全文获取类型
收费全文 | 1193篇 |
免费 | 182篇 |
国内免费 | 298篇 |
专业分类
测绘学 | 179篇 |
大气科学 | 215篇 |
地球物理 | 224篇 |
地质学 | 387篇 |
海洋学 | 317篇 |
天文学 | 28篇 |
综合类 | 114篇 |
自然地理 | 209篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 58篇 |
2021年 | 65篇 |
2020年 | 56篇 |
2019年 | 75篇 |
2018年 | 49篇 |
2017年 | 80篇 |
2016年 | 70篇 |
2015年 | 76篇 |
2014年 | 102篇 |
2013年 | 106篇 |
2012年 | 66篇 |
2011年 | 79篇 |
2010年 | 78篇 |
2009年 | 87篇 |
2008年 | 64篇 |
2007年 | 78篇 |
2006年 | 69篇 |
2005年 | 51篇 |
2004年 | 55篇 |
2003年 | 47篇 |
2002年 | 38篇 |
2001年 | 20篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 17篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有1673条查询结果,搜索用时 15 毫秒
241.
This article reconsiders the epistemic and geographic boundaries that have long separated scholarship on urban water poverty and politics in the Global North and South. We stage an encounter between the seemingly dissimilar cases of Tooleville outside of the city of Exeter in California’s Central Valley and Bommanahalli outside of Bangalore, India, to illuminate the geography of water marginalization at the fringes of urban areas, and to deepen cross-fertilization between two geographic literatures: environmental justice (EJ) and urban political ecology (UPE). We argue that there is scope for transnational learning in three arenas in particular: (1) water access, (2) state practice, and (3) political agency. In so doing, we aim to advance a genuinely post-colonial approach to theory and practice in the pressing arena of urban water politics. 相似文献
242.
《Urban geography》2013,34(1):66-82
Measuring the level of segregation often encounters two methodological issues: measures are sensitive to changes in the geographical scale of the data and the effectiveness of the measure in reflecting spatial segregation. Several spatial measures have been suggested to measure spatial segregation, but whether they are more or less sensitive to changes in spatial scale has not been investigated, while some spatial measures are relatively scale-insensitive. Using the 1990 Census data of 30 selected U.S. metropolitan areas, this paper demonstrates that these spatial measures, similar to the aspatial measure, report higher levels of segregation when smaller areal units are used in the analysis. Some spatial measures are even more sensitive to scale changes than aspatial measures. Certain patterns of the scale sensitivity were identified, but no general rules can be formulated. A preliminary explanation of the scale effect on spatial segregation measures is offered. 相似文献
243.
The determination of the gravitational potential of a prism plays an important role in physical geodesy and geophysics. However, there are few literatures that provide accurate approaches for determining the gravitational potential of a prism. Discrete element method can be used to determine the gravitational potential of a prism, and can approximate the true gravitational potential values with sufficient accuracy (the smaller each element is, the more accurate the result is). Although Nagy’s approach provided a closed expression, one does not know whether it is valid, due to the fact that this approach has not been confirmed in literatures. In this paper, a study on the comparison of Nagy’s approach with discrete element method is presented. The results show that Nagy’s formulas for determining the gravitational potential of a prism are valid in the domain both inside and outside the prism. 相似文献
244.
245.
逐点激发井深设计网格化方法的选取 总被引:1,自引:0,他引:1
随着地震勘探的不断深入,地震资料采集要求主频足够高,频带足够宽,能量足够强,而逐点激发井深设计有助于获得满意的地震信号,要设计合理的井深,网格化方法的选取非常重要。这里首先介绍了Surfer软件中十二种网格化方法原理特征,以及在逐点井深设计上的应用;然后运用Surfer软件中不同的插值方法,对BIN12工区岩性数据进行网格的效果对比与网格的密度探讨,选取了最佳的网格化方法;最后针对几种网格化方法进行井深对比试验,通过资料分析,说明了设计的井深合理,选取网格化方法的效果较好。 相似文献
246.
Armel Thibaut Kaptué Tchuenté Jean-Louis Roujean Steven M. De Jong 《International Journal of Applied Earth Observation and Geoinformation》2011
Land cover dynamics at the African continental scale is of great importance for global change studies. Actually, four satellite-derived land cover maps of Africa now available, e.g. ECOCLIMAP, GLC2000, MODIS and GLOBCOVER, are based on images acquired in the 2000s. This study aims at stressing the compliances and the discrepancies between these four land cover classifications systems. Each of them used different mapping initiatives and relies on different mapping standards, which supports the present investigation. In order to do a relative comparison of the four maps, a preamble was to reconcile their thematic legends into more aggregated categories after a projection into the same spatial resolution. Results show that the agreement between the four land cover products is between 56 and 69%. While all these land cover datasets show a reasonable agreement in terms of surface types and spatial distribution patterns, mapping of heterogeneous landscapes in the four products is not very successful. Land cover products based on remote sensing imagery can indeed significantly be improved by using smarter algorithms, better timing of image acquisition, improved class definitions. Either will help to improve the accuracy of future land cover maps at the African continental scale. Data producers may use the areas of spatial agreement for training area selection while users might need to verify the information in the areas of disagreement using additional data sources. 相似文献
247.
248.
城市高架桥合理抗震体系选择与经济性对比 总被引:1,自引:0,他引:1
探讨了基于两水准设防的城市高架桥的合理抗震设防标准与相应的结构性能目标.选取两座典型的城市高架桥结构,包括一座正线桥和一座匝道桥,分别采用延性抗震体系和减、隔震体系进行结构抗震设计.对比了不同结构抗震体系所对应的结构在各水准地震作用下具体抗震性能表现,结果表明减、隔震体系具有更优的抗震性能.在此基础上,进一步从经济性的... 相似文献
249.
250.