全文获取类型
收费全文 | 87篇 |
免费 | 45篇 |
国内免费 | 33篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 19篇 |
地球物理 | 73篇 |
地质学 | 26篇 |
海洋学 | 17篇 |
天文学 | 16篇 |
综合类 | 1篇 |
自然地理 | 1篇 |
出版年
2024年 | 3篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1989年 | 2篇 |
1985年 | 4篇 |
1982年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1968年 | 1篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1961年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1943年 | 4篇 |
1942年 | 2篇 |
1940年 | 1篇 |
1938年 | 1篇 |
1937年 | 4篇 |
排序方式: 共有165条查询结果,搜索用时 15 毫秒
41.
In this paper a series of numerical simulations are performed to investigate the vortex shedding mechanism for a solitary wave propagating over a submerged breakwater by use of Reynolds averaged Navier-Stokes (RANS) model combined with a k-ε model. Flows of different Reynolds numbers up to Re=1.4×105 corresponding to varying incident wave heights are considered in which the characteristic fluid velocity is represented by the maximum horizontal velocity above the submerged breakwater. For the verification of the accuracy of the numerical model, the incident waves and the velocity field in the vicinity of the breakwater are compared with experimental data. The result shows that the model is capable of describing vortex shedding for a solitary wave propagating over a rectangular submerged breakwater. Key features of vortex generation, evolution and dissipation are investigated. It is found that the vortex shedding and their evolution due to separated boundary layer over the breakwater are strongly related to the Reynolds number. A considerable number of vortices and complicated vortex pattern are observed as the Reynolds number increases. 相似文献
42.
HSU WeiBiao 《中国科学D辑(英文版)》2007,50(6):886-896
Numerous round to oblate opaque assemblages (OAs) are found in chondrules and matrix of the Ningqiang carbonaceous chondrite. They are mainly composed of Ni-rich metal,magnetite,Fe,Ni-sulfides,with minor amounts of phosphate,phosphoran-olivine,pyroxene and trace amounts of nano-sized platinum-group metal alloys. The mineralogy of Ningqiang OAs is very similar to that of OAs previously reported in Ca,Al-rich inclusions of CV chondrites. Being a rare mineral phase in nature,phosphoran-olivine is thought to form by nonequilibrium reactions between P-bearing molten metal and olivine crystals during rapid cooling. Its occurrence in Ningqiang OAs indicates that the precursor of OAs was locally produced during chondrule formation,rather than directly condensed from the solar nebula as previously thought. The petrographic and mineralogical characteristics of Ningqiang OAs reveal that OAs formed by low temperature alterations of pre-existing homogeneous alloys within chondrules on a planetary body. 相似文献
43.
HSU HouTse 《中国科学D辑(英文版)》2007,(6)
Sumatra-Andaman Large Earthquake on Dec. 26,2004 generated not only the Indian Ocean Tsunami but also the Earth's free oscillations (EFO). The signals of Earth's free oscillations were perfectly re-corded by the superconducting gravimeter C0-32 at Wuhan station in China. After the pre-treatment and spectral analysis on the observational data from Wuhan station,we obtained more than ninety EFO modes including 42 fundamental modes,2 radial modes and 49 harmonic modes. On the basis of the discussions on some observed harmonic modes and abnormal splitting phenomena,we considered that the real rigidity might be lower than the theoretical prediction of PREM model in the inner core and however the anisotropy of compressive wave was brightly higher than the present estimations in the inner core. This suggested that the anisotropy of the inner core could be much more complicated than our present understanding,and there might be some new geophysical phenomena in the formation process of the inner core. 相似文献
44.
45.
Based on rainfall erosion of soil and suspended sediment transport in storm events, a method is proposed to predict peak suspended sediment concentration and suspended sediment yield in watersheds based on rainfall characteristics prior to peak rainfall intensity. The rainfall characteristics factors that dominate peak suspended sediment concentration Cp are rainfall erosion factor Ref, first peak rainfall intensity of area-average rainfall ip1 and antecedent precipitation index Iap; the rainfall characteristics factors that dominate suspended sediment yield Yss in storm events are total rainfall P, suspended sediment yield factor Rsf and antecedent precipitation index Iap. This research focuses on watersheds in Liau-Kwei observation station along Lao-Nung River in southern Taiwan as the research object, and adopts the PSED-model to simulate the discharge hydrograph, suspended sediment concentration hydrograph and suspended sediment yield in 11 storm events for analysis. The analytical results show that there is a good correlation between the above-mentioned rainfall characteristics factors and Cp as well as Yss, thus enabling Cp and Yss to be predicted by using Expressions (13) and (14). These two expressions are utilized to predict Cp and Yss of Typhoon Morakot in 2009, and the results are compared with those from simulation by using the PSED-model. The result of comparison shows there is a good capability in predicting. For the watersheds where it is necessary to predict Cp and Yss of a storm event for the benefit of effective operation of water resource facilities, the aforesaid rainfall characteristics factors can be utilized to establish applicable models for prediction. 相似文献
46.
显生宙以来华北克拉通岩石圈遭到破坏,这一现象的科学问题已受到世界地学家广泛关注.本文首先将地震层析成像反演得到的P波速度扰动转化为密度扰动,以此作为初始密度模型,然后利用布格重力异常反演得到了华北克拉通岩石圈高分辨三维密度结构.为了避开大型稀疏矩阵求逆计算,提高计算效率,我们将代数重构技术用于密度反演解算.反演结果表明:华北克拉通岩石圈密度在横向和纵向上均存在明显的不均匀性,密度分布形态与地表构造格局有很好的相关性;研究区地壳整体表现为低密度异常,地壳以下岩石圈部分则以高密度异常为主;鄂尔多斯块体地壳范围内以低密度异常为主,80~120 km深度上为呈南北两端集中分布的高密度异常,并分别与秦岭造山带和阴山造山带的高密度异常分布相连,这暗示了鄂尔多斯块体可能受到了来自其南北两端造山带深部动力学过程的影响;80~120 km深度上,华北克拉通东部地区呈现出显著的南北向非均匀的高密度异常,这表明遭到破坏后该地区上地幔物质分布具有强烈的南北向非均匀性. 相似文献
47.
本文讨论了在中国北京、武汉、上海、昆明、兰州、乌鲁木齐、广州、沈阳和青岛等九处的固体潮观测结果,并且与具有海洋和液核的地球模型进行了比较。文中特别讨论了仪器标定问题。结果表明了模拟固体潮效应的精度达到了0.6μgal。 相似文献
48.
49.
由于当前GRACE(Gravity Recovery and Climate Experiment)串行式编队存在"南北向条带误差"等缺陷,因此本文基于星间速度插值法开展了利用下一代三向车轮双星编队ACR(Along-Cross-Radial)-Cartwheel提高地球重力场空间分辨率的可行性研究论证. 第一,采用GRACE卫星轨道参数和关键载荷精度,利用三向车轮双星编队ACR-Cartwheel-A/B反演了120阶地球重力场.结果表明:基于ACR-Cartwheel-A/B双星编队反演地球重力场的模拟精度较德国波茨坦地学研究中心(GFZ)公布的EIGEN-GRACE02S地球重力场模型的实测精度平均提高2.6倍,从而检验了基于下一代三向车轮双星编队ACR-Cartwheel-A/B反演地球重力场精度优于当前GRACE串行式双星编队的可行性. 第二,通过星间速度插值法,采用卫星轨道参数(初始轨道高度350 km、平均星间距离100 km、初始轨道倾角89°、初始轨道离心率0.0046)、卫星关键载荷精度指标(星间速度10-7 m·s-1、轨道位置10-3 m、轨道速度10-6 m·s-1、非保守力10-11 m·s-2)、观测时间30天和采样间隔10 s,基于经向车轮双星编队Lo-AR(Longitudinal-Along-Radial)-Cartwheel-A/B、纬向车轮双星编队La-AR(Latitudinal-Along-Radial)-Cartwheel-A/B和三向车轮双星编队ACR-Cartwheel-A/B,分别反演了120阶地球重力场;在120阶处,累计大地水准面精度分别为5.115×10-4 m、4.923×10-4m和3.488×10-4 m. 结果表明:(1)由于La-AR-Cartwheel-A/B编队的轨道稳定性优于Lo-AR-Cartwheel-A/B编队,因此基于La-AR-Cartwheel-A/B编队反演重力场精度高于Lo-AR-Cartwheel-A/B编队;(2)由于ACR-Cartwheel-A/B编队可以同时获得轨向、垂向和径向的重力场信息,卫星观测数据具有各向同性优点,因此ACR-Cartwheel-A/B编队是建立下一代高精度和高空间分辨地球重力场模型的优化选择. 相似文献
50.
由于GRACE Follow-On双星系统等效于基线长为星间距离的一维水平重力梯度仪,因此本文基于GRACE Follow-On卫星重力梯度法开展了精确和快速反演下一代地球重力场的可行性论证研究. 研究结果表明:第一,基于GRACE Follow-On卫星重力梯度法(GFO-SGGM),利用卫星轨道参数(轨道高度250 km、星间距离50 km、轨道倾角89°、轨道离心率0.001)、关键载荷测量精度(星间距离10-6 m、星间速度10-7 m·s-1、星间加速度10-10 m·s-2、轨道位置10-3 m、轨道速度10-6 m·s-1、非保守力10-11 m·s-2)、观测时间30天和采样间隔10 s反演了120阶地球重力场,在120阶处累计大地水准面精度为9.331×10-4 m. 第二,在120阶内,利用将来GRACE Follow-On双星反演地球重力场精度较现有GRACE双星平均提高61倍,因此GRACE Follow-On卫星重力梯度法是进一步提高地球重力场反演精度的优选方法. 第三,下一代GRACE Follow-On计划较当前GRACE计划的优点如下:轨道高度更低(200~300 km)、载荷精度更高(10-7 ~10-9 m·s-1)和星间距离更短(50~100 km). 相似文献