收费全文 | 742篇 |
免费 | 24篇 |
国内免费 | 15篇 |
测绘学 | 17篇 |
大气科学 | 41篇 |
地球物理 | 168篇 |
地质学 | 293篇 |
海洋学 | 79篇 |
天文学 | 103篇 |
综合类 | 8篇 |
自然地理 | 72篇 |
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 22篇 |
2013年 | 41篇 |
2012年 | 27篇 |
2011年 | 44篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 45篇 |
2007年 | 34篇 |
2006年 | 29篇 |
2005年 | 31篇 |
2004年 | 24篇 |
2003年 | 22篇 |
2002年 | 12篇 |
2001年 | 18篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1974年 | 9篇 |
1971年 | 6篇 |
1969年 | 3篇 |
1963年 | 4篇 |
Key policy insights
Our finding of design divergence indicates that policy efforts aimed at achieving integrated international markets are unlikely to be successful.
Visions of carbon market linkage will need to confront the reality that there are well-organized political coalitions, anchored in the status quo, that prefer divergence.
In linking ETS, policy-makers should devote more attention to preventing excessive capital flows that can undermine political support for linkage, while also creating incentives for convergence in trading rules over time.
Warming climate and thawing permafrost have profound impacts on groundwater flow regimes in cold regions because of the shrinkage or disappearance of the confining unit formed by the permafrost layers and improving hydraulic connections. Numerical simulations of coupled groundwater flow and heat transfer are often used to characterize the changing permafrost hydrogeology. In this study, a number of scenarios for different hydraulic gradients and lake-water depths have been used to simulate the concordant permafrost evolution and groundwater movement using a two-dimensional cylindrical coordinate model at time scales of decades to centuries in response to a warming climate. The model is applied to a representative headwater catchment in the south-central headwater area of the Yellow River on the northeastern Qinghai-Tibet Plateau, China. The results show that the presence and movement of groundwater and the deeper subpermafrost aquifer can substantially accelerate permafrost degradation, and the disappearance of residual permafrost at depth can result in the sudden establishment of deep groundwater flow paths. All hydrological impacts will become evident after the stabilization of the hydrothermal and flow fields at 100–200 years. The stable discharge rate of groundwater flow varies from 8.0 to 12.4 m3 s−1, and the stable velocity of groundwater flow varies from 1.6 × 10−7 to 4.4 × 10−7 m s−1 under different scenarios within the model domain. The modeling results also demonstrate that flow velocity and discharge rate in local groundwater flow systems can be enhanced by an increased hydraulic conductivity, leading to an accelerated degradation of isolated permafrost bodies.
相似文献![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper presents the results of an investigation into the structure of eolian kimberlite indicator minerals (KIMs) haloes present within Quaternary Kalahari Group sediments (up to 20 m thick) overlying the Late Cretaceous kimberlites in the Orapa field in North-East Botswana. A database of more than 8000 samples shows that kimberlites create a general mineralogical blanket of KIMs of various distances of transportation from primary sources in the Orapa area. Models of the reflection and dispersion patterns of KIMs derived from kimberlite pipes including AK10/ AK22/AK23 have been revealed based on 200 selected heavy mineral samples collected during diamond prospecting activities in Botswana from 2014 to 2017. Short distance eolian haloes situated close to kimberlite bodies cover gentle slopes within plains up to 500 × 1000 m in size. They have regularly have oval or conical shapes and are characterized by the presence mainly of unabraded or only slightly abraded KIMs. A sharp reduction of their concentration from hundreds and thousands of grains / 20 l immediately above kimberlites toto 10 grains/20 l at a distance of only 100–200 m from the pipes is a standard feature of these haloes. The variation of concentration, morphology and abrasion of specific KIMs with increasing distance from the primary sources has been investigated and presented herein. Sample volumes recommended for pipes present within a similar setting as those studied, with different depth of sedimentary cover are as follows: up to 10–20 m cover at 20–50 l, 20–30 m cover at 50–100 l and 30–80 m cover at 250 l. It is important to appreciate that the discovery of even single grains of unabraded or slightly abraded KIMs in eolian haloes are of high prospecting significance in this area. The results of the research can be applied to in diamond prospecting programs in various regions with similar environments.
相似文献