全文获取类型
收费全文 | 106篇 |
免费 | 2篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 12篇 |
地球物理 | 24篇 |
地质学 | 25篇 |
海洋学 | 19篇 |
天文学 | 3篇 |
自然地理 | 22篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 18篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有108条查询结果,搜索用时 15 毫秒
91.
Downscaling precipitation extremes 总被引:1,自引:1,他引:0
Rasmus E. Benestad 《Theoretical and Applied Climatology》2010,100(1-2):1-21
92.
Rasmus Heltberg Paul Bennett Siegel Steen Lau Jorgensen 《Global Environmental Change》2009,19(1):89-99
This paper presents and applies a conceptual framework to address human vulnerability to climate change. Drawing upon social risk management and asset-based approaches, the conceptual framework provides a unifying lens to examine links between risks, adaptation, and vulnerability. The result is an integrated approach to increase the capacity of society to manage climate risks with a view to reduce the vulnerability of households and maintain or increase the opportunities for sustainable development. We identify ‘no-regrets’ adaptation interventions, meaning actions that generate net social benefits under all future scenarios of climate change and impacts. We also make the case for greater support for community-based adaptation and social protection and propose a research agenda. 相似文献
93.
94.
Geochemical processes and solute transport at the seawater/freshwater interface of a sandy aquifer 总被引:2,自引:0,他引:2
Martin Søgaard Andersen Vibeke Nyvang Rasmus Jakobsen Dieke Postma 《Geochimica et cosmochimica acta》2005,69(16):3979-3994
Geochemical processes occurring at a seawater/freshwater interface were studied in a shallow coastal siliclastic aquifer containing minor amounts of calcite. Data were collected from 106 piezometers in a 120-m transect from the coastline and landward. In the first 40 m from the coastline, a wedge of saltwater is intruding below the freshwater aquifer. The aquifer is strongly reduced with mineralization of organic matter by methanogenesis in the freshwater aquifer, and sulfate reduction dominating in the most seaward part of the saline aquifer. The spatial separation of cations in the aquifer indicated a slow freshening process where Ca2+ from freshwater displaced the marine cations Na+ and Mg2+ from the exchanger complex. The resulting loss of Ca2+ from solution decreases the saturation state for calcite and possibly causes calcite dissolution. A storm-flooding event was recorded where pulses of dense seawater sank through the fresh aquifer. As a result, the terminal electron accepting process switched from methanogenesis to sulfate reduction. The pulses of sinking seawater also triggered cation exchange reactions where Ca2+ was expelled from the exchanger by seawater Na+ and Mg2+. The released Ca2+ is being flushed from the aquifer by groundwater flow, and this export of Ca2+ will, in the long term, cause decalcification of the sediment. The water composition in the aquifer is in a transient state as the result of various processes that operate on different timescales. Oxidation of organic matter occurs continuously but at a rate decreasing on a geological time scale. The freshening of the aquifer operates on the timescale of a few years. The episodic flooding and sinking of seawater through the aquifer proceeds in the course of days to weeks, but occurs irregularly with years in between. 相似文献
95.
S.J. Warren P. Møller S.M. Fall P. Jakobsen 《Monthly notices of the Royal Astronomical Society》2001,326(2):759-773
We are engaged in a programme of imaging with the STIS and NICMOS (NIC2) instruments aboard the Hubble Space Telescope ( HST ), to search for the galaxy counterparts of 18 high-redshift z >1.75 damped Ly α absorption lines and five Lyman-limit systems seen in the spectra of 16 target quasars. This paper presents the results of the imaging campaign with the NIC2 camera. We describe the steps followed in reducing the data and combining in mosaics, and the methods used for subtracting the image of the quasar in each field, and for constructing error frames that include the systematic errors associated with the PSF subtraction. To identify candidate counterparts, which are either compact or diffuse, we convolved the image and variance frames with circular top-hat filters of diameter 0.45 and 0.90 arcsec respectively, to create frames of summed S /N within the aperture. For each target quasar we provide catalogues listing positions and aperture magnitudes of all sources within a square of side 7.5 arcsec centred on the quasar, detected at S / N >6 . We find a total of 41 candidates, of which three have already been confirmed spectroscopically as the counterparts. We provide the aperture magnitude detection limits as a function of impact parameter, for both detection filters, for each field. The average detection limit for compact (diffuse) sources is H AB =25.0 (24.4) at an angular separation of 0.56 (0.79) arcsec from the quasar, improving to H AB =25.5 (24.8) at large angular separations. For the brighter sources we have measured the half-light radius and the n parameter of the best-fitting deconvolved Sersic-law surface brightness profile, and the ellipticity and orientation. 相似文献
96.
Steve W. Lyon Rasmus S⊘rensen Johan Stendahl Jan Seibert 《International journal of geographical information science》2013,27(5):723-740
Interpolation of point measurements using geostatistical techniques such as kriging can be used to estimate values at non-sampled locations in space. Traditional geostatistics are based on the spatial autocorrelation concept that nearby things are more related than distant things. In this study, additional information was used to modify the traditional Euclidean concept of distance into an adjusted distance metric that incorporates similarity in terms of quantifiable landscape characteristics such as topography or land use. This new approach was tested by interpolating soil moisture content, pH and carbon-to-nitrogen (C:N) ratio measured in both the mineral and the organic soil layers at a field site in central Sweden. Semivariograms were created using both the traditional distance metrics and the proposed adjusted distance metrics to carry out ordinary kriging (OK) interpolations between sampling points. In addition, kriging with external drift (KED) was used to interpolate soil properties to evaluate the ability of the adjusted distance metric to incorporate secondary data into interpolations. The new adjusted distance metric typically lowered the nugget associated with the semivariogram, thereby better representing small-scale variability in the measured data compared to semivariograms based on the traditional distance metric. The pattern of the resulting kriging interpolations using KED and OK based on the adjusted distance metric were similar because they represented secondary data and, thus, enhanced small-scale variability compared to traditional distance OK. This created interpolations that agreed better with what is expected for the real-world spatial variation of the measured properties. Based on cross-validation error, OK interpolations using the adjusted distance metric better fit observed data than either OK interpolations using traditional distance or KED. 相似文献
97.
Barry W. Brook Kingsley Edney Rafaela Hillerbrand Rasmus Karlsson 《Climate Policy》2016,16(6):803-813
We propose that an international ‘Low-Emissions Technology Commitment’ should be incorporated into the United Nations Framework Convention on Climate Change (UNFCCC) negotiation process in order to promote innovation that will enable deep decarbonization. The goal is to accelerate research, development, and demonstration of safe, scalable, and affordable low-emissions energy technologies. Such a commitment should be based on three elements. First, it should operate within existing UNFCCC negotiations so as to encourage developed states to offer directed funding for energy research as part of their national contributions. Second, pledges should be binding, verifiable, and coordinated within an international energy-research plan. Third, expert scientific networks and participating governments should collaborate to design a coordinated global research and technology-demonstration strategy and oversee national research efforts. To this end an Intergovernmental Panel on Low-Emissions Technology Research might be established. This proposal offers some insurance against the risk that the political impasse in international negotiations cannot be overcome. The higher costs associated with low-emissions alternatives to fossil fuels currently creates significant economic and political resistance to their widespread adoption. To breach this impasse, a mechanism supporting accelerated energy research is needed that seeks to reduce future abatement costs, share experience and ‘learning-by-doing’ in first-of-a-kind demonstrations, and thus facilitate future widespread deployments. These actions will also assist in addressing inequalities in energy access.Policy relevanceOver the past decade, global fossil-fuel use and associated carbon emissions have risen steadily, despite the majority of nations agreeing, in principle, to work to limit global warming to less than 2?°C above pre-industrial conditions (IPCC, 2014). Accelerated research, development, and demonstration of low-emissions technologies will be required for successful and economically efficient decarbonization of the global economy, but how can the current deadlock be broken? The UNFCCC does not contain adequate mechanisms to promote increased investment in research, so climate-governance institutions are not capturing the gains that could be achieved through a globally coordinated approach. Here, we outline reform proposals that would enhance both the economic effectiveness of global abatement efforts and the political feasibility of accelerated innovation. 相似文献
98.
Mapping of glaciotectonic deformation in an ice marginal environment with ground penetrating radar 总被引:1,自引:0,他引:1
A series of closely spaced parallel ground penetrating radar (GPR) profiles of glaciotectonic deformed glacio-fluvial sediments have been obtained in an ice marginal environment in Northwest Zealand, Denmark. The radar profiles can be differentiated into several radar facies with distinct reflection characteristics. The lithology and depositional environment of the radar facies is interpreted by correlation with information from profiles in gravel pits, geological maps and drill hole data. The radar facies include glaciotectonically disturbed glacio-fluvial sediments, sediments deposited penecontemporaneously with the deformations and sediments deposited post-tectonically. Several thrust planes with dip angles between 25° and 30° as well as major folds and minor faults have been interpreted from the GPR data. The deformation style of the deformed glacio-fluvial sediments is a thin-skinned pro-glacial thrust complex, with associated folding. The deformations have resulted in the present ridge morphology seen in the rim of the composite ridge. Syn- and post-tectonic sediments are deposited on top and in front of the deformed sediments, smoothing the ridge relief created by the thin-skinned thrust complex. A structural geological map constructed from the ground penetrating radar data reveals the extension of the individual radar facies in the thrust complex. Tectonic features such as thrust planes and folds can be followed throughout the mapped area. 相似文献
99.
Jens Jakobsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):103-114
Geografisk Tidsskrift, Danish Journal of Geography 106(2): 103–114, 2006 Periods characterized by agricultural change and transitions are often associated with insecurity and vulnerability regarding food production and food supplies. Forests and forest products tend to play an important buffer role during the process of change and uncertainty, where forest and fallows provide food products or income that people can temporarily fall back on. In the upland village of Que in North Central Vietnam, several different drivers are currently changing land use and land cover. The Forest Land Allocation policy, implemented in 1998, is one of the major driving forces, allocating farmers a reduced area of land for shifting cultivation in order to prevent any further deforestation and land degradation. However, the reduction in agricultural land set aside for shifting cultivation has lead to a severe decrease in hill rice production. The land use system is in a transition phase—from a conventional shifting cultivation system to a composite swiddening system. The area under shifting cultivation has been reduced, and the system has been intensified via the introduction of paddy rice cultivation, increased livestock rearing and commercial exploitation of non-timber forest products (NTFPs). Yet, the current transformation of the system has resulted in a drastic reduction in overall rice production. Thus, the collection and selling of NTFPs such as bamboo shoots, broom grass and pherynium leaves seem to prevent severe shortage of food since farmers are able to purchase food products with the money generated from the selling of NTFPs. 相似文献
100.
R. Agersborg M. Jakobsen B. O. Ruud T. A. Johansen 《Studia Geophysica et Geodaetica》2007,51(1):89-118
An effective medium model for the stress-dependent seismic properties of fractured reservoirs is developed here on the basis
of a combination of a general theory of viscoelastic waves in rock-like composites with recently published formulae for deformation
of communicating and interacting cavities (interconnected pores/cracks and fractures at finite concentration) under drained
loading. The inclusion-based model operates with spheroidal cavities at two different length scales; namely, the microscopic
scale of the pores and (grain-boundary) cracks, and the mesoscopic scale of the fractures (controlling the flow of fluid).
The different cavity types can in principle have any orientation and aspect ratio, but the microscopic pores/cracks and mesoscopic
fractures were here assumed to be randomly and vertically oriented, respectively. By using three different aspect ratios for
the relatively round pores (representing the stiff part of the pore space) and a distribution of aspect ratios for the relatively
flat cracks (representing the compliant part of the pore space), we obtained a good fit between theoretical predictions and
ultrasonic laboratory measurements on an unfractured rock sample under dry conditions. By using a single aspect ratio for
the mesoscopic fractures, we arrived at a higher-order microstructural model of fractured porous media which represents a
generalization of the first-order model developed by Chapman et al. (2002,2003). The effect of cavity size was here modelled
under the assumption that the characteristic time for wave-induced (squirt) flow at the scale of a particular cavity (pore/crack
vs. fracture) is proportional with the relevant scale-size. In the modelling, we investigate the effect of a decreasing pore
pressure with constant confining pressure (fixed depth), and hence, increasing effective pressure. The analysis shows that
the attenuation-peak due to the mesoscopic fractures in the reservoir will move downward in frequency as the effective pressure
increases. In the range of seismic frequencies, our modelling indicates that the P-wave velocities may change by more than
20% perpendicular to the fractures and close to 10% parallel to the fractures. In comparison, the vertical S-wave velocities
change by only about 5% for both polarization directions (perpendicular and parallel to the fractures) when the effective
pressure increases from 0 to 15 MPa. This change is mainly due to the overall change in porosity with pressure. The weak pressure
dependence is a consequence of the fact that the S waves will only sense if the fractures are open or not, and since all the
fractures have the same aspect ratio, they will close at the same effective pressure (which is outside the analysed interval).
Approximate reflection coefficients were computed for a model consisting of the fractured reservoir embedded as a layer in
an isotropic shale and analysed with respect to variations in Amplitude Versus Offset and aZimuth (AVOZ) properties at seismic
frequencies for increasing effective pressure. For the P-P reflections at the top of the reservoir, it is found that there
is a significant dependence on effective pressure, but that the variations with azimuth and offset are small. The lack of
azimuthal dependence may be explained from the approximate reflection coefficient formula as a result of cancellation of terms
related to the S-wave velocity and the Thomson’s anisotropy parameter δ. For the P-S reflection, the azimuthal dependence
is larger, but the pressure dependence is weaker (due to a single aspect ratio for the fractures).
Finally, using the effective stiffness tensor for the fractured reservoir model with a visco-elastic finite-difference code,
synthetic seismograms and hodograms were computed. From the seismograms, attenuation changes in the P wave reflected at the
bottom of the reservoir can be observed as the effective pressure increases. S waves are not much affected by the fractures
with respect to attenuation, but azimuthal dependence is stronger than for P waves, and S-wave splitting in the bottom reservoir
P-S reflection is clearly seen both in the seismograms and hodograms. From the hodograms, some variation in the P-S reflection
with effective pressure can also be observed. 相似文献