全文获取类型
收费全文 | 3519篇 |
免费 | 414篇 |
国内免费 | 167篇 |
专业分类
测绘学 | 127篇 |
大气科学 | 241篇 |
地球物理 | 1599篇 |
地质学 | 1169篇 |
海洋学 | 349篇 |
天文学 | 36篇 |
综合类 | 22篇 |
自然地理 | 557篇 |
出版年
2024年 | 13篇 |
2023年 | 22篇 |
2022年 | 30篇 |
2021年 | 71篇 |
2020年 | 149篇 |
2019年 | 122篇 |
2018年 | 113篇 |
2017年 | 168篇 |
2016年 | 162篇 |
2015年 | 125篇 |
2014年 | 146篇 |
2013年 | 362篇 |
2012年 | 78篇 |
2011年 | 106篇 |
2010年 | 106篇 |
2009年 | 172篇 |
2008年 | 239篇 |
2007年 | 213篇 |
2006年 | 210篇 |
2005年 | 201篇 |
2004年 | 155篇 |
2003年 | 128篇 |
2002年 | 102篇 |
2001年 | 94篇 |
2000年 | 115篇 |
1999年 | 102篇 |
1998年 | 98篇 |
1997年 | 98篇 |
1996年 | 70篇 |
1995年 | 69篇 |
1994年 | 50篇 |
1993年 | 54篇 |
1992年 | 35篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有4100条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
997.
讨论华南黑水─泉州地学断面的重磁解释。在解释中除应用常规的2.5维重磁异常反演外,还采用等密度线算法构制梯度层密度模型,用于分辨地壳密度细结构,以及计算自由地幔而深度用于分析上地幔密度的横向不均匀性。重磁模拟结果揭示了10km深度内的上地壳构造以及地壳与上地幔密度的分布。提出华南造山带以低密度上地幔为特征,它可能与上地幔的改造有关;四川盆地具有较高的上地幔密度,为未经改造的原始地幔。扬子克拉通与华南造山带的分界线与上地幔密度的分界线一致。根据布格异常、地表岩石密度和地形资料的综合分析,圈定出反映内生成矿作用深部标志的密度倒转区,可作为进一步找矿的远景区。 相似文献
998.
Three simple models of the behaviour of a series of basaltic eruptions have been tested against the eruptive history of Nyamuragira. The data set contains the repose periods and the volumes of lava emitted in 22 eruptions since 1901. Model 1 is fully stochastic and eruptions of any volume with random repose intervals are possible. Models 2 and 3 are constrained by deterministic limits on the maximum capacity of the magma reservoir and on the lowest drainage level of the reservoir respectively. The method of testing these models involves (1) seeking change points in the time series to determine regimes of uniform magma supply rate, and (2) applying linear regression to these regimes, which for models 2 and 3 are the determinsstic limits to those models. Two change points in the time series for Nyamuragira, in 1958 and 1980, were determined using a Kolmogorov-Smirnov technique. The latter change involved an increase in the magma supply rate by a factor of 2.5, from 0.55 to 1.37 m3s-1. Model 2 provides the best fit to the behavior of Nyamuragira with the ratio of variation explained by the model to total variation. R2, being greater than 0.9 for all three regimes. This fit can be interpreted to mean that there is a determinstic limit to the elastic strength of the magma reservoir 4–8 km below the summit of the volcano. 相似文献
999.
Many of the numerical techniques used for seismic zonation studies treat one-dimensional structural models and/or the incidence of plane polarized body waves. These techniques are often not adequate for laterally heterogeneous structures and for sources that are not located beneath the site of interest. In such cases a more rigorous treatment of the combined effects of the source, the path and the site response is needed. This can be accomplished with a hybrid approach combining modal summation and the finite-difference technique. To demonstrate the differences between these techniques, the ground motion in the city of Benevento (Italy) is modelled. We first compare the results obtained with one-and two-dimensional structural models for vertical incidence of plane polarized body waves. These results are then compared with those obtained with the hybrid approach for two-dimensional structural models.The comparisons have allowed us to find important differences in the response obtained with the different modelling techniques. For the same site, these differences consist of strong variations in amplitude and in the shape of the spectral amplifications. For a seismic source which is not located beneath the site, vertical incidence of waves significantly overestimates the local hazard in a laterally homogeneous structure. For a laterally heterogeneous area, we can conclude that one-dimensional modelling fails to estimate the seismic hazard, whereas for a seismic source which is not located beneath the site of interest, two-dimensional modelling with vertical incidence of plane polarized body waves may not allow reliable estimates to be made of the frequency bands at which amplifications occur. The results obtained for two-dimensional structural models are used for a zonation of the city of Benevento. 相似文献
1000.
A. N. Hanchinal P. B. V. Subba Rao Nandini Nagarajan D. R. K. Rao B. P. Singh 《Journal of Earth System Science》1994,103(3):383-400
Magnetovariational studies have been carried out in Singhbhum and surrounding regions during 1987 and 1989. Three deep-seated
linear conductors have been identified. One of them is located to the north of Ranchi, Bokaro and Purulia extending in E-W
direction coinciding with high heat flow region and Gondwana sediments. The trend of anomaly at Ranchi and Purulia at longer
periods suggests a conductivity anomaly due to the mafic and ultramafic intrusions, considered to be responsible for the uplift
of Chhotanagpur plateau. The second conductor is associated with the basin margin fault that separates the Singhbhum craton
and Chhotanagpur plateau from the West Bengal basin. This conductive zone appears to extend further south and join the high
heat flow region of Attri-Tarabalo. This conductor could be isolated only after eliminating the coast effect from the observed
induction vectors. The third conductive zone follows the trend of Mahanadi valley located south of the Sukinda thrust. Conductive
anomaly associated with the Sukinda and Singhbhum thrust zones could not be resolved due to the interference from neighbouring
conductive structures. These two thrusts may not be very deep-seated structures. The Singhbhum granite batholith is found
to be highly resistive and seems to extend to greater depths. 相似文献