全文获取类型
收费全文 | 641篇 |
免费 | 136篇 |
国内免费 | 64篇 |
专业分类
测绘学 | 62篇 |
大气科学 | 19篇 |
地球物理 | 434篇 |
地质学 | 140篇 |
海洋学 | 68篇 |
天文学 | 8篇 |
综合类 | 25篇 |
自然地理 | 85篇 |
出版年
2024年 | 3篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 22篇 |
2017年 | 31篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 31篇 |
2012年 | 37篇 |
2011年 | 31篇 |
2010年 | 27篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 53篇 |
2006年 | 51篇 |
2005年 | 42篇 |
2004年 | 45篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 24篇 |
1998年 | 15篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有841条查询结果,搜索用时 227 毫秒
591.
In this paper, a global inversion method is developed for seismic moment tensor inversion by using the body wave forms. The
algorithm depends on neither the selection of starting model nor the forms of objective function and constraints. When the
error function, measure of the difference between the observed and synthetic waveforms, is chosen as the objective function,
the best fitting source model is found; when a certain combination in seismic moment tensor elements is selected as the objective
function and the values of error function are constrained in a suitable bound, the extreme source models can be produced by
minimizing or maximizing this combination. By changing the form of the combination of moment tensor elements, a variety of
different source characteristics can be considered. Therefore the extreme solution provides an estimation of the uncertainty
in the best fitting source model. The seismic waveform data was used to evaluate the effectiveness of this algorithm.
This research was supported by the National Natural Science Foundation of China. 相似文献
592.
593.
594.
595.
The design of a monitoring system for detecting explosions is a very topical problem, both for routine data processing at seismological observatories as well as for the monitoring of a Comprehensive Test Ban Treaty. In this framework it is desirable to have the possibility to quantify the presence of the isotropic component in the seismic source. For this purpose a method is presented, which is based on waveform inversion for the full moment tensor retrieval. The method inverts either full waveforms or separate seismic phases and returns the mechanism and time history of a point source. Moreover, it allows to redefine the hypocentral depth of the event and, in a simplistic way, to optimize the structural model as well. In order to model strong laterally heterogeneous structures, different pairs of structural models can be used for each source-receiver path. The source is decomposed into a volumetric part (V), representing an explosive or implosive component, and into a deviatoric part, containing both the double couple (DC) and the compensated linear vector dipole (CLVD) components. The method is applied to an area in central Switzerland and to the network of the Swiss Seismological Service. The events of interest include both earthquakes and explosions. Despite some modelling inadequacies of the source-time function, the explosions can be well identified with the inverted isotropic component in the source, as long as the number of stations used for the inversion is larger than three. The results of the inversion are better for large epicenter-station distances of the order of 40–90 km. 相似文献
596.
We propose a model which describes the formation of a strong asperity on a fault. We consider a fault surface which differs slightly from a plane due to a jog-like topographic variation. The fault is placed in an elastic space and is subject to a uniform stress field. The orientation of the fault is such that the normal traction (which is compressive) is greater on the topographic variation, determining a higher static friction and hence an asperity. The value of friction on this asperity depends on the magnitude of shear stress. For times of seismological interest, the increase in shear stress, at rates typical of tectonic processes, does not produce a sensible increase in friction with respect to the adjacent fault segments. A considerable increase in friction and the formation of a strong asperity (or even a barrier) can occur due to repeated seismic-slip episodes on the fault. Slip results in an elastic medium deformation, causing an increase in normal traction on the asperity and hence in friction. This process is described with the aid of a tensile Somigliana dislocation. Regions with high friction undergo partial fracturing of the fault-face material, which can produce fault gouge. The tensile dislocation introduces a small non-double-couple component in the seismic moment of the seismic event, the magnitude of this component depending mainly on the relative size of the asperity. 相似文献
597.
598.
M. Radha Krishna 《Journal of Earth System Science》1995,104(4):693-706
A detailed seismicity map of the Central Indian Ridge for the period 1912–1993 is presented, and the earthquakes pertaining
to four major transforms offsetting the ridge are utilized to study the moment release pattern. The scalar moment release
for the period 1912–1993, and the summed moment rate tensors for both short period (1977–1993) and long period (1912–1993)
bring out a unified picture of moment release pattern.
The fraction of seismic slip calculated based on depths of 100°C and 400°C limiting temperatures suggests that the Marie-Celeste
transform requires a slip almost to a depth of 400°C isotherm to account for the observed moment, and the Argo transform requires
depth of faulting much above the 400°C isotherm. A very small fraction of slip is accounted seismically for Vema (53%) and
12° 12′S (23%) even to depths of 100°C isotherm, suggesting a very low order of moment release along these transforms.
The horizontal plate velocities and the corresponding strain rates obtained from moment tensor summation of long period data
(82 years) give rise to (V
y
y
; V
y
x
mm. yr−1) of 6.0 and 6.1 along Marie-Celeste, 1.3 and 0.50 along Argo, 0.06 and 0.06 along 12° 12′S, 1.6 and 0.25 along Vema transforms.
The corresponding strain rates (ε
y
y
;ε
y
x
× 10−15 S−1) are 12.7 and 6.8 along MarieCeleste, 6.9 and 1.4 along Argo, 0.27 and 0.14 along 12° 12′S, 7.3 and 0.58 along Vema transforms.
These results suggest that the strain rates were highest and almost all predicted motion is taken up seismically along the
Marie-Celeste transform. The strain rates are lower along Argo transform and the observed moment release require shallower
depth of faulting in order to slip to be accounted seismically. The Vema and 12° 12′S transforms are characterized by low
strain rates and less than 15 per cent of motion is accommodated seismically within the seismogenic layer. It is proposed
that the deficiency of moment release along the Vema and 12° 12′S multiple transform system may be due to most of the plate
motion occurring aseismically. 相似文献
599.
Experimental investigations on model counterfort retaining walls have been carried out to study the lateral movement of the
walls and the nature of the failure modes. Mild steel plates of size 1,000 × 900 × 8 mm were used as model retaining walls
and were placed in a tank of size 900 × 900 × 670 mm. Ennore sand, obtained from Madras India, and Fly ash, obtained from
Panki Thermal Power Plant, India were used as backfill material. Tests were carried out both with and without reinforced backfill.
Two types of loading conditions were applied: (i) line load and (ii) uniform surcharge. The shape and size of the failure
wedge was studied by observing displacement of bands of colored through a Perspex plate fixed on one side of the tank. Plots
of overturning moment against the rotation of a wall top show that with the increase in rotation of wall, the overturning
moment decreases. The minimum value of overturning moment is taken as the limiting value. The failure surfaces obtained in
different cases are linear and parabolic in shape. 相似文献
600.
根据南京地区2010-2014年雨滴谱观测资料,利用Gamma分布、标准Gamma分布、改进的标准Gamma分布等雨滴谱分布模型,研究了南京地区降水雨滴谱拟合模型的参数特征。结果表明:1)南京地区降水雨强标准差σR和R之间比值为2.29;2)利用阶矩法,按照Gamma模型对雨滴谱进行拟合,形状因子μ、斜率因子λ和截断参数log10N0总的平均值分别为9.2、11.6 mm-1、7.2 mm-1·m-3,众数值分别约为6.0、5.5 mm-1、4.5 mm-1·m-3,并且μ和λ之间均存在较好的二次项函数关系;3)标准化形式下的Gamma分布参数Dm和Nw随雨强的增大而逐渐增大,并且随雨强的增大,Dm增大的幅度越来越大,而Nw增大的幅度却越来越小;4)谱型参数σM随Dm增大而增大,并且Dm和σM之间存在较好的指数型函数关系。 相似文献