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   98篇
  免费   0篇
大气科学   9篇
地球物理   18篇
地质学   27篇
海洋学   12篇
天文学   13篇
自然地理   19篇
  2022年   1篇
  2021年   1篇
  2019年   1篇
  2018年   2篇
  2017年   1篇
  2016年   2篇
  2015年   2篇
  2014年   2篇
  2013年   6篇
  2012年   4篇
  2011年   7篇
  2010年   4篇
  2009年   4篇
  2008年   8篇
  2007年   2篇
  2006年   8篇
  2005年   4篇
  2004年   4篇
  2003年   6篇
  2002年   2篇
  2001年   3篇
  1999年   3篇
  1997年   3篇
  1996年   2篇
  1995年   4篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1989年   1篇
  1987年   2篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
排序方式: 共有98条查询结果,搜索用时 17 毫秒
81.
Geothermal energy is classified as a renewable energy source and it utilizes the heat generated in the earth primarily from the natural radioactive decay of isotopes of uranium, thorium and potassium. Heat is extracted from the earth to generate geothermal energy via a carrier, usually water occurring either in the liquid or steam phase. In the late 19th century and the early 20th century, the first developments of geothermal resources for power generation and household heating got underway successfully. Many of these geothermal fields are still being utilized today, proving their sustainability. Today geothermal energy is being utilized in more than 72 countries around the world and of the Nordic countries Iceland and Sweden have been in the forefront in each of their respective fields. While geothermal heat pumps are widely used for space heating in Sweden, geothermal energy covers 55% of the primary energy consumption in Iceland where it is used for space heating, power generation and industrial purposes. Future developments aim at expanding the range of viable geothermal resources by improving the capabilities to generate electricity from geothermal resources at temperatures as low as 100℃, as well as developing geothermal resources where water needs to be introduced, so-called hot dry rock resources. But the biggest expansion is expected to continue to be in the installations of geothermal heat pumps.  相似文献   
82.
ABSTRACT

China’s overseas investment flows (US$ 183 billion) and stock (US$ 4.7 trillion) reached a record peak in 2016, second only to those of the US. A major cause for concern lies in the environmental sustainability of China’s overseas investment portfolio, which is compounded by the lack of transparency of China’s main development finance arms. We intend in this paper to give an update on the magnitude of green finance in China’s overseas investment and development finance portfolio on the basis of the best available estimates, and to put these figures into a broader perspective of multilateral development banks’ commitments and practices to combat climate change. We derive practical policy recommendations that Chinese development banks could take to further align China’s overseas investment with the 2°C target of the Paris Agreement, with the first step being to revise the ‘host country standard’ principle, to ensure that Chinese development banks use the most stringent of the two environmental standards, abroad or at home.

Key policy insights
  • Chinese development banks lend, give or invest between US$ 38 billion and US$ 45 billion every year to developing countries, without either elaborating on, or integrating, the provisions of the Paris Agreement into their investment strategy.

  • Regulations and safeguards are much more stringent for China’s domestic investment than for China’s overseas investment, and this stringency gap has been widening over recent years.

  • As a step towards aligning Chinese overseas investment with the Paris Agreement, Chinese development banks could revise the ‘host country standard principle’. They could instead choose the highest among the two – recipient country or Chinese domestic – in terms of environmental stringency, consequently harmonizing overseas environmental regulation and safeguards with those that apply domestically.

  相似文献   
83.
Biomarkers of exposure and effect of pollutants were analyzed in croakers Micropogonias furnieri (Teleostei: Sciaenidae) captured in winter and summer in a polluted and in a non-polluted site at the Patos Lagoon estuary (Southern Brazil). Catalase and glutathione S-transferase activities (exposure biomarkers) and lipid peroxidation (effect biomarker) were analyzed in liver samples. Other two effect biomarkers were also studied: blood cells DNA damage (through comet assay and micronucleus test) and respiratory burst measurements. In a broad view, results point to an important seasonal variation of the biochemical biomarkers analyzed. However, data obtained clearly indicate that croakers collected in winter at the polluted site were subjected to a level of clastogenic agents sufficient to generate irreversible genetic damages (mutations) and impair the fish immune system.  相似文献   
84.
The aim of the atmospheric nitrogen inputs into the coastal ecosystem (ANICE) project is to improve transport–chemistry models that estimate nitrogen deposition to the sea. To achieve this, experimental and modelling work is being conducted which aims to improve understanding of the processes involved in the chemical transformation, transport and deposition of atmospheric nitrogen compounds. Of particular emphasis within ANICE is the influence of coastal zone processes. Both short episodes with high deposition and chronic nitrogen inputs are considered in the project. The improved transport–chemistry models will be used to assess the atmospheric inputs of nitrogen compounds into the European regional seas (the North Sea is studied as a prototype) and evaluate the impact of various emission reduction strategies on the atmospheric nitrogen loads. Assessment of the impact of atmospheric nitrogen on coastal ecosystems will be based on comparisons of phytoplankton nitrogen requirements, other external nitrogen inputs to the ANICE area of interest and the direct nitrogen fluxes provided by ANICE. Selected results from both the experimental and modelling components are presented here. The experimental results show the large spatial and temporal variability in the concentrations of gaseous nitrogen compounds, and their influences on fluxes. Model calculations show the strong variation of both concentrations and gradients of nitric acid at fetches of up to 25 km. Aerosol concentrations also show high temporal variability and experimental evidence for the reaction between nitric acid and sea salt aerosol is provided by size-segregated aerosol composition measured at both sides of the North Sea. In several occasions throughout the experimental period, air mass back trajectory analysis showed connected flow between the two sampling sites (the Weybourne Atmospheric Observatory on the North Norfolk coast of the UK and Meetpost Noordwijk, a research tower at 9 km off the Dutch coast). Results from the METRAS/SEMA mesoscale chemistry transport model system for one of these cases are presented. Measurements of aerosol and rain chemical composition, using equipment mounted on a commercial ferry, show variations in composition across the North Sea. These measurements have been compared to results obtained with the transport–chemistry model ACDEP which calculates the atmospheric inputs into the whole North Sea area. Finally, the results will be made available for the assessment of the impact of atmospheric nitrogen on coastal ecosystems.  相似文献   
85.
The distribution of waiting times between time-neighbouring events for a time series obeying the Omori law is examined theoretically and numerically with the aim of understanding the characteristics of these distributions, how these characteristics change (e.g. scale) with the parameters of the Omori series, and thus how empirical waiting time data may be correctly interpreted. It is found that the waiting time distribution, for a single Omori aftershock sequence, consists in general of two power law segments followed by a rapid decay at larger waiting times. The analyses are illustrated using real data from the SIL network on Iceland. This data often shows characteristics predominantly consistent with the Omori law, but there are significant exceptions. We conclude that waiting time distributions and related statistical analysis has meaningful potential for the analysis of earthquake data sets, as a step towards developing physical models of the earthquake process.  相似文献   
86.
87.
88.
Novotný  O.  Grad  M.  Lund  C.-E.  Urban  L. 《Studia Geophysica et Geodaetica》1997,41(1):15-28
Experimental dispersion curves of Rayleigh and Love waves along the Uppsala-Prague profile have been determined using records of several Italian earthquakes. To interpret the dispersion data, results of previous geophysical investigations in this region were first analyzed. Seven blocks of the crust and upper mantle were distinguished along the profile on the basis of deep seismic sounding and other seismic data. Layered models were proposed for these blocks. Computation of Rayleigh and Love waves shows a large differentiation of theoretical dispersion curves for the northern (Precambrian) and southern (Palaeozoic) part of the profile. A laterally inhomogeneous model for theUppsala - Prague profile, composed of the seven blocks, satisfies the surface wave data for the profile. Moreover, a mean layered model for the whole profile has also been proposed.  相似文献   
89.
90.
Hypotheses about the influence of surface shape, landscape unit and vegetation cover on gravel dispersion were tested on a shallowly dissected portion of a low-sloping granite pediment in the East Mojave Desert of California. Painted gravels (2 to 20 mm diameter) were placed at 117 nodes on a 6m × 3m grid. Gravel movements were recorded after 9.7 cm of precipitation over a four-month period. Vectors indicating the magnitude and direction of gravel movement were longest for summits (24 cm, 34 nodes observed) and shortest for backslopes (14 cm, 27 nodes observed). Gravels beneath shrub canopies were protected significantly from rainsplash transport. To describe dispersion symmetry, eccentricity values were calculated using a ratio of variances of major and minor axes of an ellipse. Mean eccentricity values ranged from about 3 to 250 with dispersion on summits being the most symmetrical and dispersion in washes being the most elongated. Erosion is the most important soil- and pediment-modifying process at upper elevations of the Granite Cove Pediment which is cut off from sediment additions because of washes incised at the base of the mountain front. Copyright © 1999 John Wiley & Sons, Ltd.  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