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   186篇
  免费   6篇
  国内免费   2篇
电工技术   5篇
综合类   7篇
化学工业   6篇
金属工艺   1篇
机械仪表   2篇
建筑科学   47篇
矿业工程   9篇
能源动力   10篇
轻工业   6篇
水利工程   14篇
石油天然气   4篇
无线电   2篇
一般工业技术   10篇
冶金工业   31篇
原子能技术   1篇
自动化技术   39篇
  2023年   1篇
  2021年   8篇
  2020年   3篇
  2019年   1篇
  2018年   5篇
  2017年   2篇
  2016年   5篇
  2015年   7篇
  2014年   13篇
  2013年   13篇
  2012年   8篇
  2011年   14篇
  2010年   10篇
  2009年   13篇
  2008年   9篇
  2007年   10篇
  2006年   8篇
  2005年   9篇
  2004年   5篇
  2003年   3篇
  2002年   1篇
  2001年   2篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1995年   7篇
  1994年   6篇
  1993年   1篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   3篇
  1987年   1篇
  1983年   1篇
  1982年   2篇
  1979年   1篇
  1977年   2篇
  1964年   1篇
  1961年   1篇
  1958年   2篇
  1955年   1篇
  1954年   1篇
排序方式: 共有194条查询结果,搜索用时 15 毫秒
1.
A dispersed flow model previously developed to study substrate utilization in unsaturated media was experimentally verified and its practical application was considered. For this purpose, measurements were made using tap water and a synthetic feed solution. The importance of the change in fluid regime as regards to the simultaneous transport and reaction within biological filters were demonstrated. The effect of drop formation and the breakage of liquid jets inside the filters on substrate utilization was also shown.  相似文献   
2.
The British otter Lutra lutra L. requires good water quality, an adequate supply of fish and certain types of vegetation or cavities (holts) adjacent to water bodies for resting and breeding sites. In the U.K. otters and their holts are legally protected. Trained surveyors are needed to confirm the presence of otters on a river as the animals are rarely seen, but their tracks and droppings (spraints) may be detected. To evaluate a river for otters, information is required on water quality, fish species and biomass, as well as available habitat. Pioneer evaluation work based on the River Corridor Survey techniques has been done on Welsh rivers with good otter populations. Riparian vegetation, especially trees, is shown to be particularly important. This work is now being extended to areas on the margins of otter distribution such as the lower river Wye in England and Wales. Such surveys provide important management information for water authorities and give opportunities for enhancement work to benefit this animal.  相似文献   
3.
Web surveys are rapidly becoming standard issue in many researchers’ toolkits; however, measurement error has been shown to affect web surveys to a greater extent than paper-and-pencil surveys (Couper, 2000, Manfreda and Vehovar, 2002). Principles of aesthetic design and social presence have been applied to web surveys to reduce the prevalence of such error with promising results, which were further investigated in this research. A sample of 181 first-year psychology undergraduate students participated in this study. Participants were randomly allocated to view one of eight web survey interfaces, which varied by aesthetic quality and social presence. Exploratory structural equation modeling using the partial least squares method revealed that classical aesthetic quality and social presence were both positively related to perceived ease of use of the web survey interface and positive state affect; social presence and perceived ease of use were positively related to trust in the web survey researcher; classical aesthetic quality was negatively related to negative state affect; and, expressive aesthetic quality was negatively related to perceived ease of use and positively related to positive state affect. Interestingly, expressive aesthetic quality was also positively related to negative state affect. These relationships between aesthetic quality and social presence should inform best practice web survey design recommendations, and future empirical work should extend and test the generalizability of these findings.  相似文献   
4.
Abstract

This study investigates the effects of gender, college status, and prior Internet experience on the use of Internet resources. The subjects were 96 patrons randomly selected from those using the Internet terminals at the University Library of the University at Albany, SUNY, during the first two months of 1995. We found that the majority of users shared the following characteristics: they are male undergraduates affiliated with the social sciences and are novice users who have less than six months experience. Respondents felt strongly that the Internet is useful, and has been an important resource for their research and assignments. Users have high expectations of searching capabilities, while they feel neutral or disappointed with browsing. Our findings indicate that libraries should provide access to the Internet. They also suggest that libraries should take the lead in developing searchable indexes and making info-bases better organized for the ease and effectiveness of browsing.  相似文献   
5.
Research using Internet surveys is an emerging field, yet research on the legitimacy of using Internet studies, particularly those targeting sensitive topics, remains under-investigated. The current study builds on the existing literature by exploring the demographic differences between Internet panel and RDD telephone survey samples, as well as differences in responses with regard to experiences of intimate partner violence perpetration and victimization, alcohol and substance use/abuse, PTSD symptomatology, and social support. Analyses indicated that after controlling for demographic differences, there were few differences between the samples in their disclosure of sensitive information, and that the online sample was more socially isolated than the phone sample. Results are discussed in terms of their implications for using Internet samples in research on sensitive topics.  相似文献   
6.
The Youth Risk Behavior Surveillance System (YRBSS) monitors priority health-risk behaviors among US high school students. To better understand the ramifications of changing the YRBSS from paper-and-pencil to Web administration, in 2008 the Centers for Disease Control and Prevention conducted a study comparing these two modes of administration. Eighty-five schools in 15 states agreed to participate in the study. Within each participating school, four classrooms of students in grades 9 or 10 were randomly assigned to complete the Youth Risk Behavior Survey questionnaire in one of four conditions (in-class paper-and-pencil, in-class Web without programmed skip patterns, in-class Web with programmed skip patterns, and “on your own” Web without programmed skip patterns). Findings included less missing data for the paper-and-pencil condition (1.5% vs. 5.3%, 4.4%, 6.4%; p < .001), less perceived privacy and anonymity among respondents for the in-class Web conditions, and a lower response rate for the “on your own” Web condition than for in-class administration by either mode (28.0% vs. 91.2%, 90.1%, 91.4%; p < .001). Although Web administration might be useful for some surveys, these findings do not favor the use of a Web survey for the YRBSS.  相似文献   
7.
In this paper, 5 investigations on the current states of power distribution grids in China have been introduced that cover the surveys of the practical distribution asset utilization, the simultaneity factor of feeder loading, the load compositions and characteristics, the urban reliability and the integration of distributed generations of renewable resources. Based on the survey results in the investigations, 12 Facts are clearly presented. It shows that the challenges to modernize the distribution grids in China are to improve the asset utilization rates, the electricity efficiencies and the reliability of distribution systems, as well as to integrate increasing amount of variable distributed renewable resources. Furthermore based on the challenges, 8 R&D opportunities have been identified.  相似文献   
8.
塔尔沟地区1/5万矿产远景调查地质特征及找矿方向   总被引:1,自引:0,他引:1  
杨国庆  杨春茂 《甘肃冶金》2009,31(5):52-56,59
祁连山西段塔尔沟地区,大地构造位置位于祁连山中间隆起带和北祁连地向斜带的结合部位。区域内构造发育,地层出露较齐全,前长城系是钨、钼、铜、铅、锌的主要赋矿层位;长城系朱龙关群浅变质低绿片岩相,是钨、钼、铜、铁的主要赋矿层位;蓟县系镜铁山群变质绿片岩相,是铁、铜矿床的主要赋矿层位。奥陶系阴沟群,为典型蛇绿岩建造,是北祁连火山岩型铜矿床的主要赋矿地层。因此,根据区域成矿条件和矿产分布规律分析,该区域为有色金属、黑色金属、贵金属矿产的产出地,矿产调查具有较好的前景。  相似文献   
9.
Extant theories of information technology (IT) usage present users' behavioural intention as the primary predictor of their IT usage behaviour. However, empirical evidence reveals only a low-to-medium effect size for this association. We call this inconsistency the ‘intention–behaviour gap’, and argue that a clearer understanding of this gap requires a deeper theoretical examination of the conditions under which intentions may or may not influence behaviour. Drawing on recent attitude theoretic research in social psychology, we distinguish between two types of attitudes – strong versus weak – and suggest that the intention–behaviour association may hold for users with strong attitudes but is likely to be weaker for those with weak attitudes. Using the elaboration-likelihood model, we propose two dimensions of attitude strength relevant to the IT usage context – personal relevance and related expertise – and theorise them to moderate the intention–behaviour association in a positive manner. Results from a longitudinal field survey of document management system usage among governmental employees at L'viv City Hall, Ukraine support our theoretical hypotheses. Theoretical and practical implications of our findings are discussed.  相似文献   
10.
This study centers on three parameters that can influence responses to Web-based surveys: personalization, the periodicity of follow-up mailings and incentives based on prize draws. The results show the need to send a lower number of reminders with personalized e-mail messages when the aim is for respondents to complete the full questionnaire. In contrast, the use of post-incentives based on prize draws was not found to have a significant effect on retention rate when used alone or in combination with personalized messages and/or a lower number of reminders. Moreover, none of the above factors, except personalization, improves response quality when used separately or in conjunction.  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