全文获取类型
收费全文 | 1421篇 |
免费 | 296篇 |
国内免费 | 412篇 |
专业分类
测绘学 | 71篇 |
大气科学 | 396篇 |
地球物理 | 224篇 |
地质学 | 755篇 |
海洋学 | 309篇 |
天文学 | 37篇 |
综合类 | 77篇 |
自然地理 | 260篇 |
出版年
2024年 | 11篇 |
2023年 | 18篇 |
2022年 | 56篇 |
2021年 | 71篇 |
2020年 | 65篇 |
2019年 | 93篇 |
2018年 | 81篇 |
2017年 | 53篇 |
2016年 | 63篇 |
2015年 | 64篇 |
2014年 | 89篇 |
2013年 | 99篇 |
2012年 | 100篇 |
2011年 | 100篇 |
2010年 | 74篇 |
2009年 | 92篇 |
2008年 | 104篇 |
2007年 | 105篇 |
2006年 | 92篇 |
2005年 | 72篇 |
2004年 | 101篇 |
2003年 | 64篇 |
2002年 | 65篇 |
2001年 | 53篇 |
2000年 | 51篇 |
1999年 | 52篇 |
1998年 | 48篇 |
1997年 | 31篇 |
1996年 | 25篇 |
1995年 | 22篇 |
1994年 | 22篇 |
1993年 | 25篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2129条查询结果,搜索用时 78 毫秒
901.
902.
在大型三维地理信息系统中,往往需要在预加载整体地形数据的基础上,对局部地形数据重新构建三角网,用于物理模拟等应用。针对这一问题,本文提出了一种三维地形的金字塔“上下采样”局部实时简化算法,实现对局部三角网地形实时高效的简化。该算法基于图像金字塔思想,通过对原始地形的三角格网执行“下采样”和“上采样”,结合“预测残差”对“下采样”的地形做局部简化,简化后的三角网十分逼近原始的高精度三角网。本文将该算法用于GeoBeans 3D平台的汽车驾驶模拟系统中。该算法生成的地形简化且稳定,随着汽车活动范围的变化,按需销毁及重构更新地形。实验证明,当预测残差阈值取0.1时,三角形个数能简化到原始数量的2/3;阈值取0.2时,三角形个数可以简化到原始个数的1/4左右。由此可见,在视觉精度允许的范围之内,该算法对地形的简化效果较好,且耗时少,满足了三维系统及车辆驾驶模拟的实时性。 相似文献
903.
Joanna Tonge Susan A. Moore Maria M. Ryan Lynnath E. Beckley 《The Australian geographer》2013,44(2):143-160
Although there have been numerous studies of the meanings ascribed to terrestrial places, their applicability or otherwise to coastal and marine places has received limited attention. Through the process of photo-elicitation, the meanings ascribed to a remote coastal camping environment are examined, with the coastline of Ningaloo Marine Park in north-western Australia the focus for this study. Thirty participants were provided with digital cameras and the ascribed place meanings were explored when their photographs were discussed in subsequent in-depth interviews. Key meanings related to the physical environment providing opportunities for escape, participating in multiple marine-based activities, bonding with family and like-minded people, and offering a rewarding experience that makes everybody happy. This emergent meaning of ‘everybody's happy’ progresses the understanding of the affective elements of place, especially those realised by families and groups of friends. The paper traces important implications of this meaning, and provides a paradoxical perspective on isolation evident from the interviews, for managing coast-based recreation. 相似文献
904.
Hans Thor Andersen M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):50-52
Andersen. Hans Thor: Urban industrial Areas. Geografisk Tidsskrift 84: 50–52. Copenhagen, January 1984. The development of the large cities has been closely connected with industrialization. However, the decentralization of industry and manufacturing jobs has accelerated from 1970. This process has left a huge stock of old. derelict industrial buildings and a pool of unemployed workes. 相似文献
905.
《International Journal of Digital Earth》2013,6(6):488-515
Abstract Digital Agriculture is one of the important applications of Digital Earth. As the global climate changes and food security becomes an increasingly important issue, agriculture drought comes to the focus of attention. China is a typical monsoon climate country as well as an agricultural country with the world's largest population. The East Asian monsoon has had a tremendous impact upon agricultural production. Therefore, a maize drought disaster risk assessment, in line with the requirements of sustainable development of agriculture, is important for ensuring drought disaster reduction and food security. Meteorology, soil, land use, and agro-meteorological observation information of the research area were collected, and based on the concept framework of ‘hazard-inducing factors assessment (hazard)-vulnerability assessment of hazard-affected body (vulnerability curve)-risk assessment (risk),’ importing crop model EPIC (Erosion-Productivity Impact Calculator), using crop model simulation and digital mapping techniques, quantitative assessment of spatio-temporal distribution of maize drought in China was done. The results showed that: in terms of 2, 5, 10, and 20 year return periods, the overall maize drought risk decreased gradually from northwest to southeast in the maize planting areas. With the 20 year return period, high risk value regions (drought loss rate ≥0.5) concentrate in the irrigated maize region of Northwest china, ecotone between agriculture and animal husbandry in Northern China, Hetao Irrigation Area, and north-central area of North China Plain, accounting for 6.41% of the total maize area. These results can provide a scientific basis for the government's decision-making in risk management and drought disaster prevention in China. 相似文献
906.
Climate types, biome types, and soil orders are commonly used among physical geographers in research and to describe natural environmental characteristics. However, little attempt has been made to quantify the percentage of global land surface that is covered by combinations of climate types, biomes, and soil orders. This research overlays a world map of 31 climate types produced based on the Köppen–Geiger criteria using gridded NCAR/NCEP reanalysis monthly mean surface air temperature and precipitation data from 1981 to 2010 with global maps of eight biomes adapted from World Wildlife Federation and 12 soil orders from United States Natural Resources Conservation Service. Areas covered by each of the 2976 combinations are then calculated. Results suggest that, as expected, a few climate/biome/soil combinations are most common, such as desert climate/desert biome/entisols, tundra climate/tundra biome/gelisols, and desert climate/desert biome/aridisols. The local nature of soil properties causes small enclaves of unexpected combinations of climate, biome, and soils, and the 10 most extensive climate/biome/soil combinations occupy only one-quarter of the global land surface. The strong correspondence between climate and biome types validates the Köppen–Geiger criteria for categorizing climates based on vegetation realms, even today, despite the general paucity of data available when the criteria were established. 相似文献
907.
Review of the influence of freeze-thaw cycles on the physical
and mechanical properties of soil 总被引:3,自引:0,他引:3
Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its
physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render
the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle
arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors
should be considered to measure the influence on the properties of soil under freeze-thaw cycles. 相似文献
908.
909.
910.
自然过程与人文过程模拟之差异比较分析 总被引:2,自引:1,他引:1
模拟是对历史事件的重现,在模拟的基础上可以加以预测用来推断事件未来的发展。以台风移动与降水和三次产业结构演进两个模拟案例为代表,对地理学两大重要分支学科自然地理学和人文地理学分别对应的自然过程模拟和人文过程模拟的差异特点进行了初步比较。主要集中在系统分析框架下的主要组成要素、构建系统框架的知识背景基础、模拟的数据来源和定量化方法以及研究核心对象与应用范式4 个方面对自然过程模拟和人文过程模拟之间的差异进行了总结,并对两者的发展趋势作了简述。最后指出无论自然过程模拟还是人文过程模拟都是区域可持续发展不可或缺的两种模拟技术,随着人地系统理论的深入发展,这两种模拟技术未来必然会逐渐相互渗透融合,界限不再简单分明。 相似文献