全文获取类型
收费全文 | 2362篇 |
免费 | 244篇 |
国内免费 | 290篇 |
专业分类
测绘学 | 743篇 |
大气科学 | 393篇 |
地球物理 | 255篇 |
地质学 | 331篇 |
海洋学 | 232篇 |
天文学 | 19篇 |
综合类 | 297篇 |
自然地理 | 626篇 |
出版年
2024年 | 8篇 |
2023年 | 32篇 |
2022年 | 94篇 |
2021年 | 126篇 |
2020年 | 112篇 |
2019年 | 130篇 |
2018年 | 65篇 |
2017年 | 144篇 |
2016年 | 131篇 |
2015年 | 144篇 |
2014年 | 175篇 |
2013年 | 136篇 |
2012年 | 203篇 |
2011年 | 198篇 |
2010年 | 157篇 |
2009年 | 116篇 |
2008年 | 143篇 |
2007年 | 131篇 |
2006年 | 143篇 |
2005年 | 78篇 |
2004年 | 79篇 |
2003年 | 73篇 |
2002年 | 53篇 |
2001年 | 43篇 |
2000年 | 32篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有2896条查询结果,搜索用时 31 毫秒
961.
人口老龄化是当前社会关注的重点问题之一,养老设施配置得合理与否对城市品质提升和社会公平地实现至关重要。当前对养老设施的研究已不在少数,但多从养老机构或社区养老设施的单一视角进行分析,评价内容集中于设施数量和空间分布的合理性,导致研究结果有所局限。因此,本文基于2018年武汉市社区级老年常住人口数据、2020年武汉市养老设施数据和道路交通等多源大数据,首先将社区养老设施纳入城市养老服务体系,并从养老设施和养老服务两大角度综合评价设施的供需匹配关系,结果表明: ① 区域层面,武汉市养老设施供需均呈现出中心城区集聚,外围分散的“核心-边缘”特征,但仍然存在数量等级体系不合理以及区域配置水平差距大等问题;② 社区层面,运用两步移动搜索法,发现武汉市养老设施供需匹配度:都市发展区>中心城区>外围城区;③ 养老服务上,武汉市医疗保健类和精神慰藉类服务供需匹配关系较差,且设施普遍缺少专业化的服务供给,高品质多样化的养老需求较难得到满足。针对武汉市养老设施和养老服务的供需匹配问题,本文从体系构建、空间布局以及实施管理方面提出了优化建议,同时运用最小设施点数模型将建议落实至空间层面,以期为类似地区养老设施规划提供有效参考。 相似文献
962.
生态系统服务功能与生态系统敏感性是衡量生态系统质量及实现高质量生态文明建设的重要依据。川藏铁路沿途跨越多个自然地理单元,生态环境保护是铁路规划、建设及运行过程中面临的关键问题。以川藏铁路西藏昌都段为研究对象,采取资料分析与野外调查结合的手段,运用生态评价模型对研究区的生态系统服务和生态脆弱性进行分析,并基于研究结果对铁路途经区域的生态保护重要性进行评价。结果表明,当前昌都境内川藏铁路涉及的生态保护极重要区、重要区和一般重要区占比分别为42.19%、52.69% 和5.12%。评价结果有助于在铁路规划、建设及运营过程中对工程活动进行合理布局,有针对性地降低对生态系统的负面影响,达到社会经济效益和生态效益双赢的目的。 相似文献
963.
Evolutionary trend of water cycle in Beichuan River Basin of China under the influence of vegetation restoration 下载免费PDF全文
To understand the influence of vegetation restoration on the water cycle in semiarid areas, the effects of vegetation restoration on evolution of the key elements of water cycle were clarified by analyzing the evolutionary trend of atmospheric precipitation, ecological consumption water, and surface runoff on a river basin scale on the basis of analytical results of the changes in vegetation coverage and the long-term meteorological and hydrological monitoring data of Beichuan River Basin. The results show that the vegetation cover in the Beichuan River basin has rapidly increased in the hilly and mountainous areas since the 1980s, especially from 2000 to 2019, with the maximum and average vegetation cover rates increased by 14.98% and 52.2%, respectively. During 1956-2016, the annual precipitation in the basin remained relatively stable; the annual surface runoff slightly declined, with an average attenuation rate of 20 million m~3/10 a. The main reason for the runoff decline is the increase in ecological water induced by the vegetation restoration, which has changed the spatial-temporal distribution of the water from atmospheric precipitation in the basin. Spatially, more precipitation was converted into ecological water. As a result, the remnant runoff supplied to the lower reaches reduced accordingly. Temporally, more precipitation participated in the soil water-groundwater cycle, thus prolonging the outward drainage period of the precipitation. Moreover, the large-scale vegetation restoration induced a significant decrease in the surface wind speed, evaporation from water surface and drought index. As a result, a virtuously mutual feedback relationship was formed between the vegetation and meteorological elements. Therefore, vegetation restoration is of great significance for the improvement in the water conservation capacity and semiarid climate conditions in the Beichuan River basin. 相似文献
964.
《China Geology》2021,4(3):498-508
The surface watershed and groundwater basin have fixed recharge scale, which are not only the basic unit for hydrologic cycle research but also control the water resources formation and evolution and its corresponding eco-geological environment pattern. To accurately identify the boundary of the surface watershed and groundwater basin is the basis for properly understanding hydrologic cycle and conducting the water balance analysis at watershed scale in complicated geologic structure area, especially when the boundary are inconsistent. In this study, the Dalinuoer Lake located in the middle of the Inner Mongolian Plateau which has complicated geologic structure was selected as the representative case. Based on the multidisciplinary comprehensive analysis of topography, tectonics, hydrogeology, groundwater dynamics and stable isotopes, the results suggest the following: (1) The surface watershed ridge and groundwater basin divide of Dalinuoer Lake are inconsistent. The surface watershed was divided into two separate groundwater systems almost having no groundwater exchange by the SW-NE Haoluku Anticlinorium Fault which has obvious water-blocking effect. The surface drainage area of Dalinuoer Lake is 6139 km2. The northern regional A is the Dalinuoer Lake groundwater system with an area of 4838 km2, and the southern regional B is the Xilamulun Riverhead groundwater system with an area of 1301 km2. (2) The groundwater in the southern of regional A and the spring-feeding river are the important recharge sources for the Dalinuoer Lake, and it has greater recharge effects than the northern Gonggeer River system. (3) It is speculated that the trend of Haoluku Anticlinorium Fault is the boundary of the westerlies and the East Asian summer Monsoon (EASM) climate systems, which further pinpoints the predecessor’s understanding of this boundary line. At present, the Dalinuoer Lake watershed is proved to have gone through a prominent warming-drying trend periods, which leads to the precipitation reduction, temperature rise, human activities water usage increasement. So the hydrological cycle and lake eco-environment at watershed scale will still bound to be change, which may pose the potential deterioration risk on the suitability of fish habitat. The results can provide basic support for better understanding water balance evolution and lake area shrinkage cause as well as the ecological protection and restoration implementation of Dalinuoer Lake watershed.© 2021 China Geology Editorial Office. 相似文献
965.
966.
967.
River ecosystems are closely linked to human economic and social development, which are the most ecosystems at risk on earth. The research of ecosystem services can provide important scientific references for the ecosystems utilization,protection and management. On basis of summarizing the basic theories,assessment frameworks,technical methods and application practices related with research findings of river ecosystem services both at home and abroad,the existing shortcomings such as weak research foundation,lack of scientific and reasonable methods in ecosystem service evaluation,narrow application scope of the research results were pointed out. In consideration of the needs of society and the research tendency,the future developing directions of river ecosystems service were described: the solid research foundation should be established by multi-disciplinary and multi-scale integrations, the standardized,normalized and scientific evaluation system for ecosystem services shall be built by innovating assessment framework and technical methodology systems comprehensively, the new research areas including trade-offs and commercialization of ecosystem services will be carried out widely to expand our research perspectives and enhance the application values of the results. 相似文献
968.
Cloud computing has been considered as the next-generation computing platform with the potential to address the data and computing challenges in geosciences. However, only a limited number of geoscientists have been adapting this platform for their scientific research mainly due to two barriers: 1) selecting an appropriate cloud platform for a specific application could be challenging, as various cloud services are available and 2) existing general cloud platforms are not designed to support geoscience applications, algorithms and models. To tackle such barriers, this research aims to design a hybrid cloud computing (HCC) platform that can utilize and integrate the computing resources across different organizations to build a unified geospatial cloud computing platform. This platform can manage different types of underlying cloud infrastructure (e.g., private or public clouds), and enables geoscientists to test and leverage the cloud capabilities through a web interface. Additionally, the platform also provides different geospatial cloud services, such as workflow as a service, on the top of common cloud services (e.g., infrastructure as a service) provided by general cloud platforms. Therefore, geoscientists can easily create a model workflow by recruiting the needed models for a geospatial application or task on the fly. A HCC prototype is developed and dust storm simulation is used to demonstrate the capability and feasibility of such platform in facilitating geosciences by leveraging across-organization computing and model resources. 相似文献
969.
徐前祥 《测绘与空间地理信息》2015,(5)
地理信息作为一种新的信息维度对国民经济和社会发展各行各业均起到重要作用,地理信息产业的核心是地理信息企业,本文以省级行政区为单位,通过研究地理信息产业的甲级企业数量、业务数量与业务分布研究地理信息产业的分布,揭示产业分布现状与发展特点.研究结果表明,地理信息产业分布不均,中国大陆共796家甲级单位,北京市甲级单位占总数的13%,直辖市以互联网地图服务业务为主,省(自治区)以工程测量业务为主. 相似文献
970.
PixGrid是高分辨率遥感影像数据一体化测图系统,然而,在实际生产使用过程中,存在一些因素影响遥感数据的处理速度.针对这个问题,本文提出了以控制点、DEM、DOM等基础空间数据库为基础,建立控制资料服务体系,采用集成PixelGrid快速实现控制点自动量测的方法,提高了航空航天遥感资料的快速处理效率. 相似文献