全文获取类型
收费全文 | 2385篇 |
免费 | 60篇 |
国内免费 | 60篇 |
专业分类
测绘学 | 67篇 |
大气科学 | 377篇 |
地球物理 | 529篇 |
地质学 | 589篇 |
海洋学 | 626篇 |
天文学 | 185篇 |
综合类 | 36篇 |
自然地理 | 96篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 21篇 |
2021年 | 37篇 |
2020年 | 40篇 |
2019年 | 48篇 |
2018年 | 116篇 |
2017年 | 110篇 |
2016年 | 159篇 |
2015年 | 76篇 |
2014年 | 152篇 |
2013年 | 211篇 |
2012年 | 103篇 |
2011年 | 142篇 |
2010年 | 145篇 |
2009年 | 145篇 |
2008年 | 136篇 |
2007年 | 135篇 |
2006年 | 107篇 |
2005年 | 101篇 |
2004年 | 103篇 |
2003年 | 67篇 |
2002年 | 54篇 |
2001年 | 48篇 |
2000年 | 33篇 |
1999年 | 32篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1968年 | 1篇 |
排序方式: 共有2505条查询结果,搜索用时 15 毫秒
951.
This study examined the effects of task demand and familiarity on students' perception and processing of spatial information upon viewing visuospatial representations. Participants in South Korea were told that they would travel through an area, either drawing a map or observing the scenery depicted in photographs. The level of familiarity in the photographs was manipulated in three categories: neighborhood, Seoul (capital city of South Korea), and foreign cities. In two experiments, this study investigated students' eye movements, memory, and response sensitivity and bias. The results indicate that the participants in the map-drawing condition focused on structural information, such as routes, and that their memory of the scenes was more accurate. Moreover, the map-drawing group students were more sensitive and prudent in their responses. The increased level of familiarity also made students focus on structural information. The findings provide useful strategies for geography educators to use visuospatial representations. 相似文献
952.
Understanding the relationship between sedimentation and tectonics is critical to the analysis of stratigraphic evolution in foreland basins. Previous models of foreland basins have explained stratal development, but were done generally under the assumption that steady allogenic forcing produces a steady stratigraphic response. They did not consider autogenic shoreline behaviour during the development of the subsidence pattern characteristic of foreland basins. We present a mathematical model and flume experiments that explore how subsidence and sediment‐supply rates control the shoreline trajectory and the stratal patterns that fill foreland basins. Through these models, we found differing autogenic responses in the rate and direction of shoreline migration, and these generated three distinct styles of stratal architecture, despite the constant external forcing (i.e. constant sediment discharge and basin substrate tilting). The first response was ‘autoretreat’, where shoreline migration switched from initial progradation to retrogradation. The second response was progradation followed by constant aggradation of the shoreline. The third response was maintained progradation with a markedly accelerating rate. We termed this latter newly observed autogenic behaviour ‘shoreline autoacceleration’. These three modes of shoreline behaviour and their accompanying stratal architecture provide a basic framework for the relationship between sedimentation and tectonic activity in foreland basins under the simplified conditions presented here. 相似文献
953.
Alexandre Ganachaud Carl Wunsch Myung-Chan Kim Byron Tapley 《Geophysical Journal International》1997,128(3):708-722
A global estimate of the absolute oceanic general circulation from a geostrophic inversion of in situ hydrographic data is tested against and then combined with an estimate obtained from TOPEX/POSEIDON altimetric data and a geoid model computed using the JGM-3 gravity-field solution. Within the quantitative uncertainties of both the hydrographic inversion and the geoid estimate, the two estimates derived by very different methods are consistent. When the in situ inversion is combined with the altimetry/geoid scheme using a recursive inverse procedure, a new solution, fully consistent with both hydrography and altimetry, is found. There is, however, little reduction in the uncertainties of the calculated ocean circulation and its mass and heat fluxes because the best available geoid estimate remains noisy relative to the purely oceano-graphic inferences. The conclusion drawn from this is that the comparatively large errors present in the existing geoid models now limit the ability of satellite altimeter data to improve directly the general ocean circulation models derived from in situ measurements. Because improvements in the geoid could be realized through a dedicated spaceborne gravity recovery mission, the impact of hypothetical much better, future geoid estimates on the circulation uncertainty is also quantified, showing significant hypothetical reductions in the uncertainties of oceanic transport calculations, Full ocean general circulation models could better exploit both existing oceanographic data and future gravity-mission data, but their present use is severely limited by the inability to quantify their error budgets. 相似文献
954.
955.
For over 30 years, IHP (International Hydrological Programme) has been actively operating as a UNESCO’s (United Nations Educational,
Scientific and Cultural Organization) international scientific cooperative programme in water research, water resources management,
education and capacity-building, and the only broadly-based science programme of the UN (United Nations) system in this region.
By a number of initiatives and networks, the IHP has progressively carried out activities on the quantity and quality of global/regional
water resources, transboundary water resources management, mitigation of water related hazards, and water education. While
addressing comprehensive areas over water challenges, greater emphasis has been placed on the role of water resources management
for sustainable development and with respect to the expected changes in climate and environmental conditions. WWAP (World
Water Assessment Programme) and its major product WWDR (World Water Development Report) in East Asia are under the framework
of IHP which supports field oriented activities on monitoring freshwater, developing case studies, enhancing national assessment
capacity, and facilitating decision making processes. In light of transboundary waters in IHP, RSC (Regional Steering Committee)
plays a focal role for facilitating regional cooperation in the Southeast and East Asia and Pacific States. Furthermore, ISI
(International Sediment Initiative) and IFI (International Flood Initiative) have significant roles, respectively, for the
management of erosion and sedimentation in line with river system or reservoir management, and for the flood management focusing
on capacity building of each country in East Asia. There are other major areas of concern under UNESCO’s IHP programme in
East Asia, specifically in aspects including, mitigating water conflicts on transboundary aquifers through ISARM (International
Shared Aquifer Resources Management), water management of arid areas through Water and Development Information for Arid Lands-
A Global Network (Asian G-WADI), and sustainable management of groundwater by UNESCO Water Chair, as well as water education
through the programme of Sustainable Water Integrated Management-Educational Component.
Author: Ramasamy Jayakumar, native of India, Ph.D, specialized in application of remote sensing, GIS, geo-statistical methods in
hydrogeological modelling and irrigation water management. 相似文献
956.
957.
This study examines the economic impacts of closing the Northwestern Hawaiian Islands bottomfish fishery, as part of a larger effort to create an effective marine protected area. An overview of the market for NWHI bottomfish in Hawaii is given using input–output data and a fishery closure analysis is conducted using public data on commercial fishing and primary information collected through interviews with wholesalers, restaurants, and retailers. Assuming the worst-case scenario, the wholesale price per pound of Onaga and Opakapaka is estimated to increase by $0.80 and $0.42, respectively. But this is unlikely, as the own-price elasticity of demand for Hawaii-caught bottomfish is found to be highly elastic and there is widespread substitution with imports. The overall economic loss is thus quite small, while the environmental gains of creating the largest marine protected area in the world could be substantial. 相似文献
958.
959.
Dinoflagellate Cysts in Coastal Sediments as Indicators of Eutrophication: A Case of Gwangyang Bay,South Sea of Korea 总被引:1,自引:0,他引:1
Diatom densities in the surface water and dinoflagellate cysts in bottom sediments of Gwangyang Bay were studied to determine changes in the phytoplankton community structure in response to anthropogenic eutrophication and to assess the use of dinoflagellate cysts as indicators of coastal eutrophication. Our results show that, in nutrient-enriched environments, diatoms are particularly benefited from the nutrients supplied and, as a consequence, heterotrophic dinoflagellates that feed on the diatoms can be more abundant than autotrophic dinoflagellates. In short-core sediment records, a marked shift in autotrophic–heterotrophic dinoflagellate cyst compositions occurred at a depth of approximately 9–10 cm corresponding to the timing of the 1970s industrialization around Gwangyang Bay. This tentatively indicates that diatom and dinoflagellate communities here have undergone a considerable change mainly due to increased nutrient loadings from both domestic sewage effluent and industrial pollution. Our study suggests a possible potential use of dinoflagellate cysts in providing retrospective information on the long-term effects of coastal eutrophication. 相似文献
960.
A new type of magnetograph has been built capable to measure weak magnetic fields in the chromosphere and corona. Measurements of magnetic field in two prominences are demonstrated as examples. 相似文献