全文获取类型
收费全文 | 4234篇 |
免费 | 817篇 |
国内免费 | 512篇 |
专业分类
测绘学 | 1349篇 |
大气科学 | 65篇 |
地球物理 | 567篇 |
地质学 | 2396篇 |
海洋学 | 553篇 |
天文学 | 126篇 |
综合类 | 291篇 |
自然地理 | 216篇 |
出版年
2024年 | 23篇 |
2023年 | 91篇 |
2022年 | 262篇 |
2021年 | 301篇 |
2020年 | 270篇 |
2019年 | 214篇 |
2018年 | 112篇 |
2017年 | 199篇 |
2016年 | 151篇 |
2015年 | 210篇 |
2014年 | 336篇 |
2013年 | 253篇 |
2012年 | 293篇 |
2011年 | 265篇 |
2010年 | 203篇 |
2009年 | 202篇 |
2008年 | 229篇 |
2007年 | 274篇 |
2006年 | 235篇 |
2005年 | 207篇 |
2004年 | 188篇 |
2003年 | 171篇 |
2002年 | 133篇 |
2001年 | 95篇 |
2000年 | 97篇 |
1999年 | 96篇 |
1998年 | 76篇 |
1997年 | 76篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 39篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5563条查询结果,搜索用时 0 毫秒
31.
This paper contributes an empirical test of key themes of the literature on natural resource conflict. Survey and interview data from an ongoing project in Azerbaijan provide insights into an unexpected lack of conflict in Azerbaijan related to the environment, resources and energy despite the predictions of resource conflict literature. We contend that questions about public perceptions about the environment and other daily concerns are critical if we are to understand who is likely (or unlikely) to be involved in conflict and why. The data presented in this paper demonstrate that Azerbaijani citizens rank environmental and resource issues among their immediate concerns and their top concerns for the country. However, compared to other day-to-day concerns such as the Nagorno-Karabakh conflict and economic concerns, environment-related concerns do not appear to be sufficient to motivate widespread violent conflict or citizen dissent related to environmental or natural resource conditions. 相似文献
32.
33.
34.
35.
本文以 1∶5万里庄幅为例 ,阐述了运用GIS系统对区调过程中各种资料的处理与编辑方法 ,并介绍了数字制图方法及工艺流程 ,提出了GIS系统在 1∶5万区调工作中的应用前景 相似文献
36.
区域视觉形象识别系统设计的理论与实践 总被引:6,自引:0,他引:6
目前,全国各地正在兴起区域形象设计与建设的浪潮,但如何把区域形象信息系统地传递出去,这方面的理论研究大大落后于实践。文章就区域形象信息传递的有效工具-区域视觉识别系统设计的主要内容,设计的原则,设计的基本流程等在理论与实践上作了较为详细的探讨,并就区域视觉识别系统设计方案的经济学论证作了一些有益探讨。 相似文献
37.
38.
Robert Gilbert 《Journal of Paleolimnology》2003,29(2):209-220
A sub-bottom acoustic survey of Devil Lake on the Canadian Shield in southern Ontario reveals three acoustic facies: (I) a moderately acoustically transparent, laminated sequence interpreted as a glacilacustrine deposit in glacial Lake Iroquois or a subsequent phase in water depths up to 200 m greater than at present, (II) a transitional more transparent, less layered facies interpreted as being deposited in a more distal glacial lake from erosion of sediment in the watershed exposed by the failure of the ice dam and lowering of the glacial lake before stabilization by the development of forests, and (III) an acoustically transparent facies with similar transmissivity to the water column, interpreted as Holocene gyttja. Each is spatially variable in extent and thickness in response to those processes. There is only a very weak relation between sediment thickness and the water depth in which it was deposited. Wave processes prevent deposition in water depths less than about 6 m and evidence of erosion to the greatest depths of the lake (>40 m) is pervasive. The data demonstrate the value of acoustic survey in assessing lacustrine processes and the history of lakes, and the significance of such documentation in planning a coring program and in interpreting the results. 相似文献
39.
Commercial alpine medicinal plants are collected from the wild by local rural households throughout the Himalaya and sold in order to increase household incomes. Recent studies indicate that this annual trade amounts to thousands of tonnes of roots, rhizomes, tubers, leaves, etc., worth millions of US dollars. The main market is in India. Based on a national survey, including the most commonly traded species, and a village study this paper investigates the importance of the alpine medicinal plant trade at national and local levels in Nepal. The national survey included standardized open-ended interviews with 232 harvesters, 64 local traders, 66 central wholesalers, 47 regional wholesalers, and 16 production companies. The village survey is based on the daily records of household activities in 15 households in a one-year period. The annual Nepalese alpine and sub-alpine medicinal plant trade is conservatively estimated to vary from 480 to 2500 t with a total harvester value of US$0.8–3.3 million; the average harvester value is estimated at US$66.0 ± 99.0. The trade in 1997/98 amounted to 1600 t with a harvester value of US$2.3 million and an export value equivalent to 2.5% of total export from Nepal. Medicinal plant harvesting was found to constitute an integrated part of local livelihood strategies, contributing from 3 to 44% (average of 12%) of the annual household income. Importance at household level depended on land and animal holdings, and the availability of adult male labour. The validity and reliability of methods and analyses is evaluated, and issues of conservation and management of alpine medicinal plant species under the community forestry scheme are discussed. 相似文献
40.