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121.
The influence of vorticity and rheology of matrix material on the development of shape-preferred orientation (SPO) of populations of rigid objects was experimentally studied. Experiments in plane strain monoclinic flow were performed to model the fabric development of two populations of rectangular rigid objects with object aspect ratios (Rob) 2 and 3. The density of the rigid object populations was 14% of the total area. Objects were dispersed in a Newtonian and a non-Newtonian, power law matrix material with a power law exponent n of 1.2. The kinematic vorticity number (Wn) of the plane strain monoclinic flow was 1, 0.8 and 0.6 with finite simple shear strain of 4.6, 3.0 and 0.9, respectively. In experiments with Rob=3, the SPO is strongly influenced by Wn and the material properties of the matrix. Deformation of a power law matrix material and low Wn resulted in a stronger SPO than deformation of a linear viscous matrix and high Wn. Strain localization coupled with particle interaction plays a significant role in the development of a shape-preferred orientation. High strain simple shear zones separate trains of rigid objects that are surrounded by low strain zones with Wn lower than the bulk Wn. In fabrics involving populations of objects with Rob=2, rheology of the matrix materials does not systematically influence the intensity of the SPO. 相似文献
122.
S-lay is a widely used method for offshore pipe installation. In recent years, S-lay has gradually applied to the deepwater condition. Because of the increasing pipe weight in deep S-lay, there exist severe and complex contact problems between the overbend pipe and roller supports of the stinger. In deep S-lay design, it is difficult to solve this nonlinear mechanics problem, and there remain confusion and difficulties to predict the roller contact forces and the pipe strain level in S-lay design.The present paper develops a refined finite element model with the framework of ABAQUS, which considers the complex surface contact behaviors in the overbend section. The features of the contact state of different rollers within one roller box are discussed, and the resultant support forces from each roller box are calculated and compared with the commercial design code. The overbend strain level of five S-lay cases is investigated and the pipelaying safety is checked by DNV rules. The simulation results show that the proposed model can provide more accurate and reasonable predictions on roller forces and pipe strain distribution for deepwater S-lay design. 相似文献
123.
A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Strain dependencies of shear modulus and damping were simply modeled. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered particularly in the large strain range. The consideration could be made by normalizing G with G′0=AF(e)(σ′m/σmr)n, the initial shear modulus for the effective confining stress of that particular loading cycle, instead of using G0. G/G′0 was expressed by a function of γ as G/G′0=1/(1+bgγ) which was almost stress level independent for clayey sands used in this study. The damping ratio was not much affected by the confining stress. The strain dependency of the damping ratio was modeled by h=ahγ/(1+bhγ). Effects of load irregularity on the shear modulus were also investigated. The excess pore pressure and the residual strain were generated especially when the major peaks in the irregular loading were applied to the specimen. However, G/G′0 for the irregular loading could be represented reasonably well by the average curve for the uniform cyclic loading, if the excess pore water pressure and the residual strain were taken into account. 相似文献
124.
125.
GPS测量所揭示的西秦岭北缘断裂带现今活动特征 总被引:5,自引:0,他引:5
西秦岭北缘断裂带是甘肃省东南部重点地震监视区内一条主要活动断裂带。为了研究该断裂的现今活动特征,在断裂两侧布设了GPS监测网,从1996~1998年完成了3期观测。测量结果表明,断裂北、南两侧存在明显的差异运动,南侧向东运动的速率比北侧大3.8mm/a。在GPS网中,缩短的这基本上为东西方向,伸长的边基本上为北西-南东方向。本区的主压应力方向为近东西向。断裂带的东部(武山附近)左旋特征明显。测量结 相似文献
126.
地下流体尤其是地壳深部的地下水 ,当它们形成具有一定封闭条件的承压系统时 ,能灵敏地反映地壳的应力应变状态 ,这种深部承压系统近似一“天然应变仪”,从这个角度出发 ,研究地下水的动态变化与地壳应力应变的关系 ,利用相关斜率分析法 ,探讨相关斜率 K值时空演变序列与地震间的关系 ,得出相关斜率具有较好的映震能力 ,且有短期预报效应 相似文献
127.
We reformulate the original model of Hatchell and Bourne and Røste, Stovas and Landrø that couples fractional velocity change to subsurface strain via a fundamental constant R. The new model combines elastic compressibility of a dual‐porosity system for a sand–shale mixture with horizontal planes of inter‐granular weakness. The majority of observed R‐factor magnitudes from post‐stack 4D seismic data in both the reservoir and overburden can thus be explained. R is predicted to depend strongly on lithology and also initial strain state. The model is also extended to predict the observed angle‐dependence of time‐lapse time‐shifts from pre‐stack data. An expression for the gradient of time‐shift with incidence angle is obtained in terms of the background VP/VS, and also the ratio of tangential to normal compliances BT/BN representing loss or creation of inter‐granular coupling. If accurately estimated from data, this compliance ratio can be used as an additional parameter to assess the post‐production state of the overburden. It is concluded that whilst R remains the over‐arching parameter controlling the magnitude of time‐shifts measured from 4D seismic data, BT/BN is a subtler parameter that may also prove of future value. 相似文献
128.
利用2013~2017年3期GPS观测资料,获得精河6.6级地震前震中附近区域水平运动速率、主应变率、面膨胀率及最大剪应变率,并结合区域构造背景分析该区域变形动态特征。结果表明:震前震中附近区域速度场速率逐渐增大,发震断裂两盘构造运动速率不均,震中附近区域GPS测点的速率和运动方向存在差异,反应了地壳应变能量积累。震中区域主压应变率变化反映出应力调整过程,沿断层走向的张压转换的形变高梯度带、最大剪应变梯度带可为地震预测提供参考。 相似文献
129.
Modelling of R/C members accounting for shear failure localisation: Finite element model and verification
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Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a computationally efficient member‐type finite element model for the hysteretic response of shear critical R/C frame elements up to the onset of axial failure is presented; it accounts for shear‐flexure interaction and considers, for the first time, the localisation of shear strains, after the onset of shear failure, in a critical length defined by the diagonal failure plane. Its predictive capabilities are verified against experimental results of column and frame specimens and are shown to be accurate not only in terms of total response, but also with regard to individual deformation components. The accuracy, versatility, and simplicity of this finite element model make it a valuable tool in seismic analysis of complex R/C buildings with shear deficient structural elements. 相似文献
130.
巴颜喀拉块体东北缘是构造变形和地震活动较强的区域, 2017年九寨沟MS7.0地震就发生在该区域内。 利用多尺度球面小波方法解算GPS应变率场, 分析巴颜喀拉块体东北缘2009年至2017年的应变率场分布特征, 该方法的优点是可以将GPS应变率场按照不同的空间尺度进行小波分解, 给出不同空间尺度的应变率场。 结果表明在2017年九寨沟地震之前, 震中附近应变积累显著, 虎牙断裂北延断裂的左旋走滑速率为3.0 mm/a, 拉张速率为3.1 mm/a, 表明该条断裂以左旋走滑为主兼有拉张特征, 与九寨沟地震的震源机制解一致。 除九寨沟震中附近外, 在岷县与漳县交界处、 理县和汶川、 青川等地区主应变率、 面应变率、 最大剪应变率也较大, 这可能与2013岷县漳县(MS6.6)、 2008年汶川(MS8.0)、 2014年理县(MS4.8)以及2014青川县(MS4.8)地震有关。 相似文献