全文获取类型
收费全文 | 179篇 |
免费 | 0篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 2篇 |
地球物理 | 83篇 |
地质学 | 54篇 |
海洋学 | 14篇 |
天文学 | 7篇 |
自然地理 | 9篇 |
出版年
2012年 | 7篇 |
2011年 | 9篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 16篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 3篇 |
排序方式: 共有182条查询结果,搜索用时 15 毫秒
71.
72.
73.
Natural attenuation of septic system nitrogen by anammox 总被引:1,自引:0,他引:1
Robertson WD Moore TA Spoelstra J Li L Elgood RJ Clark ID Schiff SL Aravena R Neufeld JD 《Ground water》2012,50(4):541-553
On-site disposal of sewage in septic systems can lead to groundwater plumes with NO(3)(-)-N concentrations exceeding the common drinking water limit of 10 mg/L. Currently, denitrification is considered as the principal natural attenuation process. However, at a large seasonal-use septic system in Ontario (256 campsites), a suboxic zone exists where nitrogen removal of up to 80% occurs including removal of NH(4)(+)-N. This zone has both NO(3)(-)-N and NH(4)(+)-N at >5 mg/L each. In the distal NH(4)(+)-rich zone, NH(4)(+)-N concentrations (8.1 ± 8.0 mg/L) are lower than in the proximal zone (48 ± 36 mg/L) and NH(4)(+)-N is isotopically enriched (concentration-weighted mean δ(15)N of +15.7‰) compared to the proximal zone (+7.8‰). Furthermore, δ(15)N-NH(4)(+) isotopic enrichment increases with depth in the distal zone, which is opposite to what would result if nitrification along the water table zone was the mechanism causing NH(4)(+) depletion. Bacterial community composition was assessed with molecular (DNA-based) analysis and demonstrated that groundwater bacterial populations were predominantly composed of bacteria from two Candidatus genera of the Planctomycetales (Brocadia and Jettenia). Together, these data provide strong evidence that anaerobic ammonium oxidation (anammox) plays an important role in nitrogen attenuation at this site. 相似文献
74.
The environmental threat from oil spills remains significant across the globe and particularly in regions of high oil production and transport such as the Gulf. The ultimate damage caused can be limited by mitigation actions that responders deploy. The responsible and appropriate use of oil spill treatment products (e.g. dispersants, sorbents etc.) can offer response options that can result in substantial net environmental benefit. However, the approval and choice of what products to use needs careful consideration. The United Kingdom has had in place a statutory approval scheme for oil spill treatment products for 30 years. It is based on measures of efficiency and environmental acceptability. Two toxicity tests form an integral part of the assessment, the Sea test and the Rocky Shore test, and work on the premise that approved products will not make the situation significantly worse when added to spilled oil. This paper outlines the UK approach and how its rationale might be applied to the approval of products specific for the Gulf region. Issues such as species choice, higher temperatures and salinity and regional environmental conditions are considered. 相似文献
75.
Several biotic indices have been proposed for the assessment of the ecological status of benthic macroinvertebrates in marine waters, although none have been generally accepted. When it comes to assessing highly stressed natural environments, such as estuaries, the controversy and uncertainty is much higher than for any given normal index. In this article, we test the behavior and suitability of different biotic indices proposed under the perspective of the Water Framework Directive (S, H, AMBI, M-AMBI, BQI, W-statistic, Taxonomic distinctness) for the assessment of estuaries in northern Spain. The low species richness and dominance of a few tolerant species in the characteristic community of these estuaries presented a challenge to the application of the biotic indices tested. Combined approaches that integrate different aspects of water quality and ecosystem functionality could increase the reliability of the ecological assessment of these transitional waters. 相似文献
76.
洪水预报中的不确定性是由作为输入的降水观测和预报的误差所决定的。误差大小受雨量计站网密度(大多与天气雷达联合运用),降水强度和所采用的降水预报方法的影响。在不更颠南部,采用一种经验方法来量化降水观测及预报的不确定性性,数据由两个密集的雨量计站网和天气雷达共同提供。降水不确定性对洪水预报的影响,通过在伦敦附近的泰晤士流域一个综合实验研究进行了检验。此项研究就模型和流域对洪水预报不确定性的相地影响也很 相似文献
77.
78.
79.
80.
Pryor RJ 《Population geography : a journal of the Association of Population Geographers of India》1981,3(1-2):57-68
The relationships between migration trends and changes in socioeconomic structures, settlement systems, and regional development programs in developing countries are analyzed. Current and possible future trends in urbanization in Southeast Asia are summarized, with a focus on the effects of migration. The impact of internal migration on spatial distibution in Thailand, Malaysia, Indonesia, and the Philippines is examined. The need for taking cultural traditions into consideration in the formulation of population policies and programs is emphasized. 相似文献