全文获取类型
收费全文 | 5591篇 |
免费 | 531篇 |
国内免费 | 351篇 |
专业分类
测绘学 | 1094篇 |
大气科学 | 305篇 |
地球物理 | 820篇 |
地质学 | 1539篇 |
海洋学 | 1183篇 |
天文学 | 26篇 |
综合类 | 505篇 |
自然地理 | 1001篇 |
出版年
2024年 | 13篇 |
2023年 | 30篇 |
2022年 | 93篇 |
2021年 | 146篇 |
2020年 | 174篇 |
2019年 | 168篇 |
2018年 | 147篇 |
2017年 | 271篇 |
2016年 | 222篇 |
2015年 | 256篇 |
2014年 | 322篇 |
2013年 | 400篇 |
2012年 | 324篇 |
2011年 | 363篇 |
2010年 | 320篇 |
2009年 | 322篇 |
2008年 | 374篇 |
2007年 | 368篇 |
2006年 | 350篇 |
2005年 | 287篇 |
2004年 | 243篇 |
2003年 | 187篇 |
2002年 | 203篇 |
2001年 | 159篇 |
2000年 | 129篇 |
1999年 | 139篇 |
1998年 | 86篇 |
1997年 | 84篇 |
1996年 | 44篇 |
1995年 | 51篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有6473条查询结果,搜索用时 15 毫秒
971.
海洋空间规划是一个对海洋资源可持续开发利用的规划和管理过程。文章采用可视化工具CiteSpace,基于WOS核心合集和CNKI数据库,系统梳理分析2000—2020年海洋空间规划领域的国内外研究主题及其突现词演变路径。结果表明:当前国内外海洋空间规划相关研究数量总体呈上升趋势,美国、澳大利亚和英国3国占比超过50%,各机构间合作度较高、跨国交流活跃;国际方面,栖息地、海洋保护区域、渔业发展、生物多样性是热点研究方向,国内则更加关注陆海统筹和可持续发展;近20年来,国际研究趋势变化为"空间规划体系的构建-空间规划尺度的拓展及跨界研究-经验总结与环境保护",国内规划时期则从"空间规划政策综合管理-具体功能区划分-可持续发展"不断发展;在此基础上提出未来深入探索的重点领域以及建议。 相似文献
972.
台湾海峡海洋捕捞业管理策略和投资方向 总被引:1,自引:0,他引:1
本文收集了1985 ̄1994年福建省在台湾海峡生产的具有代表性的50对拖网渔船、120艘单拖渔船、48组灯光围网渔船、38对大围缯渔船、31艘定置网渔船的技术参数及生产资料,计算并分析了其适正捕捞力量、经济指标,得出了一些有益的结论:(1)根据台湾海峡渔业资源,把握正确的投资方向,已成为进一步发展海洋捕捞业的关键。(2)由于台湾海峡的渔业资源正遭受越来越大的压力,为了保护渔业资源,应当限制捕捞力量 相似文献
973.
莱芜市钢城区地理位置优越,交通便利,矿藏丰富。随着经济的高速发展,新农村建设及城市建设速度的加快,涉及土地征用、征地补偿、权属纠纷等方面的矛盾相对突出,涉及土地方面的信访事件相对增多。重点针对土地管理信访问题进行了调查分析,并就如何处置信访事件提出了意见和建议。 相似文献
974.
975.
Mara Almeida Carlos Guerra Teresa Pinto-Correia 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):97-108
The high nature value (HNV) concept, proposed by the European Environment Agency, recognizes that specific farming systems support high biodiversity levels, mainly as a result of extensive management practices. The Portuguese montado is one of the most significant HNV systems in southern Europe. However, considering the great complexity characterizing these systems both in land management and in landscape structure, a specific context-oriented methodology to assess which montado areas are likely to be classified as HNV farmland is needed. In this sense, the aim of this study is to explore a methodological approach which makes it possible to assess land management pressures through land cover information on these complex silvo-pastoral systems. The proposed methodology was tested through a local case study in a montado area in southern Portugal, assessing the relation between management practices and a vegetation cover index. Results show that in similar montado areas different land management strategies varying in stocking density, but also in type of grazing animals and shrub control practices, configure different vegetation cycles. These results indicate there is a way to develop a straightforward methodology to assess the HNV value of Mediterranean silvo-pastoral systems based on land cover indicators. These would make it possible to assess the HNV of montado areas with direct and objective information and independent of farmer’s surveys or other farm-based data. 相似文献
976.
Hydrogeochemical investigations and groundwater provinces of the Friuli Venezia Giulia Plain aquifers,northeastern Italy 总被引:2,自引:0,他引:2
Water resources are a key factor, particularly for the planning of the sustainable regional development of agriculture, as
well as for socio-economic development in general. A hydrochemical investigation was conducted in the Friuli Venezia Giulia
aquifer systems to identify groundwater evolution, recharge and extent of pollution. Temperature, pH, electric conductivity,
total dissolved solids, alkalinity, total hardness, SAR, Ca2+, Na+, K+, Mg2+, Cl−, SO4
2−, NO3
−, HCO3
−
, water quality and type, saturation indexes and the environmental stable isotope δ18O were determined in 149 sampling stations. The pattern of geochemical and oxygen stable isotope variations suggests that
the sub-surface groundwater (from phreatic and shallow confined aquifers) is being recharged by modern precipitations and
local river infiltrations. Four hydrogeological provinces have been recognised and mapped in the Friuli Venezia Giulia Plain
having similar geochemical signatures. These provinces have different degrees of vulnerability to contamination. The deep
confined groundwater samples are significantly less impacted by surface activities; and it appears that these important water
resources have very low recharge rates and would, therefore, be severely impacted by overabstraction. 相似文献
977.
3G技术与现代物流管理技术的集成模式研究 总被引:3,自引:1,他引:3
3G技术能够对现代物流作业与管理进行有效地监督和控制,3G技术与现代物流管理技术的集成是物流业发展的客观需要。探讨了3G技术与现代物流管理技术的集成模式,对于以GIS技术为平台支撑、以定位技术和无线通信技术为辅助手段的分布式空间物流信息系统的建设具有一定的意义。 相似文献
978.
针对旅游线路推荐过程中的数据稀疏与冷启动问题,本文提出了一种融合用户特征与群体智慧的多目标旅游线路推荐方法。首先,通过携程网、望路行程、百度指数等网站获取景点信息与对应的群体智慧数据,包括景点的位置、票价,用户评论、评分、浏览数据等;其次,结合用户特征与群体智慧数据构建景点对不同特征用户的综合吸引力并计算旅游线路吸引力指数;最后,定义旅游线路推荐多目标优化函数并利用多目标遗传算法NSGA2生成线路推荐列表。相较于传统旅游线路推荐方法,本文所提出的方法充分考虑了用户实际需求(消费侧)与景点吸引力(供给侧),使得用户能够以较少的时间开销,尽可能多地游览热门景点。同时,推荐过程中根据用户的性别、年龄、出行方式、出行时间对用户群体进行划分,使得推荐准确性更高。实验结果表明,该方法考虑的因子可以有效提高用户在路线规划过程中的满意度,所推荐的旅游线路不仅具有更高的综合吸引力指数,还能够有效减少路程时间。此外,推荐结果也更加具有多样性,有助于推动智能化旅游线路推荐的发展。 相似文献
979.
The Tibesti massif, one of the most prominent features of the Sahara desert, covers an area of some 100,000 km2. Though largely absent from scientific inquiry for several decades, it is one of the world’s major volcanic provinces, and
a key example of continental hot spot volcanism. The intense activity of the TVP began as early as the Oligocene, though the
major products that mark its surface date from Lower Miocene to Quaternary (Furon (Geology of Africa. Oliver & Boyd, Edinburgh
(trans 1963, orig French 1960), pp 1–377, 1963)); Gourgaud and Vincent (J Volcanol Geotherm Res 129:261–290, 2004). We present here a new and consistent analysis of each of the main components of the Tibesti Volcanic Province (TVP), based
on examination of multispectral imagery and digital elevation data acquired from the Advanced Spaceborne Thermal Emission
and Reflection Radiometer (ASTER). Our synthesis of these individual surveys shows that the TVP is made up of several shield
volcanoes (up to 80 km diameter) with large-scale calderas, extensive lava plateaux and flow fields, widespread tephra deposits,
and a highly varied structural relief. We compare morphometric characteristics of the major TVP structures with other hot
spot volcanoes (the Hawaiian Islands, the Galápagos Islands, the Canary and Cape Verdes archipelagos, Jebel Marra (western
Sudan), and Martian volcanoes), and consider the implications of differing tectonic setting (continental versus oceanic),
the thickness and velocity of the lithosphere, the relative sizes of main volcanic features (e.g. summit calderas, steep slopes
at summit regions), and the extent and diversity of volcanic features. These comparisons reveal morphologic similarities between
volcanism in the Tibesti, the Galápagos, and Western Sudan but also some distinct features of the TVP. Additionally, we find
that a relatively haphazard spatial development of the TVP has occurred, with volcanism initially appearing in the Central
TVP and subsequently migrating to both the Eastern and Western TVP regions.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
980.