首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14篇
  免费   1篇
  国内免费   4篇
测绘学   1篇
地球物理   4篇
地质学   7篇
海洋学   2篇
天文学   1篇
自然地理   4篇
  2020年   1篇
  2019年   1篇
  2015年   1篇
  2014年   1篇
  2013年   1篇
  2012年   1篇
  2010年   2篇
  2009年   1篇
  2007年   1篇
  2005年   1篇
  2004年   1篇
  2003年   1篇
  2001年   2篇
  1994年   1篇
  1993年   1篇
  1991年   2篇
排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
第三代相干体算法(C3算法)具有分辨率高、压制噪声能力强的优点,但是该算法需要计算协方差矩阵的特征值,所以耗时较多。为提高大矩阵特征值分解的运算速度,提出了一种估计最大特征值的快速收敛算法,通过运用A2k矩阵的迹来构造一种收敛速度更快的特征值估计方法,并给出了这种方法的误差估计表达式,实现计算精度的有效控制。文中还讨论了地震数据体边缘补地震道方法,解决了将递推算法应用到平面方向时空间窗越过边界的问题。实例表明,本算法的计算效率明显高于常规的C3算法。  相似文献   
2.
This paper analyzes the dynamic behaviour of continuous bridges with transverse abutment restraint. These are a particular class of multi‐span bridges whose transverse motion is restrained at the abutments. The transverse dynamic behaviour of these partially‐restrained bridges is described by a model consisting of a two‐dimensional simply‐supported beam with intermediate visco‐elastic restraints. A minimal set of characteristic problem parameters that completely describe the dynamic response is initially identified and an analytical solution is developed for particular configurations. The influence of these characteristic parameters on the properties of the dynamic systems are analyzed by considering the undamped and the damped free vibrations separately. Successively, in order to cover more general and complex configurations of realistic bridges, an extension of the definition of the characteristic parameters is proposed. The results obtained considering selected case studies are finally presented. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
3.
岩土样本力学参数的模糊统计特征研究   总被引:7,自引:5,他引:7  
徐卫亚  蒋中明 《岩土力学》2004,25(3):342-346
岩土工程参数中的各种信息都存在模糊性。通过对岩土样本力学参数试验值的研究,提出当分析样本统计特征时,应该充分考虑模糊不确定性因素对参数特征值的影响。在确定的参数隶属函数基础上,推导了岩土样本力学参数模糊统计特征值的计算公式,并证明了公式的合理性。应用实例表明,由于文中提出的计算方法考虑了参数模糊性的影响,其计算结果比按常规统计方法得到的结果更具合理性。在任何情况下,模糊方差和模糊变异系数都比常规统计方法得到的方差和变异系数小。分析结果表明,该方法具有广泛的推广价值。  相似文献   
4.
This paper examines the eigenvalues of multi‐span seismically isolated bridges in which the transverse displacement of the deck at the end abutments is restricted. With this constraint the deck is fully isolated along the longitudinal direction, whereas along the transverse direction the deck is a simple‐supported beam at the end abutments which enjoys concentrated restoring forces from the isolation bearings at the center piers. For moderate long bridges, the first natural period of the bridge is the first longitudinal period, while the first transverse period is the second period, given that the flexural rigidity of the deck along the transverse direction shortens the isolation period offered by the bearings in that direction. This paper shows that for isolated bridges longer than a certain critical length, the first transverse period becomes longer than the first longitudinal period despite the presence of the flexural rigidity of the deck. This critical length depends on whether the bridge is isolated on elastomeric bearings or on spherical sliding bearings. This result is also predicted with established commercially available numerical codes only when several additional nodes are added along the beam elements which are modeling the deck in‐between the bridge piers. On the other hand, this result cannot be captured with the limiting idealization of a beam on continuous distributed springs (beam on Wrinkler foundation)—a finding that has practical significance in design and system identification studies. Finally, the paper shows that the normalized transverse eigenperiods of any finite‐span deck are self‐similar solutions that can be represented by a single master curve and are independent of the longitudinal isolation period or on whether the deck is supported on elastomeric or spherical sliding bearings. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
5.
张新宇  韩佳  王骁  石爱国 《海洋学报》2019,41(11):15-24
为探索海浪波面信息的实时预报方法,以三阶非线性薛定谔(NLS)方程的逆散射变换求解为基础,通过理论推导,给出了一种由实测波高时历数据计算其NLS方程本征值的方法,进一步实现了对波浪包络时空演变的预报。通过预报结果与实测波列的比对,验证了方法的有效性和准确性。该方法可为船舶或海上平台的大浪预警,以及为大波浪中海上作业寻找窗口期等提供一条新的技术途径。  相似文献   
6.
We have calculated several families of classical periodic orbits in simple Hamiltonian systems of two degrees of freedom and the corresponding quantum mechanical eigenvalues and eigenfuctions. We have found that in most cases the eigenfunctions have their maxima and minima on some simple periodic orbits. These periodic orbits are of several resonant types and can be either stable or unstable. In the latter case the quantum Poincaré surfaces of section are very different from the classical Poincaré surfaces of section.  相似文献   
7.
Samples of macrofabric data obtained from colluvial deposits near the late-Wisconsinan glacial margin display widely divergent characteristics. Those from highly weathered and jointed sandstone plot as girdle distributions. Samples from red colluvium of early-Wisconsinan age form moderately strong clusters. Fabrics from shallow depth in medium-textured brown colluvium of late-Wisconsinan age generally have modes aligned with the local slope but are weak, and appear to have been modified by frost heaving. Clasts in the basal layers of an overlying loess unit were emplaced by frost heaving from the brown colluvium and have very weak or uniform fabrics. Particle shape exerts an influence on fabric strength in the brown colluvium, with samples composed of more elongated clasts displaying stronger fabrics. Fabrics from near-surface deposits show generally weaker shape and strength characteristics and higher inclinations than those at depth. Calculated seasonal frost penetration is consistent with the depth to which weaker, more steeply inclined fabrics are found. Sampling in relict periglacial deposits should be performed only below the level of disturbance by seasonal frost.  相似文献   
8.
The usefulness of principal component analysis for understanding the temporal variability of monsoon rainfall is studied. Monthly rainfall data of Karnataka, spread on 50 stations for a period of 82 years have been analysed for interseasonal and interannual variabilities. A subset of the above data comprising 10 stations from the coherent west zone of Karnataka has also been investigated to bring out statistically significant interannual signals in the southwest monsoon rainfall. Conditional probabilities are proposed for a few above normal/below normal transitions. A sample prediction exercise for June–July using such a transition probability has been found to be successful.  相似文献   
9.
BP神经网络的道路场景杆状地物自动分类   总被引:1,自引:0,他引:1  
针对车载激光扫描数据中杆状地物分类精度不高、自动化程度低的问题,本文提出一种基于BP神经网络的分类方法。首先根据杆状地物点云特征选取10个特征值,获取杆状地物聚类单元的特征向量,构建特征矩阵;然后使用样本集训练BP神经网络模型并保存该分类模型;最后使用BP神经网络分类模型对试验区内的杆状地物进行分类。试验结果表明,该方法对杆状地物的分类精度可达95.34%,验证了文中所述方法对杆状地物分类的有效性。  相似文献   
10.
Winter desiccation-induced foliage loss at high-elevation locations is an important determinant of positive carbon balance for trees and thus influences the location of the alpine treeline ecotone. In this study, data are presented that describe the amount of winter desiccation incurred by krummholz growth forms of subalpine fir ( Abies lasiocarpa (Hook) Nutt.) at treeline locations in Glacier National Park, Montana, USA, for the winter of 1998/1999. An average 8.68% of the krummholz canopy was lost due to desiccation.
Winter desiccation is not predictable based on any single environmental variable. When outliers are removed, winter desiccation shows a strong correlation with elevation ( r = 0.97). Patch level winter desiccation amounts are, however, highly predictable from elevation, slope, aspect and topographic context when considered together. In general, injury increases with elevation and on more southwesterly facing hillslopes. High slopes and sheltered locations decrease winter desiccation.
Within patches, most winter desiccation is located at the windward edge of the patch. This trend may be modified by the presence of leaders above the mean canopy surface of the krummholz patch, or by local microtopographic features such as dead branches or the proximity of large rocks.
The winter of 1998/1999 was a high winter desiccation year compared to the two previous winters. The winter of 1998/1999 had high snowfall, and meltout did not occur until later than the previous two winters. The extended period of snow cover is hypothesized to be one of the causes of the increased winter desiccation for the 1998/1999 winter.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号