全文获取类型
收费全文 | 1849篇 |
免费 | 280篇 |
国内免费 | 230篇 |
专业分类
测绘学 | 137篇 |
大气科学 | 133篇 |
地球物理 | 396篇 |
地质学 | 620篇 |
海洋学 | 301篇 |
天文学 | 4篇 |
综合类 | 153篇 |
自然地理 | 615篇 |
出版年
2024年 | 8篇 |
2023年 | 32篇 |
2022年 | 85篇 |
2021年 | 84篇 |
2020年 | 89篇 |
2019年 | 90篇 |
2018年 | 77篇 |
2017年 | 87篇 |
2016年 | 114篇 |
2015年 | 95篇 |
2014年 | 142篇 |
2013年 | 125篇 |
2012年 | 119篇 |
2011年 | 111篇 |
2010年 | 88篇 |
2009年 | 113篇 |
2008年 | 95篇 |
2007年 | 109篇 |
2006年 | 94篇 |
2005年 | 97篇 |
2004年 | 75篇 |
2003年 | 65篇 |
2002年 | 52篇 |
2001年 | 47篇 |
2000年 | 53篇 |
1999年 | 34篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有2359条查询结果,搜索用时 15 毫秒
41.
Three-dimensional urban cartography is needed for city changes’ assessment. The variety of studies using 3D calculations of urban elements grows each year. Building and vegetation volumes are necessary to assess and understand spatio-temporal urban changeable environments. However, there are technical questions as to which method can improve 3D urban cartographic accuracy. The innovative part of this current study is the creation of a six-band hybrid obtained from LIDAR and WorldView2 synergy. Two different enhancement algorithms demonstrated the most important spectral features for the urban development and vegetation classes. Results indicated an improvement in accuracy by up to 21.3%, according to the Kappa coefficient. Both infra-red band and intensity band were the most significant, according to the principal components analysis. The synergy delimited classes and polygons, as well as the direct display of information regarding heights of elements and improving the extraction of roads, buildings and vegetation classes. 相似文献
42.
以国家自然科学基金2000—2019年资助的560项旅游类课题为数据来源,对课题立项的时空分布、承担单位、负责人等进行统计分析,构建由6个主类和15个亚类组成的旅游地理问题分类体系,运用词频统计和内容分析法,总结我国旅游地理研究格局和热点发展态势。研究发现:2000年至2019年间,自然基金委对旅游类课题的资助力度不断加强,总体呈先缓慢、后迅速增长、再大幅提升后保持平稳发展的态势,资助空间分布呈“东高西低”的特点,课题依托单位明显优势集中,课题承担人则呈离散分布;旅游流、旅游产业发展、旅游交通等研究主题热度逐渐减弱,旅游者行为和感知、旅游的社会文化影响、旅游地空间、典型旅游地保护和开发、旅游生态环境等主题热度明显上升,在此基础上对各热点主题历年变化特征和规律进行归纳总结。本文更新和拓展了以往同类研究发现,对旅游学者进行研究选题和课题申报有参考和指导意义。 相似文献
43.
珞珈一号夜间灯光影像在建设用地提取中的应用:以武汉市为例 总被引:1,自引:0,他引:1
城市建设用地能够反映城市建设发展在地域空间上的分布形态,是规划主管部门监测城市建设和扩张的关键指标.2018-06-02发射的珞珈一号卫星可提供130 m分辨率的夜间灯光数据,在城市建设用地的提取方面具有较大潜力.首先整合珞珈一号夜间灯光影像与Landsat 8多光谱影像以及网络地图兴趣点数据;然后分别采用人类居住合成... 相似文献
44.
Sergio Freire Marcello Schiavina Aneta J. Florczyk Kytt MacManus Martino Pesaresi Christina Corbane 《International Journal of Digital Earth》2020,13(1):61-77
ABSTRACTData on global population distribution are a strategic resource currently in high demand in an age of new Development Agendas that call for universal inclusiveness of people. However, quality, detail, and age of census data varies significantly by country and suffers from shortcomings that propagate to derived population grids and their applications. In this work, the improved capabilities of recent remote sensing-derived global settlement data to detect and mitigate major discrepancies with census data is explored. Open layers mapping built-up presence were used to revise census units deemed as ‘unpopulated’ and to harmonize population distribution along coastlines. Automated procedures to detect and mitigate these anomalies, while minimizing changes to census geometry, preserving the regional distribution of population, and the overall counts were developed, tested, and applied. The two procedures employed for the detection of deficiencies in global census data obtained high rates of true positives, after verification and validation. Results also show that the targeted anomalies were significantly mitigated and are encouraging for further uses of free and open geospatial data derived from remote sensing in complementing and improving conventional sources of fundamental population statistics. 相似文献
45.
46.
47.
Joe Weber 《The Professional geographer》2019,71(2):239-252
In the twenty-first century, there are three American Wests, which cut across cultural, political, physical, and economic boundaries. Parts of the West are booming, building homes, and adding population; others are legally off limits to such development; and much of the West has been bypassed by such development and growth. These are called here the Booming West, Protected West, and Bypassed West. Maps of climate, political boundaries, ethnic and racial identities, or presidential voting patterns do not match these three Wests. Each West has a different relationship to the others and might see them as threats or opportunities, and each West can be expected to grow in different areas at the expense of other Wests. The boundaries between the three Wests could be important locations; sharp transitions can exist between Wests, perhaps nowhere more so than where a fast growing metro area abuts a national park or forest boundary. Finally, the effects of climate change cut across the three Wests and have different implications for their future. Continued population growth will further emphasize the boundaries between each of the three Wests and raise the stakes for their control. 相似文献
48.
Probabilistic aftershock hazard assessment (PAHA) has been introduced by Wiemer (Geophys Res Lett 27:3405–3408, 2000). The method, in its original form, utilizes attenuation relations in evaluating peak ground velocity (PGV) exceedence probability.
We substitute the attenuation relations together with their uncertainties by strong ground motion simulations for a set of
scenarios. The main advantage of such an approach is that the simulations account for specific details of the aftershock source
effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGVs and their standard deviations
are retrieved from the simulation results obtained by the new hybrid k-squared source model, and they are used for the PAHA analysis at a station under study. The model chosen for the testing
purposes is inspired by the Izmit A25 aftershock (M
w
= 5.8) that occurred 26 days after the mainshock. The PAHA maps are compared with (1) those obtained by the use of attenuation
relations and (2) the peak values of ten selected strong-motion recordings written by the aftershock at epicentral distances
<50 km. We conclude that, although the overall hazard decay with increasing fault distance is similar, the PAHA maps obtained
by the use of simulations exhibit remanent radiation pattern effect and prolongation in the strike direction due to the directivity
effect pronounced for some of the scenarios. As regard the comparison with real data, we conclude that the PAHA maps agree
with observed peak values due to appropriate attenuation model adopted in the analysis. 相似文献
49.
地电化学方法作为覆盖区矿产资源勘查的一种有效手段,其原理是在人工外加电场作用下,将近地表介质中呈电活动态的物质选择性地提取,通过研究电提取元素组合、含量分布及异常特征,进而提供找矿信息的一种勘查方法。笔者通过在内蒙古洛恪顿矿区开展地电化学勘查研究,验证了地电化学法在内蒙古东乌旗风成砂覆盖区勘查的有效性,并通过对不同提取时间、不同密度的载体物质等提取条件的对比研究,确定在该区进行地电化学勘查的提取时间为24 h,载体物质选用高密度泡塑。 相似文献
50.
Bettina Reimann 《Applied geography (Sevenoaks, England)》1997,17(4):301-313
The constitutional decision to return to their original owners all real-estate property in East Germany that had either been expropriated or placed under state administration (the restitution principle) has had significant consequences for urban development and urban renewal. Experiences from East Berlin's innercity residential areas illustrate the effects on the state of repair of housing, the character of residential neighbourhoods, the tenants living in the areas affected, and the future structure of real-estate ownership. The case studies reveal a picture of a contradictory development of residential neighbourhoods, including shifting power relations and new polarizations, especially between tenants and landlords. 相似文献