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Gerd Wendler Brian Hartmann Chris Wyatt Martha Shulski Henry Stone 《Boundary-Layer Meteorology》2005,117(1):131-148
During a ship voyage from Tasmania to Antarctica in summer 2000/01, radiative and meteorological measurements were continuously
made, from which the surface energy budget was calculated. Sea conditions throughout the voyage ranged from open water to
broken pack and finally to snow-covered unbroken sea ice in McMurdo Sound. The global radiation increased on average during
the trip (to higher latitudes) as we travelled poleward. The net radiation, which was positive (toward the surface) on average,
decreased however, mostly due to the increase in surface albedo. For open water, most of the net radiation is used for evapouration
(61%), while for broken sea-ice conditions, nearly all energy is used for melting of the sea ice or heating of the ocean (96%).
For unbroken snow-covered sea ice, the net radiation lies close to zero, due to the high surface albedo, which reached a mean
value of 0.81. The sensible heat flux becomes the largest heat source and nearly all the energy is used for warming of the
surface. Finally, a Radarsat image, on which the ship track was visible, was used to compare the ship observations with satellite
derived ice types. 相似文献
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Gerd Bürger 《水文研究》2017,31(22):4039-4042
A main obstacle to trend detection in time series occurs when they are autocorrelated. By reducing the effective sample size of a series, autocorrelation leads to decreased trend significance. Numerous recipes attempt to mitigate the effect of autocorrelation, either by adjusting for the reduced effective sample size or by removing the autocorrelated components of a series. This short note deals with the latter, also called prewhitening (PW). It is known that removal of autocorrelation also removes part of the trend, which may affect the signal‐to‐noise ratio. Two popular methods have dealt with this problem, the trend‐free prewhitening (TFPW) and the iterative prewhitening. Although it is generally accepted that both methods reduce the adverse effects of PW on the trend magnitude, corresponding effects on statistical significance have not been clearly stated for TFPW. Using a Monte Carlo approach, it is demonstrated that both methods entail quite different Type‐I error rates. The iterative prewhitening produces rates that are generally close to the nominal significance level. The TFPW, however, shows very high Type‐I error rates with increasing autocorrelation. The corresponding rate of false trend detections is unacceptable for applications, so that published trends based on TFPW need to be reassessed. 相似文献
55.
Richard Black W. Neil Adger Nigel W. Arnell Stefan Dercon Andrew Geddes David Thomas 《Global Environmental Change》2011
The influence of the environment and environmental change is largely unrepresented in standard theories of migration, whilst recent debates on climate change and migration focus almost entirely on displacement and perceive migration to be a problem. Drawing on an increasing evidence base that has assessed elements of the influence of the environment on migration, this paper presents a new framework for understanding the effect of environmental change on migration. The framework identifies five families of drivers which affect migration decisions: economic, political, social, demographic and environmental drivers. The environment drives migration through mechanisms characterised as the availability and reliability of ecosystem services and exposure to hazard. Individual migration decisions and flows are affected by these drivers operating in combination, and the effect of the environment is therefore highly dependent on economic, political, social and demographic context. Environmental change has the potential to affect directly the hazardousness of place. Environmental change also affects migration indirectly, in particular through economic drivers, by changing livelihoods for example, and political drivers, through affecting conflicts over resources, for example. The proposed framework, applicable to both international and internal migration, emphasises the role of human agency in migration decisions, in particular the linked role of family and household characteristics on the one hand, and barriers and facilitators to movement on the other in translating drivers into actions. The framework can be used to guide new research, assist with the evaluation of policy options, and provide a context for the development of scenarios representing a range of plausible migration futures. 相似文献
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A five-member ensemble of regional climate model (RCM) simulations for Europe, with a high resolution nest over Germany, is analysed in a two-part paper: Part I (the current paper) presents the performance of the models for the control period, and Part II presents results for near future climate changes. Two different RCMs, CLM and WRF, were used to dynamically downscale simulations with the ECHAM5 and CCCma3 global climate models (GCMs), as well as the ERA40-reanalysis for validation purposes. Three realisations of ECHAM5 and one with CCCma3 were downscaled with CLM, and additionally one realisation of ECHAM5 with WRF. An approach of double nesting was used, first to an approximately 50 km resolution for entire Europe and then to a domain of approximately 7 km covering Germany and its near surroundings. Comparisons of the fine nest simulations are made to earlier high resolution simulations for the region with the RCM REMO for two ECHAM5 realisations. Biases from the GCMs are generally carried over to the RCMs, which can then reduce or worsen the biases. The bias of the coarse nest is carried over to the fine nest but does not change in amplitude, i.e. the fine nest does not add additional mean bias to the simulations. The spatial pattern of the wet bias over central Europe is similar for all CLM simulations, and leads to a stronger bias in the fine nest simulations compared to that of WRF and REMO. The wet bias in the CLM model is found to be due to a too frequent drizzle, but for higher intensities the distributions are well simulated with both CLM and WRF at the 50 and 7 km resolutions. Also the spatial distributions are close to high resolution gridded observations. The REMO model has low biases in the domain averages over Germany and no drizzle problem, but has a shift in the mean precipitation patterns and a strong overestimation of higher intensities. The GCMs perform well in simulating the intensity distribution of precipitation at their own resolution, but the RCMs add value to the distributions when compared to observations at the fine nest resolution. 相似文献
57.
Christian Savu-Krohn Gerd Rantitsch Peter Auer Frank Melcher Torsten Graupner 《Natural Resources Research》2011,20(3):177-191
Two modern machine learning techniques, Linear Programming Boosting (LPBoost) and Support Vector Machines (SVMs), are introduced
and applied to a geochemical dataset of niobium–tantalum (“coltan”) ores from Central Africa to demonstrate how such information
may be used to distinguish ore provenance, i.e., place of origin. The compositional data used include uni- and multivariate
outliers and elemental distributions are not described by parametric frequency distribution functions. The “soft margin” techniques
of LPBoost and SVMs can be applied to such data. Optimization of their learning parameters results in an average accuracy
of up to c. 92%, if spot measurements are assessed to estimate the provenance of ore samples originating from two geographically
defined source areas. A parameterized performance measure, together with common methods for its optimization, was evaluated
to account for the presence of uneven datasets. Optimization of the classification function threshold improves the performance,
as class importance is shifted towards one of those classes. For this dataset, the average performance of the SVMs is significantly
better compared to that of LPBoost. 相似文献
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Acta Geotechnica - While Terzaghi justified his principle of effective stress for water-saturated soil empirically, it can be derived by means of the neutrality of the mineral with respect to... 相似文献