全文获取类型
收费全文 | 2190篇 |
免费 | 132篇 |
国内免费 | 243篇 |
专业分类
测绘学 | 101篇 |
大气科学 | 119篇 |
地球物理 | 691篇 |
地质学 | 1200篇 |
海洋学 | 246篇 |
天文学 | 60篇 |
综合类 | 14篇 |
自然地理 | 134篇 |
出版年
2024年 | 27篇 |
2023年 | 76篇 |
2022年 | 60篇 |
2021年 | 88篇 |
2020年 | 185篇 |
2019年 | 123篇 |
2018年 | 149篇 |
2017年 | 205篇 |
2016年 | 136篇 |
2015年 | 162篇 |
2014年 | 258篇 |
2013年 | 381篇 |
2012年 | 246篇 |
2011年 | 35篇 |
2010年 | 41篇 |
2009年 | 28篇 |
2008年 | 29篇 |
2007年 | 45篇 |
2006年 | 37篇 |
2005年 | 41篇 |
2004年 | 41篇 |
2003年 | 28篇 |
2002年 | 36篇 |
2001年 | 9篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2565条查询结果,搜索用时 15 毫秒
31.
L. Sedda P.M. Atkinson M.R. Filigheddu G. Cotzia S. Dettori 《International journal of geographical information science》2013,27(7):1083-1096
Cork oak is one of the most valuable natural forest genera in the Mediterranean basin. Modelling cork oak growth has been a challenge for foresters in recent years because of strong site and genetic influences, below-ground competition, management regimes and age effects. Because cork productivity is related to forest height, which is, in turn, related directly with site characteristics, an increase in the accuracy of height prediction implies improved productivity estimation. A Bayesian maximum entropy (BME) geostatistical model was applied to characterize the space–time pattern of height of young cork oak in a forest stand from central Sardinia in the years 2000, 2002, 2003, 2006 and 2008. Cork oak height maps were produced for each of the 5 years. The main goals were to analyse and interpret through time (i) the changes in spatial correlation and (ii) the changes in spatial distribution of cork oak height. The plantation was characterized by an increasing spatial dependence through time, whereas the temporal range was 2 years. Cork oak height was significantly correlated with wind speed (reduced by a neighbouring forest) in all the years implying a single trend. The correlations were larger for 2006 and 2008 than for previous years. Three other environmental variables (shade, elevation and slope) were less significant and their influence restricted to 2 years only. This research has several implications for the management of cork oak in the young phase. 相似文献
32.
Ling Yin 《International journal of geographical information science》2013,27(5):742-761
Exploring the evolution of people’s social interactions along with their changing physical locations can help to achieve a better understanding of the processes that generate the relationships between physical distance and social interactions, which can benefit broad fields of study related to social networks. However, few studies have examined the evolving relationships between physical movements and social closeness evolution. This is partially related to the shortage of longitudinal data in both physical locations and social interactions and the lack of an exploratory analysis environment capable of effectively investigating such a process over space and time. With the increasing availability of sociospatiotemporal data in recent years, it is now feasible to examine the relationships between physical separation and social interactions at the individual level in a space–time context. This research was intended to offer a spatiotemporal exploratory analysis approach to address this challenge. The first step was to propose the concept of a social closeness space–time path, which is an extension of the space–time path concept in time geography, to represent evolving human relationships in a social closeness space. A space–time geographical information system (GIS) prototype was then designed to support the representation and analysis of space–time paths in both physical and social closeness spaces. Finally, the effectiveness of the proposed concept and design in gaining insight into the impact of physical migration on online social closeness was demonstrated through an empirical study. The contributions of this study include an extension of the time–geographic framework from physical space to social closeness space, the development of a multirepresentation approach in a GIS to integrate an individual’s space–time paths in both physical and social closeness spaces, and an exploratory analysis of the evolving relationships between physical separation and social closeness over time. 相似文献
33.
34.
1 IntroductionKnowledge of suspended particle size and distri-bution is the key elements for better understandingthe sediment transport processes ( Wang et al.,2004), primary production (Ning et al., 2004),water quality controlling and pollution predictio… 相似文献
35.
Zhi Ding Fenzhen Su Yanan Chen Ying Liu Xue Feng Wenqiu Hu Fengqin Yan He Li Pujia Yu Xuguang Tang 《海洋学报(英文版)》2023,42(2):163-174
Increasing intense human activities have largely changed the coastal landscape and caused many environmental issues. However, whether human-induced activities could change the coastal land use gradient pattern, an important coastal zonal characteristic along the sea–land direction, remains unclear. Manila Bay was selected as the study area in this work. According to the distance of the land use and land cover(LULC) to the coastline, we clustered the typical coastal land use sequence patterns(CLU... 相似文献
36.
Jinshui Liu Shuai Li Kaifei Liao Yuchi Cui Lei Shao Peijun Qiao Yi Lu Yuanli Hou Thian Lai Goh Yongjian Yao 《海洋学报(英文版)》2023,42(3):89-100
Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin. Clarifying the source suppliers and restoring source-to-sink transport routes are of great significance to the future petroleum and gas undertakings. Previous researchers were largely confined by either limitation of geological records, highly dependence on a singular method or low-precision dating techniques. Our study integrated heavy mineral assemblages, geochemica... 相似文献
37.
38.
39.
埕岛油田海区海底地形变化及预防措施 总被引:2,自引:2,他引:2
综合在胜利石油管理局埕岛油田海区多年来工程测绘与地质勘察资料 ,对埕岛油田海区地形地貌特征及其变化与发育趋势进行了论述 ,同时讨论了埕岛油田海上工程中需要重视的问题以及有关的工程防护问题。 相似文献
40.