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   19篇
  免费   0篇
大气科学   1篇
地球物理   1篇
地质学   7篇
天文学   8篇
自然地理   2篇
  2018年   1篇
  2017年   2篇
  2016年   2篇
  2012年   1篇
  2011年   1篇
  2010年   1篇
  2009年   2篇
  2008年   3篇
  2005年   2篇
  2003年   1篇
  2002年   1篇
  1998年   1篇
  1986年   1篇
排序方式: 共有19条查询结果,搜索用时 312 毫秒
11.
Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.  相似文献   
12.
The study quantified rainfall variability for March–May (MAM) and October–December (OND) seasons in Tharaka district, Kenya. The parameters analysed were inter-annual variability of seasonal rainfall, onset and cessation using daily rainfall data in three agro-ecological zones’ stations. Percentage mean cumulative method was used to determine onset and cessation, and seasonal variability was estimated using rainfall variability indices. Although both seasons are highly variable, OND has been persistently below mean over time while MAM shows high within-season variability. Despite the near uniformity in the mean onset and cessation dates, the former is highly variable on an inter-annual scale. The two rainfall seasons are inherently dissimilar and therefore require specific cropping in agro-ecological zone LM4 and LM4-5. It is possible that farmers in IL5 are missing an opportunity by under-utilising MAM rainfall. The results should be incorporated in implications of climate variability and vulnerability assessment in semi-arid Tharaka district.  相似文献   
13.
14.
In the debate on urban and regional competitiveness, it has become fashionable to stress the growing importance of creativity for economic development. Especially scientist-consultants with a keen eye for what politicians and business people want to hear have taken centre stage in this discussion. Each city and region in the advanced capitalist world seems to prefer a label as creative city or region, and all look after the same type of industries and try to produce the same set of conditions, while investing in higher education and research institutes, networking and lobbying institutions, and the promotion of spin-off companies. A vast number of leaders and spokesmen of local and regional (quasi) governments believe that a major thing to do is to become more attractive places to live for creative knowledge workers or the ‘creative class’, as it is euphemistically labelled.However, in academia there is a lot of scepticism with regard to the use of these concepts and their meaning for urban and regional competitiveness. Also citizen movements and NGOs, and some political parties, voice their concern about the extent to which policies that apply these concepts and ideas might only benefit an elite of higher educated, well- paid professionals while at the same time these policies might result in decline of other activities and in social polarisation and poverty as well.In this paper we contribute to the critical discussion through a critical appraisal of local experts’ views on developments in seven European city-regions, first with regard to policies towards the development of creative and knowledge-intensive industries; and secondly with regard to the impact the development of ‘creative knowledge regions’ may have in social and other respects. In contrast to the rather homogeneous yet dominant advice to facilitate ‘the creative class’, in this paper we will argue that a range of parameters related to the firms and regional institutional, geographical and historical contexts promote a much more diversified view on urban economic development.  相似文献   
15.
We have developed a wide-field mosaic CCD camera, MOA-cam3, mounted at the prime focus of the Microlensing Observations in Astrophysics (MOA) 1.8-m telescope. The camera consists of ten E2V CCD4482 chips, each having 2k×4k pixels, and covers a 2.2 deg2 field of view with a single exposure. The optical system is well optimized to realize uniform image quality over this wide field. The chips are constantly cooled by a cryocooler at ??80° C, at which temperature dark current noise is negligible for a typical 1–3 min exposure. The CCD output charge is converted to a 16-bit digital signal by the GenIII system (Astronomical Research Cameras Inc.) and readout is within 25 s. Readout noise of 2–3 ADU (rms) is also negligible. We prepared a wide-band red filter for an effective microlensing survey and also Bessell V, I filters for standard astronomical studies. Microlensing studies have entered into a new era, which requires more statistics, and more rapid alerts to catch exotic light curves. Our new system is a powerful tool to realize both these requirements.  相似文献   
16.
Socioeconomic inequality is on the rise in major European cities, as are concerns over it, since it is seen as a threat to social cohesion and stability. Surprisingly, relatively little is known about the spatial dimensions of rising socioeconomic inequality. This paper builds on a study of socioeconomic segregation in 12 European cities: Amsterdam, Athens, Budapest, London, Madrid, Oslo, Prague, Riga, Stockholm, Tallinn, Vienna, and Vilnius. Data used derive from national censuses and registers for 2001 and 2011. The main conclusion is that socioeconomic segregation has increased. This paper develops a rigorous multifactor approach to understand segregation and links it to four underlying, partially overlapping, structural factors: social inequalities, globalization and economic restructuring, welfare regimes, and housing systems. Taking into account contextual factors resulted in a better understanding of actual segregation levels, while introducing time lags between structural factors and segregation outcomes will likely further improve the theoretical model.  相似文献   
17.
Many postindustrial cities across Europe and other contexts are marked by growing social–spatial inequalities, housing liberalization, and gentrification, which limit the housing options of low-income households. We investigated changes in the residential moves of different low-income households (working poor, low-to-middle income, and unemployed) in the Amsterdam and Rotterdam urban regions for the time period 2004–2013. We found an overarching trend for the suburbanization of poverty toward the urban peripheries and surrounding regions. While this trend appears to be relatively crisis resistant in the tight Amsterdam housing context, it is more cyclical in Rotterdam and has slowed following the global financial crisis. Low-to-middle income and unemployed households are increasingly moving to the urban regions surrounding cities, particularly to higher density satellite towns. Nevertheless, a growing number of working poor households remain highly urbanized, employing various coping strategies to acquire housing. This paper reveals how the suburbanization of poverty is both a direct process of poor households moving from city to suburb, and a broader indirect process caused by exclusionary mechanisms such as the decreasing accessibility and affordability of inner-urban neighborhoods, which reflect broader changes in the geography and socioeconomic patterning of urban regions.  相似文献   
18.
Segregation is a central concept in the debate on urban issues, both in scientific literature and in society in general. The process of globalisation is particularly expected to increase polarisation and segregation in cities, resulting in the emergence of ‘ghettos’ or – as they are called in the Netherlands – ‘income neighbourhoods’. This paper tries to judge the situation in Dutch cities by studying changes over time; by looking at segregation within cities as well as between cities and the wider metropolitan area; and by comparing socio-economic differences with socio-cultural and socio-demographic characteristics. The analysis shows that the empirical facts are quite different from the ongoing debate. It establishes that socio-economic segregation is more moderate than segregation with respect to the other two dimensions. Contrary to suggestions from the vernacular debate, segregation within cities is scarcely increasing, but between cities and the surrounding area it is rising with respect to all three dimensions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
19.
Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany rift intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual rift intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest rift intrusion, however, results in a slight extension of the subaerial portion of the south flank.Horizontal strain measurements along the south flank are used to locate the January 1983 east-rift intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66°E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow rift earthquakes.  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