全文获取类型
收费全文 | 4417篇 |
免费 | 676篇 |
国内免费 | 622篇 |
专业分类
测绘学 | 104篇 |
大气科学 | 329篇 |
地球物理 | 592篇 |
地质学 | 1875篇 |
海洋学 | 1049篇 |
天文学 | 27篇 |
综合类 | 263篇 |
自然地理 | 1476篇 |
出版年
2024年 | 16篇 |
2023年 | 61篇 |
2022年 | 177篇 |
2021年 | 168篇 |
2020年 | 169篇 |
2019年 | 198篇 |
2018年 | 169篇 |
2017年 | 180篇 |
2016年 | 163篇 |
2015年 | 143篇 |
2014年 | 253篇 |
2013年 | 288篇 |
2012年 | 226篇 |
2011年 | 210篇 |
2010年 | 209篇 |
2009年 | 230篇 |
2008年 | 252篇 |
2007年 | 271篇 |
2006年 | 316篇 |
2005年 | 266篇 |
2004年 | 239篇 |
2003年 | 207篇 |
2002年 | 231篇 |
2001年 | 223篇 |
2000年 | 163篇 |
1999年 | 126篇 |
1998年 | 122篇 |
1997年 | 88篇 |
1996年 | 84篇 |
1995年 | 56篇 |
1994年 | 46篇 |
1993年 | 36篇 |
1992年 | 34篇 |
1991年 | 21篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1979年 | 1篇 |
排序方式: 共有5715条查询结果,搜索用时 31 毫秒
961.
《The Professional geographer》2013,65(3):376-387
This paper investigates the historical relationship between the development of marine-based tourism and representations of marine space. Over the past 100 years, the Caribbean Sea has been transformed from a transportation surface connecting exotic ports of call into a commodity itself. Imagined by early travelers as a two-dimensional space to be crossed, the Caribbean has became part of a new tropical marine aesthetic, a three-dimensional spectacle to be actively consumed and conserved. These changing representations of the marine environment as a space of consumption have been paralleled by changes in the relationships between marine and terrestrial political economies. As marine-based tourism has intensified, the balance of power among coastal resource users has shifted. The increasingly conflictive consequences of this shift are illustrated by the case of Soufrière in St. Lucia where new uses of marine space have re-configured social and economic relationships. Soufrière's coastal economy has been transformed and its marine space increasingly politicized as competing representations of the sea have been used to assert conflicting claims to resource access. This paper attempts to elucidate the power of these representations by investigating their historical relationship to the changing role of the Caribbean Sea in the international tourism industry. 相似文献
962.
《The Professional geographer》2013,65(1):23-36
The grassroots environmental movement often protests locally unwanted land uses. Many grassroots groups have, however, expanded their agenda to the scale of environmental justice. Explanations for this scale transformation include historical circumstances, individuals' radicalization through activism, and the growth of environmental justice networks. This case study, grassroots environmentalists' opposition to a proposed electricity transmission line in Monroe County, WV, explores another explanation: appeals for environmental justice are also a strategic response to siting regulatory procedures. With concepts emerging from the political geography of scale, I interpret the Monroe Countians' efforts and show how their strategies link the grassroots scale with that of environmental justice. 相似文献
963.
《The Professional geographer》2013,65(4):469-491
This article addresses the need to better understand the complex interactions between climate, human activities, vegetation responses, and surface ozone so that more informed air-quality policy recommendations can be made. The impacts of intraseasonal climate variations on ozone levels in Tucson, Arizona from April through September of 1995 to 1998 are determined by relating variations in ozone levels to variations in atmospheric conditions and emissions of ozone's precursor chemicals, volatile organic compounds (VOCs) and nitrogen oxides (NOx), and by determining month-specific atmospheric conditions that are conducive to elevated ozone levels. Results show that the transport of ozone and its precursor chemicals within the Tucson area causes the highest ozone levels to be measured at a downwind monitor. The highest ozone levels occur in August, due in part to the presence of the North American monsoon. Atmospheric conditions conducive to elevated ozone concentrations differ substantially between the arid foresummer (May and June) and the core monsoon months ( July and August). Transport of pollution from Phoenix may have a substantial impact on elevated ozone concentrations during April, May, and June, while El Paso/Ciudad Juarez –derived pollution may contribute significantly to elevated ozone concentrations in August and September. Two broad policy implications derive from this work. Regional pollutant transport, both within the U.S. and between the U.S. and Mexico, is a potential issue that needs to be examined more intensively in future studies. In addition, spatiotemporal variations in sensitivities of ozone production require the adoption of both NOx and VOC control measures to reduce ozone levels in the Tucson area. 相似文献
964.
965.
《The Professional geographer》2013,65(4):428-436
Recognized for years as a major environmental disruption, El Niño generated intense public interest in 1982–1983. During its last occurrence, this phenomenon, which develops in the tropical Pacific and usually affects rimlands of the Pacific basin, exceeded its boundaries and its effects were transmitted to continental North America, Europe, Africa and East Asia. Notwithstanding its vast areal extent, the interest of geographers in El Niño events, past and recent, has been comparatively less than that demonstrated by natural scientists and ecologists: little has been accomplished to place these climatic-ecological crises within global perspective. Lessons from El Niño include the acknowledgement of new concepts of climatic transitivity, ocean dynamics and energy exchanges that must find a place within the conceptual wealth of geography if this science intends to keep up with the rapid progress of other geosciences. 相似文献
966.
《The Professional geographer》2013,65(4):574-586
Abstract Environmental justice laws protect certain populations against discriminatory actions that may result from a myriad of enterprises, including transportation activities. Previous environmental equity studies examining the effects of transportation-engendered externalities have been criticized on several points, including (1) that the choice of a reference population for comparison to the criterion variable may influence the outcome of research results and (2) that the selection and use of inappropriate methodologies intended to identify and characterize populations may foreordain research outcomes. This article examines the potentially confounding effects of selected spatial scale and population assignment strategies as applied to a study of excessive noise levels at a large Midwestern airport, finding that reported outcomes can vary significantly as a function of methodological choices. 相似文献
967.
Rates of soil disruption from hikers and vehicle traffic are poorly known, particularly for arid landscapes. We conducted an experiment in Organ Pipe Cactus National Monument (ORPI) in western Arizona, USA, on an air-dry very fine sandy loam that is considered to be vulnerable to disruption. We created variable-pass tracks using hikers, an all-terrain vehicle (ATV), and a four-wheel drive vehicle (4WD) and measured changes in cross-track topography, penetration depth, and bulk density. Hikers (one pass = 5 hikers) increased bulk density and altered penetration depth but caused minimal surface disruption up to 100 passes; a minimum of 10 passes were required to overcome surface strength of this dry soil. Both ATV and 4WD traffic significantly disrupted the soil with one pass, creating deep ruts with increasing passes that rendered the 4WD trail impassable after 20 passes. Despite considerable soil loosening (dilation), bulk density increased in the vehicle trails, and lateral displacement created berms of loosened soil. This soil type, when dry, can sustain up to 10 passes of hikers but only one vehicle pass before significant soil disruption occurs; greater disruption is expected when soils are wet. Bulk density increased logarithmically with applied pressure from hikers, ATV, and 4WD. 相似文献
968.
As managers and researchers of protected natural areas continue to seek balance in promoting visitor use but limiting negative experiential and natural resource impacts, the integration of social and physical spatial data may play a critical role in understanding how visitors and the community interface with the landscape within these protected areas. These spatial considerations are important for inventorying, monitoring, and managing the conditions of natural resources within parks. Specifically related to the visitor impacts of natural resources in parks are the use and condition of multiple-use trails. Technology such as GPS and GIS may allow for a unique assessment of the relationship between factors that influence this resource. This paper focuses on how visitor use distribution (measured through GPS tracking), activity type, and trail design influence the impacts to trail conditions. This paper also addresses statistical concerns related to spatial dependency. Results suggest that failure to account for spatial dependency can lead to erroneous Type I findings. Additionally, activity type (specifically horseback riders) and trail design were found to best predict trail impacts when controlling for spatial dependency. 相似文献
969.
Carlos Guerra Marc J. Metzger João Honrado Joaquim Alonso 《International journal of geographical information science》2013,27(10):2077-2098
When establishing environmental monitoring programmes, it crucial to make reliable cost estimates, especially where a field survey is involved. This paper presents a methodology for creating a spatial measure of a field survey effort (SE). A set of relevant variables affecting a SE (e.g. areas with rough terrain, or distant from the main road network) was classified using fuzzy sets and then combined to produce spatially explicit effort indicators, which were integrated to a single measure using an analytic hierarchy process (AHP). To evaluate this approach and identify the limits for its application, three spatially nested case studies were used to test the spatial expression of SE and the scalable capacity of the method itself. The presented methodology could cope with variations in the scale and data resolution, retrieving a coherent estimate of SE across the different case studies. The presented methodology is therefore useful for (i) testing the network designs for sampling bias related to SE, (ii) comparing alternative sampling designs, (iii) assessing the sampling costs and (iv) supporting the human and logistical resource management. 相似文献
970.
Hilary McMillan Alberto Montanari Christophe Cudennec Hubert Savenije Heidi Kreibich Tobias Krueger 《水文科学杂志》2013,58(7):1174-1191
ABSTRACTIn 2013, the International Association of Hydrological Sciences (IAHS) launched the hydrological decade 2013–2022 with the theme “Panta Rhei: Change in Hydrology and Society”. The decade recognizes the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions. This paper reports on the first Panta Rhei biennium 2013–2015, providing a comprehensive resource that describes the scope and direction of Panta Rhei. We bring together the knowledge of all the Panta Rhei working groups, to summarize the most pressing research questions and how the hydrological community is progressing towards those goals. We draw out interconnections between different strands of research, and reflect on the need to take a global view on hydrology in the current era of human impacts and environmental change. Finally, we look back to the six driving science questions identified at the outset of Panta Rhei, to quantify progress towards those aims.
Editor D. Koutsoyiannis; Associate editor not assigned 相似文献