全文获取类型
收费全文 | 193篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
大气科学 | 11篇 |
地球物理 | 31篇 |
地质学 | 57篇 |
海洋学 | 22篇 |
天文学 | 63篇 |
综合类 | 2篇 |
自然地理 | 15篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 12篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 5篇 |
2009年 | 13篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1989年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有201条查询结果,搜索用时 359 毫秒
81.
Estimating cropland carbon mitigation potentials in China affected by three improved cropland practices 总被引:1,自引:0,他引:1
Fei Lun Josep G. Canadell Lu He Bo Yang Mou-cheng Liu Zheng Yuan Mi Tian Jun-guo Liu Wen-hua Li 《山地科学学报》2016,13(10):1840-1854
Agriculture is a large source of carbon emissions. The cropland practices of fertilizer substitution, crop straw and conservation tillage are beneficial and help to rebuild local soil carbon stocks and reduce soil carbon emissions, in addition to reducing the consumption of fertilizers and fossil fuels. These improved cropland practices can directly and indirectly mitigate carbon emissions, benefiting the sustainability of croplands. For these three improved practices, we estimated carbon mitigation potentials in rice, wheat and maize croplands in China. The combined contribution of these practices to carbon mitigation was 38.8 Tg C yr-1, with fertilizer substitution, crop straw return, and conservation tillage contributing 26.6, 3.6 and 8.6 Tg C yr-1, respectively. Rice, wheat and maize croplands had potentials to mitigate 13.4, 11.9 and 15.5 Tg C yr-1, respectively, with the combined direct and indirect potential of 33.8 and 5.0 Tg C yr-1. Because of differences in local climate and specific diets, the regional cropland carbon mitigation potentials differed greatly among provinces in China. In China, 18 provinces had a “target surplus” for which the carbon mitigation from these three practices was larger than the mitigation target set for 2020. At the national level, a net “target surplus” of 4.84 Tg C yr-1 would be attained for Chinese croplands with full implementation of the three improved practices. Regional cooperation must be developed to achieve carbon mitigation targets using such measures as carbon trading, establishing regional associations, and strengthening research programs to improve practices. 相似文献
82.
基于2000年、2010年人口普查及2005年、2015年人口抽样调查数据,采用相互作用关系模型计算了中国“人口流动系统”和“单向相互作用关系值”。结果表明:① 人口流动具有明显的凝聚性,东部地区对流动人口的吸引力依然具有绝对优势;② 省际人口流动呈“非对称双向迁移模式”,人口回流的趋势已不容忽视;③ 长三角地区逐渐代替珠三角成为新的人口流动中心,人口流动开始北移;④ 中西部地区的人口流动分中心某种意义上已经出现,人口就近转移日渐凸显。将2010-2015年间省际人口流动新规律和特征与1995-2010年进行动态对比,对于制定未来人口和区域发展政策,继续缩小东西部地区之间的差距,最终实现区域协调发展具有重要意义。 相似文献
83.
84.
85.
86.
Grouting of water-conducting fractures with low-alkali cement is foreseen for the potential future repository for spent nuclear fuel in Finland (ONKALO site). A possible consequence is the formation of high-pH solutions which will be able to react with the host rock. Calculations have been performed including the hydration and simultaneous leaching of the grout. The effect of different possible groundwater compositions has been studied. The results show that after grouting, the duration of the initial high-pH peak is short (<0.5 a), which compares well with observations at a test borehole. Magnesium in the groundwater induces the precipitation of brucite at the grout–fracture interface, which consumes OH−. In the longer term, the results show a gradually decaying pH tail (pH < 9) controlled by the precipitation of calcite at the grout–fracture interface. The duration of this tail correlates inversely with the carbonate content of the inflowing groundwater. 相似文献
87.
Montserrat Corbera Josep Maria Cors Jaume Llibre 《Celestial Mechanics and Dynamical Astronomy》2011,109(1):27-43
We consider the Newtonian four-body problem in the plane with a dominat mass M. We study the planar central configurations of this problem when the remaining masses are infinitesimal. We obtain two different
classes of central configurations depending on the mutual distances between the infinitesimal masses. Both classes exhibit
symmetric and non-symmetric configurations. And when two infinitesimal masses are equal, with the help of extended precision
arithmetics, we provide evidence that the number of central configurations varies from five to seven. 相似文献
88.
Many mountain belts exhibit significant along‐strike variation in structural style with changes in the width of the orogen, the geometry and kinematics of the crustal‐scale thrust system, and the degree of partitioning between pro‐ and retro‐wedge deformations. Although the main factors controlling first‐order structural style are understood, the cause of these lateral variations remains to be resolved. Here we focus on the Pyrenees, characterized by significant lateral variation in structural style with a thrust system involving more and thinner thrust sheets in the eastern section than in the western part. Similarly, the prior Mesozoic rifting event was characterized by significant lateral variation in structure. We integrate available geological and geophysical data with forward lithospheric scale numerical models. We show that lateral variation in crustal strength attributed to inherited Variscan crustal composition accentuated during Mesozoic rifting explains the variation in structural style observed during Pyrenean mountain building. 相似文献
89.
Hydraulic head response to stream-stage variations can be used to explore the hydraulic properties of stream-aquifer systems at a relatively large scale. These stream-stage response tests, also called flooding tests, are typically interpreted using one- or two-dimensional models that assume flow perpendicular to the river. Therefore, they cannot be applied to systems that are both horizontally and vertically heterogeneous. In this work, we use the geostatistical inverse problem to jointly interpret data from stream-stage response and pumping tests. The latter tests provide flow data (which are needed to resolve aquifer diffusivity into transmissivity and storage coefficient) and may supply supplementary small-scale information. Here, we summarize the methodology for the design, execution, and joint numerical interpretation of these tests. Application to the Aznalcóllar case study allows us to demonstrate that the proposed methodology may help in responding to questions such as the continuity of aquitards, the role and continuity of highly permeable paleochannels, or the time evolution of stream-aquifer interaction. These results expand the applicability and scope of stream-stage response tests. 相似文献
90.
Ercilla G Córdoba D Gallart J Gràcia E Muñoz JA Somoza L Vázquez JT Vilas F;Prestige Group 《Marine pollution bulletin》2006,53(5-7):208-219
The tanker Prestige sank off NW Iberia on the 19th November 2002. The stern and bow of the Prestige wreck are located on the southwestern edge of the Galicia Bank, at 3565 m and 3830 m water depths, respectively. This bank is a structural high controlled by major faults with predominant N-S, NNE-SSW, and NNW-SEE trends. It is characterized by moderate to low seismic activity. The faults have controlled the local depositional architecture, deforming, fracturing, relocating and distributing sediments since the Valangian (early Cretaceous). The Prestige sinking area corresponds to an asymmetric half-graben structure with a N-S trend, which conditions the present-day morphology. The faulted flank outcrops and its activity and erosion have favoured the occurrence of mass-movements (slumps, slump debris, mass-flows and turbidity currents), building valleys and depositional lobes. Nearsurface sediments comprise mostly terrigenous and biogenous turbiditic muds and sands with a minor presence of hemipelagic muds, except on the fault scarp where pelagites predominate. Potential geological hazards resulting from tectonic and sedimentary processes affect almost the entire Prestige sinking area. 相似文献