全文获取类型
收费全文 | 155篇 |
免费 | 1篇 |
专业分类
大气科学 | 16篇 |
地球物理 | 20篇 |
地质学 | 63篇 |
海洋学 | 10篇 |
天文学 | 42篇 |
自然地理 | 5篇 |
出版年
2020年 | 2篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 6篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 3篇 |
2007年 | 9篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有156条查询结果,搜索用时 15 毫秒
11.
Wusi Yue Marc B. Parlange Charles Meneveau Weihong Zhu René van Hout Joseph Katz 《Boundary-Layer Meteorology》2007,124(2):183-203
Turbulent flow in a corn canopy is simulated using large-eddy simulation (LES) with a Lagrangian dynamic Smagorinsky model.
A new numerical representation of plant canopies is presented that resolves approximately the local structure of plants and
takes into account their spatial arrangement. As a validation, computational results are compared with experimental data from
recent field particle image velocimetry (PIV) measurements and two previous experimental campaigns. Numerical simulation using
the traditional modelling method to represent the canopy (field-scale approach) is also conducted as a comparison to the plant-scale
approach. The combination of temporal PIV data, LES and spatial PIV data allows us to couple a wide range of relevant turbulence
scales. There is good agreement between experimental data and numerical predictions using the plant-scale approach in terms
of various turbulence statistics. Within the canopy, the plant-scale approach also allows the capture of more details than
the field-scale approach, including instantaneous gusts that penetrate deep inside the canopy. 相似文献
12.
Particle image velocimetry (PIV) data obtained in a wind-tunnel model of a canopy boundary layer is used to examine the characteristics
of mean flow and turbulence. The vector spacing varies between 1.7 and 2.5 times the Kolmogorov scales. Conditional sampling
based on quadrants, i.e. based on the signs of velocity fluctuations, reveals fundamental differences in flow structure, especially
between sweep and ejection events, which dominate the flow. During sweeps, the downward flow generates a narrow, highly turbulent,
shear layer containing multiple small-scale vortices just below canopy height. During ejections, the upward flow expands this
shear layer and the associated small-scale flow structures to a broad region located above the canopy. Consequently, during
sweeps the turbulent kinetic energy (TKE), Reynolds stresses, as well as production and dissipation rates, have distinct narrow
peaks just below canopy height, whereas during ejections these variables have broad maxima well above the canopy. Three methods
to estimate the dissipation rate are compared, including spectral fits, measured subgrid-scale (SGS) energy fluxes at different
scales, and direct measurements of slightly underresolved instantaneous velocity gradients. The SGS energy flux is 40–60%
of the gradient-based (direct) estimates for filter sizes inside the inertial range, while decreasing with scale, as expected,
within the dissipation range. The spectral fits are within 5–30% of the direct estimates. The spectral fits exceed the direct
estimates near canopy height, but are lower well above and below canopy height. The dissipation rate below canopy height increases
with velocity magnitude, i.e. it has the highest values during sweep and quadrant 1 events, and is significantly lower during
ejection and quadrant 3 events. Well above the canopy, ejections are the most dissipative. Turbulent transport during sweep
events acts as a source below the narrow shear layer within the canopy and as a sink above it. Transport during ejection events
is a source only well above the canopy. The residual term in the TKE transport equation, representing mostly the effect of
pressure–velocity correlations, is substantial only within the canopy, and is dominated by sweeps. 相似文献
13.
14.
15.
16.
Jerusalem was hit by earthquakes several times in its history, in the course of which none of the holy sites of the three
main faiths of the western world escaped damage. Intensities of the last ML 6.2, July 11, 1927 Dead Sea earthquake, reached MSK VIII in the Old City of Jerusalem and the surrounding villages. As future
strong earthquakes are inevitable, the need for the evaluation of earthquake-related hazards is obvious. Only general geotechnical
properties of the section exposed in the mountainous area of Jerusalem are available; therefore, the hazard assessment was
conducted from a geological perspective. The hazards identified in this study are: (1) amplification of seismic acceleration
due to soft rock and soil conditions; (2) amplification due to mountainous topography; (3) dynamic instability of natural
slopes; and (4) potential failure of slopes that have undergone engineering development and were weakened due to damaging,
steepening, overloading, and wetting beyond their natural state. We formulated relative grades of vulnerability for each of
the hazards and delineated the zones that require further specific investigation. For practical use we constructed a summary
map that combines the different hazard categories. Looking at the summary map, the ground at the central N–S axis zone across
Jerusalem is the least vulnerable. The bedrock there is mostly hard carbonate, the topography is mild, and thus only the alluvial
cover, if thicker than 3 m, should be considered sensitive. Yet although the natural hazard in this area is limited, the risk
should not be underrated. Much of the city lies there, including buildings constructed before antiseismic codes were regulated,
and traditional engineering practice should not be taken for granted as antiseismic proof either. Eastwards, the shear wave
velocity (Vs) contrast between the hard and soft rocks as well as the notable topography in places, impose the potential for
amplification. Slopes, either naturally or artificially cutting into the soft chalk, may expose the area to dynamic instability;
thus, the ongoing extensive development of the city in this direction should certainly take into account all of this. West
of the central axis, the potential of failure of both steep natural and urbanized slopes appears. Being a plausible direction
for future urban expansion, these areas specifically call for careful environmental and engineering planning. For engineering
purposes, however, a specific site investigation is still necessary. Nevertheless, the summary map established in this study
sets up for Jerusalem, for the first time, a practical tool for environmental and municipal planning, emergency response planning,
and civil protection. 相似文献
17.
Non-stationary extreme value analysis in a changing climate 总被引:1,自引:0,他引:1
This paper introduces a framework for estimating stationary and non-stationary return levels, return periods, and risks of climatic extremes using Bayesian inference. This framework is implemented in the Non-stationary Extreme Value Analysis (NEVA) software package, explicitly designed to facilitate analysis of extremes in the geosciences. In a Bayesian approach, NEVA estimates the extreme value parameters with a Differential Evolution Markov Chain (DE-MC) approach for global optimization over the parameter space. NEVA includes posterior probability intervals (uncertainty bounds) of estimated return levels through Bayesian inference, with its inherent advantages in uncertainty quantification. The software presents the results of non-stationary extreme value analysis using various exceedance probability methods. We evaluate both stationary and non-stationary components of the package for a case study consisting of annual temperature maxima for a gridded global temperature dataset. The results show that NEVA can reliably describe extremes and their return levels. 相似文献
18.
19.
Guangyou Zhu Shuichang Zhang Barry Jay Katz Jin Su Xue Wang Zihui Feng Jie Cui Xingwang Liu 《Chemie der Erde / Geochemistry》2014
The Western Slope of the Songliao Basin is rich in heavy oil resources (>70 × 108 bbl), around which there are shallow gas reservoirs (∼1.0 × 1012 m3). The gas is dominated by methane with a dryness over 0.99, and the non-hydrocarbon component being overwelmingly nitrogen. Carbon isotope composition of methane and its homologs is depleted in 13C, with δ13C1 values being in the range of −55‰ to −75‰, δ13C2 being in the range of −40‰ to −53‰ and δ13C3 being in the range of −30‰ to −42‰, respectively. These values differ significantly from those solution gases source in the Daqing oilfield. This study concludes that heavy oils along the Western Slope were derived from mature source rocks in the Qijia-Gulong Depression, that were biodegraded. The low reservoir temperature (30–50 °C) and low salinity of formation water with neutral to alkaline pH (NaHCO3) appeared ideal for microbial activity and thus biodegradation. Natural gas along the Western Slope appears mainly to have originated from biodegradation and the formation of heavy oil. This origin is suggested by the heavy δ13C of CO2 (−18.78‰ to 0.95‰) which suggests that the methane was produced via fermentation as the terminal decomposition stage of the oil. 相似文献
20.