全文获取类型
收费全文 | 1846篇 |
免费 | 123篇 |
国内免费 | 187篇 |
专业分类
测绘学 | 124篇 |
大气科学 | 173篇 |
地球物理 | 111篇 |
地质学 | 112篇 |
海洋学 | 513篇 |
天文学 | 28篇 |
综合类 | 184篇 |
自然地理 | 911篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 87篇 |
2021年 | 90篇 |
2020年 | 82篇 |
2019年 | 86篇 |
2018年 | 75篇 |
2017年 | 90篇 |
2016年 | 96篇 |
2015年 | 76篇 |
2014年 | 81篇 |
2013年 | 176篇 |
2012年 | 90篇 |
2011年 | 100篇 |
2010年 | 67篇 |
2009年 | 73篇 |
2008年 | 81篇 |
2007年 | 93篇 |
2006年 | 86篇 |
2005年 | 73篇 |
2004年 | 56篇 |
2003年 | 59篇 |
2002年 | 57篇 |
2001年 | 38篇 |
2000年 | 45篇 |
1999年 | 37篇 |
1998年 | 30篇 |
1997年 | 27篇 |
1996年 | 17篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 27篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 7篇 |
排序方式: 共有2156条查询结果,搜索用时 343 毫秒
321.
复合1992-2012年DMSP/OLS稳定夜间灯光等多源遥感数据和统计数据,运用多种城市规模分布理论方法,对城市用地与人口规模分布时空演变特征进行系统比较。结果表明:环渤海地区城市用地规模增长速度明显快于城市人口规模增长速度,城市人口规模分布比城市用地规模分布更为均衡;城市用地规模呈首位型分布但首位优势在减弱,城市人口规模呈位次型分布但首位优势在增强;位序迅速上升的城市主要位于山东省和河北省,位序显著下降的城市主要位于辽宁省。环渤海地区城市规模空间分布呈显著的区域差异和空间极化特征,且城市用地规模分布空间特征比城市人口规模分布更为突出。研究结论可为优化区域城市空间开发格局、促进人地系统可持续发展提供参考。 相似文献
322.
基于CMIP5的逐日最高温度模拟资料、GGI情景数据库逐年代人口数据,在RCP4.5情景下,以对应栅格高温日数与人口数量的乘积作为人口对高温的暴露度指标,通过多模式集合平均预估未来中国人口对不同强度高温的暴露度变化。结果表明:相比于基准时段(1981-2010年),中国人口对高温和强危害性高温的暴露度从2021-2040年开始明显增加,至2081-2100年暴露度分别增加了5.7倍和17.5倍;除了中国西部部分地区外,全国大部地区人群均受高温的影响,在21世纪中后期中东部大部人口对高温的暴露度超过10.0×106人?d;相比基准时段,随着年代的增长,中国人口对强危害性高温的暴露度在范围和强度上均有明显增加;2081-2100年,人口对高温和强危害性高温的暴露度增幅减缓。从气象地理区域上看,未来各时段人口对高温、强危害性高温的暴露度均有一定程度增加,但增加明显的区域主要集中在华北、黄淮、江南和江淮地区,华南地区对强危害性高温的暴露度增幅较小。高温日数变化对全国人口对高温暴露度的变化所产生的作用最明显。多模式集合的预估结果可以为防控未来高温风险提供重要的参考价值。 相似文献
323.
水松[Glyptostrobus pensilis(Stanunt.)K. Koch]为我国 I级重点保护野生植物之一,曾于珠江三角洲地区普遍生长。但由于近 50 a 来人类活动的强烈干扰,其野生种群和个体数量骤减,世界自然保护联盟(IUCN)已将水松评估为“极危”状态。文章以实测法进行野外调查,结果表明:广州市野生水松古树在近 5 a 间快速消亡,现仅存 8 个种群共 14 株个体,且半数处于生长不良或濒死状态;种群个体数量少,仅包括 1~4 株水松,无法进行自然更新;这些水松长期未得到科学合理的保护,如不采取有效保育措施,残酷的生存压力可能导致大部分种群的快速死亡。因此,在广州地区开展水松的就地和迁地保护、扩大种群的个体数量、开展水松的保护遗传学和监测人工林种群的遗传结构变化情况等研究,应成为目前保护和拯救本地区水松种群及其遗传多样性的必要策略。 相似文献
324.
VognimaryMarieOdette 《地球空间信息科学学报》2005,8(2):152-156
This paper focuses on the public participation in environmental planning. After the decade for inaccessible information related to the decision taken, actually, the program of public parti,cipation is the reference of all the decision making process. However, there are some factors that limit this process, such as poverty, illiteracy, ignorance and often the social inequality. Therefore, this study focuses first on the benefits of public participation in environmental planning, then the involvement of the local population, and finally the decision making access using a case study of Madagascar. 相似文献
325.
326.
Incorporating GIS Building Data and Census Housing Statistics for Sub-Block-Level Population Estimation 总被引:1,自引:0,他引:1
This article presents a deterministic model for sub-block-level population estimation based on the total building volumes derived from geographic information system (GIS) building data and three census block-level housing statistics. To assess the model, we generated artificial blocks by aggregating census block areas and calculating the respective housing statistics. We then applied the model to estimate populations for sub-artificial-block areas and assessed the estimates with census populations of the areas. Our analyses indicate that the average percent error of population estimation for sub-artificial-block areas is comparable to those for sub-census-block areas of the same size relative to associated blocks. The smaller the sub-block-level areas, the higher the population estimation errors. For example, the average percent error for residential areas is approximately 0.11 percent for 100 percent block areas and 35 percent for 5 percent block areas. 相似文献
327.
Samuel M. Otterstrom 《The Professional geographer》2013,65(1):147-149
Ryan, James R. Picturing Empire: Photography and theVisualization of the British Empire Sizoo, Edith (ed.) Women's Lifeworlds: Women's Narratives on Shaping their Realities. Teaford, Jon Post-Suburbia Government and Politics in the Edge Cities. Warhus, Mark Another America: Native American Maps and the Historyof Our Land Yeung, Y. M. and Chu, David K. Y. (eds.) Guangdong: Survey of aProvince Undergoing Rapid Change Young, E. M. World Hunger 相似文献
328.
Darkness on the Edge of Town: Mapping Urban and Peri-Urban Australia Using Nighttime Satellite Imagery 总被引:1,自引:1,他引:0
Paul C. Sutton Andrew R. Goetz Stephen Fildes Clive Forster Tilottama Ghosh 《The Professional geographer》2013,65(1):119-133
This article explores the use of nighttime satellite imagery for mapping urban and peri-urban areas of Australia. A population-weighted measure of urban sprawl is used to characterize relative levels of sprawl for Australia's urban areas. In addition, the expansive areas of low light surrounding most major metropolitan areas are used to map the urban–bush interface of exurban land use. Our findings suggest that 82 percent of the Australian population lives in urban areas, 15 percent live in peri-urban or exurban areas, and 3 percent live in rural areas. This represents a significantly more concentrated human settlement pattern than presently exists in the United States. 相似文献
329.
《The Professional geographer》2013,65(2):143-150
This paper questions the validity and relevance of the application of procedures of classical statistical inference to population data in geography. Arguments for such procedures include the notions of temporal and spatial samples, measurement error, modifiable areal units, data vetting and stochastic processes. It is concluded that such arguments cannot be justified in terms of statistical theory. 相似文献
330.
Luca Salvati 《Urban geography》2013,34(3):440-453
This study assesses changes in population distribution and the expansion of urban settlements in Southern Italy between 1871 and 2011. Four demographic phases are identified: (i) spatially balanced, mild population growth (1871–1921); (ii) moderate population increase concentrated in coastal and lowland areas (1921–1951); (iii) rapid and diffused population growth (1951–1981); and (iv) population stability with settlement dispersion (1981–2011). While urban growth in the years preceding the 1980s reinforced the polarization in rich and poor areas along the urban-to-rural gradient, since the early 1990s both urban and rural areas showed population dynamics that consolidated low-density settlements scattered around the largest cities. This path, however, does not reflect the evolution towards a more spatially balanced urban development, as observed in other European regions. Causes and consequences of the persistence of a fragmented urban hierarchy with dense settlements and sprawl concentrated around the main cities are finally discussed. 相似文献