全文获取类型
收费全文 | 4471篇 |
免费 | 153篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 67篇 |
综合类 | 10篇 |
化学工业 | 571篇 |
金属工艺 | 75篇 |
机械仪表 | 83篇 |
建筑科学 | 324篇 |
矿业工程 | 14篇 |
能源动力 | 140篇 |
轻工业 | 418篇 |
水利工程 | 46篇 |
石油天然气 | 19篇 |
无线电 | 355篇 |
一般工业技术 | 746篇 |
冶金工业 | 731篇 |
原子能技术 | 21篇 |
自动化技术 | 1015篇 |
出版年
2024年 | 9篇 |
2023年 | 23篇 |
2022年 | 40篇 |
2021年 | 73篇 |
2020年 | 56篇 |
2019年 | 72篇 |
2018年 | 103篇 |
2017年 | 126篇 |
2016年 | 111篇 |
2015年 | 100篇 |
2014年 | 118篇 |
2013年 | 305篇 |
2012年 | 236篇 |
2011年 | 303篇 |
2010年 | 231篇 |
2009年 | 217篇 |
2008年 | 283篇 |
2007年 | 243篇 |
2006年 | 231篇 |
2005年 | 175篇 |
2004年 | 130篇 |
2003年 | 124篇 |
2002年 | 143篇 |
2001年 | 86篇 |
2000年 | 86篇 |
1999年 | 90篇 |
1998年 | 117篇 |
1997年 | 103篇 |
1996年 | 78篇 |
1995年 | 64篇 |
1994年 | 56篇 |
1993年 | 51篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 28篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1976年 | 22篇 |
1975年 | 11篇 |
排序方式: 共有4635条查询结果,搜索用时 15 毫秒
61.
Ilias Maglogiannis Demosthenes Vouyioukas Chris Aggelopoulos 《Personal and Ubiquitous Computing》2009,13(1):95-101
This paper presents an integrated system for emotion detection. In this research effort, we have taken into account the fact
that emotions are most widely represented with eye and mouth expressions. The proposed system uses color images and it is
consisted of three modules. The first module implements skin detection, using Markov random fields models for image segmentation
and skin detection. A set of several colored images with human faces have been considered as the training set. A second module
is responsible for eye and mouth detection and extraction. The specific module uses the HLV color space of the specified eye
and mouth region. The third module detects the emotions pictured in the eyes and mouth, using edge detection and measuring
the gradient of eyes’ and mouth’s region figure. The paper provides results from the system application, along with proposals
for further research. 相似文献
62.
R. A. Olson B. J. Christensen R. T. Coverdale S. J. Ford G. M. Moss H. M. Jennings T. O. Mason E. J. Garboczi 《Journal of Materials Science》1995,30(20):5078-5086
The d.c. conductivity, , and low-frequency relative dielectric constant, k, of Portland cement paste were monitored, using impedance spectroscopy, during cooling from room temperature down to -50 °C. Dramatic decreases in the values of and k, as great as two orders of magnitude, occurred at the initial freezing point of the aqueous phase in the macropores and larger capillary pores. This result provides strong experimental support for the dielectric amplification mechanism, proposed in Part II of this series, to explain the high measured low-frequency relative dielectric constant of hydrating Portland cement paste. Only gradual changes in the electrical properties were observed below this sudden drop, as the temperature continued to decrease. The values of and k of frozen cement paste, at a constant temperature of -40 °C, were dominated by properties of calcium-silicate-hydrate (C-S-H) and so increased with the degree of hydration of the paste, indicating a C-S-H gel percolation threshold at a volume fraction of approximately 15%–20%, in good agreement with previous predictions. Good agreement was found between experimental results and digital-image-based model computations of at -40 °C. Freeze-thaw cycling caused a drop in the dielectric constant of paste in the unfrozen state, indicating that measurements of k could be useful for monitoring microstructural changes during freeze-thaw cycling and other processes that gradually damage parts of the cement paste microstructure. 相似文献
63.
The assessment of the social impacts of road traffic is usually based on objective indicators or on expert judgement, without input from the affected communities. This paper considers the perceptions and priorities of local residents about traffic impacts and possible mitigation measures, using as a case study a rural area that will be affected by traffic associated with the construction of a nuclear power station. The study consisted of a qualitative phase followed by a stated preference survey. Econometric models were used to measure the relative priority of different impacts and mitigation measures. The most impactful aspects were noise, vibration and increased car or bus travel times. The most preferred measures were night-time restrictions to HGVs, parking restrictions and safety measures for pedestrians and cyclists. There were significant differences in preferences according to residence location, gender, employment status and household composition. The results provide information about aspects that tend to be aggregated in existing assessment frameworks, separating the reduction in the utility of some activities (like walking and driving) and the suppression of those activities. 相似文献
64.
Formal Specification and Quantitative Analysis of a Constellation of Navigation Satellites 下载免费PDF全文
Zhaoguang Peng Yu Lu Alice Miller Tingdi Zhao Chris Johnson 《Quality and Reliability Engineering International》2016,32(2):345-361
Navigation satellites are a core component of navigation satellite‐based systems such as Global Positioning System, Global Navigation Satellite System and Galileo, which provide location and timing information for a variety of uses. Such satellites are designed for operating on orbit to perform tasks and have lifetimes of 10 years or more. Reliability, availability and maintainability analysis of systems has been indispensable in the design phase of satellites in order to achieve minimum failures or to increase mean time between failures and thus to plan maintenance strategies, optimise reliability and maximise availability. In this paper, we present formal models of both a single satellite and a navigation satellite constellation and logical specification of their reliability, availability and maintainability properties, respectively. The probabilistic model checker PRISM has been used to perform automated analysis of these quantitative properties. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
65.
Triple Emulsion Drops with An Ultrathin Water Layer: High Encapsulation Efficiency and Enhanced Cargo Retention in Microcapsules 下载免费PDF全文
66.
67.
Chris E. Mohn 《Materials and Manufacturing Processes》2018,33(2):174-179
Genetic algorithms (GAs) together with classical pair potentials and density functional theory (DFT) are used to investigate cation order in MgAl2O4 (Spinel). To efficiently locate the global minimum/minima on the system potential energy surface, corresponding to the ordered and fully equilibrated low-temperature phase, local structural optimizations are essential. Such energy minimizations are expensive at the DFT level, but a comparison of the distribution of the energy minima from DFT and popular classical pair potentials allows one to rapidly tune the GA parameters. We show that GAs are able to find, not only the global minimum on the potential energy, but also other low-energy cation configurations representing possible frozen-in disordered or metastable phases after quenching. The nature of these low-energy configurations can help to interpret the extent of kinetic trapping which hampers the comparison between different experimental studies. 相似文献
68.
Alessandra Di Pierro Chris Hankin Herbert Wiklicky 《International Journal of Information Security》2011,10(2):61-61
Preface
Preface 相似文献69.
Attribute selection with fuzzy decision reducts 总被引:2,自引:0,他引:2
Rough set theory provides a methodology for data analysis based on the approximation of concepts in information systems. It revolves around the notion of discernibility: the ability to distinguish between objects, based on their attribute values. It allows to infer data dependencies that are useful in the fields of feature selection and decision model construction. In many cases, however, it is more natural, and more effective, to consider a gradual notion of discernibility. Therefore, within the context of fuzzy rough set theory, we present a generalization of the classical rough set framework for data-based attribute selection and reduction using fuzzy tolerance relations. The paper unifies existing work in this direction, and introduces the concept of fuzzy decision reducts, dependent on an increasing attribute subset measure. Experimental results demonstrate the potential of fuzzy decision reducts to discover shorter attribute subsets, leading to decision models with a better coverage and with comparable, or even higher accuracy. 相似文献
70.
Ferreira N Lins L Fink D Kelling S Wood C Freire J Silva C 《IEEE transactions on visualization and computer graphics》2011,17(12):2374-2383
Birds are unrivaled windows into biotic processes at all levels and are proven indicators of ecological well-being. Understanding the determinants of species distributions and their dynamics is an important aspect of ecology and is critical for conservation and management. Through crowdsourcing, since 2002, the eBird project has been collecting bird observation records. These observations, together with local-scale environmental covariates such as climate, habitat, and vegetation phenology have been a valuable resource for a global community of educators, land managers, ornithologists, and conservation biologists. By associating environmental inputs with observed patterns of bird occurrence, predictive models have been developed that provide a statistical framework to harness available data for predicting species distributions and making inferences about species-habitat associations. Understanding these models, however, is challenging because they require scientists to quantify and compare multiscale spatialtemporal patterns. A large series of coordinated or sequential plots must be generated, individually programmed, and manually composed for analysis. This hampers the exploration and is a barrier to making the cross-species comparisons that are essential for coordinating conservation and extracting important ecological information. To address these limitations, as part of a collaboration among computer scientists, statisticians, biologists and ornithologists, we have developed BirdVis, an interactive visualization system that supports the analysis of spatio-temporal bird distribution models. BirdVis leverages visualization techniques and uses them in a novel way to better assist users in the exploration of interdependencies among model parameters. Furthermore, the system allows for comparative visualization through coordinated views, providing an intuitive interface to identify relevant correlations and patterns. We justify our design decisions and present case studies that show how BirdVis has helped scientists obtain new evidence for existing hypotheses, as well as formulate new hypotheses in their domain. 相似文献