全文获取类型
收费全文 | 3229篇 |
免费 | 569篇 |
国内免费 | 807篇 |
专业分类
测绘学 | 254篇 |
大气科学 | 1016篇 |
地球物理 | 808篇 |
地质学 | 1533篇 |
海洋学 | 522篇 |
天文学 | 22篇 |
综合类 | 149篇 |
自然地理 | 301篇 |
出版年
2024年 | 17篇 |
2023年 | 28篇 |
2022年 | 93篇 |
2021年 | 92篇 |
2020年 | 104篇 |
2019年 | 139篇 |
2018年 | 90篇 |
2017年 | 135篇 |
2016年 | 129篇 |
2015年 | 137篇 |
2014年 | 154篇 |
2013年 | 183篇 |
2012年 | 142篇 |
2011年 | 150篇 |
2010年 | 148篇 |
2009年 | 220篇 |
2008年 | 225篇 |
2007年 | 247篇 |
2006年 | 209篇 |
2005年 | 221篇 |
2004年 | 199篇 |
2003年 | 156篇 |
2002年 | 167篇 |
2001年 | 144篇 |
2000年 | 162篇 |
1999年 | 136篇 |
1998年 | 110篇 |
1997年 | 111篇 |
1996年 | 115篇 |
1995年 | 81篇 |
1994年 | 94篇 |
1993年 | 64篇 |
1992年 | 55篇 |
1991年 | 43篇 |
1990年 | 22篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有4605条查询结果,搜索用时 15 毫秒
281.
Numerical modelling ofSH wave seismograms in media whose material properties are prescribed by a random distribution of many perfectly elastic cavities and by intrinsic absorption of seismic energy (anelasticity) demonstrates that the main characteristics of the coda waves, namely amplitude decay and duration, are well described by singly scattered waves in anelastic media rather than by multiply scattered waves in either elastic or anelastic media. We use the Boundary Integral scheme developed byBenites
et al. (1992) to compute the complete wave field and measure the values of the direct waveQ and coda wavesQ in a wide range of frequencies, determining the spatial decay of the direct wave log-amplitude relation and the temporal decay of the coda envelope, respectively. The effects of both intrinsic absorption and pure scattering on the overall attenuation can be quantified separately by computing theQ values for corresponding models with (anelastic) and without (elastic) absorption. For the models considered in this study, the values of codaQ
–1 in anelastic media are in good agreement with the sum of the corresponding scatteringQ
–1 and intrinsicQ
–1 values, as established by the single-scattering model ofAki andChouet (1975). Also, for the same random model with intrinsic absorption it appears that the singly scattered waves propagate without significant loss of energy as compared with the multiply scattered waves, which are strongly affected by absorption, suggesting its dominant role in the attenuation of coda waves. 相似文献
282.
283.
284.
285.
In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed. 相似文献
286.
287.
A quality investigation of global vertical datum connection 总被引:3,自引:0,他引:3
Peiliang Xu 《Geophysical Journal International》1992,110(2):361-370
288.
289.
Tectonic Units and Their Fundamental Characteristics on the Northern Margin of the Alxa Block 总被引:6,自引:0,他引:6
Wu Tairan Geology Department China University of Geosciences Beijing He Guoqi Geology Department Peking University Jiang Minxi 《《地质学报》英文版》1993,67(4)
The northern margin of the Alxa block is the junction of a tectonic units. Four first-order tectonic units are distinguished: 1. the Yagan structural zone characteristic of an immature island arc; 2. the Zhusileng-Hangwula structural zone, which was a passive continental margin in the Early Palaeozoic and was transformed into an active continental margin in the Late Palaeozoic;3. the Shalazha structural zone characteristic of a mature island arc; 4. the Nuru-Langshan structural zone, which was a Proterozoic orogenic belt and later evolved into an extensional transtional crust in the Palaeozoic. The above-mentioned tectonic units differ remarkably in sedimentary formations, magmatic rock associations, metamorphism and geochemistry and are bounded by faults between one another. 相似文献
290.
利用引进的近地表化探系统,在济阳拗陷东营凹陷南坡的草桥油田进行了化探资料的采集、分析、处理及解释。研究证明:该系统在资料采集和现场质量控制方面有着明显的技术优势,在己知油田的断层、油水边界和油层尖灭线都有明显的地化异常。通过各种方法实验,对烃类在纵向上、横向上的丰度变化进行了初步探索。 相似文献