全文获取类型
收费全文 | 406篇 |
免费 | 257篇 |
国内免费 | 152篇 |
专业分类
测绘学 | 28篇 |
大气科学 | 5篇 |
地球物理 | 23篇 |
地质学 | 684篇 |
海洋学 | 28篇 |
天文学 | 3篇 |
综合类 | 26篇 |
自然地理 | 18篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 26篇 |
2020年 | 33篇 |
2019年 | 29篇 |
2018年 | 28篇 |
2017年 | 24篇 |
2016年 | 36篇 |
2015年 | 23篇 |
2014年 | 27篇 |
2013年 | 44篇 |
2012年 | 41篇 |
2011年 | 41篇 |
2010年 | 28篇 |
2009年 | 31篇 |
2008年 | 13篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 24篇 |
2004年 | 29篇 |
2003年 | 21篇 |
2002年 | 33篇 |
2001年 | 25篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有815条查询结果,搜索用时 31 毫秒
1.
Deborah F. Shmueli 《Geoforum》2008,39(6):2048-2061
When applied to environmental concerns, framing offers a rigorous conceptual and analytic approach with potentially practical significance for dealing with complex issues relevant to geography. The purpose of this article is to introduce framing concepts, typology and modes of analysis to address issues which geographers commonly treat: disputes over land ownership and uses, competition for water resources, cultural clashes over control of territory and resources and the impact of spatial patterns and structures when siting noxious sites. Framing analysis is applied to three cases of environmental conflict in Israel and, more generally, for understanding conflicts revolving around the management of human habitats in relation to the physical environment. 相似文献
2.
3.
ABSTRACT Environmental sustainability and the long-term wellbeing of Māori (the indigenous people of New Zealand) are interdependent and degradation of landscapes risks the progressive degradation of Māori wellbeing. The present study developed an analysis framework based on Ki Uta Ki Tai (holistic-mountains to the sea- management philosophy advocated by Ngāi Tahu) for exploring relationships between landcover and Māori values to enable predictions of cultural values through space and time. We used this framework to predict how two Māori values (Overall Health and Cultural Land Use) have been altered as a result of landcover change between 2001–2012 in three Canterbury catchments. The area of native vegetation declined while exotic pasture increased between 2001–2012, and there were corresponding declines in both cultural health scores. These results suggest that the change in landcover has reduced the ability of the landscape to support Māori values. This framework for assessing changes in Māori values with respect to changing environmental conditions may identify opportunities for Māori to better engage in land use management decisions. 相似文献
4.
Extreme value analysis provides a semiparametric method for analyzing the extreme long tails of skew distributions which may be observed when handling mining data. The estimation of important tail characteristics, such as the extreme value index, allows for a discrimination between competing distribution models. It measures the thickness of such long tailed distributions, if only a limited sample is available. This paper stresses the practical implementation of extreme value theory, which is used to discriminate a lognormal from a mixed lognormal distribution in a case study of size distributions for alluvial diamonds. 相似文献
5.
6.
N. V. Chalapathi Rao 《Journal of Earth System Science》2006,115(1):161-183
Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites,
dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic
pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous
but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’
mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in
understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (∼ 1100
Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota
pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite
and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan
and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite
source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting
during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics,
such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is
attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the
asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting
induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper
is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar
occurrences elsewhere. 相似文献
7.
Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system 总被引:1,自引:0,他引:1
O. M. Rosen L. K. Levskii D. Z. Zhuravlev A. Ya. Rotman Z. V. Spetsius A. F. Makeev N. N. Zinchuk A. V. Manakov V. P. Serenko 《Stratigraphy and Geological Correlation》2006,14(6):581-601
Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced. 相似文献
8.
基于线性四叉树的全球离散格网索引 总被引:8,自引:0,他引:8
将四元三角剖分的三角形格网组织成四叉树剖分的菱形块格网,以菱形块单元来进行数据的组织索引,通过线性四叉树成熟的Morton编码作为关键字来标识查找菱形块,并在此基础上经过改进来索引三角形格网、进行邻域搜索。 相似文献
9.
该钻头用于坚硬地层取心。河南油田以往常用园柱聚晶、三角聚晶钻头以及烧结孕镶金刚石钻头,取心效率低、钻速慢、成本高。近两年采用低温电镀孕镶金刚石钻头取心后,平均单筒进尺由原来的4.20m/筒提高到7.62m/筒,平均取心机械钻速由原来的0.21m/h提高到的0.84m/h。该钻头生产工艺完全改变原来高温(1000℃以上)烧结为低温(室温)电镀工艺,极大地避免了金刚石热损伤,采用高强度大颗粒的金刚石,提高了取心机械钻速。 相似文献
10.