全文获取类型
收费全文 | 447篇 |
免费 | 82篇 |
国内免费 | 66篇 |
专业分类
测绘学 | 75篇 |
大气科学 | 31篇 |
地球物理 | 191篇 |
地质学 | 184篇 |
海洋学 | 45篇 |
天文学 | 5篇 |
综合类 | 44篇 |
自然地理 | 20篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 2篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 22篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 22篇 |
2015年 | 20篇 |
2014年 | 20篇 |
2013年 | 25篇 |
2012年 | 28篇 |
2011年 | 27篇 |
2010年 | 32篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 21篇 |
2006年 | 34篇 |
2005年 | 22篇 |
2004年 | 26篇 |
2003年 | 27篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 4篇 |
排序方式: 共有595条查询结果,搜索用时 15 毫秒
61.
62.
Bankfull discharge was identified in some 30 gravel-bed rivers representing in total c. 40 gauging stations. The catchment sizes cary from 4km2 to nearly 2700km2. Bankfull discharge value increases with basin size. In the case of gravel-bed rivers developed on an impermeable substratum, the following equation emerges: Qb=0·087 A1·044. Bankfull discharge recurrence interval was determined by fitting maximum annual floods (Ta) into Gumbel's distribution and then using the partial duration series (Tp) in this same distribution. Recurrence interval is below 0·7 years (Tp) for small pebble-bed rivers developed on an impermeable substratum; it reaches 1·1 to 1·5 years when the catchment size of these rivers exceeds 250km2. Rivers incised in the soft schists of the Famenne show larger channel capacity at bankfull stage, a small width/depth ratio and thus higher recurrence intervals (1·4–5·3 years with Ta and 1–4·4 years with Tp). Baseflow-dominated gravel-bed streams and sandy or silty rivers experience less frequent bankfull discharges, with a recurrence interval higher than 2 or even 3 years (Tp). © 1997 John Wiley & Sons, Ltd. 相似文献
63.
为探究不同充填间隔时间(FTS)和料浆浓度对胶结充填体长期强度影响机制,配制70%、72%、75%三个浓度、充填间隔时间为12、24、36、48 h的两分层胶结充填体试件,开展单轴抗压强度(UCS)试验并探究其力学特性及其破坏形式。试验结果表明,(1)胶结充填体峰值抗压强度随充填间隔时间增大而呈递减趋势,充填间隔时间一定时胶结充填体抗压强度随料浆浓度增大而增大,且峰值抗压强度与充填间隔时间呈多项式函数规律;(2)胶结充填体试件加载过程中表现为压密阶段、线弹性阶段、裂纹扩展阶段和破坏发展4个阶段,随充填间隔时间延长,胶结充填体的破坏形式可能表现为张拉破坏–拉剪破坏过渡–拉剪混合破坏的损伤模式。研究结论能够为后期充填体强度设计和稳定性控制提供有益参考。 相似文献
64.
Over the past geological and historical period, tens of thousands of landslides occurred in the upper reaches of the Minjiang River, an area which is characterized by alpine valleys and has been densely populated over the past several hundreds of years. Discussing the triggering factor of these landslides is of great significance to geological hazard mitigation and prevention in this region. In this paper, we focus on four aspects of regional rainfall, shape features of landslide slopes, the corresponding relationship between landslide area and earthquake magnitude, and the recurring features of the reconstructed palaeoearthquake record at Diexi. Compared with those in Nepal, both mean seasonal rainfall accumulation and mean daily rainfall for the past 30 years are too low to reach the threshold values triggering landslides in the upper reaches of the Minjiang River. Secondly, landslides in the study area are usually absent of inner gorges(canyon topography)on the hillslope toes, which are confirmed in previous studies as typical features of landslides triggered by storms. Thirdly, wide distribution of the landslides in the study area supports our notion of earthquake-triggering because the landslides triggered by storms commonly distribute locally. Fourthly, periodicity analysis of the reconstructed palaeoearthquake record at Diexi provides a few cycles of twenty to thirty years, possibly corresponding to the earthquakes of magnitudes>5.0 or 5.5 which are believed to have caused soft-sediment deformation in the study area. In contrast, like the 2008 MS8.0 Wenchuan earthquake, the average recurrence interval of the large earthquakes in the study area is 2.6ka. They caused tens of thousands of landslides and provided more coarse silt particles for the nearby lake sediments at least in 330 years for each time. This is consistent with exponential increase of earthquake magnitude from large to medium and of the landslide area with the increased earthquake magnitude. To sum up, we suggest that tens of thousands of landslides in the upper reaches of the Minjiang River were most likely triggered by earthquakes instead of storms. This preliminary viewpoint needs further examination in the future. 相似文献
65.
基于上海气象站历史风速观测资料,采用极值I型和皮尔逊III型分布估算了上海市不同重现期最大风速的时间变化以及各区(县)不同重现期最大和极大风速的空间分布。结果表明,1901~2011年,上海市10、30、50和100 a重现期的最大风速分别为21.0、24.9、26.7和29.2 m/s。1974~2011年期间,上海各区(县)10 m高度10、30、50和100 a重现期的最大风速都是以南部沿海地区南汇或金山最大,分别为19.0、21.4、22.6和24.1 m/s;各重现期极大风速也是以南汇或金山最大,分别为32.3、36.4、38.4和41.0 m/s。中心城区各重现期的最大和极大风速都最小。 相似文献
66.
高频对流层延迟(ZTD)的提取对于反映水汽含量的高时间分辨率瞬时变化及其在暴雨短临预报中的应用具有重要意义。基于精密单点定位技术(PPP)分析了不同采样间隔的卫星钟差对PPP-ZTD精度的影响。结果表明,卫星钟差的时间间隔小于30 s时,所获得的PPP-ZTD(RMS<4 mm)比5 min间隔的(RMS<6 mm)精度要高;而5 s与30 s采样间隔的卫星钟差所获得的ZTD精度相当。 相似文献
67.
Holocene slip rate and paleoearthquake records of the Salt Lake segment of the Northern Zhongtiaoshan Fault,Shanxi Province 总被引:1,自引:0,他引:1
The Northern Zhongtiaoshan Fault is a major deep fault at the southern margin of the Yuncheng Basin. There have been few studies on the fault, and the historical earthquakes are few and weak. However, the intensity of activity on the fault should never be underestimated. Through interpretations of aerial images, topography measurements and excavation of trenches, this paper studied the fault distribution, the surface deformation and the activity of the normal fault south of Salt Lake near the city of Yuncheng. By tracing faults in the three trenches, it was found that there had been at least three large paleoseismic events, at 1–3.5, 3.6–4.4 and 7.4–8.8 ka BP. Employing 14 C dating, we determined the same gravel layers in the uplifted side and downthrown side. Making differential Global Positioning System measurements of the vertical difference and topographic profile, we obtained the mean slip rate of the Northern Zhongtiaoshan Fault since 24.7 ka BP(0.75±0.05 mm/a). Using the results of relevant studies, we calculated the possible vertical fault displacement of one earthquake(2.35 m) and obtained the recurrence interval of characteristic earthquakes as 2940–3360 a after dividing the displacement by the mean slip rate. 相似文献
68.
弧形间隔排桩-桩顶拱梁空间抗滑结构理论研究 总被引:1,自引:0,他引:1
为充分利用地形、地质结构和混凝土的材料特性,优化直线排桩的不利受力状态和提高其整体稳定性,提出了弧形间隔排桩-桩顶拱梁新型空间抗滑结构,即根据滑坡地形及地质条件弧形布设抗滑桩,桩顶设置连系梁,连系梁两端设置抗力桩,形成空间结构以抵抗滑坡推力。以抗滑桩与连系梁之间的作用力为冗力,分别建立了连系梁和抗滑桩的计算模型,并对连系梁的内力和抗滑桩的位移进行了理论分析,根据连系梁与抗滑桩连接处的位移协调条件,建立了力法典型方程求解冗力。最终得出了连系梁的弯矩、剪力和轴力以及抗滑桩的位移、内力理论计算公式。通过算例分析并与悬臂桩及直线排桩-桩顶连系梁抗滑结构比较,结果表明:空间抗滑结构中弧形连系梁的内力分布更加合理,弧形连系梁对抗滑桩的位移约束效果明显。 相似文献
69.
70.
野外地质地貌调查表明,龙陵-瑞丽断裂(南支)北段是以左旋走滑为主兼具一定正断分量的区域性活动断裂.断裂晚更新世以来的平均水平滑动速率为2.2mm/a,平均垂直滑动速率为0.6mm/a;全新世以来的平均水平滑动速率为1.8-3.0mm/a,平均垂直滑动速率为0.5mm/a.断裂在晚更新世以来的滑动速率在不同的时间尺度上变化不大,反映出该断裂晚更新世以来的活动强度比较稳定.利用Poisson模型、Lognormal模型、BPT模型三种概率模型计算获得未来50a强震发震概率分别是:6.32%、0.08%、0.05%;三种模型分别取权重0.28、0.36、0.36,获得龙陵-瑞丽断裂北段未来50a特征地震发震概率为1.82%. 相似文献