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   552篇
  免费   22篇
  国内免费   4篇
测绘学   8篇
大气科学   32篇
地球物理   154篇
地质学   143篇
海洋学   40篇
天文学   152篇
综合类   3篇
自然地理   46篇
  2023年   3篇
  2022年   5篇
  2021年   6篇
  2020年   5篇
  2019年   15篇
  2018年   12篇
  2017年   13篇
  2016年   10篇
  2015年   12篇
  2014年   18篇
  2013年   38篇
  2012年   25篇
  2011年   22篇
  2010年   13篇
  2009年   25篇
  2008年   17篇
  2007年   20篇
  2006年   20篇
  2005年   28篇
  2004年   16篇
  2003年   18篇
  2002年   21篇
  2001年   15篇
  2000年   8篇
  1999年   15篇
  1998年   20篇
  1997年   11篇
  1996年   9篇
  1995年   9篇
  1994年   11篇
  1993年   12篇
  1992年   11篇
  1991年   7篇
  1990年   5篇
  1989年   5篇
  1988年   5篇
  1987年   3篇
  1986年   5篇
  1985年   5篇
  1984年   8篇
  1982年   5篇
  1981年   4篇
  1980年   8篇
  1979年   3篇
  1978年   4篇
  1976年   3篇
  1975年   4篇
  1973年   3篇
  1972年   4篇
  1970年   4篇
排序方式: 共有578条查询结果,搜索用时 15 毫秒
91.
Environmental governance aims to reconcile an expanding set of societal objectives at ever-larger scales despite the challenges that remain in integrating conservation and development at smaller scales. We interrogate Solomon Islands’ engagement in the Coral Triangle Initiative on Coral Reefs, Fisheries and Food Security to contribute new insight on the scalar politics of multi-level marine governance. We show how regional objectives are re-interpreted and prioritized as they translate into national policy and practice. Our data suggest that enhanced coordination of finances and activities, integration of objectives in shared protocols and priority geographies, and a subtle shift in power relations between the state, donors, and implementation partners have resulted from processes of re-scaling. We discuss important procedural adjustments in cross-level and cross-scale governance across jurisdictional, institutional, and sectoral scales. We also reflect on the changing role of national governments in shifts toward large-scale, multi-national initiatives.  相似文献   
92.
93.
94.
The VLBA has been used over a period of four years to study the internal motions within a sample of quasars and AGN. In most sources, features appear to propagate away from the central engine along a well collimated radio jet with apparent transverse velocities between zero and 10c, with some evidence for apparent accelerations and decelerations. The distribution of apparent velocity is not consistent with any simple ballistic model and appears to require either a spread in intrinsic velocity or a difference between the bulk velocity and pattern velocity. The dependence of apparent angular velocity with redshift is consistent with standard Friedmann world models. Further observations of a larger source sample, especially at large redshift may lead to meaningful constraints on world models.  相似文献   
95.
"The panel provided good, solid, interdisciplinary advice on a variety of challenging, state-of-the-art issues."  相似文献   
96.
This column focuses on recent work in Europe. The intent is to present to American readers relevant studies they would not normally see. Much of the following was presented at the 9th International Congress of Pesticide Chemistry last summer in London. The congress was jointly sponsored by the International Union of Pure & Applied Chemistry and the Royal Society of Chemistry.  相似文献   
97.
This study compares the geochemical response of stream sediments and adjacent vegetation samples, with variations in drainage catchment lithology and the occurrence of mineralisation, within a 14,000-km2 block of the northeastern region of New South Wales, Australia. The area contains a range of lithologies within a Devonian–Permian accretionary complex and Mesozoic sedimentary basin, as well as a wide range of mineral deposits. Sampling was designed to confine each sub-catchment to a single lithological group (mafic and ultramafic rocks, acid intrusives, volcanics, metasedimentary and sedimentary rocks or alluvium). Leaves of over 20 genera, dominated by (Allo-)Casuarina, Eucalyptus, Acacia, Callistemon and Melaleuca, and the <250-μm fraction of the stream sediments were analysed by INAA. The uptake of most trace elements varied between genera, with Callistemon displaying the highest median As and La contents and Eucalyptus the highest Co contents. The stream sediment and vegetation geochemistry reflect both hydromorphic and mechanical dispersion within sub-catchments, with regional patterns dominant over local influences. The vegetation appears to be influenced to a greater extent by hydromorphic dispersion, as indicated by differences in the ratio of leaf to sediment Cr concentrations in sub-catchments draining serpentinites and basalts. Although most known mineral deposits in the region produced anomalies in at least one medium, there was little correlation between the trace element concentrations of the vegetation and stream sediments on a site-by-site basis. A number of Au targets were only detected on the basis of the biogeochemistry and others were only reflected in the stream sediment geochemistry. In general, vegetation displayed more extensive dispersion trains away from mineralisation than did the stream sediments. Differences in the response of the two sampling media suggest their joint use in exploration or environmental surveys to maximise the probability of detecting mineralisation.  相似文献   
98.
Fuentes  William  Wichtmann  Torsten  Gil  Melany  Lascarro  Carlos 《Acta Geotechnica》2020,15(6):1513-1531
Acta Geotechnica - The hypoplastic model for sands proposed by Wolffersdorff (Mech Cohes Frict Mater 1: 251–271, 1996) combined with the intergranular strain anisotropy by Fuentes and...  相似文献   
99.
Geochemical patterns from two lag anomalies in the Cobar region of central New South Wales are described. The region is semi-arid, deeply weathered and some areas are covered by variable thicknesses of aeolian and alluvial transported overburden.Lag morphology and mineralogy are related to landform. In erosional landforms the surface is covered by lag, which is composed of coarse fragments derived locally from bedrock and displays varying degrees of ferruginization, together with a range of secondary pisoids. In depositional landforms the lag is less abundant and contains more pisoids. Deflation by sheetwash may lead to lag being partially buried by alluvium. In a large proportion of pisoid lag, hematite and goethite have been converted to maghemite, allowing ready separation into magnetic and non-magnetic fractions. The non-magnetic fraction is dominated by the lithic lag whereas the magnetic fraction is dominated by pisoid lag.The magnetic and non-magnetic components of the 2–11 mm lag fraction, milled to < 75 μm and subjected to HF-HNO3-HClO4 attack, give rise to distinct geochemical patterns at targets related to a variant of the Cobar style of Pb-Zn mineralization with variable silicification and to Zn mineralization in a swarm of quartz and carbonate veinlets. The patterns are influenced by metal source, lag type, surface chemical conditions and landtbrm. Differences in the correlation between metal contents in the magnetic and non-magnetic lag components, and between trace elements and Fe. indicate variable loss of Cu and Zn from the magnetic lag at some targets but retention of Pb. The presence of a readily cxtractable base metal component in the lag has implications for detecting anomalies in transported cover in the region.  相似文献   
100.
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