全文获取类型
收费全文 | 40篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 2篇 |
地球物理 | 14篇 |
地质学 | 14篇 |
海洋学 | 3篇 |
天文学 | 7篇 |
自然地理 | 2篇 |
出版年
2022年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2013年 | 2篇 |
2012年 | 2篇 |
2011年 | 1篇 |
2010年 | 4篇 |
2009年 | 1篇 |
2006年 | 2篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有47条查询结果,搜索用时 15 毫秒
1.
Multiple Enrichment Processes and their Relationships in the Subcrustal Lithosphere Beneath the Eifel (Germany) 总被引:5,自引:4,他引:1
Three types of enrichment processes may be distinguished inspinel peridotite mantle xenoliths from the West Eifel (Germany):
- Enrichmentof light rare earth elements (LREE) occurs in wholerocks andclinopyroxenes in conjunction with the formation ofTi-pooramphiboles (<05%) in a low-tempetature suite(900C).
- Enrichment in high field strength elements (HFSE; Ti and Hf)is associated with strong zoning of TiO2 in amphibole adjacentto mica hornblendite veins. A reheating from 900 to 1050C associatedwith this vein formation is reflected by the zoning profilesin orthopyroxenes with Ca, Al, and Cr increasing from core torim.
- Moderate enrichment of LREE without amphibole formationin ahigh-temperature suite (1125C) is observed at the contactofperidotites to pyroxenite veins yielding the same temperature.
- Based on geochemical and isotopic evidence, enrichment process(1) is inferred to be due to interaction of peridotites fromthe subcrustal lithosphere with low-density fluids. Process(2) represents a subsequent interaction of amphibole-bearingperidotites formed during the first process with basic meltsmoving through a system of cross-cutting dykes and veins. Processes(2) and (3) are linked to the Quaternary West Eifel volcanism.Geothermobarometry of the xenoliths shows that these processesare related to different depth regimes of the lower lithosphere.
2.
Effects of forest roads on the hydrological response of a small‐scale mountain watershed in Greece
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro‐meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small‐scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
The performances of least-squares orthogonal polynomial and relaxation techniques in the separation of regional and residual anomalies have been evaluated with a view to minimizing personal biasing. The advantage of orthogonal over nonorthogonal polynomials is their ability to estimate an optimum order of polynomial to represent the predominant regional trend in the data using an approximate 2D difference table, the Z-matrix. The correlation coefficients between residuals of two consecutive orders also give the same result. In the relaxation technique, a linear trend is assumed within each cell of the mesh of a square grid. A set of such linear segments can approximate any complicated regional trend. The performances of these two techniques have been evaluated using simulated gravity anomalies produced by 2D and 3D complex regional structures superimposed on residual fields due to cylinders and prismatic bodies, as well as three field examples taken from the published literature. The analyses have revealed that the relaxation technique produces excellent results when an optimum polynomial order rather than an arbitrary fixed one is used for computing the boundary conditions along the periphery of the map. Analyses have revealed that such boundary conditions provide minimum distortion near the two ends of the profile. 相似文献
4.
The study of the problem of the black coloration of feldspathoids of the sodalitic group (nosean, haüyne, sodalite) reveals iron as a main factor.A statistical study of the global compositions of these minerals proves that their enriching inFe is accompanied by a decrease in Al, but also by an increase in Si.A substitution of Fe+++ to Al in the structure in the feldspathoids is suggested.The analysis with an electron microprobe confirms this hypothesis and allows us to state a fondamental difference between the formation of miaskitic phonolites rich in Fe++ and that of agpaitic phonolites rich in Fe+++. 相似文献
5.
A 29-year time-series of four-times-daily atmospheric effective angular momentum (EAM) estimates is used to study the atmospheric
influence on nutation. The most important atmospheric contributions are found for the prograde annual (77 μas), retrograde
annual (53 as), prograde semiannual (45 as), and for the constant offset of the pole (δψsinɛ0=−86 as, δɛ=77 as). Among them only the prograde semiannual component is driven mostly by the wind term of the EAM function,
while in all other cases the pressure term is dominant. These are nonnegligible quantities which should be taken into account
in the new theory of nutation. Comparison with the VLBI corrections to the IAU 1980 nutation model taking into account the
ocean tide contribution yields good agreement for the prograde annual and semiannual nutations. We also investigated time
variability of the atmospheric contribution to the nutation amplitudes by performing the sliding-window least-squares analysis
of both the atmospheric excitation and VLBI nutation data. Almost all detected variations of atmospheric origin can be attributed
to the pressure term, the biggest being the in-phase annual prograde component (about 30 as) and the retrograde one (as much
as 100200 as). These variations, if physical, limit the precision of classical modeling of nutation to the level of 0.1 mas.
Comparison with the VLBI data shows significant correlation for the retrograde annual nutation after 1989, while for the prograde
annual term there is a high correlation in shape but the size of the atmospherically driven variations is about three times
less than deduced from the VLBI data. This discrepancy in size can be attributed either to inaccuracy of the theoretical transfer
function or the frequency-dependent ocean response to the pressure variations. Our comparison also yields a considerably better
agreement with the VLBI nutation data when using the EAM function without the IB correction for ocean response, which indicates
that this correction is not adequate for nearly diurnal variations.
Received: 10 September 1997 / Accepted: 5 March 1998 相似文献
6.
陕西省略阳县杨家坝多金属矿区成矿作用地球化学示踪 总被引:3,自引:1,他引:2
本文以陕西省略阳县杨家坝多金属矿区为例,通过对该矿区岩(矿)石和各类脉体的岩相学、稀土和微量元素及流体包裹体地球化学示踪发现,多金属中重晶石的形成及硅化、碳酸盐化、滑石化、纤闪石化、绢云母化和绿泥石化和透闪石岩的含氟浅闪石及隐晶硅质玻璃和微晶硅质,这表明与成矿蚀变有关的热液流体是一种不同于一般地壳流体的富硅、钛、铁、碱质和挥发份,并具备熔体性质的成矿流体。各类样品的稀土元素配分模式明显富集LREE,在Ce、Eu、Yb异常的组合上也各具特征。LREE富集是地幔流体作用的显著特征之一;矿石和脉体的负Ce、正Eu和负Yb异常以及流体包裹体中H2O-C6H6成分,是高温还原地幔流体的重要标志;正Ce和负Eu异常的出现,以及Ce、Eu、Yb异常的减弱和消失则是壳幔混染叠加改造的显示。综合研究表明:矿区成矿过程可能统一受制于秦岭地区碰撞造山背景下具高温还原性质的地幔流体作用,且由此引发壳幔强烈混染的叠加改造作用在成矿过程中发挥了重要作用。 相似文献
7.
CH. HEMON 《Geophysical Prospecting》1978,26(4):790-821
The method of finite differences is applied to the computation of multi-dimensional synthetic seismograms. This paper gives a study of the mathematical and numerical formulations of the problem, the boundary conditions, the convergence conditions and how to simulate the source in both one solid or a liquid. It is shown that the numerical formulation chosen is valid both for direct and inverse problems (i.e. for modeling and migration). This formulation makes it possible to use the normal incidence reflection coefficients for P and S waves, whether they travel horizontally or vertically. The examples shown have been chosen on purpose in order to be easily interpreted. They do not give a full idea of the possibilities of the algorithm which allows to consider non-planar interfaces, except close to the vertical axis. 相似文献
8.
RAMA CH. RAO V. VIJAYAKUMAR G. VIRUPAKSHI M. B. S. V. RAO 《Geophysical Prospecting》1985,33(5):746-752
The concept of relation figures is utilized in the case of a thin infinite sheet for identification and determination of the causative source geometry, and its various parameters. The plot of ?T versus ?V is a conic, the plots between the respective symmetric components and the respective asymmetric components are straight lines, and the resulting diagram between the first horizontal versus the first vertical derivative of either ?T or ?V is a cardioid. The authors are grateful to Shri V. Babu Rao and Dr R. K. Verma for their encouragement. They would like to thank the Director of the N. G. R. I. for permission to publish this paper. The neat drawing of Sri P. Sundara Rao is appreciated. 相似文献
9.
The rapid polar motion for periods below 20 days is revisited in light of the most recent and accurate geodetic and geophysical
data. Although its amplitude is smaller than 2 mas, it is excited mostly by powerful atmospheric processes, as large as the
seasonal ones. The residual amplitude, representing about 20% of the total excitation, stems from the oceans. Rapid polar
motion has an irregular nature that is well explained by the combined influence of the atmosphere and the oceans. An overall
spectrum reveals cycles principally at 20, 13.6 (fortnightly tidal period) and 10 days (corresponding to the normal atmospheric
mode Y31{\Psi_3^1}), but this is only an averaged feature hiding its strong variability over seasonal time scales. This explains why it is so
delicate to determine an empirical model of the tidal effect on polar motion. The variability in both amplitude and phase
of the 13.6-day term is probably caused by a lunar barometric effect, modulated by some sub-seasonal thermal processes. The
irregularities of the prominent cycles of the short-term polar motion are well explained by the atmospheric and oceanic excitations.
The oceanic variability reinforces the atmospheric one, as they were triggered by the same agent, maybe seasonal and inter-annual
thermal variations. 相似文献
10.