全文获取类型
收费全文 | 1106篇 |
免费 | 212篇 |
国内免费 | 275篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 87篇 |
地球物理 | 716篇 |
地质学 | 442篇 |
海洋学 | 253篇 |
天文学 | 2篇 |
综合类 | 49篇 |
自然地理 | 19篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 28篇 |
2021年 | 35篇 |
2020年 | 46篇 |
2019年 | 65篇 |
2018年 | 50篇 |
2017年 | 49篇 |
2016年 | 38篇 |
2015年 | 65篇 |
2014年 | 77篇 |
2013年 | 55篇 |
2012年 | 74篇 |
2011年 | 92篇 |
2010年 | 67篇 |
2009年 | 69篇 |
2008年 | 81篇 |
2007年 | 82篇 |
2006年 | 85篇 |
2005年 | 72篇 |
2004年 | 73篇 |
2003年 | 71篇 |
2002年 | 71篇 |
2001年 | 41篇 |
2000年 | 43篇 |
1999年 | 30篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有1593条查询结果,搜索用时 281 毫秒
471.
张建刚 《广东海洋大学学报》1993,(2)
对作横向振动的转轴用能量法分为连续和离散两种模型,计算其一阶临界转速,同时将此法应用于一个实例,并进行了误差分析。 相似文献
472.
介绍基础隔震结构的工作原理和两种计算模型,结合工程实例采用时程分析法和Matlab程序模拟计算结构隔震和不隔震时的顶层响应,计算结果表明多层建筑采用基础隔震可以有效地降低结构的地震反应。 相似文献
473.
南京某综合办公楼桩基工程采用震动沉管桩,由于该区地层的粉砂层存在不同端阻力分界面,因上层长时间的震动,下层粉砂层发生液化,导致桩尖与沉管脱离,桩管内出现水泥浆:为此在施工中采用活瓣桩尖,并用0.5m^3的砼封底,有效地解决了桩管冒浆问题。 相似文献
474.
475.
In this study, we determine an updated finite element model of a reinforced concrete building—which was damaged from shaking during 1994 Northridge earthquake—using forced‐vibration test data and a novel model‐updating technique. Developed and verified in the companion paper (viz. BVLSrc, Earthquake Eng. Struct. Dyn. 2006; this issue), this iterative technique incorporates novel sensitivity‐based relative constraints to avoid ill conditioning that results from spatial incompleteness of measured data. We used frequency response functions and natural frequencies as input for the model‐updating problem. These data were extracted from measurements obtained during a white‐noise excitation applied at the roof of the building using a linear inertial shaker. Flexural stiffness values of properly grouped structural members, modal damping ratios, and translational and rotational mass values were chosen as the updating parameters, so that the converged results had direct physical interpretations, and thus, comparisons with common parameters used in seismic design and evaluation of buildings could be made. We investigated the veracity of the updated finite element model by comparing the predicted and measured dynamic responses under a second, and different type of forced (sine‐sweep) vibration, test. These results indicate that the updated model replicates the dynamic behaviour of the building reasonably well. Furthermore, the updated stiffness factors appear to be well correlated with the observed building damage patterns (i.e. their location and severity). Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
476.
477.
Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake 总被引:3,自引:0,他引:3
S. S. Ivanovi M. D. Trifunac E. I. Novikova A. A. Gladkov M. I. Todorovska 《Soil Dynamics and Earthquake Engineering》2000,19(6):974
Results of two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, are presented. Both surveys were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (ML=5.3, epicenter 1.5 km west from the building site) and its early aftershocks. The first survey was conducted on 4 and 5 February 1994, and the second one on 19 and 20 April 1994, about one month after the 20 March aftershock (ML=5.3, epicenter 1.2 km north–west from the building site). The apparent frequencies and two- and three-dimensional mode shapes for longitudinal, transverse and vertical vibrations were calculated. The attempts to detect the highly localized damage by simple spectral analyses of the ambient noise data were not successful. It is suggested that very high spatial resolution of recording points is required to identify localized column and beam damage, due to the complex building behavior, with many interacting structural components. The loss of the axial capacity of the damaged columns could be seen in the vertical response of the columns, but similar moderate or weak damage typically would not be noticed in ambient vibration surveys. Previous analysis of the recorded response of this building to 12 earthquakes suggests that, during large response of the foundation and piles, the soil is pushed sideways and gaps form between the foundation and the soil. These gaps appear to be closing during “dynamic compaction” when the building site is shaken by many small aftershocks. The apparent frequencies of the soil–foundation–structure system appear to be influenced significantly by variations in the effective soil–foundation stiffness. These variations can be monitored by a sequence of specialized ambient vibration tests. 相似文献
478.
In order to effectively control vibration related problems, the development of a reliable vibration monitoring system and the proper assessment of attenuation characteristics of various vibrations are essential. Various ground vibrations caused by train loading, blasting, friction pile driving and hydraulic hammer compaction were measured using 3D geophones inside of the borehole as well as on the ground surface, and the propagation and attenuation characteristics of various source generated vibrations were investigated by analyzing particle motions. For the geometric modeling of various vibrations, the types of various sources and their induced waves were characterized and the geometric damping coefficients were determined. The measured attenuation data matched well with the predicted data when using the suggested geometric damping coefficient, and the estimated soil damping ratios were quite reasonable taking soil type of the site and experiencing strain level into consideration. 相似文献
479.
480.