全文获取类型
收费全文 | 305篇 |
免费 | 47篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 27篇 |
地球物理 | 75篇 |
地质学 | 87篇 |
海洋学 | 43篇 |
天文学 | 42篇 |
综合类 | 14篇 |
自然地理 | 42篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 13篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 11篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 20篇 |
2008年 | 17篇 |
2007年 | 25篇 |
2006年 | 16篇 |
2005年 | 8篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 22篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有377条查询结果,搜索用时 15 毫秒
261.
采用有限元直接迭代算法实现了线源频率域测深电磁响应的二维正演计算. 首先给出了线源正演问题的有限元直接迭代格式,然后由迭代法进行求解. 在处理奇异源问题上,采用向内递推的组合网格技巧,在源点附近可进行局部加密,并实现粗细网格的对接,从而较好地解决了奇异源附近的计算问题. 还提出一种迭代求取全区视电阻率的方法,避免了远近区的划分. 通过对均匀半空间、层状介质和二维模型电磁响应的计算,获得了与大地电磁测深相似的视电阻率曲线,验证了算法的正确性;通过对计算结果的分析,在理论上说明了线源频率域近区测深的可行性. 相似文献
262.
263.
The southern margin of the East European Craton: new results from seismic sounding and potential fields between the North Sea and Poland 总被引:1,自引:0,他引:1
U. Bayer M. Grad T. C. Pharaoh H. Thybo A. Guterch D. Banka J. Lamarche A. Lassen B. Lewerenz M. Scheck A. -M. Marotta 《Tectonophysics》2002,360(1-4):301-314
The extension of eastern Avalonia from Britain through the NE German Basin into Poland is, in some sense, a virtual structure. It is covered almost everywhere by late Paleozoic and younger sediments. Evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks. During the last two decades, much geophysical and geological information has been gathered since the European Geotraverse (EGT), which was followed by the BABEL, LT-7, MONA LISA, DEKORP-Basin'96, and POLONAISE'97 deep seismic experiments. Based on seismic lines, a remarkable feature has been observed between the North Sea and Poland: north of the Elbe Line (EL), the lower crust is characterised by high velocities (6.8–7.0 km/s), a feature which seems to be characteristic for at least a major part of eastern Avalonia (far eastern Avalonia). In addition, the seismic lines indicate that a wedge of the East European Craton (EEC) (or Baltica) continues to the south below the southern Permian Basin (SPB)—a structure which resembles a passive continental margin. The observed pattern may either indicate an extension of the Baltic crust much farther south than earlier expected or oceanic crust of the Tornquist Sea trapped during the Caledonian collision. In either case, the data require a reinterpretation of the docking mechanism of eastern Avalonia, and the Elbe–Odra Line (EOL), as well as the Elbe Fault system, together with the Intra-Sudedic Faults, appear to be related to major changes in the deeper crustal structures separating the East European crust from the Paleozoic agglomeration of Middle European terranes. 相似文献
264.
265.
266.
井地电阻率成像法利用井套管作电流源向井下供入大功率直流电流,在地表测量由地下介质的电性变化形成的电位分布,通过反演可得到地下介质的电阻率分布.针对大斜度井和水平井开展井地三维电阻率数值模拟和反演研究,对油田注水及压裂效果监测具有重要意义.基于井地电阻率成像法原理,采用有限差分法和不完全切勒斯基共轭梯度法进行了三维正演模拟,研究了大斜度井和水平井的井地电位响应特征.提出了采用层状约束阻尼最小二乘法由浅到深地进行大斜度井和水平井的多层联合反演,并对实际水平井井地电位各个层段数据进行了三维反演.模拟结果表明,倾斜线源和水平线源会对地面电位响应产生明显影响,在反演中需要考虑线源形态.实际水平井井地电位反演成像表明,考虑倾斜线源或者水平线源的联合反演得到了准确的水平井三维注水层成像图,得出注水层的真电阻率分布,能够判断注水运移方向. 相似文献
267.
Summary From the theoretical investigation ofLetfus andApostolov (1974) it follows that under flare conditions the intensive X-ray emission lines in the 1–8 Å range have an insignificant contribution to the ionization state of the lower ionosphere in comparison with the enhanced emission of the continuum. This result is experimentally confirmed by direct comparison of the intensity variations of the emission line 1.87 Å (Fe XXV) during the solar flare of 25 July 1967 measured onboard of the OSO III satellite with simultaneous ground observations of the ionization state variations of the lower ionosphere made by the A3 method. 相似文献
268.
Olu Agunloye 《Pure and Applied Geophysics》1981,119(5):1003-1023
A simple numerical inversion scheme for estimatingn-layer model parameters from observed geoelectrical resistivity data can be used in either the space or wavenumber domain. The technique utilizes Madden's Transmission Line Analogy to compute the resistivity transforms and linear filter theory to accomplish the excursions between the space and wavenumber domains. The inversion is effected by an iterative refinement scheme employing the stochastic inverse which is approximate to the generalized inverse. No singular decomposition analysis is required and the scheme is stable under ill conditions. The inversion scheme not only gives the desired estimates; it exposes redundant parameters and irrelevant data and is easily programmed on a desk-top mini computer. Examples of inverse modeling with hypothetical and field data are discussed. 相似文献
269.
270.
在分析大量监测资料的基础上,将水化前兆异常变化归结为3种基本曲线类型,将这些基本曲线与水动力弥散曲线进行对比分析,进而提出了水化前兆信息传递机制实质是一种水动力弥散的新观点,并就水动力弥散理论在水化前兆信息机制研究中的应用进行了讨 相似文献