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   864篇
  免费   33篇
电工技术   6篇
化学工业   149篇
金属工艺   6篇
机械仪表   7篇
建筑科学   39篇
矿业工程   3篇
能源动力   41篇
轻工业   140篇
水利工程   10篇
石油天然气   20篇
无线电   60篇
一般工业技术   109篇
冶金工业   216篇
原子能技术   5篇
自动化技术   86篇
  2023年   6篇
  2022年   14篇
  2021年   25篇
  2020年   19篇
  2019年   11篇
  2018年   21篇
  2017年   23篇
  2016年   23篇
  2015年   12篇
  2014年   21篇
  2013年   34篇
  2012年   43篇
  2011年   46篇
  2010年   53篇
  2009年   22篇
  2008年   39篇
  2007年   37篇
  2006年   35篇
  2005年   29篇
  2004年   23篇
  2003年   20篇
  2002年   18篇
  2001年   17篇
  2000年   19篇
  1999年   19篇
  1998年   61篇
  1997年   26篇
  1996年   25篇
  1995年   18篇
  1994年   16篇
  1993年   15篇
  1992年   10篇
  1991年   10篇
  1990年   5篇
  1989年   9篇
  1988年   4篇
  1987年   6篇
  1986年   8篇
  1985年   5篇
  1984年   5篇
  1981年   2篇
  1980年   3篇
  1979年   4篇
  1978年   5篇
  1977年   3篇
  1976年   5篇
  1972年   4篇
  1971年   2篇
  1966年   2篇
  1956年   2篇
排序方式: 共有897条查询结果,搜索用时 31 毫秒
21.
To effectively manage forested ecosystems an accurate characterization of species distribution is required. In this study we assess the utility of hyperspectral Airborne Imaging Spectrometer for Applications (AISA) imagery and small footprint discrete return Light Detection and Ranging (LiDAR) data for mapping 11 tree species in and around the Gulf Islands National Park Reserve, in coastal South-western Canada. Using hyperspectral imagery yielded producer's and user's accuracies for most species ranging from > 52-95.4 and > 63-87.8%, respectively. For species dominated by definable growth stages, pixel-level fusion of hyperspectral imagery with LiDAR-derived height and volumetric canopy profile data increased both producer's (+ 5.1-11.6%) and user's (+ 8.4-18.8%) accuracies. McNemar's tests confirmed that improvements in overall accuracies associated with the inclusion of LiDAR-derived structural information were statistically significant (p < 0.05). This methodology establishes a specific framework for mapping key species with greater detail and accuracy then is possible using conventional approaches (i.e., aerial photograph interpretation), or either technology on its own. Furthermore, in the study area, acquisition and processing costs were lower than a conventional aerial photograph interpretation campaign, making hyperspectral/LiDAR fusion a viable replacement technology.  相似文献   
22.
Directly linking air quality and watershed models could provide an effective method for estimating spatially-explicit inputs of atmospheric contaminants to watershed biogeochemical models. However, to adequately link air and watershed models for wet deposition estimates, each model’s temporal and spatial representation of precipitation needs to be consistent. We explore how precipitation implemented within the Community Multi-Scale Air Quality Model (CMAQ) model algorithms, and multiple spatially-explicit precipitation datasets that could be used to improve the CMAQ model deposition estimates, links with the standard precipitation sources used to calibrate watershed models (i.e., rain gage data) via modeled water fluxes. Simulations are run using a grid-based watershed mercury model (GBMM) in two watersheds. Modeled monthly runoff suggests that multiple resolution Parameter-elevations Regressions on Independent Slopes Model (PRISM) and National Multi-sensor Precipitation Analysis Stage IV (NPA) data generate similar monthly runoff estimates, with comparable or greater accuracy when evaluated against stream gage data than that produced by the base rain gage data. However, across longer time periods, simulated water balances using 36 km Pennsylvania State University/National Center for Atmospheric Research mesoscale model (MM5) data are similar to that of base data. The investigation also examines the implications our results, providing suggestions for linking air quality and watershed fate and transport models.  相似文献   
23.
This work‐in‐process literature review gives an overview of recent insight in the incorporation of social media in risk and crisis communication. By marrying literature and examples of social media use with best practices in risk and crisis communication, this study demonstrates how communicators can embrace social media tools to better manage a risk or crisis. Best practices in risk and crisis communication are summarized, examples of social media tools used to manage risks and crises are expounded, and recommendations for practitioners are provided to incorporate social media tools in risk and crisis communication.  相似文献   
24.
The body of a walking human is an elaborated dynamic system that operates adaptively in various conditions such as fast walking. Due to dynamic redundancies, the individual motor control strategies for speeding up the walking can be different among normal subjects. However, in reality, we see that the pattern of motion is quite similar among people and it is only the profile of hip joint motion along its path which determines the speed. The objective of the current paper is to develop a mathematical framework to investigate time optimal motion of a human during walking. To this end, a nine-link planar biped model is used. The motion is considered to take place in sagittal plane and to follow a normal pattern of motion. The solution is obtained using a phase plane method to solve minimum time problem which is subjected to inequality constraints of variable maximum joint torques and stability conditions. The solution method can be used to find the maximum possible speed of a human with specific body characteristics and to obtain a hip joint trajectory which could produce that speed. The proposed method can be utilized to study quantitative effect of different parameters such as joint strength in fast walking.  相似文献   
25.
Work organization and team membership is highly complex for modern workers. Teams are often dynamic as personnel change during a project. Dynamic team members have to be actively recruited and personnel changes make it harder for participants to retain group focus. Workers are often members of multiple groups. Though prior work has identified the prevalence of multi-teaming and dynamic teams, it has been unable to explain how workers cope with the challenges the new style of work should cause. This paper systematically characterizes the modern organizational landscape from an individual perspective, by studying how people typically organize work across their multiple collaborative groups. A unique contribution of our work is to examine the interrelationships between the collaborative groups individuals typically participate in. We introduce the notion of a collaboration profile to characterize these interrelations. We expected workers to be overburdened by contributing to multiple teams often with shifting personnel. However, we found that multi-teaming involves productive interrelationships between collaborative groups that ease some of the documented challenges of dynamic teams, such as goal setting, recruiting, and group maintenance. We define a typology that describes the various types of collaborative groups workers participate in, and provide examples of productive interrelations between collaborations. In characterizing interrelations between collaborations, we provide detailed examples of how people exploit resources across their different collaborations to address the problems of working in multiple dynamic teams.  相似文献   
26.
The authors tested 90 rhesus monkeys (Macaca mulatta) on a task of spatial memory, the spatial Delayed Recognition Span Test. The results showed that performance declined significantly with age, males had greater scores than females, and the rate of apparent decline with age was greater in males than in females. Both working and reference memory declined with age, but only working memory showed sex differences. The authors compared these data with that of 22 monkeys who were trained on a simpler version of the task before formal testing. Training had no effect on males but dramatically improved working memory in young females. The results confirm a male advantage in spatial working memory at a young age and confirm a greater decline with age in males than in females. It is important to note that prior training completely reverses the deficits of young females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
27.
Reviews the book Protecting children from domestic violence: Strategies for community intervention, edited by Peter J. Jaffe, Linda L. Baker, and Alison J. Cunningham (see record 2005-04430-000). The book emerged from the International Conference on Children Exposed to Domestic Violence that was held in London, Ontario in 2001. It begins with an excellent chapter by Jeffrey Edleson synthesizing the literature on the impact of exposure to domestic violence on children. Edleson's chapter is followed by two papers examining emerging assessments and treatment programs. The second section of the book addresses current thinking about individual and group intervention approaches. The third section of the book examines broader system level responses, including public awareness and school-based campaigns, as well as responses by the courts and police. This is a well-organized collection of papers that provides a good overview of the state of knowledge and innovative practice in an emerging field of practice. Protecting Children from Domestic Violence provides practitioners, policy makers, and researchers with an excellent overview of current knowledge and practices in working with children exposed to domestic violence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
28.
The objective of this study was to investigate the antimicrobial effects of carvacrol and cinnamaldehyde incorporated into apple, carrot, and hibiscus‐based edible films against Salmonella Newport in bagged organic leafy greens. The leafy greens tested included organic Romaine and Iceberg lettuce, and mature and baby spinach. Each leafy green sample was washed, dip inoculated with S. Newport (107 CFU/mL), and dried. Each sample was put into a Ziploc® bag. Edible films pieces were put into the Ziploc bag and mixed well. The bags were sealed and stored at 4 °C. Samples were taken at days 0, 3, and 7 for enumeration of survivors. On all leafy greens, 3% carvacrol films showed the best bactericidal effects against Salmonella. All 3 types of 3% carvacrol films reduced the Salmonella population by 5 log10 CFU/g at day 0 and 1.5% carvacrol films reduced Salmonella by 1 to 4 log10 CFU/g at day 7. The films with 3% cinnamaldehyde showed 0.5 to 3 log reductions on different leafy greens at day 7. The films with 0.5% and 1.5% cinnamaldehyde and 0.5% carvacrol also showed varied reductions on different types of leafy greens. Edible films were the most effective against Salmonella on Iceberg lettuce. This study demonstrates the potential of edible films incorporated with carvacrol and cinnamaldehyde to inactivate S. Newport on organic leafy greens.  相似文献   
29.
30.
A tethered viewpoint in an operator interface visualizes remote situations according to a robot’s heading direction. The tethered view, adhering to the line-of-sight requirement, results lower visual momentum when visualizing dense environments, such as during indoor teleoperation tasks. This problem occurs because the tethered view only partially visualizes spatial information, unlike the bird’s-eye view. Operators are thus inhibited to build their spatial mental model because the transitions happen as the robot moves. This paper presents an approach to improve the visual momentum of the tethered view by complementing the omitted spatial information. The approach augments simplified spatial cues on the excluded areas of a tethered view. The cues are purportedly used to illuminate the basic spatial structure of the surroundings and can thus help operators in constructing their spatial mental models. Evaluation of the presented approach was conducted using a simulated telerobot environment. The results indicated that the augmented view possessed a higher visual momentum, which exhibited by the lowered workload and enhanced levels of both spatial perception and situational awareness.  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