全文获取类型
收费全文 | 205篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 9篇 |
地球物理 | 36篇 |
地质学 | 111篇 |
海洋学 | 16篇 |
天文学 | 15篇 |
自然地理 | 24篇 |
出版年
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有213条查询结果,搜索用时 15 毫秒
1.
A new approach to constraining seawater δ34S and sulphate concentration using francolite‐bound sulphate reveals an abrupt increase in δ34S to +50‰ around the Early–Middle Cambrian boundary. Such high δ34S values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500–700 μgL?1. We argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the Kalkarindji Large Igneous Province of northern Australia and that it triggered the collapse of early metazoan reef ecosystems during the latest Early Cambrian. Mass extinctions of the last 260 Myr have all coincided with enhanced volcanic activity, while several are also associated with positive shifts in seawater δ34S. Extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution. Terra Nova, 18, 257–263, 2006 相似文献
2.
3.
4.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
5.
6.
7.
Apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of pH, temperature, solution saturation state, and on non-carbonated and carbonated apatite compositions: igneous fluorapatite (FAP) and sedimentary carbonate fluorapatite (CFA), respectively. From 2 <pH <6, the rate of release from dissolution of all apatite components [calcium (Ca), phosphorus (P), and fluoride (F)] increased with decreasing pH for FAP. From 6 < pH < 8.5, the FAP dissolution rate is pH independent. Measuring apatite dissolution rates at pH > 8.5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of FAP. For the CFA compositions studied, the dissolution rate decreased with increasing pH from 4 < pH < 7. During early stages of the dissolution reaction for both FAP and CFA, mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P and Ca:F being greater than mineral stoichiometric ratios, suggesting that Ca was preferentially released compared to P and F from the mineral structure during the early stages of dissolution. An increase in reacted solution pH accompanies this early elevated release of Ca. As the dissolution reaction proceeded to steady state, dissolution became congruent. When normalized to BET measured surface area, FAP dissolved faster from 4 < pH < 7 compared to CFA. The apparent Arrhenius activation energy (Ea) of FAP dissolution over the temperature range of 25-55°C at pH = 3.0, I = 0.1, and pCO2 = 0 is 8.3 ± 0.2 kcal mol−1. Both the apparent exchange of solution H+ for solid-bound Ca at low pH in the early stage of dissolution and the Ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for FAP and CFA. The degree of undersaturation of the solution, ΔGR, with respect to FAP was important in determining the dissolution rate. At pH = 3.0, I = 0.1, and pCO2 = 0, the dissolution rate of FAP was ∼ 5× greater in the far-from-equilibrium region compared to the near-equilibrium slope region.A simple apatite weathering model incorporating the experimental results from this study was constructed, and numerical calculations suggest that during the Phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the P weathering flux from apatite dissolution. It is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early- to mid-Paleozoic resulted in elevated P weathering fluxes, which along with climatic evolutionary pressures of the Neoproterozoic, facilitated the radiation of multicellular organisms, large-scale phosphorite deposition, and abundance of calcium phosphate shelled organisms during the early Cambrian. 相似文献
8.
A geopotential error analysis for a non planar satellite to satellite tracking mission 总被引:1,自引:0,他引:1
This study is concerned with gravity field recovery from low-low satellite to satellite range rate data. Compared against
a coplanar mission an improvement is predicted in errors associated with certain parts of the geopotential by the separation
of the orbital planes of the two satellites. Using Hill's equations an analytical scheme is developed to model the range rate
residuals. It is flexible enough to model the residuals between pairs of satellites in the same orbital plane or whose planes
are separated in right ascension. This scheme should allow the possibility of larger planar separations than previously since
no small angle approximation is made. The effects of such an orientation on gravity field recovery can therefore be analysed
by means of an extensive error analysis. The results of this analysis indicate that a significant improvement in the errors
of the near sectorial coefficients are obtained when the satellite's orbital planes are separated.
Received: 9 April 1996; Accepted: 26 September 1996 相似文献
9.
10.
Natural Hazards - Driving after natural disasters entails a substantial amount of stress; therefore, the number of motor vehicle crashes may increase. However, few studies have examined this issue.... 相似文献