收费全文 | 2282篇 |
免费 | 412篇 |
国内免费 | 816篇 |
测绘学 | 161篇 |
大气科学 | 340篇 |
地球物理 | 919篇 |
地质学 | 1159篇 |
海洋学 | 679篇 |
天文学 | 38篇 |
综合类 | 147篇 |
自然地理 | 67篇 |
2024年 | 2篇 |
2023年 | 31篇 |
2022年 | 41篇 |
2021年 | 75篇 |
2020年 | 93篇 |
2019年 | 109篇 |
2018年 | 96篇 |
2017年 | 107篇 |
2016年 | 114篇 |
2015年 | 125篇 |
2014年 | 141篇 |
2013年 | 207篇 |
2012年 | 158篇 |
2011年 | 142篇 |
2010年 | 148篇 |
2009年 | 171篇 |
2008年 | 189篇 |
2007年 | 185篇 |
2006年 | 170篇 |
2005年 | 169篇 |
2004年 | 155篇 |
2003年 | 146篇 |
2002年 | 100篇 |
2001年 | 77篇 |
2000年 | 79篇 |
1999年 | 76篇 |
1998年 | 59篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 49篇 |
1994年 | 42篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1973年 | 1篇 |
The process of mingling of magmas is simulated using a three-dimensional chaotic dynamical system consisting of stretching and folding processes. The intensity of mingling is measured by calculating the interfacial area between interacting magmas and the fractal dimension, as for natural magma mixing structures. Results suggest that, as in the natural case, the fractal dimension is linearly correlated with the logarithm of the interfacial area allowing to conclude that magma mixing can be regarded as a chaotic process.
Since chemical exchange and physical dispersion of one magma inside another by stretching and folding are closely related, we performed coupled numerical simulations of chaotic advection and chemical diffusion in three dimensions. Our analysis reveals the occurrence in the same system of “active mixing regions” and “coherent regions” analogous to those observed in nature. We will show that the dynamic processes are able to generate magmas with wide spatial heterogeneity related to the occurrence of magmatic enclaves inside host rocks in both plutonic and volcanic environments. 相似文献
For the Eastern United States (CEUS), due to the paucity of strong motion data for cratonic regions worldwide, estimation of strong ground motions for engineering design is based entirely on calibrated models. The models are usually calibrated and validated in the WUS where sufficient strong motion data are available and then recalibrated for applications to the CEUS. Recalibration generally entails revising parameters based on available CEUS ground motion data as well as indirect inferences through intensity observations. Known differences in model parameters such as crustal structure between WUS and CEUS are generally accommodated as well. These procedures are examined and discussed. 相似文献