全文获取类型
收费全文 | 1032篇 |
免费 | 165篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 78篇 |
地球物理 | 659篇 |
地质学 | 348篇 |
海洋学 | 52篇 |
天文学 | 18篇 |
综合类 | 25篇 |
自然地理 | 26篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 20篇 |
2019年 | 27篇 |
2018年 | 33篇 |
2017年 | 27篇 |
2016年 | 36篇 |
2015年 | 33篇 |
2014年 | 60篇 |
2013年 | 38篇 |
2012年 | 38篇 |
2011年 | 76篇 |
2010年 | 46篇 |
2009年 | 71篇 |
2008年 | 71篇 |
2007年 | 69篇 |
2006年 | 60篇 |
2005年 | 54篇 |
2004年 | 60篇 |
2003年 | 36篇 |
2002年 | 56篇 |
2001年 | 28篇 |
2000年 | 43篇 |
1999年 | 40篇 |
1998年 | 40篇 |
1997年 | 25篇 |
1996年 | 35篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1249条查询结果,搜索用时 562 毫秒
921.
依据邯郸地区地质构造及20多年的观测资料,系统研究了地下水位、地壳形变的正常与异常动态变化及其相互关系.本区地形变的主控因素是西部太行山隆起和东部华北平原大幅度沉降的继承性运动,造成地形变向东南方向倾斜;在大区域的周期性强降水后由于地质构造因素地形变向西北向倾斜,形成水位和形变的正常动态变化.采用有效的定量方法提取异常,显示一部分反向西北倾斜的异常与华北的中强震有较好的对应关系.故强降水引起的地倾斜变化不应看作干扰,而是一种引起地壳变形地震前兆的外动力因素,应予高度关注. 相似文献
922.
923.
地应力观测是目前我国进行地震前兆观测的重要手段之一。利用汶川地震前刘家峡台地应力观测资料,通过分析,获得汶川地震前刘家峡台地应力观测资料的异常特征,解释了汶川地震的震源机制。对现有地震预测方法中存在的一些问题进行了讨论并提出了一些解决办法。 相似文献
924.
The paper aims to evaluate the way Eurocode 8 treats the consideration of asynchronous earthquake ground motion during the
seismic design of bridges, and to discuss alternative solutions for cases wherein existing provisions do not lead to satisfactory
results. The evaluation of EC8-2 new provisions and simplified methods is performed through comparison with a more refined
approach whereas an effort is made to quantitatively assess the relative importance of various design and analysis assumptions
that have to be made when spatial variability of ground motion is taken into consideration, based on the study of the dynamic
response of 27 different bridges. It is concluded that, despite the complexity of the problem, there are specific cases where
EC8 provisions can be safely and easily applied in practice, while in other cases ignoring the effect of asynchronous excitation
or performing simplified calculations can significantly underestimate the actual seismic demand. 相似文献
925.
A revised Italian strong motion archive has become available since July 2007, including all the records of the strongest events
occurred from 1972 to 2004. It contains the uncorrected and corrected accelerograms and the metadata relevant to seismic events,
recording stations and instruments added after a careful revision. The availability of this archive allowed us to perform
a first step towards an update of the reference ground motion prediction equations for Italy, which were evaluated by Sabetta
and Pugliese in (Bull Seismol Soc Am 77:1491–1513, 1987), for peak ground acceleration and velocity, and subsequently extended
to the 5% damped pseudovelocity response spectra in 1996. A subset with the 27 major earthquakes occurred in Italy from 1972
to 2002, in the magnitude range 4.6–6.9, was extracted and 235 good quality waveforms were selected, recorded at distances
up to 183 km. The goodness of fit of the Sabetta and Pugliese (Bull Seismol Soc Am 86:337–352, 1996) model was explored using
two independent statistical approaches (Spudich et al. Bull Seismol Soc Am 89:1156–1170, 1999 and Scherbaum et al. Bull Seismol
Soc Am 94:2164–2185, 2004). The results obtained show that the Sabetta and Pugliese (Bull Seismol Soc Am 77:1491–1513, 1987)
does not adequately fit the new strong-motion data set, for its small standard deviation and its non-zero bias. In particular,
the most noteworthy result is that the Sabetta and Pugliese (Bull Seismol Soc Am 77:1491–1513, 1987) over-predicts peak ground
acceleration and velocity at rock sites. New coefficients for the prediction of horizontal peak ground acceleration, peak
ground velocity and acceleration response spectra, adopting the same functional form in Sabetta and Pugliese (Bull Seismol
Soc Am 77:1491–1513, 1987), were then evaluated in order to fit the new data set. This paper illustrates the steps made to
update the existing ground motion prediction equations for Italy, discusses their limitations and provides the basis for future
developments. 相似文献
926.
Structural identification of Egnatia Odos bridges based on ambient and earthquake induced vibrations
Evaggelos Ntotsios Christos Karakostas Vasilios Lekidis Panagiotis Panetsos Ioannis Nikolaou Costas Papadimitriou Thomas Salonikos 《Bulletin of Earthquake Engineering》2009,7(2):485-501
The dynamic characteristics of two representative R/C bridges on Egnatia Odos motorway in Greece are estimated based on low
amplitude ambient and earthquake-induced vibrations. The present work outlines the instrumentation details, algorithms for
computing modal characteristics (modal frequencies, damping ratios and modeshapes), modal-based finite element model (FEM)
updating methods for estimating structural parameters, and numerical results for the modal and structural dynamic characteristics
of the two bridges based on ambient and earthquake induced vibrations. Transverse, bending and longitudinal modes are reliably
identified and stiffness-related properties of the piers, deck and elastomeric bearings of the FEMs of the two bridges are
estimated. Results provide qualitative and quantitative information on the dynamic behavior of the bridge systems and their
components under low-amplitude vibrations. Modeling assumptions are discussed based on the differences in the characteristics
identified from ambient and earthquake vibration measurements. The sources of the differences observed between the identified
modal and structural characteristics of the bridges and those predicted by FEMs used for design are investigated and properly
justified. 相似文献
927.
利用统计学和气象学原理,对德州2008年1月1日—12月31日德州70 cm高度的气温(用T70表示)与地面温度(用T0表示)中08、14时和20时及日平均资料进行分析。结果表明:冬半年08时T70>T0(或T70≈T0);夏半年T70<T0,6月差值最大,为-2.6℃。14时全年都是T70<T0,3月差值最大,为-12.1℃。20时全年基本都是T70>T0。就日平均而言,全年都是T70<T0。运用回归分析法建立了以T0为基础的T70预测模型,经检验表明,3—9月预测准确率较高,可以满足当地农事需要。 相似文献
928.
探地雷达数值模拟中,时域有限差分法在时间和空间上一般采用二阶精度的中心差分近似(FDTD(2,2)),其形式简单,但数值色散误差较大,在复杂模型模拟时不能很好地反映模型的精细变化.高阶时域有限差分法能很好地改善数值色散带来的误差,提高模拟精度.本文基于三维高阶时域有限差分法的基本原理实现了探地雷达正演模拟,采用单轴各向异性完全匹配层(UPML)作为吸收边界条件,可以有效地吸收外向传播的电磁波,在大大地提高计算效率的同时,也能很好地改善边界的吸收效果.分析对比正演模拟结果,通过三维高阶时域有限差分正演能获得目标体准确电磁响应信息,并能很好的提高模拟精度. 相似文献
929.
2010年4月14日在我国青海省玉树藏族自治州发生了Ms7.1级地震.地震给当地群众的生命财产带来巨大损失,其中最严重的破坏发生在震中东南的玉树县城.我们利用反演远场地震波形得到的震源破裂模型和Crust2.0提供的当地的地壳模型,计算了近断层地面运动(速度场和位移场),再现了地震发生时当地的地面运动图像.根据这个图像,震源的单侧破裂过程导致了明显的多普勒效应.地震波自震中向四周扩散开去,但沿着断层向东南方向传播的地震波的幅度更大、波峰更密.玉树县城恰好位于地面静态位移较大的区域,也位于较强烈的位移波和速度波穿越的地带.与实际的地面运动相比,虽然我们的计算还不够精确,但无容置疑,破裂过程导致的多普勒效应是玉树县城遭受严重破坏的主要原因. 相似文献
930.