全文获取类型
收费全文 | 251篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 9篇 |
地球物理 | 61篇 |
地质学 | 84篇 |
海洋学 | 18篇 |
天文学 | 20篇 |
综合类 | 1篇 |
自然地理 | 66篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 17篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 5篇 |
2009年 | 12篇 |
2008年 | 12篇 |
2007年 | 6篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有267条查询结果,搜索用时 15 毫秒
61.
62.
63.
Resilience is an increasingly important concept within urban studies, economic geography, and evolutionary economics for measuring the capacity of city-regions to respond to economic shocks. In this article, we provide a sympathetic critique of the resilience metaphor in urban studies, which we explicate through an analysis of the recent history of the Vancouver economy. On the surface, Vancouver seemingly showed resilience when it overcame the abrupt decline of its resource-based economy in the 1980s, and established an alternative flourishing “new economy” by the 1990s. But over the last five years, the key local “creative” industries such as video game development and film production have suffered, with a number of large firms leaving Vancouver, and industry employment declining sharply. Drawing on more than 40 interviews conducted over a five-year period with members of the local video game community, our paper documents the rise and more recent decline of Vancouver’s “new economy” sector. Our research raises questions about the value of the resilience metaphor in urban studies and highlights the difficulties facing city-regions reliant on highly mobile “new economy” industries. 相似文献
64.
Following the 2010–2011 earthquakes in Christchurch, New Zealand, many nonprofit organizations changed or expanded services to address emergent or compounded risks. This research is based on interviews with thirty local community nonprofit managers and discussions with five staff focus groups conducted in 2014. Preexisting nonprofits with flexible organizational structures and emergent nonprofits succeeded in providing services during the emergency response and early recovery phases; nonprofits contracted with the government were better suited for long-term recovery. Shared resources among nonprofit agency connections contributed to successful transitions from response to recovery. Similar organizational resilience factors might occur in other major cities following disasters. 相似文献
65.
Ron Abler 《The Professional geographer》1970,22(5):270-274
66.
3-D Shoreline Extraction from IKONOS Satellite Imagery 总被引:1,自引:0,他引:1
Shorelines are recognized as unique features on Earth. They have valuable properties for a diverse user community. At present, photogrammetry is the most popular technique used to capture a shoreline. With improved resolution and accuracy, commercial high-resolution satellite imagery is demonstrating a great potential in the photogrammetry application domain. One example is the utilization of IKONOS satellite imagery in shoreline extraction. IKONOS panchromatic imagery has a resolution of approximately one meter as well as the capabilities of stereo imaging. This article presents the results of an experiment in which we attempted to improve IKONOS Rational Functions (RF) for a better ground accuracy and to employ the improved RF for 3-D shoreline extraction using 1-meter panchromatic stereo images in a Lake Erie coastal area. Two approaches were investigated. One was to rectify the ground coordinates derived from vendor-provided RF coefficients using ground control points (GCPs). The other was to refine the RF coefficients using the GCPs. We compare the results from these two approaches. An assessment of the shoreline extracted from IKONOS images compared with the existing shoreline is also conducted to demonstrate the potential of the IKONOS imagery for shoreline mapping. 相似文献
67.
Cypermethrin induces glutathione S-transferase activity in the shore crab,Carcinus maenas 总被引:2,自引:0,他引:2
Gowlan BT Moffat CF Stagg RM Houlihan DF Davies IM 《Marine environmental research》2002,54(2):169-177
Cypermethrin is a synthetic pyrethroid that is particularly toxic to crustacea. It is therefore applied as a chemotherapeutant in the salmonid aquaculture industry for the treatment of sea lice infestations. After use, cypermethrin is released directly into the marine environment, to be diluted by fresh seawater. The shore crab, Carcinus maenas is found in the vicinity of fish farms, and may come into contact with released cypermethrin. The detoxification enzyme, glutathione S-transferase (GST) has been implicated in cypermethrin metabolism in terrestrial arthropods, but this has not yet been demonstrated in crustacea. In this paper we investigate the response of GST activity in Carcinus to cypermethrin exposure, and also the time course of the induction process. GST activity is significantly increased in Carcinus exposed to nominal concentrations of 50 and 500 ng/l of water-borne cypermethrin. Carcinus demonstrate a significant elevation in GST activity following intra-cephalothoracic injection with 10 ng of cypermethrin. GST activity returns to basal levels after 36 h. The potential application of GST activity in Carcinus as a biomarker of cypermethrin exposure is discussed. 相似文献
68.
69.
Linearly Organized Turbulence Structures Observed Over a Suburban Area by Dual-Doppler Lidar 总被引:1,自引:1,他引:0
Dual-Doppler lidar observations are used to investigate the structure and evolution of surface-layer flow over a suburban
area. The observations were made during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City, U.S.A. in the summer
of 2003. This study focuses specifically on a 10-h sequence of scan data beginning shortly after noon local time on 7 July
2003. During this period two coherent Doppler lidars performed overlapping low elevation angle sector scans upwind and south
of Oklahoma City’s central business district. Radial velocity data from the two lidars are processed to reveal the structure
and evolution of the horizontal velocity field in the surface layer throughout the afternoon and during the evening transition
period. The retrieved velocity fields clearly show a tendency for turbulence structures to be elongated in the direction of
the mean flow throughout the entire 10-h study period. In order to quantify the observed anisotropy and its dependence on
stability, integral length scales are estimated directly from the spatially resolved velocity retrievals. As the flow became
more stably stratified the characteristic cross-stream dimension of the linear structures decreased. The streamwise component
was consistently more anisotropic than the cross-stream component, and both velocity components exhibited maximum anisotropy
under neutral conditions. The ratio of the streamwise to cross-stream length scale was estimated to be about eight for the
streamwise component, and four for the cross-stream component under neutral conditions. 相似文献
70.