全文获取类型
收费全文 | 190篇 |
免费 | 16篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 5篇 |
地球物理 | 76篇 |
地质学 | 53篇 |
海洋学 | 30篇 |
综合类 | 6篇 |
自然地理 | 26篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 14篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 4篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 15篇 |
2003年 | 8篇 |
2002年 | 16篇 |
2001年 | 3篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有225条查询结果,搜索用时 31 毫秒
31.
从板式橡胶支座及混凝土挡块抗震设计角度,以一座典型的3跨预应力混凝土连续梁桥为例,结合概率地震需求分析及桥墩、支座等抗震关键构件极限破坏状态,建立不同支座及挡块分析模型的中小跨径梁桥地震易损性曲线,研究考虑支座滑移效应及挡块破坏的中小跨径梁桥的易损性特征。研究结果表明:不考虑橡胶支座的滑移效应及混凝土挡块破坏,桥墩地震破坏概率明显增大,且会低估支座破坏概率;桥梁系统易损性受支座破坏状态的影响显著,需设置合理的限位装置;在中小跨径梁桥地震易损性分析中,考虑支座的滑移效应及混凝土挡块的破坏十分必要。 相似文献
32.
This paper presents a three-dimensional (3D) continuum nonlinear analysis of the Meloland Road Overpass (MRO) near El Centro, California. The modeling methodology and the computational tools are discussed in detail. The performance of the computational model is evaluated by comparing the computed responses with the responses recorded at the bridge site during the 1979 Imperial Valley and 2010 El Mayor-Cucapah earthquakes. Amongst the recorded earthquake events at the bridge site, these two events caused the strongest shaking. The comparison shows that the 3D model is potentially an effective tool for detailed analysis of a full bridge system including foundation soils, pile foundations, embankments, supporting columns, and the bridge structure itself in a unified system without relying on any ancillary models such as Winkler springs. Additional response parameters such as displacements, rockings, and bending moments are also evaluated although none of these was measured during the seismic events. 相似文献
33.
34.
35.
The dynamic responses of the Tsing Ma suspension bridge and the running behaviors of trains on the bridge under turbulent
wind actions are analyzed by a three-dimensional wind-train-bridge interaction model. This model consists of a spatial finite
element bridge model, a train model composed of eight 4-axle identical coaches of 27 degrees-of-freedom, and a turbulent wind
model. The fluctuating wind forces, including the buffeting forces and the self-excited forces, act on the bridge only, since
the train runs inside the bridge deck. The dynamic responses of the bridge are calculated and some results are compared with
data measured from Typhoon York. The runnability of the train passing through the Tsing Ma suspension bridge at different
speeds is researched under turbulent winds with different wind velocities. Then, the threshold curve of wind velocity for
ensuring the running safety of the train in the bridge deck is proposed, from which the allowable train speed at different
wind velocities can be determined. The numerical results show that rail traffic on the Tsing Ma suspension bridge should be
closed as the mean wind velocity reaches 30 m/s. 相似文献
36.
This study developed a finite element method with the effect of soil–fluid–structure interaction to calculate bridge natural frequencies. The finite element model includes bridge girders, piers, foundations, soil, and water. The effective mass above the soil surface was then used to find the first natural frequency in each direction. A field experiment was performed to validate that the natural frequencies calculated using the proposed finite element method had acceptable accuracy. The calculated natural frequencies with the fluid–structure interaction effect are always smaller than those without this effect. However, the frequency change due to the fluid effect is not obvious, so using the soil–structure interaction model is accurate enough in the bridge natural frequency analysis. The trend of the frequency decreases with the increase of the scour depth, but the curve is not smooth because of non-uniform foundation sections and layered soils. However, when the scour depth is such that pile cap is exposed, the changes in natural frequency with the scour depth are more obvious, and this is useful for measurement of the depth using bridge natural frequencies. 相似文献
37.
Anatoly V. Lozhkin Patricia Anderson Wendy R. Eisner Tatiana B. Solomatkina 《Quaternary Research》2011,76(3):383-392
New palynological and sedimentological data from St. Lawrence Island present a rare view into late-glacial and Holocene environments of the central Bering Land Bridge. The late glaciation was a time of dynamic landscape changes in south-central Beringia, with active thermokarst processes, including the formation and drainage of thaw lakes. The presence of such a wet, unstable substrate, if widespread, probably would have had an adverse impact on food sources and mobility for many of the large mammal populations. The establishment of Betula shrub tundra on the island suggests late-glacial summers that were warmer than present, consistent with regional paleoclimatic interpretations. However, the increasing proximity to the Bering Sea, as postglacial sea levels rose, modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of Beringia at this time. The mid- to late Holocene is marked by more stable land surfaces and development of Sphagnum and Cyperaceae peat deposits. The accumulation of organic deposits, decline of shrub Betula, and decrease in thermokarst disturbance suggest that conditions were cooler than the previous. A recent decline in peat accumulation at the study sites may relate to local geomorphology, but similar decreases have been noted for other arctic regions. 相似文献
38.
在苏通大桥松散软弱的地层条件,实施超长(〉100 m)、超大(2.5 m)摩擦桩桩底后压浆工程,在我国是首次运用。结合工程实践,就压浆工程的设计、施工的技术要点进行全面介绍。通过对钻孔取样分析,指出浆液初凝时间地表实验与地下实际存在较大差异;通过施工体验,结合取样显示的浆液扩散渗透状况,提出可渗透地层以注浆量为控制参数,压力不列为控制参数的思路。 相似文献
39.
D.M.D. James 《Geological Journal》2005,40(5):593-601
New palaeocurrent data from the country northeast and southwest of Corris (central Wales) indicate that Telychian sandstones in the Devil's Bridge Formation hereabouts were transported from both the northeast and northwest, consistent with topographical control by down‐to‐southeast movement on the Bala Lineament. This conclusion is supported by considerations of thickness variation and by evidence for listric detachment faulting in the formation at Bwlch y Groes. Towards Plynlimon, flow is broadly southerly and suggests confinement by the northward extension of the Bronnant Fault. A facies and palaeocurrent map is presented for the utilis sub‐Biozone of the Telychian which links with work by the British Geological Survey between Aberyswyth and Rhayader where, by contrast, palaeoflow is to the NNW. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
40.
Edward H. Stehmeyer III Dimitris C. Rizos 《Soil Dynamics and Earthquake Engineering》2008,28(6):468-479
This paper utilizes and expands on existing coupled BEM–FEM (finite element method) methods for the investigation of the effects of soil structure interaction (SSI) on both an un-retrofitted and seismically isolated typical bridge structure. A simple numerical model of the bridge and surrounding soil is formulated and excited by an earthquake excitation. Utilizing Newmark's β FEM solution method along with the closed form B-spline BIRF method, the structural damped period, composite damping ratio, pier relative displacement, and base shear demand are monitored. From these results, the effects of SSI on this structure are identified. Additionally, the importance of the relative rigidity between the soil-foundation system and the bridge structure is also investigated. The results of the studies indicate that the response of the complete structure system considered is affected by the inclusion of SSI effects. Furthermore, the efficiency of the isolation measures designed using fixed base conditions is decreased by considering SSI over a certain relative rigidity range that is quantified using the structure to soil-foundation natural frequency ratio. 相似文献