全文获取类型
收费全文 | 777篇 |
免费 | 104篇 |
国内免费 | 266篇 |
专业分类
测绘学 | 291篇 |
大气科学 | 74篇 |
地球物理 | 104篇 |
地质学 | 411篇 |
海洋学 | 138篇 |
天文学 | 5篇 |
综合类 | 80篇 |
自然地理 | 44篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 36篇 |
2021年 | 48篇 |
2020年 | 58篇 |
2019年 | 46篇 |
2018年 | 38篇 |
2017年 | 55篇 |
2016年 | 51篇 |
2015年 | 59篇 |
2014年 | 63篇 |
2013年 | 56篇 |
2012年 | 66篇 |
2011年 | 64篇 |
2010年 | 56篇 |
2009年 | 48篇 |
2008年 | 53篇 |
2007年 | 66篇 |
2006年 | 28篇 |
2005年 | 47篇 |
2004年 | 34篇 |
2003年 | 38篇 |
2002年 | 23篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
排序方式: 共有1147条查询结果,搜索用时 15 毫秒
41.
Short-period teleseismicP waves from the Nevada Test Site (NTS) show systematic variations in amplitudes and travel times, with low amplitudes corresponding to fast travel times, suggesting elastic focussing-defocussing effects. Also, the azimuthal amplitude and travel time patterns for events at the Pahute Mesa subsite are systematically different from those at the Yucca Flat subsite, indicating the presence of a near-source component in both the amplitude and travel-time variations. This component is isolated by removing the mean station pattern for all of NTS from the observations. A very-near-source component in the Pahute Mesa observations is also isolated by removing subsite station means from the measurements, whereas the Yucca Flat observations exhibited no coherent very-near-source component. These anomalies are back-projected through laterally homogeneous structure to form thin lens models at various depths. Travel-time delays are predicted from the amplitude variations using the equation for wavefront curvature. The long-wavelength components of the predicted and observed time delays correlate well, at depths of 25 km for the very-near-source component under Pahute Mesa and 160 km for the regional component under NTS. The time delay surfaces predicted by the amplitudes at these depths are mapped into warped velocity discontinuities suitable for the calculation of synthetic seismograms using the Kirchhoff-Helmholtz integral formulation. Both the intersite (near-source) and intrasite (very-near-source) differences in amplitudes are qualitatively predicted very well, although the range of variation is somewhat underpredicted. This deficiency is likely due to the destructive interference of anomalies inherent in back-projection to a single layer. 相似文献
42.
We present the results of the application of three-dimensional Hilbert transformation to the analysis of airborne total field magnetic anomalies over part of Southeastern Nigeria. This study not only substantiates the usefulness of 3-D Hilbert transforms in the interpretation of magnetic anomaly maps but also more clearly delineates the structural pattern of the area, of study. Results from the previous study are discussed in relation to the results of previous geological and geophysical studies of the area. 相似文献
43.
发展了一个三维水动力学模型.该模型在水底磨擦项计算中,采用了流速的平方根法;在湍流扩散系数的估算中,采用了带稳定度函数的参数化方案;对垂直方向上的坐标进行了压缩,引入σ坐标;对时间变量则采用了分离模式技术,即外部模式(快过程)与内部模式(慢过程);而求解外部模式时,采用了显式一隐式格式交错法(ADI),从而使模型不仅计算时间缩短,且可应用于水很深而水平空间尺度很小,又有热力分层的水域中.最后作为该模型的一个实用性试验,选择了美国犹他州East Canyon水库,利用该模型探讨了温跃层对风、人流及出流变化的响应情况. 相似文献
44.
多部多普勒雷达同步探测三维风场反演系统 总被引:18,自引:5,他引:18
“我国重大气候和天气灾害的形成机理与预测理论研究”项目首次启用双多普勒雷达组网同步观测,如何从同步观测的暴雨资料中反演三维场,具有重要的理论和现实意义,根据项目需要,建立了国内首套多部多普勒天气雷达同步探测三维风场反演软件系统,并反演出2001年7月13日由双多普勒雷达同步观测到的一个中β尺度暴雨系统的三维风场,结果显示,该三维风场结构合理,系统能满足外场试验的要求。 相似文献
45.
46.
城市地铁复杂洞群浅埋暗挖法的有限元模拟 总被引:17,自引:2,他引:17
以北京地铁复-八线王府井至东单区间隧道的施工为例,论述了城市复杂洞群浅埋暗挖法的有限元模拟,应用三维有限元理论研究、分析了施工效应问题,并对复杂洞群系统施工工艺进行了优化,解决了一系列施工中的难题,取得了很好效益。 相似文献
47.
48.
V. Pereyra 《Pure and Applied Geophysics》1996,148(3-4):345-386
We describe an integrated forward and inverse three-dimensional modeling system that can deal with complex geological structures. The system has been designed to handle large-scale problems by using a distributed approach. It uses seismic ray tracing for forward simulation, time-to-depth mapping, and nonlinear travel-time inversion.A novel decomposition method is our tool to attack large-scale problems in a parallel approach. The system is fully implemented and we demonstrate its performance with synthetic examples.This research was partially supported by the National Science Foundation under SBIR Grant III-9300992. 相似文献
49.
《地震学报(英文版)》1993,6(3):619-629
In the present study the long period surface wave records of 238 wave-paths from 79 earthquakes within China and its adjacent
regions received by 30 seismic network stations are measured by using the improved match-filtering frequency-time analysis
technique and the grid dispersion inversion method to obtain the rayleigh pure-path dispersion values for 147 slant grids
of 4° × 4° in this area, then a three-dimensional shear wave velocity model of the crust and upper mantle beneath south China
area to a depth of 170 km is inversed.
It is found that there are obvious differences among the main structural units, and there are also certain differences among
the subordinate elements even in the individual unit. The crustal thickness of this area is ranging from 30 to 43 km, and
is getting thicker gradually from the east to the west. The average shear velocity of crust is ranging form 3.48 to 3.68 km/s
with the lowest in the northeast part and highest in the west part. No obvious crustal low velocity layer of large scale is
detected. There exist upper mantle low velocity zones in the most of south China area with the starting depth ranging from
75 to 106 km. The lowest shear velocity within the low velocity zones is about 4.28–4.38 km/s. Despite of the existing of
upper mantle low velocity zones beneath the most of south China area, the interfaces between the important layers are quite
clear, the variation of the bedding surfaces is very gentle, and the lateral changes measured in a larger scale of the underground
structure are rather small. It may indicate that the crustal and upper mantle structure of the main part of south China area
belongs to the relatively stable structure of the continental blocks except for the fringe areas such as the fold-faulted
region in the west part and the fault system along the southeastern coast which may belong to the tectonically active area.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 159–167, 1993.
This subject is supported by the National Science Foundation of China. 相似文献
50.
半拉格朗日、半隐式欧拉方程组大气数值模式研究 总被引:2,自引:1,他引:1
介绍了一个具有较高时间积分效率的三维弹性大气数值模式。其中,控制方程为能够描述大气非静力及可压缩性的欧拉方程组,时间积分采用了高效率的“半拉格朗日、半隐式”方案。通过引用一个简化的“云物理过程”参数化方案,针对大气中深厚湿对流过程的若干问题进行了数值试验,结果表明,模式能够对该过程中的一些基本和复杂现象进行有效地模拟。试验结果还表明,动力学框架具有很好的稳定性,能够实现高效率的时间积分,它还具有较好的频散特性,保证了空间计算的精度,从而完好地描述了风暴的形态。 相似文献