全文获取类型
收费全文 | 699篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 79篇 |
金属工艺 | 7篇 |
机械仪表 | 10篇 |
建筑科学 | 34篇 |
矿业工程 | 5篇 |
能源动力 | 29篇 |
轻工业 | 48篇 |
水利工程 | 14篇 |
石油天然气 | 1篇 |
无线电 | 84篇 |
一般工业技术 | 115篇 |
冶金工业 | 121篇 |
原子能技术 | 3篇 |
自动化技术 | 174篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 30篇 |
2013年 | 36篇 |
2012年 | 42篇 |
2011年 | 70篇 |
2010年 | 35篇 |
2009年 | 52篇 |
2008年 | 51篇 |
2007年 | 40篇 |
2006年 | 40篇 |
2005年 | 41篇 |
2004年 | 17篇 |
2003年 | 21篇 |
2002年 | 20篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1972年 | 3篇 |
排序方式: 共有731条查询结果,搜索用时 15 毫秒
41.
Schulte Gary SL Aultman-Hall L McCourt M Stamatiadis N 《Accident; analysis and prevention》2003,35(5):641-648
This study examines the characteristics of alcohol-related crashes in wet versus dry counties in the state of Kentucky, USA and incorporates the location of driver residences through use of geographic information system (GIS) analysis. Between 1991 and 1997, 39344 alcohol-related crashes by Kentucky residents on Kentucky State roads were reported. The location of the crash and the home ZIP code from the driver's address were used to consider distance from home in the GIS. Analysis of the crash data revealed that a similar proportion of crashes in wet and dry counties are alcohol-related but that a higher proportion of dry counties residents are involved in an alcohol-related crash. However, when the distance from home variable is considered, several results suggest that dry county residents may be driving further when consuming alcohol. In part due to the rural nature of dry counties, drivers from dry counties have both alcohol-related and non-alcohol related crashes farther from their homes than residents from wet counties. Alcohol-related crashes by dry county residents in wet counties are the greatest average distance from home while crashes by wet county residents in wet counties are the smallest average distance. Drivers from dry counties over 21 years of age have alcohol-related crashes significantly farther from home than those under 21 who would not legally be admitted to drinking establishments in the wet counties. Furthermore, residents from dry counties that do not border wet counties have alcohol-related crashes on average farther from home than the border county residents. These last three results provide circumstantial evidence that some dry county drivers may be driving to wet counties to consume alcohol thus increasing impaired driving exposure. In conclusion, by considering crash location and driver residence, these findings indicate that county-level prohibition is not necessarily effective in improving highway safety. 相似文献
42.
Quinn M Smith L Mayley G Husbands P 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2003,361(1811):2321-2343
We report on recent work in which we employed artificial evolution to design neural network controllers for small, homogeneous teams of mobile autonomous robots. The robots were evolved to perform a formation-movement task from random starting positions, equipped only with infrared sensors. The dual constraints of homogeneity and minimal sensors make this a non-trivial task. We describe the behaviour of a successful system in which robots adopt and maintain functionally distinct roles in order to achieve the task. We believe this to be the first example of the use of artificial evolution to design coordinated, cooperative behaviour for real robots. 相似文献
43.
44.
Matt Apanius Pankaj B. Kaul Alexis R. Abramson 《Sensors and actuators. A, Physical》2007,140(2):168-175
Pattern deposition of metals with controlled and microscale dimensions can be a challenging task if traditional photolithography is not a practical option. This is a particularly valid concern for the case of certain polymer substrates, which are gaining in importance in the microelectronics and related industries. Therefore, a novel design and process flow for batch fabricating low cost reusable silicon shadow masks was developed. Of note was the corner compensation scheme employed to avoid over-etching of the convex corners in the design. These shadow masks enabled deposition of metals or other suitable materials with feature sizes ranging from approximately 3 to 250 μm and were successfully utilized to form patterned metal heater lines and pads on various samples. The heaters, required for conducting thermal conductivity measurements of the underlying films/substrates using the three omega (3ω) method, showed resistance–temperature linearity, confirming theoretical estimates to within 0.2%. Moreover, the room temperature thermal conductivity of an amorphous SiO2 film as well as a polyaniline thick film were measured, further validating the deposition through shadow mask technique. 相似文献
45.
Problem-focused coping, and active and avoidant emotional coping were examined as correlates of grief and posttraumatic stress disorder (PTSD) severity among 123 college students reporting the unexpected death of an immediate family member, romantic partner, or very close friend. The authors administered to participants, via the Internet, 5 survey instruments that measured demographic characteristics, traumatic event exposure (Stressful Life Events Screening Questionnaire; L. Goodman, C. Corcoran, K. Turner, N. Yuan, & B. L. Green, 1998), complicated grief (CG) severity (Inventory of Complicated Grief--Revised--Short Form; A. E. Latham & H. G. Prigerson, 2004; H. G. Prigerson & S. C. Jacobs, 2001), PTSD severity (PTSD Checklist; F. W. Weathers, B. T. Litz, D. S. Herman, J. A. Huska, & T. M. Keane, 1993), and coping style use (Brief COPE; C. S. Carver, 1997). Results demonstrated that CG and PTSD severity were both significantly positively correlated with problem-focused, and active and avoidant emotional coping styles. The authors used path analysis to control for time since the loss and trauma frequency and found that only avoidant emotional coping remained significant in predicting CG and PTSD severity. Results are discussed in terms of their clinical implications for treating individuals with traumatic losses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
47.
This study deals with some of the judgmental factors involved in selecting effect sizes from within the studies that enter a meta-analysis. Particular attention is paid to the conceptual redundancy rule that Smith, Glass, and Miller (1980) used in their study of the effectiveness of psychotherapy for deciding which effect sizes should and should not be counted in determining an overall effect size. Data from a random sample of 25 studies from Smith et al.'s (1980) population of psychotherapy outcome studies were first recoded and then reanalyzed meta-analytically. Using the conceptual redundancy rule, three coders independently coded effect sizes and identified more than twice as many of them per study as did Smith et al. Moreover, the treatment effect estimates associated with this larger sample of effects ranged between .30 and .50, about half the size claimed by Smith et al. Analyses of other rules for selecting effect sizes showed that average effect estimates also varied with these rules. Such results indicate that the average effect estimates derived from meta-analyses may depend heavily on judgmental factors that enter into how effect sizes are selected within each of the individual studies considered relevant to a meta-analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
In 1675, English scientist Robert Hooke discovered “the true... ...manner of arches for building,” which he summarized with
a single phrase: “As hangs the flexible line, so but inverted will stand the rigid arch.” In the centuries that followed,
Hooke’s simple idea has been used to understand and design numerous important works. Recent research at MIT on the interactive
analysis of structural forces provides new graphical tools for the understanding of arch behavior, which are useful for relating
the forces and geometry of masonry structures. The key mathematical principle is the use of graphical analysis to determine
possible equilibrium states. 相似文献
49.
Frost RL Erickson KL Weier ML McKinnon AR Williams PA Leverett P 《Applied spectroscopy》2004,58(7):811-815
Infrared spectroscopy has been used to study a series of synthetic agardite minerals. Four OH stretching bands are observed at around 3568, 3482, 3362, and 3296 cm(-1). The first band is assigned to zeolitic, non-hydrogen-bonded water. The band at 3296 cm(-1) is assigned to strongly hydrogen-bonded water with an H bond distance of 2.72 A. The water in agardites is better described as structured water and not as zeolitic water. Two bands at around 999 and 975 cm(-1) are assigned to OH deformation modes. Two sets of AsO symmetric stretching vibrations were found and assigned to the vibrational modes of AsO(4) and HAsO(4) units. Linear relationships between positions of infrared bands associated with bonding to the OH units and the electronegativity of the rare earth elements were derived, with correlation coefficients >0.92. These linear functions were then used to calculate the electronegativity of Eu, for which a value of 1.1808 on the Pauling scale was found. 相似文献
50.
Recognition of naturally occurring objects is a challenging task. In particular, the recognition of clouds is particularly
challenging as the texture of such objects is extremely variable under different atmospheric conditions. There are several
benefits of a practical system that can detect and recognise clouds in natural images especially for applications such as
air traffic control. In this paper, we test well-known texture feature extraction approaches for automatically training a
classifier system to recognise cumulus, towering cumulus, cumulo-nimbus clouds, sky and other clouds. For cloud recognition,
we use a total of five different feature extraction methods, namely autocorrelation, co-occurrence matrices, edge frequency,
Law’s features and primitive length. We use the k-nearest neighbour and neural network classifiers for identifying cloud types in test images. This exhaustive testing gives
us a better understanding of the strengths and limitations of different feature extraction methods and classification techniques
on the given problem. In particular, we find that no single feature extraction method is best suited for recognising all classes.
Each method has its own merits. We discuss these merits individually and suggest further improvements in this difficult area. 相似文献