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181.
Many natural phenomena exhibit size distributions that are power laws or power law type distributions. Power laws are specific in the sense that they can exhibit extremely long or heavy tails. The largest event in a sample from such distribution usually dominates the underlying physical or generating process (floods, earthquakes, diamond sizes and values, incomes, insurance). Often, the practitioner is faced with the difficult problem of predicting values far beyond the highest sample value and designing his system either to profit from them, or to protect against extreme quantiles. In this paper, we present a novel approach to estimating such heavy tails. The estimation of tail characteristics such as the extreme value index, extreme quantiles, and percentiles (rare events) is shown to depend primarily on the number of extreme data that are used to model the tail. Because only the most extreme data are useful for studying tails, thresholds must be selected above which the data are modeled as power laws. The mean square error (MSE) is used to select such thresholds. A semiparametric bootstrap method is developed to study estimation bias and variance and to derive confidence limits. A simulation study is performed to assess the accuracy of these confidence limits. The overall methodology is applied to the Harvard Central Moment Tensor catalog of global earthquakes. 相似文献
182.
应用吉尔吉斯斯坦地震研究所介绍的空区参数法,对新疆天山地区进行分时空扫描计算和R值评分检验,筛选出有一定预报效能的10个小区,确定了异常判据和预测规则。1993年10月,根据A1、A2小区出现的空区参数异常,对1993年12月1日疏附6.0级地震作出预报,预报三要互完全正确。 相似文献
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A non‐parametric statistical method of tracking rapidly changing dynamical systems is introduced. The method implements the non‐linear wavelet thresholding estimator to estimate the evolutionary transfer function of the system. The consistency and optimality of the resulting estimate of our method on rapidly changing systems are stated, while no linear estimator can achieve the same optimality. Two examples of real data are studied using this non‐parametric method, including two vertical seismic array case studies and a series of seismic slope experiments. The analysis results are consistent with previous research for the vertical seismic array data. Moreover, our estimate is superior to those from previous research in the sense that our estimate is neither over‐smoothed nor under‐smoothed. The ana‐ lysis results are also consistent with the experimental observations for the seismic slope experimental data. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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The authors have verified a regression model for the evaluation of the daily amplitude of sea surface temperature (ΔSST) proposed
by Kawai and Kawamura (2002). The authors investigated the accuracy of satellite data used for the evaluation and showed that
ΔSST error caused by satellite data error is less than ±0.7 K. The evaluated ΔSSTs were compared with in situ values. Its
root-mean-square error is about 0.3 K or less, except for a coastal region, and it has a bias of more than +0.1 K in the tropics.
This bias can be removed by considering latent heat flux.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
189.
为研究型钢混凝土柱在反复荷载下的受扭损伤,完成了11根型钢混凝土柱和1根钢筋混凝土柱复合受扭试验。通过试验观察了构件的受力过程和破坏特征,研究两种不同型钢混凝土柱的裂缝开展与分布规律。基于能量守恒定律,考察了柱截面配钢形式、扭弯比、轴压比、混凝土强度等级、配箍率以及配钢率对累积损伤的影响。研究结果表明:型钢混凝土柱的损伤演变分为3个阶段:弹性阶段、弹塑性阶段和破坏阶段;配钢形式、扭弯比和配箍率是影响型钢混凝土柱损伤程度的重要因素;配型钢,降低扭弯比和提高配箍率对于损伤指标分别最大降低了22.1%、14.3%和14.0%;损伤指标受轴压比、配钢率和混凝土强度等级影响程度较小。 相似文献
190.
为了提高变形监测中地铁隧道断面点截取的效率,文章提出了基于kd-tree和法向量估计的局部点云简化方法,对BaySAC算法的三维激光点云二次参数曲面拟合方法进行改进:利用kd-tree建立点云数据的空间拓扑关系,计算出每个数据点的k邻域;然后使用平面拟合方法获取法矢量;最后根据点云数据法矢量变化程度,采用法矢量自适应得到压缩后的点云数据。实验证明该方法既能较大程度地简化点云,简化结果比较均匀,又具有不破坏细小特征的特点,进一步改进了BaySAC算法的二次参数曲面拟合方法。 相似文献