全文获取类型
收费全文 | 973篇 |
免费 | 172篇 |
国内免费 | 225篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 5篇 |
地球物理 | 674篇 |
地质学 | 392篇 |
海洋学 | 231篇 |
天文学 | 2篇 |
综合类 | 41篇 |
自然地理 | 8篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 30篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 45篇 |
2017年 | 45篇 |
2016年 | 28篇 |
2015年 | 54篇 |
2014年 | 59篇 |
2013年 | 43篇 |
2012年 | 57篇 |
2011年 | 82篇 |
2010年 | 58篇 |
2009年 | 63篇 |
2008年 | 73篇 |
2007年 | 75篇 |
2006年 | 76篇 |
2005年 | 65篇 |
2004年 | 68篇 |
2003年 | 61篇 |
2002年 | 66篇 |
2001年 | 35篇 |
2000年 | 36篇 |
1999年 | 29篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有1370条查询结果,搜索用时 234 毫秒
991.
This paper presents the variations of vibration under different traffic conditions on the Fatih Sultan Mehmet suspension bridge in Istanbul, Turkey.The main intention is to determine the vibration amplifications under heavy-traffic as opposed to no-traffic conditions. This is the first study in this particular area that has been performed on this bridge, over which an average of 200,000 cars pass daily. Two full-scale ambient vibration surveys were carried out on two different days to determine the response of the bridge to diverse traffic conditions. Initial measurements were taken as the bridge experienced heavy stress conditions caused by rush-hour traffic. Secondary measurements were recorded after closing the bridge to traffic. The data were analyzed to gauge the vibration effects of heavy-traffic conditions on the bridge and to determine the effects of different traffic conditions on the free vibration characteristics of the bridge. The analyses were performed utilizing different amplification methods. Results show that there are important differences in the amplifications of the vibration amplitudes. Especially heavy-traffic on the bridge causes the vibration response of the bridge to be intensified in comparison to no-traffic conditions. Additionally, predominant frequencies are shifted as a direct result of traffic load acting on the bridge. Even more importantly and is probably analogous for all long-span bridges, is the fact that any movement causing vibration on the bridge is carried and amplified along its length. These significant amplifications indicate the important effect of varying traffic loads and how the bridge responds to the diverse movements it experiences. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
992.
为探讨城市轨道交通U型梁车桥系统车桥耦合振动对周边环境的影响,采用线性化轮轨模型建立了31个自由度的车辆动力学模型。以重庆市轨道交通一号线工程中梁山以西高架区间所采用标准跨径为30m的单线小U结构为对象,采用自编程序和通用对机车车辆过桥时的车桥耦合振动进行了分析,实测了周边地面受到车桥耦合振动的响应,并通过计算与实测结果的对比分析对所建立的理论模型和编制的程序进行了验证,对U梁引起的环境振动进行了评价。结果表明,U型梁具有良好的环境振动控制效果。 相似文献
993.
This paper presents a study of site effects in the urban area of Tecoman in Colima, Mexico. A variety of instruments (both accelerometers and seismometers) were used to record earthquakes and ambient vibration throughout the city. Earthquake records were analysed using several techniques to estimate site effects: spectral ratios relative to a reference station, spectral ratios of the horizontal components relative to the vertical recorded at the same site, and a parametric inversion of Fourier spectra. Ambient noise records were used to estimate a local transfer function using horizontal to vertical spectral ratios. The results show that local amplification at Tecoman is significant. Dominant frequency varies between 0.5 and 0.7 Hz, suggesting a large thickness of the soft sedimentary deposits. We did not observe systematic variations throughout the city. Our more reliable estimates indicate that maximum amplification is comprised between a factor 6 and 8. Comparisons among different sensors and recorders show that all combinations between velocimeters, accelerometers, and recorders provide reliable results provided that the electronic noise is smaller than the noise being recorded. This is notably not the case for accelerometers at quiet sites and for frequencies smaller than 2 Hz. This explains why previous studies disagree as to the usefulness of accelerometers to record ambient noise for site effect studies. This factor is, however, a function of noise amplitude at each site. 相似文献
994.
995.
996.
The fatigue life of top tensioned risers under vortex-induced vibrations (VIVs) with consideration of the effect of internal
flowing fluid on the riser is analyzed in the time domain. The long-term stress histories of the riser under VIVs are calculated
and the mean stresses, the number of stress cycles and amplitudes are determined by the rainflow counting method. The Palmgren-Miner
rule for cumulative damage theory with a specified S-N curve is used to estimate the fatigue life of the riser. The corresponding
numerical programs numerical simulation of vortex-induced vibrations (NSVIV) which can be used to calculate the VIV response
and fatigue life of the riser are compiled. Finally the influences of the riser’s parameters such as flexural rigidity, top
tension and internal flow velocity on the fatigue life of the riser are analyzed in detail and some conclusions are drawn. 相似文献
997.
在动三轴试验过程中,加载频率对动模量和阻尼比的影响目前还没有定论。基于室内动三轴试验结果,采用二维颗粒流程序PFC2D模拟了筑坝反滤料在不同加载频率(f = 1.0、0.5、0.1、0.05 Hz)条件下的室内动三轴试验。数值模拟结果与试验结果基本吻合,试验结果表明,(1)当 f ≥ 0.1 Hz时,频率对动模量和阻尼比的影响可以忽略;当 f < 0.1 Hz时,模量在小应变情况下会有所降低,但随着应变的增大会趋于一致。(2)阻尼比在f = 0.05 Hz时波动比较大,但与其他频率条件下的阻尼比相比都在一个较小的区域内,可以认为频率对阻尼比基本没有影响 相似文献
998.
微差爆破降震效果影响因素分析 总被引:3,自引:0,他引:3
依托单段实测爆破振动信号,借助Matlab软件编程,分析了特性各异的子信号在不同微差时间下叠加信号的时频特征,通过引入“降幅率”和“振速比例”的概念,提出了微差爆破叠加信号各特性随微差时间、起爆顺序及子信号特性的变化规律。分析发现,使叠加信号达到一定降幅率的时差并非某一具体时差点,而是多个间断的时差区间,其主频随微差时间的不同呈阶跃锯齿型变化;合理微差时间下,两单段信号的振动特性越相近,干扰降震效果越明显;若装药已定,优先起爆小药量的段别所达到的降震效果更佳。现场试验数据显示,研究结果基本符合微差爆破的现实运作规律 相似文献
999.
基于青藏铁路北麓河试验段的机车现场实时振动监测,在三轴流变试验的基础上,利用ABAQUS有限元软件中的时间硬化与Druker-Prager屈服破坏准则耦合的蠕变模型,对青藏铁路多年冻土区的普通素土路基在等效机车荷载作用下的蠕变效应进行分析。研究表明,ABAQUS软件中时间硬化与蠕变模型能较好地模拟路基运营过程中的时间效应,素土路基的竖向位移由路基顶部中心位置向路基内部和两侧逐渐减小,一年中的最大位移达14 mm,与该段的年沉降变形观测值一致。路基中心的蠕变应变值大于路基顶面和天然地表的应变值,路基中心受机车荷载的振动影响最大 相似文献
1000.
上海打桩振害监测与分析 总被引:1,自引:0,他引:1
分析研究了打桩振害机理、振动理论计算、打桩监测设备和技术方法、振害判断依据、振害防治等,并结合工程实例探讨了上海地区打桩振动的特性。 相似文献