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71.
Using a combination of Quick Scatterometer (QuikSCAT), Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E),
and Lagrangian drifter measurements, we demonstrate that wind data alone are not sufficient to derive ocean surface stress
(momentum flux) over mid-latitude ocean fronts, specifically the Kuroshio Extension. There was no continuous and large-scale
stress measurement over ocean until the launch of the scatterometers. Stress had been derived from winds through a drag coefficient,
and our concept of stress distribution may be largely influenced by our knowledge of wind distribution. QuikSCAT reveals that
the variability of stress could be very different from wind. The spatial coherence between the magnitude of stress and sea
surface temperature (SST), between the divergence of surface stress and the downwind SST gradient, and between the vorticity
of stress and crosswind SST gradient, are the inherent characteristics of stress (turbulence production by buoyancy) that
would exist even under a uniform wind field. The coherence between stress vorticity and SST gradient is masked by the rotation
of ocean currents over the Kuroshio meanders. Surface stress rotates in the opposite direction to surface currents because
stress is the vector difference between wind and current. The results are in agreement with a previous study of the Agulhas
Extension and confirm the unique stress measuring capability of the scatterometer. 相似文献
72.
首先通过对作用于渐扩散水跃的压力分析,阐述了渐扩散水跃跃长总比非扩散水跃跃长短的原理。在此理论基础上,考虑边墙扩散角的影响,建立了渐扩散水跃表面质点运动方程,并结合动量方程和连续方程,推导出渐扩散水跃跃长的半理论、半经验公式。同时,引入非扩散水跃跃长经验公式,使渐扩散水跃跃长公式大大简化。其次,对该理论的局限性进行了分析,得到了该公式的适用范围。在该范围内,该公式能较好地吻合实验结果,从而该理论得以证实。最后对各家渐扩散水跃跃长经验公式进行分析归类,并推荐工程适用公式,以便工程运用。 相似文献
73.
Steven P. Oncley Thomas Foken Roland Vogt Wim Kohsiek H. A. R. DeBruin Christian Bernhofer Andreas Christen Eva van Gorsel David Grantz Christian Feigenwinter Irene Lehner Claudia Liebethal Heping Liu Matthias Mauder Andrea Pitacco Luis Ribeiro Tamas Weidinger 《Boundary-Layer Meteorology》2007,123(1):1-28
An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art
measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where
closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery
and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance
were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an
estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement
error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause
this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required
to balance the budget.
The National Center for Atmospheric Research is supported by the National Science Foundation 相似文献
74.
水汽螺旋度及其在一次江淮暴雨分析中的应用 总被引:3,自引:0,他引:3
构造了新的诊断量--水汽螺旋度,并对影响水汽螺旋度变化的因子做了分析.利用MM5模式输出资料对2003年7月4日的暴雨过程进行诊断分析,结果表明:水汽螺旋度与暴雨强度和暴雨落区都有较好的相关,螺旋度通量散度和湿螺旋散度对暴雨也有比较明显的指示作用,其中螺旋度通量散度对暴雨落区和强度的指示作用都很好,而湿螺旋散度与暴雨落区对应得稍差. 相似文献
75.
76.
G. Pigeon A. Lemonsu C. S. B. Grimmond P. Durand O. Thouron V. Masson 《Boundary-Layer Meteorology》2007,124(2):269-290
This study quantifies the processes that take place in the layer between the mean building height and the measurement level
of an energy balance micrometeorological tower located in the dense old core of a coastal European city. The contributions
of storage, vertical advection, horizontal advection and radiative divergence for heat are evaluated with the available measurements
and with a three-dimensional, high-resolution meteorological simulation that had been evaluated against observations. The
study focused on a summer period characterized by sea-breeze flows that affect the city. In this specific configuration, it
appears that the horizontal advection is the dominant term. During the afternoon when the sea breeze is well established,
correction of the sensible heat flux with horizontal heat advection increases the measured sensible heat flux up to 100 W m−2. For latent heat flux, the horizontal moisture advection converted to equivalent latent heat flux suggests a decrease of
50 W m−2. The simulation reproduces well the temporal evolution and magnitude of these terms. 相似文献
77.
78.
针对不同时期高分辨率遥感影像变化检测中城区建筑物因投影差差异所产生的误检测现象,提出了一种综合应用光谱和纹理特征的建筑物变化检测方法。以变化和未发生变化地物影像的散度作为可分性依据,首先对光谱差分影像在混合高斯密度模型下建模,并采用马尔可夫最小错误概率准则提取初始变化区域,往往含有错判的建筑物。然后将误判建筑物影像类和真实变化影像类构成训练集,通过引入多通道Gabor滤波器,提取训练集的纹理差分特征,并采用分类别PCA变换实施纹理差分特征的选择。最后对选择出的纹理差分特征依据高斯混合密度模型建模,并用马尔可夫最小错误概率提取真变化区域,即可去除光谱信息检测所产生的伪变化。试验表明,本文方法能够较好地解决建筑物变化的错判问题,提高了影像变化检测的精度。 相似文献
79.
80.
"98.7"连续暴雨过程诊断分析 总被引:5,自引:2,他引:3
曹晓岗 《南京气象学院学报》2000,23(1):133-138
给出了“98.7”连续暴雨过程期间江西及其附近地区逐日物理量的绝对极大值,对这次连续暴雨过程的最强降水日进行了诊断分析。得到了盛夏季节连续暴雨的动力、水汽、稳定度等条件均明显强于江西雨季(4月至7月上旬)产生暴雨的相应条件。计算结果表明,螺旋度、Q矢量散度在这次暴雨过程中与降水强弱有较好的对应关系。 相似文献