首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   432篇
  免费   32篇
  国内免费   40篇
测绘学   75篇
大气科学   37篇
地球物理   43篇
地质学   133篇
海洋学   35篇
天文学   5篇
综合类   26篇
自然地理   150篇
  2023年   3篇
  2022年   6篇
  2021年   8篇
  2020年   13篇
  2019年   16篇
  2018年   4篇
  2017年   21篇
  2016年   18篇
  2015年   20篇
  2014年   24篇
  2013年   42篇
  2012年   24篇
  2011年   34篇
  2010年   19篇
  2009年   27篇
  2008年   16篇
  2007年   36篇
  2006年   22篇
  2005年   17篇
  2004年   18篇
  2003年   13篇
  2002年   14篇
  2001年   12篇
  2000年   10篇
  1999年   7篇
  1998年   6篇
  1997年   7篇
  1996年   3篇
  1995年   5篇
  1994年   3篇
  1993年   2篇
  1992年   5篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1985年   4篇
  1984年   8篇
  1983年   1篇
  1982年   1篇
  1954年   1篇
排序方式: 共有504条查询结果,搜索用时 125 毫秒
41.
Three dispersion measures of a random variable, i.e., the standard deviation, the mean deviation (MD) about the mean and the second L-moment, are analyzed in terms of their properties and mutual relationships. Emphasis is placed on the MD, as it is less recognized than two other dispersion measures. The relationships between the dispersion measures are derived for distributions commonly applied in flood frequency analysis (FFA). For distributions that are unbounded, there is a distribution-dependent constant value of the ratio of dispersion measures, or equivalently of respective coefficients of variation. For two-parameter distributions that are lower-bounded, the relationship between the coefficients of variation is also distribution dependent and is not linear. For lower-bounded three-parameter distributions, the dispersion measure ratios, or equivalently the ratios of coefficients of variation, depend on the coefficient of skewness and show a strong distributional dependence. For selected distributions, the three dispersion measures are compared both in terms of the robustness to the largest samples element and the accuracy of upper quantile estimation. The MD statistics may be highly competitive to the two other dispersion measure statistics if applied in FFA for parameters estimation.  相似文献   
42.
周兰云  尚艳丽  马传顺 《地下水》2006,28(2):53-54,57
为合理开发利用地下水资源提供科学依据,确保地下水资源可持续利用,防止由于超采地下水而诱发环境危害,对泰安市世行贷款二期项目区地下水动态变化规律、水资源的分布特征进行了分析研究,提出了地下水合理开发利用的建议.  相似文献   
43.
International labor migration is produced and patterned through the activities of government and private institutions, such as labor recruiters and government officials. Recently, labor recruitment agencies have utilized the World Wide Web as a means of facilitating the procurement of foreign employment contracts. The purpose of this research is to examine the institutional usage of the Web as a means to facilitate the global flow of labor. Based on a qualitative assessment of 27 recruitment-related Web sites, I suggest that Web-based recruitment reinforces global patterns of gendered, racial, and occupational segregation. Moreover, Web-based recruitment offers the potential for revolutionizing patterns and processes of international labor migration.  相似文献   
44.
周世健  陈永奇 《测绘工程》1998,7(3):23-28,33
变形体的变形模式确定的情况下,应用灵敏度准则进行监测网的设计;根据Tayor展式,导出了监测网顾及灵敏度准则的二类设计模型,并对其解算及模拟算例加以说明。  相似文献   
45.
1981年以来对察尔汗盐湖三次渗漏试验结果表明,盐田渗漏是盐田土层与外界条件综合作用的结果,在盐田建设和生产管理过程中,应结合不同地点的土层特性、工程地质条件和其它有关条件,采取不同的处理措施。  相似文献   
46.
When two vessels are moored side-by-side with a narrow gap between them, intense free surface motions may be excited in the gap as a result of complex hydrodynamic interactions. These influence the motions of the two vessels, and the forces in any moorings. The present paper uses first and second order wave diffraction analysis to investigate this phenomenon. Key theoretical aspects of the numerical analysis are first summarised, including the vital need to suppress “irregular frequency” effects; and results are given to validate the code used. The case of a tanker alongside a large floating FLNG barge is then considered in detail.  相似文献   
47.
Coastal freshwater and tidal wetland habitats are being transformed as a result of increasing demand for commercial, residential and tourism activities. The consequence is a habitat seascape complex, comprising a mosaic of natural and engineered coastal features. This study used the freely available mapping tool (Google Earth) to define the extent of coastal engineering structures in the Great Barrier Reef World Heritage Area (GBR; Australia), a marine ecosystem of global biodiversity and cultural significance. Continuing threats to the heritage estate concomitant with expanding urban and industrial developments has raised concerns directed at the future conservation and resilience of the reef ecosystems, along with maintaining expected human lifestyles and livelihoods it provides. The data here shows that break walls and pontoons/jetties dominate development, contributing to approximately 10% (equivalent) of the coastline linear length. Most (60%) development occurs along the coastline or within the first few kilometres upstream along estuaries. While conservation and protection of natural coastal habitats is still preferred for the objective of fisheries production and biodiversity, managers must consider seascape implication/benefits more broadly when approving new marine infrastructure rather than a case-by-case approach which further contributes to an ad hoc mosaic seascape of natural and engineered habitats. Not only within the GBR heritage estate, but more broadly, coastal managers need to regard wider seascape connectivity processes during the assessment of any new development. There is an urgent need for policy and planning instrument reform that is inclusive of accumulative impacts of urban and industrial development in this heritage estate. Opportunities to include eco-friendly (green engineering) solutions, in the repair and revitalisation of existing artificial structures, is necessary in any new proposed urban and industrial development and expansion.  相似文献   
48.
天地图·河南是"天地图"的有机组成部分保质保量实现天地图.河南影像数据一年更新两次目标,需要研究如何快速处理影像数据,提高工作效率,有必要从软件与硬件应用两个方面探讨影像数据处理关键技术。  相似文献   
49.
The role of intellectual property rights (IPRs) in the development and transfer of climate change technologies has been a contentious issue in negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). Irreconcilable differences seem to oppose those who believe IPRs are an inherent barrier to the transfer of climate change technologies and those who argue they are an essential incentive to innovation. After providing an overview of the polarized debate on this issue, this article reviews the existing literature and empirical evidence and looks into some practical initiatives and recent developments. Finally, it seeks to identify a way forward that could help overcome the current stalemate in international deliberations by suggesting a number of parameters to structure the discussion on this complex issue.  相似文献   
50.
驳施雅风“冰臼”“负球状风化”成因论   总被引:2,自引:0,他引:2  
韩同林 《地质论评》2010,56(4):538-542
施雅风院士最近撰文指出笔者等近年来在中国东部发现的若干"冰臼"并非冰川遗迹,而是花岗岩经"负球状风化"而成。然而,他所谓的"负球状风化说"与当地的气候环境条件和客观存在的事实完全相悖。冰臼是地表负地形之一,现今是"堆积区"而不是"侵蚀区",以现代常见的侵蚀作用产生冰臼的所谓"风说"、"壶说"、"风雨说"、"差异风化说"、"负球状风化"等,都是不可能的。这些假说是对过去业己形成冰臼群进行不同成因推断,是对冰臼群成因的最大误解。冰臼只能由大量冰川融水沿冰川裂隙自上向下,以滴水穿石的方式形成滚流水钻,强烈冲击下伏基岩产生。从河流流水动力学特点上看,急流旋涡主要产生水平力为主,而冰臼的形成主要是垂直力才有可能产生,因此河流流水也是无法产生冰臼的。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号