全文获取类型
收费全文 | 2990篇 |
免费 | 424篇 |
国内免费 | 564篇 |
专业分类
测绘学 | 509篇 |
大气科学 | 526篇 |
地球物理 | 672篇 |
地质学 | 838篇 |
海洋学 | 289篇 |
天文学 | 213篇 |
综合类 | 218篇 |
自然地理 | 713篇 |
出版年
2024年 | 12篇 |
2023年 | 48篇 |
2022年 | 90篇 |
2021年 | 103篇 |
2020年 | 119篇 |
2019年 | 146篇 |
2018年 | 127篇 |
2017年 | 150篇 |
2016年 | 151篇 |
2015年 | 168篇 |
2014年 | 167篇 |
2013年 | 237篇 |
2012年 | 219篇 |
2011年 | 194篇 |
2010年 | 151篇 |
2009年 | 164篇 |
2008年 | 182篇 |
2007年 | 193篇 |
2006年 | 179篇 |
2005年 | 131篇 |
2004年 | 142篇 |
2003年 | 111篇 |
2002年 | 103篇 |
2001年 | 90篇 |
2000年 | 115篇 |
1999年 | 81篇 |
1998年 | 75篇 |
1997年 | 67篇 |
1996年 | 46篇 |
1995年 | 37篇 |
1994年 | 37篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3978条查询结果,搜索用时 31 毫秒
41.
对常规气象要素、卫星云图和T106物理量诊断产品进行分析,得出2001年10月2~3日发生在桂东南局地强降水成因及中尺度系统特征。 相似文献
42.
通过引人泊松括号,分析了无限维Hamilton的性质,并将其推广到广义Hamilton系统,且从理论和实用角度讨论了这类广义Hamilton系统的辛格式构造问题,从而为辛几何算法在一般的时间发展方程的数值求解提供新的具体途径。 相似文献
43.
The effects of damping in various laminated rubber bearings (LRB) on the seismic response of a ?‐scale isolated test structure are investigated by shaking table tests and seismic response analyses. A series of shaking table tests of the structure were performed for a fixed base design and for a base isolation design. Two different types of LRB were used: natural rubber bearings (NRB) and lead rubber bearings (LLRB). Three different designs for the LLRB were tested; each design had a different diameter of lead plug, and thus, different damping values. Artificial time histories of peak ground acceleration 0.4g were used in both the tests and the analyses. In both shaking table tests and analyses, as expected, the acceleration responses of the seismically isolated test structure were considerably reduced. However, the shear displacement at the isolators was increased. To reduce the shear displacement in the isolators, the diameter of the lead plug in the LLRB had to be enlarged to increase isolator damping by more than 24%. This caused the isolator stiffness to increase, and resulted in amplifying the floor acceleration response spectra of the isolated test structure in the higher frequency ranges with a monotonic reduction of isolator shear displacement. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
44.
45.
东营市森林火险天气等级预报系统 总被引:2,自引:0,他引:2
利用9210传输的气象资料,选用国家气象中心T106和HLAFS数值预报产品中的要素作为火险天气因子,根据森林火险原因,建立了东营市森林火险天气等级预报系统。 相似文献
46.
47.
David Delaney 《The Professional geographer》2002,54(1):6-14
This essay is a revision of a paper prepared for an NSF workshop on race and geography. Participants in the workshop were asked to offer their views on the topic and our suggestions for further research. This contribution explores some aspects of the relationship and relevance of geography to the question of race in North America. It touches on three “places” that constitute the discipline: the place of research, the place of teaching, and the workplace. With respect to research, it suggests some promising lines of inquiry. Among these are studies of the relationship of scale to the politics of identity and studies of “passing” in connection with studies of geographies of experience and geographies of power. 相似文献
48.
Geographically or sociologically defined resource management units, such as buffer zones or community resource management territories, seek to harmonize local land–use practices with protected–area management objectives. The geographically restricted nature of these models often results in simplistic representations of society–nature relations over time and space. Conservation areas are misrepresented as ecologically and socially homogeneous, as well as politically neutral. This study examines the limits of a spatially defined conservation and development project designed around the physical geographical unit of the watershed at Lake Nakuru National Park, Kenya. It argues that politically motivated violence that has plagued the area since the early 1990s has severely undermined the suitability of such narrowly defined conservation territories. Specifically, the case study points to the permeability of the Lake Nakuru watershed to national and regional political forces that ultimately constrain participation in conservation activities. The spaces of conservation and development must be enlarged to include these extralocal arenas and processes if environmental problems are to be effectively addressed. 相似文献
49.
基于GTP的地下工程与围岩一体化真三维空间构模 总被引:10,自引:5,他引:10
针对地下工程开挖体的基本特征及其真三维建模要求,在广义三棱柱(GTP)模型的基础上进行扩展,提出采用E—GTP模型来构建地下工程开挖体的真三维模型。通过与其围岩地质体的G—GTP模型的耦合,实现了基于GTP的工程开挖体与围岩地质体的一体化建模。该模型将地下三维空间实体抽象为点、线、面、体四类对象,通过结点、TIN边、侧边、TIN面、侧面和GTP体元共6个基本几何元素进行统一表达。该文重点讨论了E—GTP的建模原理与方法,并介绍了基于面向对象思想的一体化空间数据结构。 相似文献
50.