全文获取类型
收费全文 | 9750篇 |
免费 | 2355篇 |
国内免费 | 784篇 |
专业分类
测绘学 | 112篇 |
大气科学 | 82篇 |
地球物理 | 7721篇 |
地质学 | 2966篇 |
海洋学 | 563篇 |
天文学 | 22篇 |
综合类 | 466篇 |
自然地理 | 957篇 |
出版年
2024年 | 17篇 |
2023年 | 75篇 |
2022年 | 244篇 |
2021年 | 304篇 |
2020年 | 367篇 |
2019年 | 444篇 |
2018年 | 359篇 |
2017年 | 321篇 |
2016年 | 299篇 |
2015年 | 379篇 |
2014年 | 479篇 |
2013年 | 505篇 |
2012年 | 557篇 |
2011年 | 588篇 |
2010年 | 477篇 |
2009年 | 553篇 |
2008年 | 570篇 |
2007年 | 705篇 |
2006年 | 722篇 |
2005年 | 591篇 |
2004年 | 600篇 |
2003年 | 523篇 |
2002年 | 438篇 |
2001年 | 324篇 |
2000年 | 349篇 |
1999年 | 300篇 |
1998年 | 293篇 |
1997年 | 235篇 |
1996年 | 268篇 |
1995年 | 211篇 |
1994年 | 193篇 |
1993年 | 175篇 |
1992年 | 111篇 |
1991年 | 71篇 |
1990年 | 50篇 |
1989年 | 53篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 16篇 |
1978年 | 1篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
111.
Surface waves image the top of the Eifel plume 总被引:1,自引:0,他引:1
Jan P. Mathar Joachim R. R. Ritter Wolfgang Friederich 《Geophysical Journal International》2006,164(2):377-382
112.
113.
A general tomographic technique is designed in order (i) to operate in anisotropic media; (ii) to account for the uneven seismic sampling and (iii) to handle massive data sets in a reasonable computing time. One modus operandi to compute a 3-D body wave velocity model relies on surface wave phase velocity measurements. An intermediate step, shared by other approaches, consists in translating, for each period of a given mode branch, the phase velocities integrated along ray paths into local velocity perturbations. To this end, we develop a method, which accounts for the azimuthal anisotropy in its comprehensive form. The weakly non-linear forward problem allows to use a conjugate gradient optimization. The Earth's surface is regularly discretized and the partial derivatives are assigned to the individual grid points. Possible lack of lateral resolution, due to the inescapable uneven ray path coverage, is taken into account through the a priori covariances on parameters with laterally variable correlation lengths. This method allows to efficiently separate the 2ψ and the 4ψ anisotropic effects from the isotropic perturbations. Fundamental mode and overtone phase velocity maps, derived with real Rayleigh wave data sets, are presented and compared with previous maps. The isotropic models concur well with the results of Trampert & Woodhouse. Large 4ψ heterogeneities are located in the tectonically active regions and over the continental lithospheres such as North America, Antarctica or Australia. At various periods, a significant 4ψ signature is correlated with the Hawaii hotspot track. Finally, concurring with the conclusions of Trampert & Woodhouse, our phase velocity maps show that Rayleigh wave data sets do need both 2ψ and 4ψ anisotropic terms. 相似文献
114.
115.
We have found that the extensively used finite difference scheme time3d produces time fields which are 'asymmetric' in the sense that traveltimes computed to the right of the source are faster than traveltimes computed to the left. All finite difference schemes will, as they are approximations to the wave equation, to some extent fail to obey reciprocity perfectly. We show, however, that the errors in time3d may be significant—and unnecessarily large. An asymmetry in the point source initialization has been identified, and after correction time3d produces time fields with an improved reciprocity. 相似文献
116.
在分析戈壁沙漠地区地球物理特征的基础上,针对性的提出了解决煤田地质构造问题的方法,包括三维地震野外施工方法的选取、施工因素的选择、资料处理手段;并以获得的实际地质成果证实三维地震在解决复杂地质构造问题的可行性。 相似文献
117.
Seismic Hazards Assessment for Radioactive Waste Disposal Sites in Regions of Low Seismic Activity 总被引:4,自引:0,他引:4
Clark H. Fenton John Adams Stephen Halchuk 《Geotechnical and Geological Engineering》2006,24(3):579-592
A comparative tectonic quiescence and lack of earthquakes make the stable centres of continents attractive for siting long-term
radioactive waste storage facilities. The low rates of deformation in such regions, however, make it difficult to characterize
their long-term seismotectonic behaviour, leading to uncertain estimates for the very low probability hazard estimates required
by society. In an attempt to overcome the deficiency of both contemporary seismicity and paleoseismic data in central Canada,
we have used earthquake histories from regions with similar seismotectonic characteristics from around the world. Substituting
space for time, we estimate a long-term rate per 106 km2 of 0.004 magnitude ≥6 earthquakes per annum, of which 33–100% might rupture to the surface. 相似文献
118.
WANG Da-wei 《现代地质》2006,(4)
从差异波形特征的角度出发,分析时移地震差异波形特征与砂泥岩互层油藏中油层速度变化的关系。通过建立由5层地层组成的楔形地质模型,运用褶积公式及时移地震求差公式,得到泥岩速度为2 400 m/s和砂岩速度为2 700m/s条件下,互层中砂岩速度变化±150 m/s的时移地震响应。研究结果表明:砂泥岩互层的差异波形是一个多峰复合波,泥岩夹层的厚度是决定差异波形特征的一个主要因素,并且存在一个临界值,即四分之一主波长;如果泥岩夹层的厚度小于这一临界值,就会发生遮掩效应,即顶部油层的时移地震响应可以掩盖中、下部油层的时移地震响应。 相似文献
119.
HUANG Ling YANG Guang-da HAN Li-guo .Geophysical Exploration Company of Jilin Petroleum Group Co. Ltd Songyuan China .Jilin Petroleum Group Company Songyuan China .College of GeoExploration Science Technology Jilin University Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
深层地震勘探野外资料采集的关键是在保证原始资料一定信噪比的基础上,同时兼顾分辨率,激发井深是决定资料品质的重要因素之一。通过对虚反射滤波作用分析,提出了充分利用虚反射能量设计最佳激发井深,增强下传地震波能量的采集方法。理论分析和试验资料表明,在高速层下4~7m的最佳激发岩性深度是深层勘探的理想井深。 相似文献
120.