全文获取类型
收费全文 | 184篇 |
免费 | 39篇 |
国内免费 | 51篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 1篇 |
地球物理 | 40篇 |
地质学 | 170篇 |
海洋学 | 31篇 |
综合类 | 3篇 |
自然地理 | 28篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 18篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 1篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 8篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有274条查询结果,搜索用时 554 毫秒
11.
The behaviour of spudcan foundations during the installation and preloading in two-layer sand sediments was investigated through large deformation finite element (LDFE) analyses. The LDFE analyses were carried out using the coupled Eulerian-Lagrangian approach, modifying Mohr-Coulomb soil model to capture hardening and subsequent softening effects of sand. Parametric analyses were undertaken varying the top layer thickness, relative density of sand and spudcan diameter. Both loose to medium dense-over-dense and dense-over-loose to medium dense sand deposits were explored. The results showed that, for the investigated relatively thin top layer thickness of ≤ 5 m, spudcan behaviour was dictated by the bottom sand layer with a minimal influence of the top layer. For assessing the penetration resistance profile in two-layer sands, the performance of the ISO, SNAME, InSafeJIP, and other existing theoretical design methods were evaluated. 相似文献
12.
ISA model: A constitutive model for soils with yield surface in the intergranular strain space 下载免费PDF全文
In this article, a new constitutive model for soils is proposed. It is formulated by means of plasticity, but in contrast to the precedent works, it presents a yield function describing a surface within the intergranular strain space. This latter is a state variable providing information of the recent strain history. An expression for the plastic strain rate has been proposed to guarantee the stress rate continuity. Under the application of medium or large strain amplitudes, the constitutive equation becomes independent of the intergranular strain and delivers a mathematical structure similar to some Karlsruhe hypoplastic models. Some simulations of monotonic and cyclic triaxial test are provided to evaluate and analyze the model performance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
13.
Rodrigo Salgado 《国际地质力学数值与分析法杂志》2011,35(15):1605-1635
In recent years, pile jacking has become a viable alternative installation method for displacement piles. Pile jacking produces minimal noise, vibration and air pollution during installation. In addition, it is possible, at the end of jacking, to have a good estimate of the ultimate static capacity of the pile. In this paper, the shaft resistance of piles jacked into sand is studied using one‐dimensional finite element analysis. The finite element simulations, using a two‐surface plasticity model, demonstrate the effects of relative density and confinement on the unit shaft resistance of piles jacked in sand. The impact of the number of jacking strokes on the unit shaft capacity is also assessed. Based on the numerical results, we developed equations for shaft resistance quantifying the effects of relative density, initial confinement and number of jacking strokes. Predictions using these equations are compared with data obtained from centrifuge tests and field tests. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
14.
通过断裂分析及构造演化,并结合油气地化指标,综合研究认为,哈得逊油气的总体运移特征为“多期充注,晚期成藏”,即有垂向又有横向。海西末期-喜山期主干断层继承性活动,形成断穿石炭系底部的复活断层及伴生断层,沟通寒武系、奥陶系油源。晚加里东期、晚海西期来自寒武-奥陶系的油气沿羊屋2 井区深大断裂纵向运移,哈得逊石炭系整体南倾,未发育有效圈闭,两期油气均未有效成藏。晚喜山期受南北向造山运动影响,石炭系地层发生翘倾作用,形成有效圈闭。同时,古生界的深大油源断裂复活,聚集在奥陶系古油藏中的油气沿断裂垂向调整至石炭系东河砂岩,并在北倾斜坡的背景下,油气自北向南短距离侧向运移,聚集于哈得逊石炭系圈闭中,形成现今哈得逊油藏。 相似文献
15.
16.
This paper presents a finite‐element (FE) model for simulating injection well testing in unconsolidated oil sands reservoir. In injection well testing, the bottom‐hole pressure (BHP) is monitored during the injection and shut‐in period. The flow characteristics of a reservoir can be determined from transient BHP data using conventional reservoir or well‐testing analysis. However, conventional reservoir or well‐testing analysis does not consider geomechanics coupling effects. This simplified assumption has limitations when applied to unconsolidated (uncemented) oil sands reservoirs because oil sands deform and dilate subjected to pressure variation. In addition, hydraulic fracturing may occur in unconsolidated oil sands when high water injection rate is used. This research is motivated in numerical modeling of injection well testing in unconsolidated oil sands reservoir considering the geomechanics coupling effects including hydraulic fracturing. To simulate the strong anisotropy in mechanical and hydraulic behaviour of unconsolidated oil sands induced by fluid injection in injection well testing, a nonlinear stress‐dependent poro‐elasto‐plastic constitutive model together with a strain‐induced anisotropic permeability model are formulated and implemented into a 3D FE simulator. The 3D FE model is used to history match the BHP response measured from an injection well in an oil sands reservoir. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
17.
The geomorphology, lithology and chronostratigraphy of extensive, late Pleistocene inland and river dune sands, aeolian sand sheets (‘cover sands’) and loess deposits of periglacial origin in northwestern Europe are well known. However, the idea that some of these aeolian sediments result from niveo-aeolian processes is still an open question, as no diagnostic sedimentary features have yet been reported. Moreover, actual niveo-aeolian sediments and related denivation forms, reported from various cold-climate regions, are not suitable analogues. Recent observations in active dune fields in northwestern Alaska indicate that interstratification of wind-driven snow and sand preferentially occurs on slip faces of transverse, barchanoid or parabolic dune ridges. Annual denivation forms develop: e.g. snow ramparts, sinkholes, snow hummocks, snow meltwater fans and tensional cracks. The surface consists of a cracked wet sand layer with a dimpled surface and spongy structure. Although the preservation potential of these features is low in this specific case, similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators. The niveo-aeolian concept should therefore not specifically be related to late Pleistocene cover sand deposition in northwestern Europe, as previously assumed. 相似文献
18.
本文介绍了砂土本构模型研究的历史及现状,特别是对国内较少涉及的动弹塑性本构模型研究情况作了详细的介绍,并就作者的理解体会作了一些评价。 相似文献
19.
Freddy Brugmans 《地球表面变化过程与地形》1983,8(6):527-534
Two types of wind ripples are distinguished in an active drift sand area near Hulshorst in The Veluwe (Central Netherlands). The common type has amplitudes of about 0·5 cm and wavelengths of some 11 cm, the atypical ripple has amplitudes of about 1 cm and wavelengths of some 16 cm. In both cases, the sand grains in the crests are coarser than those in the troughs. However, the coarseness of the grains in the crests of the higher ripples is much more pronounced than that of the lower. It is tentatively suggested that wind ripples are initiated by a regular downwind alternation in the impact energy of the descending grains in saltation, possibly due to fixed gravity waves in the sheared flows of air with grains which have strong density gradients with height. 相似文献
20.
The trigonometric relationship between slope inclination, the horizontally acting time‐averaged traction force and the vertical depth of transport allows the estimation of one factor, when both others are known. Depth–transport functions can be deduced by comparing the depth distributions of living organisms and their skeletal remains, and this paper simplifies this comparison using foraminifera in which a single test represents an individual. Differences in distribution parameters between living individuals and empty tests allow depth–transport functions to be determined; these functions differ between species at a single transect according to the varying buoyancies of the tests. Within a single species, differences in depth–transport functions between locations are based on either slope inclination or traction intensities. After establishing a mean depth–transport function by averaging species‐characteristic functions, the time‐averaged traction force acting on the studied transect can be calculated. Transport intensities are also estimated using an erosion–deposition diagram that combines the relative frequency distributions of living individuals and empty tests. The proportion of ‘eroded’, ‘parautochthonous’ and ‘allochthonous’ tests mirrors the influence of both slope inclination and traction force for the deposition of empty tests. To test the model, six species of symbiont‐bearing benthic foraminifers were investigated at two transects in front of a NW Pacific coral reef. One transect is distinguished by a strong slope flattening below the steep reef slope (30 m), whereas further steepening characterizes the equivalent part in the other transect. These differences are mirrored in the depth–transport functions as well as in the erosion–deposition diagrams of all species. The time‐averaged traction forces differ in intensities between transects, because of the position of the reef front with respect to the predominant wind direction. However, the form of the functions is identical and distinguished by an increase from the surface to 35 m depth, followed by a decrease down to 105 m. This can be explained by successive onshore and offshore forces acting on the shallow slope, such as the tropical cyclones that cross the region every summer. 相似文献