全文获取类型
收费全文 | 820篇 |
免费 | 113篇 |
国内免费 | 63篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 77篇 |
地球物理 | 239篇 |
地质学 | 263篇 |
海洋学 | 34篇 |
天文学 | 4篇 |
综合类 | 41篇 |
自然地理 | 315篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 35篇 |
2021年 | 33篇 |
2020年 | 48篇 |
2019年 | 39篇 |
2018年 | 46篇 |
2017年 | 34篇 |
2016年 | 56篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 73篇 |
2012年 | 47篇 |
2011年 | 46篇 |
2010年 | 38篇 |
2009年 | 52篇 |
2008年 | 46篇 |
2007年 | 48篇 |
2006年 | 50篇 |
2005年 | 43篇 |
2004年 | 15篇 |
2003年 | 34篇 |
2002年 | 25篇 |
2001年 | 14篇 |
2000年 | 14篇 |
1999年 | 17篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有996条查询结果,搜索用时 406 毫秒
141.
142.
The Ethiopian highlands are a center of diversity for numerous globally important crops. Heterogeneous landscapes, traditional agricultural practices, and inaccessibility have created and maintained diverse subsistence agroecosystems. We surveyed sixty-three farms in twelve communities of the Gamo highlands and found high levels of on-farm diversity of crop species and varieties. The extent and nature of this diversity are related to both ecological factors, namely elevation, and anthropogenic factors such as land-use history, accessibility to markets and extension, and strength and scale of farmer exchange networks. These human landscape features have the potential to both enhance and mediate effects of elevation and other environmental factors on crop diversity. The interaction of environmental and anthropogenic forces on the diversity of crops grown by farmers affects the strategies farmers employ to adapt their farming to changing conditions. 相似文献
143.
Luca Salvati Sofia Bajocco Tomaso Ceccarelli Luigi Perini 《The Professional geographer》2013,65(4):647-663
This article analyzes the territorial disparities in the level of land vulnerability (TDLV) to soil degradation caused by five processes (soil erosion, salinization, sealing, contamination, and compaction) as well as by climate variations in Italy in 1990 and 2000. The analysis reveals, for each soil degradation process, a typical spatial distribution across Italy. Three processes (soil salinization, compaction, and sealing) contribute significantly to the increase in land vulnerability, which is mainly concentrated in risky areas. The observed disparities highlight a growing environmental divide between northern Italy (an economically developed region, not at risk of desertification) and southern Italy and the two main islands (dry, disadvantaged regions at risk of desertification). The knowledge of such a territorial divide and of the underlying soil degradation processes is regarded as important for environmental policies at the country and regional scales aimed at sustaining the economic and socioenvironmental cohesion between areas that are either vulnerable or nonvulnerable to soil degradation. The proposed approach should be seen as part of a decision-making tool informing policies and supporting the design of management solutions, hopefully reversing disparities in land vulnerability to soil degradation. 相似文献
144.
《The Professional geographer》2013,65(2):120-133
Abstract Water-related diseases continue to pose major threats to children's survival and well-being in many places in the developing world. This article develops a theoretical perspective on the ways in which children's vulnerability to water-related disease hazard is produced within the everyday circumstances of livelihood and child care. Central to this analysis is the role that household resources play in mediating or shaping particular microenvironments of health risk. Further, the effects of local geographies of gender on how household resources are accessed and on how child care is structured are examined. Children's vulnerability is evaluated in a community in the District of Gilgit in northern Pakistan, a region presently undergoing tremendous social and economic transformation. The case study highlights household-level response and adaptation to child health risks associated with diarrheal disease transmission and infection in this mountain environment. The case study draws from ethnographic fieldwork involving qualitative household microstudies and interviewing to elicit mothers' resource and risk-response strategies in the context of changes in livelihood systems and household dynamics. 相似文献
145.
Abstract Creating resiliency, accomplished in part by individuals preparing for disaster, is the primary strategy outside of law enforcement for responding to the threat of urban terrorism. Individuals prepare when they perceive a need to do so, yet little is known about what shapes a person's awareness of vulnerability to terrorism. Because evidence indicates that social contacts act as conduits of information and affect perception of risk to natural hazards, it is possible that such contacts also affect terrorism vulnerability awareness. Because social contacts are also known to be systematically segmented by gender and location, we hypothesized that conversations about terrorism vary by gender and place, specifically the home and work place. Drawing on data from 93 interviews with householders in Boston, the study demonstrates that: (1) family networks generated discussions of home preparedness, whereas workplace networks engaged a wider variety of topics; (2) women discussed terrorism more frequently and in greater depth than did men; and (3) women heard more preparedness messages for the home than did men, whereas men undertook preparedness activities external to the home. The findings bridge geography and terrorism studies by theorizing emplaced and subjective human experiences that prompt conversations about terrorism. These conversations, in turn, help urban emergency managers and risk-hazards geographers promote rational dialogue and action vis-à-vis terrorism. Hazards researchers have shown that the more people discuss terrorism, the less they seek extreme and unwarranted responses. 相似文献
146.
Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD tower in Bucharest, Romania 总被引:1,自引:0,他引:1
Matthieu Perrault Philippe Gueguen Alexandru Aldea Sorin Demetriu 《地震工程与工程振动(英文版)》2013,12(4):643-658
The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This study aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest, Romania, a RC building with permanent instrumentation. A three-step methodology is applied: (1) adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson's criteria, (2) computation of the structure's response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements (IM), and (3) construction of the fragility curves by comparing numerical interstory drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd ) as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology. 相似文献
147.
ABSTRACTThis review article discusses the climate, water resources and historical droughts of Africa, drought indices, vulnerability, impact of global warming and land use for drought-prone regions in West, southern and the Greater Horn of Africa, which have suffered recurrent severe droughts in the past. Recent studies detected warming and drying trends in Africa since the mid 20th century. Based on the Fourth Assessment Report of the Intergovernmental Panel on Climate Change and the Coupled Model Intercomparison Project Phase 5 (CMIP5), both northern and southern Africa are projected to experience drying, such as decreasing precipitation, runoff and soil moisture in the 21st century and could become more vulnerable to the impact of droughts. The daily maximum temperature is projected to increase by up to 8°C (RCP8.5 of CMIP5), precipitation indices such as total wet day precipitation (PRCPTOT) and heavy precipitation days (R10 mm) could decrease, while warm spell duration (WSDI) and consecutive dry days (CDD) could increase. Uncertainties of the above long-term projections, teleconnections to climate anomalies such as ENSO and the Madden-Julian Oscillation, which could also affect the water resources of Africa, and capacity building in terms of physical infrastructure and non-structural solutions are also discussed. Given that traditional climate and hydrological data observed in Africa are generally limited, satellite data should also be exploited to fill the data gap for Africa in the future.
Editor D. Koutsoyiannis; Associate editor N. Ilich 相似文献
148.
149.
150.
The 2009 L’Aquila, Italy earthquake highlighted the seismic vulnerability of historic masonry building structures due to improper "strengthening" retrofit work that has been done in the last 50 years. Italian seismic standards recommend the use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete (RC) or steel elements, inserting RC tie-beams in the masonry and new RC floors, and using RC jacketing on the shear walls. The L’Aquila earthquake revealed the numerous limitations of these interventions, because they led to increased seismic forces (due to greater additional weight) and to deformation incompatibilities of the incorporated elements with the existing masonry walls. This paper provides a discussion of technical issues pertaining to the seismic retrofit of the Santa Maria di Collemaggio Basilica and in particular, the limitations of the last (2000) retrofit intervention. Considerable damage was caused to the church because of questionable actions and incorrect and improper technical choices. 相似文献