全文获取类型
收费全文 | 1979篇 |
免费 | 339篇 |
国内免费 | 472篇 |
专业分类
测绘学 | 106篇 |
大气科学 | 304篇 |
地球物理 | 500篇 |
地质学 | 1073篇 |
海洋学 | 227篇 |
天文学 | 87篇 |
综合类 | 281篇 |
自然地理 | 212篇 |
出版年
2024年 | 2篇 |
2023年 | 39篇 |
2022年 | 91篇 |
2021年 | 117篇 |
2020年 | 87篇 |
2019年 | 77篇 |
2018年 | 125篇 |
2017年 | 102篇 |
2016年 | 122篇 |
2015年 | 115篇 |
2014年 | 139篇 |
2013年 | 104篇 |
2012年 | 114篇 |
2011年 | 128篇 |
2010年 | 139篇 |
2009年 | 116篇 |
2008年 | 92篇 |
2007年 | 103篇 |
2006年 | 89篇 |
2005年 | 73篇 |
2004年 | 60篇 |
2003年 | 56篇 |
2002年 | 52篇 |
2001年 | 53篇 |
2000年 | 62篇 |
1999年 | 78篇 |
1998年 | 72篇 |
1997年 | 57篇 |
1996年 | 45篇 |
1995年 | 54篇 |
1994年 | 41篇 |
1993年 | 29篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1958年 | 3篇 |
排序方式: 共有2790条查询结果,搜索用时 15 毫秒
91.
A Survey of the Spatio-Temporal Data Model 总被引:1,自引:0,他引:1
Traditional GIS(Geographic Information System)mostly can only describe the transient state data and does not have the ability to deal with the temporal dynamic data. When the data changes, new data will take the place of the old data, namely the transient state change into another, and the old data will disappear. Therefore, it is unable to make an analysis of the updating changes of the data and predict the development trend of the future. In this case, TGIS (Temporal Geographic Information System) emerges and expands the time dimension on the basis of traditional GIS. Spatio-temporal data model is the key to TGIS. Spatio-temporal data modeling is not only related to dynamic expression of spatio-temporal objects, but also gives an important support for spatio-temporal analysis and reasoning. This paper summarized the theories and applications status at home and abroad of spatio-temporal data model in detail, illustrated family tree of spatio-temporal data model for the nearly fifty years, discussed improvement and application status of Base State with Amendments Model, Event-based Spatio-temporal Data Model, Object-oriented Data Model and other spatio-temporal data models, and raised the existing problems of spatio-temporal data model. The current existing problems mainly includes: ①There are a lot of spatio-temporal data models put forward, but some of them only focus on semantic design and neglect the verified; ②Most of existing spatio-temporal data model are for vector data, only the Event-based Spatio-temporal Data Model is raster data structure; ③At present, the expression the time-space information of geographic entity is relative separated with spatio-temporal data model; ④Spatio-temporal data model is mainly used in cadastral management, land use and forestry data updating, less application in other fields. In the end, the future development direction was put forward of spatio-temporal data model. In the time of big data and “Internet plus”, it is necessary to explore the big data spatio-temporal data model that supports multiple data formats. 相似文献
92.
δ~(18)O variations;;ice core;;outgoing longwave radiation;;meridional wind;;northeastern Tibetan Plateau 相似文献
93.
As an effective livelihood approach to alleviate poverty without rural population migration, ethnic tourism has become the primary choice of economic development in ethnic areas worldwide in addition to traditional livelihood approaches. This article applies the theories of livelihood to study the community evolution driven by tourism livelihood and examine three mountainous tourism communities in different stages of tourist area life cycle. Drawing on the methods of GIS spatial analysis, semi-structured interviews and questionnaires, this article proposes a sustainable livelihood framework for ethnic tourism to explore the evolution of ethnic tourism communities by identifying changes in livelihood assets (natural, financial, social, cultural and human capitals) in the process of tourism development. The results show that the development of ethnic tourism has led to changes in the increase of building land, and the diversification of land use functions with a trend of shifting from meeting local villagers' living needs to satisfying tourists, income composition and uneven distribution of tourism income spatially. Ethnic tourism also led to the deterioration of traditional social management structure, collapse of neighboring relationship, the over- commercialization and staged authenticity of ethnic culture, as well as the gradual vanish of agricultural knowledge with a trend of increasing modern business knowledge and higher education. In addition, these changes, involving livelihood assets from natural, economic, human, social and cultural aspects are interrelated and interactive, which form new evolution characters of ethnic community. This study reveals the conflicts over livelihood approaches which have formed new vulnerabilities to impact on sustainable evolution of ethnic communities. This research provides implications for achieving the sustainable development of ethnic communities with the driving force of tourism livelihood. 相似文献
94.
95.
96.
97.
98.
99.
100.
Wetland economic valuation approaches and prospects in China 总被引:1,自引:0,他引:1
Ecosystem services valuation seeks to increase the social relevance of ecosystem characteristics, the underlying biological mechanisms that support services, by making the contribution of ecosystems to human well-being explicit. Economic valuation can help management by clarifying the full range of benefits and costs of proposed management actions. In the past two decades, economic valuation of wetland ecosystem services has become one of the most significant scientific priorities for wetland protection. In this paper, we provide an overview of ecosystem services, and summarize the main interdisciplinary approaches to measure and value wetland ecosystem services. We identified four main methodological gaps preventing progress on wetland valuation of ecosystem services in China, which are: 1) confusion on terminology like intermediate and final ecosystem services, 2) lack of ecological production functions to link ecosystem characteristics to final ecosystem services, 3) static valuation making it difficult to evaluate the trade-offs and synergies among ecosystem services, and 4) lack of clear guidance on relating ecological compensation programs to conservation targets. Overcoming these gaps is important to inform wetland compensation mechanisms and conservation policies. We propose future research on wetland ecosystem services in China should be focused on: 1) defining final ecosystem services based on beneficiary preferences and underlying biophysical mechanisms, 2) establishing wetland monitoring programs at specific sites to collect data on final ecosystem service indicators and ecosystem characteristic metrics to create ecological production functions for economic valuation and rescaling techniques, and 3) incorporating wetland ecosystem service values into decision-making processes to inform wetland management. 相似文献