全文获取类型
收费全文 | 2478篇 |
免费 | 335篇 |
国内免费 | 413篇 |
专业分类
测绘学 | 417篇 |
大气科学 | 438篇 |
地球物理 | 498篇 |
地质学 | 626篇 |
海洋学 | 217篇 |
天文学 | 192篇 |
综合类 | 174篇 |
自然地理 | 664篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 75篇 |
2021年 | 87篇 |
2020年 | 108篇 |
2019年 | 114篇 |
2018年 | 107篇 |
2017年 | 122篇 |
2016年 | 131篇 |
2015年 | 141篇 |
2014年 | 136篇 |
2013年 | 182篇 |
2012年 | 184篇 |
2011年 | 152篇 |
2010年 | 113篇 |
2009年 | 130篇 |
2008年 | 151篇 |
2007年 | 157篇 |
2006年 | 141篇 |
2005年 | 101篇 |
2004年 | 116篇 |
2003年 | 88篇 |
2002年 | 84篇 |
2001年 | 83篇 |
2000年 | 98篇 |
1999年 | 72篇 |
1998年 | 65篇 |
1997年 | 47篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有3226条查询结果,搜索用时 343 毫秒
861.
862.
By the theories of potential flow and structural vibration, the formulae for evaluating the ‘wet’ (with water) frequencies and mode shapes of the beam‐supported aqueduct are derived through a simplified fluid‐structure interaction analysis. The time‐history formulae of structural responses to the vertical seismic excitation are obtained. Applying the response‐spectrum principle, the equivalent vertical earthquake load exerted on the beam and the corresponding effects are also derived. Several illustrative examples are conducted. The analytical results show that: (i) The ‘wet’ frequencies of the structure are lower than the corresponding ‘dry’ (without water) frequencies due to the participating water mass, but the ‘wet’ mode shapes are identical to the corresponding ‘dry’ ones. (ii) The water mass plays an important role in the vertical seismic response, which varies with the different geological sites. For the different seismic inputs, the deeper the water is, the greater are the structural responses. (iii) The vertical seismic effects on the beam are generally not too small to be neglected and should be considered in the structural designs of a beam‐supported aqueduct. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
863.
864.
Scale and the other: Levinas and geography 总被引:2,自引:0,他引:2
Richard Howitt 《Geoforum》2002,33(3):299-313
This paper seeks to contribute to Geography's recent conversation of identity, landscape, scale and difference. It brings into dialogue previously divergent discussions about space, place and difference and proposes an approach that treats time, space, place and scale as co-equal conceptual and/or analytical elements of cultural landscapes. It argues that many philosophical debates about embodiment, emplacement and difference abstract a universalized notion of `place', `body' and `self' which confounds and conflates scale issues and consequently confuses the dialectical interplay of `time', `space', `being' and `culture' across scales. The paper takes the work of Emmanuel Levinas (1906-1995) and the discursive communities around it as a philosophical entry point into these debates. 相似文献
865.
南水北调西线工程可调水量分析中几个主要问题的探讨 总被引:14,自引:0,他引:14
南水北调西线工程规划从长江上游的通天河、雅砻江、大渡河调水入黄河,以解决西北及华北部分地区的干旱缺水问题。调水工程可调水量是开展各项工作的基础。在现有资料的基础上,通过对引水坝址径流量、引水坝址上下游用水要求、水库下泄水量、工程规模等因素的分析,提出了各因素对可调水量的影响程度,并估算了各引水坝址适宜的可调水量。 相似文献
866.
867.
GIS环境下空间数据多尺度特征及其关键问题探讨 总被引:12,自引:0,他引:12
介绍了GIS环境下空间数据多尺度特征的基本概念,并对与空间数据多尺度表达相关的技术作了探讨,其中主要包括它们的最新研究进展、主要方法、存在的问题及应用前景。 相似文献
868.
869.
Street names and the scaling of memory: the politics of commemorating Martin Luther King, Jr within the African American community 总被引:7,自引:0,他引:7
Derek H Alderman 《Area》2003,35(2):163-173
Streets named for Martin Luther King, Jr are common yet controversial features in cities across the United States. This paper analyses the politics of naming these streets as a 'scaling of memory'– a socially contested process of determining the geographic extent to which the civil rights leader should be memorialized. Debates over the scaling of King's memory revolve around the size of the named street, the street's level of prominence within a hierarchy of roads, and the degree to which the street transcends the spatial confines of the black community. A street-naming struggle in Eatonton, Georgia (USA) exposes how the scaling of memory can become a point of division and contest within the black community as activists seek to fulfil different political goals. Analysing these intra-racial contests allows for a fuller appreciation of the historical consciousness and geographic agency of African Americans rather than seeing them as a single, monolithic group. 相似文献
870.
The method for simulating the temporal and spatial distribution patterns of leaf area index (LAI) and biomass at landscape scale using remote sensing images and surface data was discussed in this paper. The procedure was: (1) annual maximum normalized difference vegetation index (NDVI) over the landscape was calculated from TM images; (2) the relationship model between NDVI and LAI was built and annual maximum LAI over the landscape was simulated; (3) the relationship models between LAI and biomass were built and annual branch, stem, root and maximum leaf biomass over the landscape were simulated; (4) spatial distribution patterns of leaf biomass and LAI in different periods all the year round were obtained. The simulation was based on spatial analysis module GRID in ArcInfo software. The method is also a kind of scaling method from patch scale to landscape scale. A case study of Changbai Mountain Nature Reserve was dissertated. Analysis and primary validation were carried out to the simulated LAI and biomass for the major vegetation types in the Changbai Mountain in 1995. 相似文献