, underscoring the importance of preexisting Corynebacterium spp. IMI for the transmission of Corynebacterium spp. within lactation pens. The estimated basic reproduction numbers (R0) in the 2 farms were 1.18 and 0.98, respectively. The nonsignificant disparity in R0 was associated with significant differences in cure rates between farms.  相似文献   
105.
Abstract

Objective: Complexation was investigated as an approach to enhance the entrapment of the cationic neurotherapeutic drug, galantamine hydrobromide (GH) into cationic chitosan nanoparticles (CS-NPs) for Alzheimer’s disease management intranasally. Biodegradable CS-NPs were selected due to their low production cost and simple preparation. The effects of complexation on CS-NPs physicochemical properties and uptake in rat brain were examined.

Methods: Placebo CS-NPs were prepared by ionic gelation, and the parameters affecting their physicochemical properties were screened. The complex formed between GH and chitosan was detected by the FT-IR study. GH/chitosan complex nanoparticles (GH-CX-NPs) were prepared by ionic gelation, and characterized in terms of particle size, zeta potential, entrapment efficiency, in vitro release and stability for 4 and 25?°C for 3 months. Both placebo CS-NPs and GH-CX-NPs were visualized by transmission electron microscopy. Rhodamine-labeled GH-CX-NPs were prepared, administered to male Wistar rats intranasally, and their delivery to different brain regions was detected 1?h after administration using fluorescence microscopy and software-aided image processing.

Results: Optimized placebo CS-NPs and GH-CX-NPs had a diameter 182 and 190?nm, and a zeta potential of +40.4 and +31.6?mV, respectively. GH encapsulation efficiency and loading capacity were 23.34 and 9.86%, respectively. GH/chitosan complexation prolonged GH release (58.07%?±?6.67 after 72?h), improved formulation stability at 4?°C in terms of drug leakage and particle size, and showed insignificant effects on the physicochemical properties of the optimized placebo CS-NPs (p?>?0.05). Rhodamine-labeled GH-CX-NPs were detected in the olfactory bulb, hippocampus, orbitofrontal and parietal cortices.

Conclusion: Complexation is a promising approach to enhance the entrapment of cationic GH into the CS-NPs. It has insignificant effect on the physicochemical properties of CS-NPs. GH-CX-NPs were successfully delivered to different brain regions shortly after intranasal administration suggesting their potential as a delivery system for Alzheimer’s disease management.  相似文献   
106.
In this study, the effect of the voids growth on the damage of PP/talc micro-composite was analyzed using experimental and numerical approaches. Pure PP was filled with four proportions of treated talc: 5, 10, 40 and 50%. Tensile tests were performed on specimens manufactured from this composite. The Gurson–Tvergaard–Needleman model was implemented in FE model to predict the damage of the PP/talc. The predicted results were compared to the experimental ones. There is a good agreement between the numerical and the experimental results for pure PP, PP?+?40% of talc and the PP?+?50% of talc. We noted a significant divergence between the experimental and the numerical results for the PP reinforced with 5 and 10% of talc.  相似文献   
107.
This study assess the impact of ICT diffusion on corruption by using instrumental variables method on a panel data set of 175 countries over the period 1996–2014. We check for the stability of the ICT-corruption nexus for different levels of economic development. Our results show that ICT diffusion clearly acts as an effective tool to control corruption. The study also reports that as the countries develop economically they improve their corruption level. Moreover, as per the per capita GDP, estimation outcomes suggest that both trade openness and better institutions are associated with lower corruption levels. However, results show robust support to suggest that as the general price level increases, bribery increases. This effect is more pronounced for the developing countries than for developed ones, which may witness higher inflation rates and therefore a higher cost of living. Drawn on our results, our study addresses important insights and policy implications mainly for developing countries.  相似文献   
108.
Microscopic image analysis is one of the challenging tasks due to the presence of weak correlation and different segments of interest that may lead to ambiguity. It is also valuable in foremost meadows of technology and medicine. Identification and counting of cells play a vital role in features extraction to diagnose particular diseases precisely. Different segments should be identified accurately in order to identify and to count cells in a microscope image. Consequently, in the current work, a novel method for cell segmentation and identification has been proposed that incorporated marking cells. Thus, a novel method based on cuckoo search after pre‐processing step is employed. The method is developed and evaluated on light microscope images of rats’ hippocampus which used as a sample for the brain cells. The proposed method can be applied on the color images directly. The proposed approach incorporates the McCulloch's method for lévy flight production in cuckoo search (CS) algorithm. Several objective functions, namely Otsu's method, Kapur entropy and Tsallis entropy are used for segmentation. In the cuckoo search process, the Otsu's between class variance, Kapur's entropy and Tsallis entropy are employed as the objective functions to be optimized. Experimental results are validated by different metrics, namely the peak signal to noise ratio (PSNR), mean square error, feature similarity index and CPU running time for all the test cases. The experimental results established that the Kapur's entropy segmentation method based on the modified CS required the least computational time compared to Otsu's between‐class variance segmentation method and the Tsallis entropy segmentation method. Nevertheless, Tsallis entropy method with optimized multi‐threshold levels achieved superior performance compared to the other two segmentation methods in terms of the PSNR.  相似文献   
109.
Proteins in dairy streams result in organic fouling and function loss for ceramic membrane's porous structure. Synchrotron-based X-ray microtomography (SR-µCT) is a new method with a high signal to noise ratio and accordingly significant level of accuracy. The goal of this study was to perform an in situ assessment of ceramic membrane fouling in the dairy stream filtration process, using SR-µCT. This study attempted to assess porosity variation and membrane fouling through different layers from the top, middle, and bottom layers of the ceramic microfiltration membrane before and after skimming milk filtration. Molecular dynamics simulation (MDS) was used for depth understanding of milk protein interactions with the ceramic membrane. Fouling was found to be more intense on the top of the ceramic membrane even though the top layer was slightly more porous, which indicates that top layers were more prone to fouling. A regression model was derived to correlate the porosity loss due to membrane fouling at different membrane thicknesses. The MDS results showed more affinity of the milk proteins to the ceramic membrane compared to water molecules. The MDS studies showed how the presence of the milk's protein macromolecules could change the hydrophilicity trend on the membrane's surface.  相似文献   
110.
Grafting of vinyl monomers onto cellulose-thiocarbamate was carried out using ceric ammonium sulfate (CAS) as an initiator. The graft yield was found to depend on the amount of thiocarbamate groups, initiator, and monomer concentrations as well as temperature. The graft yield increased with increasing (CAS) concentration. The reactivity of vinyl monomers studied followed the order ethyl acrylate>acrylonitrile. A comparison between the graft yields obtained with the modified cullulose indicated that cellulose thiocarbamates having less than 1.1% nitrogen showed lower graft yields than the unmodified cellulose. Above this, cellulose thiocarbamate was much more amenable to grafting than the unmodified cellulose. The grafted cellulose thiocarbamates exhibited high antifungal activity and had no effect on gram-negative, gram-positive bacteria and yeast. The maximum zone of inhibition was obtained after grafting with 2 h which resulted in 43 and 50% add-on polymer in the cases of acrylonitrile and ethyl acrylate, respectively. Grafted cellulose thiocarbamates with acrylonitrile had higher potency for antifungal activity than that grafted with ethyl acrylate.  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-23

京公网安备 11010802026262号