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1.
本文运用福建省沿海气象要素的异常变化,作台湾省的中、短期地震预报,取得了成功的效果。采用长乐历年各月14时最低气压的距平值,作台湾省未来4~7个月内出现强震的预报依据,并采用热异常进行短临跟踪。当秋冬季节连续4d 长乐、福州、台北的气温均比广州累计高出10℃时,预报未来1~5d 台湾省出现7级强震。又根据近百年来台湾发生的强震,统计其活动季节,得到近20年来7级地震发生的时间,绝大部分在9~12月。 相似文献
2.
卫星遥感技术可用于海岛资源调查。Sentinel-2A与Landsat 8两颗卫星都可免费提供空间分辨率较高的多光谱遥感影像,在海岛调查中的应用潜力较大。本文以浙江舟山普陀山岛为例开展了针对这两种影像在海岛植被分类中的应用效果的研究,分别利用Sentinel-2A多光谱成像仪(MSI)和Landsat 8陆地成像仪(OLI)影像基于最大似然法分类获得了该岛阔叶林、针阔混交林、针叶林、灌丛、草丛等植被及其他地物的分布情况,并进行了精度检验,结果表明MSI的总体分类精度略高于OLI。 相似文献
3.
霍艳芬 《CT理论与应用研究》1995,4(4):32-33
本文报告26例由于外力作用致使眼面部广泛异物存留。临床应用X线的归咎常见漏诊及定位困难,因此采取CT定位达到异物诊断治疗目的。 相似文献
4.
5.
The ensemble Kalman filter (EnKF) has been shown repeatedly to be an effective method for data assimilation in large-scale
problems, including those in petroleum engineering. Data assimilation for multiphase flow in porous media is particularly
difficult, however, because the relationships between model variables (e.g., permeability and porosity) and observations (e.g.,
water cut and gas–oil ratio) are highly nonlinear. Because of the linear approximation in the update step and the use of a
limited number of realizations in an ensemble, the EnKF has a tendency to systematically underestimate the variance of the
model variables. Various approaches have been suggested to reduce the magnitude of this problem, including the application
of ensemble filter methods that do not require perturbations to the observed data. On the other hand, iterative least-squares
data assimilation methods with perturbations of the observations have been shown to be fairly robust to nonlinearity in the
data relationship. In this paper, we present EnKF with perturbed observations as a square root filter in an enlarged state
space. By imposing second-order-exact sampling of the observation errors and independence constraints to eliminate the cross-covariance
with predicted observation perturbations, we show that it is possible in linear problems to obtain results from EnKF with
observation perturbations that are equivalent to ensemble square-root filter results. Results from a standard EnKF, EnKF with
second-order-exact sampling of measurement errors that satisfy independence constraints (EnKF (SIC)), and an ensemble square-root
filter (ETKF) are compared on various test problems with varying degrees of nonlinearity and dimensions. The first test problem
is a simple one-variable quadratic model in which the nonlinearity of the observation operator is varied over a wide range
by adjusting the magnitude of the coefficient of the quadratic term. The second problem has increased observation and model
dimensions to test the EnKF (SIC) algorithm. The third test problem is a two-dimensional, two-phase reservoir flow problem
in which permeability and porosity of every grid cell (5,000 model parameters) are unknown. The EnKF (SIC) and the mean-preserving
ETKF (SRF) give similar results when applied to linear problems, and both are better than the standard EnKF. Although the
ensemble methods are expected to handle the forecast step well in nonlinear problems, the estimates of the mean and the variance
from the analysis step for all variants of ensemble filters are also surprisingly good, with little difference between ensemble
methods when applied to nonlinear problems. 相似文献
6.
由新疆维吾尔自治区气象信息中心提供的1977—2006年吐鲁番气象资料统计得知:近29年气候有变暖趋势,线性变暖速率为每10年0.72℃,29年来吐鲁番地区年平均气温共上升2.06℃。结合吐鲁番沙漠植物园沙拐枣属植物的物候观测积累资料,分析了4个组的芽膨胀、开始展叶、同化枝开始变色、同化枝初落的时间变化趋势及其与温度变化的响应关系。结果表明:(1)1977年以来,沙拐枣属(Calligonum L.)植物刺果组(Sect.Medusa Sosk.et Alexandr)物候期最晚;同化枝开始变色为泡果组(Sect.Calliphysa(Fisch.et Mey.)Borszcz)晚于翅果组;其他3种物候期中,泡果组物候期最早,基翅组(Sect.Calligonum)和翅果组(Sect.Pterococcus(Pall.)Borszcz)均居中。4个组的芽膨胀和开始展叶时间大部分呈提前趋势,同化枝开始变色和同化枝初落时间呈推后趋势。(2)4个组的芽膨胀与年平均气温、春季气温呈显著负相关(p0.05)。年平均气温每升高1℃,泡果组、刺果组、基翅组、翅果组的芽膨胀时间分别提前4.5d、4.3d、4.1d、8.3d;同化枝开始变色和同化枝初落时间变化不明显。芽膨胀对温度变化的响应程度显著大于同化枝开始变色和同化枝初落。 相似文献
7.
Precipitation in the arid region of Northwest China (NWC) shows high spatial and temporal variability,in large part because of the region's complex topography and moisture conditions.However,rain gauges in the area are sparse,and most are located at altitudes below 2000 m,which limits our understanding of precipitation at higher altitudes.Interpolated precipitation products and satellite-based datasets with high spatiotemporal resolution can potentially be a substitute for rain gauge data.In this study,the spatial and temporal proper-ties of precipitation in the arid region of NWC were analyzed using two gridded precipitation products:SURF_CLI_CHN_PRE_DAY_GRID_0.5 (CHN) and Tropical Rainfall Measuring Mission (TRMM) 3B43.The CHN and TRMM 3B43 data showed that in summer,precipitation was more concentrated in southern Xinjiang than in northern Xinjiang,and the opposite was true in winter.The largest difference in precipitation between mountainous areas and plains appeared in summer.High-elevation areas with high precipitation showed more stable annual precipitation.Different sub-regions showed distinctive precipitation distributions with elevation,and both datasets showed that the maximum precipitation zone appeared at high altitude. 相似文献
8.
MODIS影像的大气校正及在太湖蓝藻监测中的应用 总被引:7,自引:0,他引:7
MODIS 数据有免费、波段丰富、时间分辨率高等优点,是进行太湖蓝藻监测的重要数据源,由于MODIS传感器接收的是地物反射太阳辐射的信号,太阳辐射与地球大气的相互作用会引起传感器接收到的信号失真,为了提高利用MODIS数据监测太湖蓝藻的精度,必须对其进行大气校正.本文介绍了FIAASH大气校正模型的基本原理,并对2007年4月25日MODIS数据的前七个波段进行试验,对比分析了影像大气校正前后的NDVI值以检测大气校正的效果;分析表明,大气校正前后NDVI的变化趋势基本上相同,但大气校正后的NDVI动态范围更大,校正后NDVI的平均值和标准差增大,大气校正在一定程度上有效地降低了大气对遥感影像的影响,达到了增强信息的目的;最后,利用大气校正获取的地表真实反射率数据的第二波段与第一波段的比值,运用阈值法提取蓝藻信息,经试验当阈值为1.9时提取出来的蓝藻分布图基本上与实际相符.利用MODIS影像可以快速、及时地监测蓝藻爆发的位置及爆发程度. 相似文献
9.
Natural Hazards - To evaluate urban flood risk while considering spatial and temporal characteristics, this paper establishes an assessment method based on a coupled hydrodynamic model and a fuzzy... 相似文献
10.
利用福建沿海地区GPS基本网2003—2010年4期观测资料,运用GAMIT/GLOBK软件及块体整体旋转线性应变模型,得到了各站相对于整个块体的形变速度和块体上的应变图像。结果显示:福建沿海地区具有一致的东南向运动,大小在35 mm/a左右;邵武-河源断裂带附近的剪切应变较大,政和-海丰断裂带与永安-晋江断裂带交汇处剪切应变相对较小,长乐-诏安断裂带从南到北的剪切应变经历了一个南弱北强到南强北弱的变化过程,政和-海丰断裂带和永安-晋江断裂带交汇处最大和最小主应变由压应变转为张应变;福建地区从西北到东南沿海经历了由张到压-由压到张-由张到压的变化过程。 相似文献