全文获取类型
收费全文 | 70篇 |
免费 | 5篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 21篇 |
地球物理 | 10篇 |
地质学 | 21篇 |
海洋学 | 2篇 |
天文学 | 16篇 |
综合类 | 1篇 |
自然地理 | 3篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2020年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 4篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
排序方式: 共有75条查询结果,搜索用时 15 毫秒
41.
42.
43.
In this paper we present a method that combines evolution strategies (ES) and standard optimization algorithms to solve the
problem of fitting line profiles of stellar spectra. This method provides a reliable decomposition and a reduction in computing
time over conventional algorithms. Using a stellar spectrum as input, we implemented an evolution strategy to find an approximation
of the continuum spectrum and spectral lines. After a few generations, the parameters found by ES are given as starting search
point to a standard optimization algorithm, which then finds the correct spectral decomposition. We used Gaussian functions
to fit spectral lines and the Planck function to represent the continuum spectrum. Our experimental results present the application
of this method to real spectra, showing that they can be approximated very accurately.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
44.
We investigate dominant processes modulating the coastal West African atmospheric boundary layer during August and September 2006. We evaluated boundary-layer attributes using upper air soundings, tower-based observations, and information from the European Centre for Medium-Range Weather Forecasts reanalyses. Boundary-layer thermodynamics exhibited continental and maritime attributes in response to influences from regional onshore (sea to land) flows and local land–atmosphere exchanges of energy and moisture. Onshore flows transported maritime air inland and gave rise to deep (>1 km) nighttime mixed layers whose heat and moisture content resulted in maximum virtual potential temperatures of 306 K and specific humidities up to 20 g kg−1. The presence of the Saharan Air Layer corresponded with capping inversions greater than 4 K and lapse rates exceeding 7 K km−1 above the mixed layer. Mixed layers at these times became deeper than expected (≈1 km) because dust layer events were often concurrent with strong onshore flows. Despite diurnally variable land–atmosphere fluxes of sensible and latent heat that reached maximum values of 200 and 400 W m−2, respectively, the mixed-layer depth exhibited little diurnal variation due to the influences of onshore flows. Daytime heating of the land, the upward transport of moisture, and onshore flows produced boundary layers with high convective available potential energy that often exceeded 3,000 J kg−1. These results demonstrate that the atmospheric boundary-layer thermodynamics in western Senegal can be favorable for storm development during both day and night. Mesoscale and regional models applied in this region should include several processes controlling the boundary-layer attributes to realistically estimate the energy available for storm development. 相似文献
45.
—Broad band digital three-component data recorded at UNM, a GEOSCOPE station, were used to estimate Lg coda Q for 34 medium size (3.9 ≤m b ≤ 6.3) earthquakes with travel paths laying in different geological provinces of southern Mexico in an effort to establish the possible existence of geological structures acting as wave guides and/or travel paths of low attenuation between the Pacific coast and the Valley of Mexico. The stacked spectral ratio method proposed by XIE and NUTTLI (1988) was chosen for computing the coda Q. The variation range of Q 0 (Q at 1?Hz) and the frequency dependence parameter η estimates averaged on the frequency interval of 0.5 to 2?Hz for the regions and the three components considered are: i) Guerrero region 173 ≤Q¯ 0≤ 182 and 0.6 ≤Q¯ 0 ≤ 0.7, ii) Oaxaca region 183 ≤Q¯ 0 ≤ 198 and 0.6 ≤Q¯ 0 ≤ 0.8, iii) Michoacan-Jalisco region 187 ≤Q¯ 0 ≤ 204 and 0.7 ≤Q¯ 0 ≤ 0.8 and iv) eastern portion of the Transmexican Volcanic Belt (TMVB) 313 ≤Q 0≤ 335 and η = 0.9. ¶The results show a very high coda Q for the TMVB as compared to other regions of southern Mexico. This unexpected result is difficult to reconcile with the geophysical characteristics of the TMVB, e.g., low seismicity, high volcanic activity and high heat flow typical of a highly attenuating (low Q) region. Visual inspection of seismograms indicates that for earthquakes with seismic waves traveling along the TMVB, the amplitude decay of Lg coda is anomalously slow as compared to other earthquakes in southern Mexico. Thus, it seems that the high Q value found does not entirely reflect the attenuation characteristics of the TMVB but it is probably contaminated by a wave-guide effect. This phenomenon produces an enhancement in the time duration of the Lg wave trains travelling along this geological structure. This result is important to establish the role played by the transmission medium in the extremely long duration of ground motion observed during the September 19, 1985 Michoacan earthquake. ¶The overall spatial distribution of coda Q values indicates that events with focus in the Michoacan-Jalisco and Oaxaca regions yield slightly higher values than those from Guerrero. This feature is more pronounced for the horizontal component of coda Q. A slight dependence of average coda Q ?1 on earthquake focal depth is observed in the frequency range of 0.2 to 1.0?Hz approximately on the horizontal component. Deeper (h > 50?km) events yield lower values of Q ?1 than shallower events. For frequencies higher than 1.0?Hz no clear dependence of Q ?1 on focal depth is observed. However, due to the estimates uncertainties this result is not clearly established. 相似文献
46.
47.
48.
49.
J. D. Fuentes B. Geerts T. Dejene P. D’Odorico E. Joseph 《Theoretical and Applied Climatology》2008,92(3-4):181-193
Summary This study reports the findings of TRMM (Tropical Rainfall Measuring Mission) satellite data analyses undertaken to investigate
differences in intensity and depth of precipitating systems in the transition region from continental to maritime environments
in West Africa during the rainy season of June to September in 1998–2004. The results of this study are interpreted in the
context of regional thermodynamic variables such as equivalent potential temperature and equivalent convective available potential
energy to discern the processes governing storm development. Over continental West Africa, convective-type precipitating storms
exhibit a substantially larger vertical extent compared to the ones over the eastern Atlantic Ocean. In contrast, the stratiform
precipitating systems show similar vertical reflectivity patterns, depth and intensity over both land and adjacent ocean in
West Africa. The differences in the attributes of storms, as they move from the continent to the ocean, can be partly explained
in terms of the surface-atmosphere interactions that provide the necessary transports of energy and water vapor from the surface
to the cloud layer.
Authors’ addresses: Jose D. Fuentes, Teferi Dejene, Paolo D’Odorico, Department of Environmental Sciences, University of Virginia,
291 McCormick Road, Clark Hall, Charlottesville, VA 22904, USA; Bart Geerts, Department of Atmospheric Science, University
of Wyoming, Laramie, WY 82071, USA; Everette Joseph, Department of Physics, Howard University, Washington, DC 20059, USA. 相似文献
50.
Mariano?PoissonEmail author Pascal?Démoulin Marcelo?López Fuentes Cristina?H.?Mandrini 《Solar physics》2016,291(6):1625-1646
The photospheric spatial distribution of the main magnetic polarities of bipolar active regions (ARs) present during their emergence deformations are known as magnetic tongues. They are attributed to the presence of twist in the toroidal magnetic-flux tubes that form the ARs. The aim of this article is to study the twist of newly emerged ARs from the evolution of magnetic tongues observed in photospheric line-of-sight magnetograms. We apply the procedure described by Poisson et al. (Solar Phys. 290, 727, 2015a) to ARs observed over the full Solar Cycle 23 and the beginning of Cycle 24. Our results show that the hemispherical rule obtained using the tongues as a proxy of the twist has a weak sign dominance (53 % in the southern hemisphere and 58 % in the northern hemisphere). By defining the variation of the tongue angle, we characterize the strength of the magnetic tongues during different phases of the AR emergence. We find that there is a tendency of the tongues to be stronger during the beginning of the emergence and to become weaker as the AR reaches its maximum magnetic flux. We compare this evolution with the emergence of a toroidal flux-rope model with non-uniform twist. The variety of evolution of the tongues in the analyzed ARs can only be reproduced when using a broad range of twist profiles, in particular having a large variety of twist gradients in the direction vertical to the photosphere. Although the analytical model used is a special case, selected to minimize the complexity of the problem, the results obtained set new observational constraints to theoretical models of flux-rope emergence that form bipolar ARs. 相似文献