全文获取类型
| 收费全文 | 120篇 |
| 免费 | 37篇 |
| 国内免费 | 6篇 |
专业分类
| 大气科学 | 6篇 |
| 地球物理 | 69篇 |
| 地质学 | 32篇 |
| 海洋学 | 8篇 |
| 综合类 | 2篇 |
| 自然地理 | 46篇 |
出版年
| 2021年 | 2篇 |
| 2020年 | 1篇 |
| 2019年 | 1篇 |
| 2018年 | 3篇 |
| 2017年 | 2篇 |
| 2016年 | 5篇 |
| 2015年 | 4篇 |
| 2014年 | 3篇 |
| 2013年 | 3篇 |
| 2012年 | 2篇 |
| 2011年 | 9篇 |
| 2010年 | 7篇 |
| 2009年 | 10篇 |
| 2008年 | 12篇 |
| 2007年 | 11篇 |
| 2006年 | 10篇 |
| 2005年 | 9篇 |
| 2004年 | 13篇 |
| 2003年 | 7篇 |
| 2002年 | 8篇 |
| 2001年 | 1篇 |
| 2000年 | 1篇 |
| 1999年 | 1篇 |
| 1998年 | 4篇 |
| 1997年 | 4篇 |
| 1996年 | 12篇 |
| 1995年 | 6篇 |
| 1994年 | 5篇 |
| 1993年 | 2篇 |
| 1992年 | 3篇 |
| 1991年 | 1篇 |
| 1989年 | 1篇 |
排序方式： 共有163条查询结果，搜索用时 484 毫秒
61.
Realistic numerical modeling of ground penetrating radar (GPR) using the finite-difference time-domain (FDTD) method could greatly benefit from the implementation of subgrids – supporting finer spatial resolution – into the conventional FDTD mesh. This is particularly important, when parts of the computational domain need to be modeled in detail or when there are features or regions in the overall computational mesh with values of high dielectric constant supporting propagation of waves at very short wavelengths. A scheme that simplifies the process of implementing these subgrids into the traditional FDTD method is presented. This scheme is based on the combination of the standard FDTD method and the unconditionally stable alternating-direction implicit (ADI) FDTD technique. Because ADI-FDTD is unconditionally stable its time-step can be set to any value that facilitates the accurate calculation of the fields. By doing so, the two grids can efficiently communicate information across their boundary without requiring to use a costly time-interpolation scheme. This paper discusses the performance of ADI-FDTD subgrids when implemented into the traditional FDTD method, using different communication schemes for the information exchange at the boundary of the two grids. The developed algorithm, can handle cases where the subgrid crosses dielectrically inhomogeneous media. In addition, results from the comparison between the proposed scheme and a commonly employed purely FDTD subgridding technique are presented. 相似文献
62.
63.
如何有效压制数值频散是有限差分正演模拟研究中的关键问题之一.近年来,许多学者对二阶声波方程的差分算子开展了大量的优化工作,在压制频散方面取得不错的效果.一阶压强-速度方程广泛用于研究地震波在地下变密度模型中传播规律,目前针对一阶方程的优化工作大多只是在空间差分算子上展开.本文在前人研究的基础上,推导出一阶声波方程中压强场与偏振速度场之间的解析关系,据此在传统交错网格基础上给出一种高精度的显式时间递推格式,该递推格式将时间差分与空间差分算子结合在一起,并采用共轭梯度法得到精确时间递推匹配系数,实现时空差分算子的同时优化.在编程实现算法的基础上,通过频散分析与三个典型模型测试表明:本文方法能够较为有效地压制时间频散与空间频散,提高数值计算精度;同时对复杂模型也有很好适用性. 相似文献
64.
Scattering attenuation in short wavelengths has long been interesting to geophysicists. Ultrasonic coda waves, observed as the tail portion of ultrasonic wavetrains in laboratory ultrasonic measurements, are important for such studies where ultrasonic waves interact with small-scale random heterogeneities on a scale of micrometers, but often ignored as noises because of the contamination of boundary reflections from the side ends of a sample core. Numerical simulations with accurate absorbing boundary can provide insight into the effect of boundary reflections on coda waves in laboratory experiments. The simulation of wave propagation in digital and heterogeneous porous cores really challenges numerical techniques by digital image of poroelastic properties, numerical dispersion at high frequency and strong heterogeneity, and accurate absorbing boundary schemes at grazing incidence. To overcome these difficulties, we present a staggered-grid high-order finite-difference (FD) method of Biot’s poroelastic equations, with an arbitrary even-order (2L) accuracy to simulate ultrasonic wave propagation in digital porous cores with strong heterogeneity. An unsplit convolutional perfectly matched layer (CPML) absorbing boundary, which improves conventional PML methods at grazing incidence with less memory and better computational efficiency, is employed in the simulation to investigate the influence of boundary reflections on ultrasonic coda waves. Numerical experiments with saturated poroelastic media demonstrate that the 2L FD scheme with the CPML for ultrasonic wave propagation significantly improves stability conditions at strong heterogeneity and absorbing performance at grazing incidence. The boundary reflections from the artificial boundary surrounding the digital core decay fast with the increase of CPML thicknesses, almost disappearing at the CPML thickness of 15 grids. Comparisons of the resulting ultrasonic coda Q sc values between the numerical and experimental ultrasonic S waveforms for a cylindrical rock sample demonstrate that the boundary reflection may contribute around one-third of the ultrasonic coda attenuation observed in laboratory experiments. 相似文献
65.
低速带具有“自由表面、低速度、高吸收”的特征,能引起反射波能量减弱,产生很强的频散,造成近地表波场畸变,严重影响地震勘探的精度。而地震采集过程又不可避免遇到以下低速带问题:①低速带存在与否会对地震波传播造成什么影响;②近地表变化大,怎么才能得到精确的低速带参数;③存在低速带时,激发井深、最佳的药量(与子波频率有关)、最佳的耦合(与低速带速度相关)等采集参数会对采集资料的品质产生什么影响。本文通过数值模拟,集中对低速带与地震波激发的井深、速度、子波主频等核心采集参数的关系进行分析研究,同时在低速带背景下对数值模拟的网格、边界等问题也进行了讨论。模拟得到的波场特征及低速带参数影响的机理分析,对做好野外地震波激发,获取高品质的地震资料,具有理论意义和指导作用。 相似文献
66.
67.
双相各向异性介质中偶数阶精度有限差分数值模拟 总被引：1，自引：1，他引：0
To improve the accuracy of the conventional finite-difference method, finitedifference numerical modeling methods of any even-order accuracy are recommended. We introduce any even-order accuracy difference schemes of any-order derivatives derived from Taylor series expansion. Then, a finite-difference numerical modeling method with any evenorder accuracy is utilized to simulate seismic wave propagation in two-phase anisotropic media. Results indicate that modeling accuracy improves with the increase of difference accuracy order number. It is essential to find the optimal order number, grid size, and time step to balance modeling precision and computational complexity. Four kinds of waves, static mode in the source point, SV wave cusps, reflection and transmission waves are observed in two-phase anisotropic media through modeling. 相似文献
68.
利用昆明市区的人工地震资料的Pg震相,通过三维有限差分方法对昆明地区浅部速度分布及构造进行反演,探讨了速度结构与隐伏断裂的关系以及主要活动断裂向深部的伸展情况. 其中,普渡河——西山断裂在各种深度速度分布图上都在低速异常区的西边界上,是昆明盆地西侧的边界断裂, 表现为以陡倾角向东倾斜, 且向深部延伸深度较大. 而普吉——韩家村断裂和黑龙潭——官渡断裂则控制盆地中部的低速异常区,向深部延伸深度相对较小,未穿过盆地基底界面. 相似文献
69.
In order to image the 3-D velocity structure of its shallow crust in Kunming region,China,finite-difference seis-mic tomography is used to invert the seismic data selected carefully from six-shot data. The result lays a founda-tion for the discussion of the relationship between the obtained velocity structure and the hidden faults,and for the illumination of the depth extents of main active faults surrounding Kunming city. Puduhe-Xishan fault lies on the western margin of the Kunming basin and is just situated on the west edge of the low velocity anomaly zone found at all depth levels. This indicates that this fault is a borderline fault of the Kunming basin. It can be concluded that the fault dips eastwards with a steep angle and its depth extent is large. Puji-Hanjiacun fault and Heilong-tan-Guandu fault play a role in controlling the low velocity anomaly zone in middle basin. The depth extents of the two faults are comparatively small,without traversing the interface of basin floor. 相似文献
70.
由于在正交坐标系中斜度井边界处理的复杂性,提出一种非正交计算方法,即在非正交坐标系计算了斜度井中感应测井的响应.首先,利用Maxwell方程组和逐次逼近法推导出矢量电位在非正交坐标系下的解析解;然后,通过有限差分法计算接收线圈处的感应电动势,得到视电导率的值;最后,计算了无井无侵地层模型在不同厚度和倾斜角度影响下的响应,计算结果与理论解及前人结果具有很好的一致性.结果表明,该方法具有数值网格与边界吻合的特点,而且只要较少的离散网格就可以达到较高的精度,计算速度快,是求解斜度井中感应响应的有效方法. 相似文献