全文获取类型
收费全文 | 421篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 25篇 |
地球物理 | 66篇 |
地质学 | 168篇 |
海洋学 | 28篇 |
天文学 | 101篇 |
综合类 | 1篇 |
自然地理 | 49篇 |
出版年
2021年 | 7篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 18篇 |
2012年 | 17篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 20篇 |
2007年 | 20篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 14篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1968年 | 2篇 |
1934年 | 1篇 |
1882年 | 1篇 |
1877年 | 2篇 |
排序方式: 共有447条查询结果,搜索用时 15 毫秒
81.
The Chaman left‐lateral strike‐slip fault bounds the rigid Indian plate boundary at the western end of the Himalayan‐Tibetan orogen and is marked by contrasting topographic relief. Deformed landforms along the fault provide an excellent record for understanding this actively evolving intra‐continental strike‐slip fault. The geomorphic response of an active transpessional stretch of the Chaman fault was studied using digital elevation model (DEM) data integrated with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible and Near Infrared/Short Wave Infrared (VNIR/SWIR) and images from GeoEye‐1. Geologic and geomorphic mapping helped in reconstructing the Late Quaternary landscape history of this transpessional strand of the Chaman strike‐slip fault and the associated Spinatizha thrust fault in western Pakistan. Topographic analysis of a part of the transpression (the thrust bounded Roghani ridge) revealed northward growth of the Spinatizha fault with the presence of three water gaps and two corresponding wind gaps. Geomorphic indices including stream length‐gradient index, mountain front sinuosity, valley floor width to valley height ratios, and entrenchment of recent alluvial fan deposits were used to define the lateral growth and direction of propagation of the Spinatizha fault. Left‐lateral displacement along Chaman fault and uplift along the Spinatizha fault was defined using topographic analysis of the Roghani ridge and geomorphic mapping of an impressive alluvial fan, the Bostankaul fan. The landforms and structures record slip partitioning along the Indian plate boundary, and account for the convergence resulting from the difference in the Chaman fault azimuth and orientation of the velocity vector of the Indian plate. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
82.
This paper assesses how far community led rural visions accord with the current thrust of rural planning policy delivery in
the UK. Adapting conventional visioning methods, qualitative techniques were used on eight different communities across urban,
exurban and rural Wales to elicit views relating to the kind of local countryside(s) that were desired. The results show that
the communities’ visions reflect an emerging consensus around local countryside priorities: multifunctionality, integration,
wider countryside protection, development based on need, and local distinctiveness according with the thrust of current planning
policy at national and local levels. However, there is a clear dichotomy between this and the reality of what communities
actually experienced in developments affecting their countryside. Here, universal criticism was encountered over the type,
pace and scale of development, the lack of rural specificity and the failure to take account of local community needs and
priorities. It is hypothesized that tensions between national and local politics and stakeholder power relations are playing
a crucial role in distorting the delivery of town and country planning. It is recommended that rural policy delivery must
become more “joined up” and rural proofed at national and local levels concomitant with a change in the operational culture
of agencies at the forefront of rural delivery. Essentially, effective engagement of top down approaches synergising with
bottom up community led ideas is long overdue. 相似文献
83.
84.
J. Victor Owen Joanna L. Casey John D. Greenough Dorothy Godfrey‐Smith 《Geoarchaeology》2013,28(4):394-411
The mineralogy and bulk chemical compositions of 15 Kintampo (Late Stone Age) potsherds from the Birimi site on the Gambaga Escarpment and eight samples of local sediment were determined with the intent of characterizing these wares and identifying the material used in their manufacture. Sediment from clay pits still used by potters north of the escarpment contains iron‐rich laterite clasts (100 × XFeOt = 100 × FeOt/[FeOt + Al2O3 + SiO2] ≥10). Sedimentary clasts in stream sediments are relatively siliceous and iron‐poor (100 × XFeOt < 10). Bulk geochemical data together with the compositions of lithic clasts (laterite, siltstone/sandstone) link the pottery to sediment sources, including escarpment sediments not presently used by Ghanaian potters. Fresh granite clasts found in some of the sherds were not found in the analyzed sediment samples, although some of their distinctive mineralogical constituents (e.g., variably barian alkali feldspar) are present. The analytical data suggest that pots found at Birimi were made locally by mixing escarpment sediment with clay and stream sediment brought in from below the escarpment. This contrasts with present‐day practice, whereby the pots themselves are imported. The place where Birimi pottery was made and the outcrop source of aluminous sediment (mudstone with an “escarpment” trace element signature) used in these wares, however, remain unidentified. © 2013 Wiley Periodicals, Inc. 相似文献
85.
Hagger JA Jones MB Lowe D Leonard DR Owen R Galloway TS 《Marine pollution bulletin》2008,56(6):1111-1118
To answer the requirement of the European Commission's Water Framework Directive (WFD) for biological-effects endpoints to classify the ecological health of aquatic ecosystems, we propose the biomarker response index (BRI). The BRI, based on a suite of biomarkers at different levels of biological response at the individual level, provides an integrated relative measure of the general health status of coastal invertebrates. Using the BRI, the health of mussels (Mytilus edulis) from 10 estuaries classified by the Environment Agency of England and Wales under the WFD was compared. Eight sites were healthier than predicted and two showed a similar health status to that of the predicted point-source pollution risk classification. Results indicate that the BRI offers a potential measure of organism health that can be used in monitoring under the WFD as an additional aid to reduce uncertainty in defining risk classification and to provide better evidence of existing impact. 相似文献
86.
胶北地块粉子山群石榴云母片岩中石榴石变斑晶内包裹物迹线明显,保留了岩石形成过程中的多期变质变形信息。电子探针成分面扫描图显示石榴石成分环带明显,可分为核部、幔部和边部。石榴石中MgO、FeO、MnO和CaO含量变化特征表明其核部到边部温度先升高后降低,对应进变质及退变质过程。根据原位独居石Y元素成分面扫描图显示,部分独居石颗粒由核部到边部Y含量呈现逐渐降低趋势,说明测得的232.6±1.1Ma~229.5±3.7Ma的独居石U-Pb年龄,对应石榴石的进变质生长过程。结合1869±72Ma的锆石U-Pb年龄数据,可推断粉子山群石榴云母片岩至少经历了古元古代及三叠纪两期变质事件的改造。粉子山群石榴云母片岩卷入了苏鲁超高压变质带的俯冲碰撞造山事件。电子探针成分分析结果表明粉子山群石榴云母片岩中的石榴石属于铁铝榴石,反映出经受中级区域变质作用的特征。说明粉子山群石榴云母片岩虽然参与了三叠纪苏鲁超高压变质带的俯冲碰撞造山过程,但俯冲深度较浅。这可用大陆俯冲过程中上盘的俯冲剥蚀来解释,并可为陆-陆碰撞俯冲剥蚀模式提出的扬子板片在240~220Ma的深俯冲作用过程中拽动胶北地块向下俯冲又折返的运动过程提供佐证,但胶北地块是否经历了深俯冲超高压变质作用,还需要进一步验证。 相似文献
87.
Soil erosion assessment and prediction play critical roles in addressing problems associated with erosion control or soil conservation. The past dynamics of soil erosion can provide valuable information for us to understand the relations of soil erosion to environmental change and anthropogenic activity. The present paper has compared Holocene climatic changes in northwestern China with those in southern Norway, and investigated the past dynamics of erosion activity during the Holocene. Modern soil erosion on the Loess Plateau is a combination of the intensive natural erosion and human-induced erosion, the latter being four times greater than the former. Because of global warming and increasing human activities, climate on the Loess Plateau is becoming dryer and more unstable, causing an enhanced erosion problem and water scarcity. In the arctic-alpine region of southern Norway, however, the global warming and regional wetting caused expansion of the largest European ice cap. This has accentuated the erosion in that region, with a higher frequency of avalanches and debris flows. 相似文献
88.
Erin F. Owen Alan D. Wanamaker Jr. Bernd R. Schöne 《Geochimica et cosmochimica acta》2008,72(19):4687-4698
The relationship between stable isotope composition (δ13C and δ18O) in seawater and in larval shell aragonite of the sea scallop, Placopecten magellanicus, was investigated in a controlled experiment to determine whether isotopes in larval shell aragonite can be used as a reliable proxy for environmental conditions. The linear relationship between δ13CDIC and δ13Caragonite (r2 = 0.97, p < 0.0001, RMSE = 0.18) was:
δ13CDIC=1.15(±0.05)∗δ13Caragonite-0.85(±0.04) 相似文献
89.
Owen J. Furuseth 《The Professional geographer》1997,49(4):391-403
Over the past six years hog farming in North Carolina has undergone a significant restructuring. For most of this century raising hogs was a casual farm activity found throughout the state. During the past decade hog farming has been transformed along industrial-corporate lines. In the process, the swine population has expanded rapidly (exploded) and simultaneously collapsed in geographical bounds (imploded). This paper examines the linkage between the development of the industrial-corporate hog farming regime, the rapid growth in hog populations, and the geographical concentration of hog production in a newly emerging high-density hog production district in the south central area of the Coastal Plain region. 相似文献
90.