全文获取类型
收费全文 | 3636篇 |
免费 | 743篇 |
国内免费 | 958篇 |
专业分类
测绘学 | 296篇 |
大气科学 | 304篇 |
地球物理 | 1730篇 |
地质学 | 2285篇 |
海洋学 | 200篇 |
天文学 | 25篇 |
综合类 | 203篇 |
自然地理 | 294篇 |
出版年
2024年 | 12篇 |
2023年 | 43篇 |
2022年 | 127篇 |
2021年 | 161篇 |
2020年 | 140篇 |
2019年 | 180篇 |
2018年 | 167篇 |
2017年 | 135篇 |
2016年 | 180篇 |
2015年 | 229篇 |
2014年 | 250篇 |
2013年 | 242篇 |
2012年 | 241篇 |
2011年 | 245篇 |
2010年 | 229篇 |
2009年 | 280篇 |
2008年 | 238篇 |
2007年 | 278篇 |
2006年 | 268篇 |
2005年 | 237篇 |
2004年 | 250篇 |
2003年 | 193篇 |
2002年 | 169篇 |
2001年 | 123篇 |
2000年 | 118篇 |
1999年 | 107篇 |
1998年 | 76篇 |
1997年 | 89篇 |
1996年 | 75篇 |
1995年 | 49篇 |
1994年 | 28篇 |
1993年 | 42篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 25篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有5337条查询结果,搜索用时 296 毫秒
911.
Dong Yinfeng Li Yingmin Xiao Mingkui Lai Ming 《Soil Dynamics and Earthquake Engineering》2008,28(1):7-19
Some limitations of the Hilbert–Huang transform (HHT) for nonlinear and nonstationary signal processing are remarked. As an enhancement to the HHT, a time varying vector autoregressive moving average (VARMA) model based method is proposed to calculate the instantaneous frequencies of the intrinsic mode functions (IMFs) obtained from the empirical mode decomposition (EMD) of a signal. By representing the IMFs as time varying VARMA model and using the Kalman filter to estimate the time varying model parameters, the instantaneous frequencies are calculated according to the time varying parameters, then the instantaneous frequencies and the envelopes derived from the cubic spline interpolation of the maxima of IMFs are used to yield the Hilbert spectrum. The analysis of the length of day dataset and the ground motion record El Centro (1940, N–S) shows that the proposed method offers advantages in frequency resolution, and produces more physically meaningful and readable Hilbert spectrum than the original HHT method, short-time Fourier transform (STFT) and wavelet transform (WT). The analysis of the seismic response of a building during the 1994 Northridge earthquake shows that the proposed method is a powerful tool for structural damage detection, which is expected as the promising area for future research. 相似文献
912.
A Survey of Techniques for Predicting Earthquake Ground Motions for Engineering Purposes 总被引:2,自引:0,他引:2
Over the past four or five decades many advances have been made in earthquake ground-motion prediction and a variety of procedures
have been proposed. Some of these procedures are based on explicit physical models of the earthquake source, travel-path and
recording site while others lack a strong physical basis and seek only to replicate observations. In addition, there are a
number of hybrid methods that seek to combine benefits of different approaches. The various techniques proposed have their
adherents and some of them are extensively used to estimate ground motions for engineering design purposes and in seismic
hazard research. These methods all have their own advantages and limitations that are not often discussed by their proponents.
The purposes of this article are to: summarise existing methods and the most important references, provide a family tree showing
the connections between different methods and, most importantly, to discuss the advantages and disadvantages of each method.
相似文献
John DouglasEmail: |
913.
A fully nonstationary stochastic model for strong earthquake ground motion is developed. The model employs filtering of a discretized white‐noise process. Nonstationarity is achieved by modulating the intensity and varying the filter properties in time. The formulation has the important advantage of separating the temporal and spectral nonstationary characteristics of the process, thereby allowing flexibility and ease in modeling and parameter estimation. The model is fitted to target ground motions by matching a set of statistical characteristics, including the mean‐square intensity, the cumulative mean number of zero‐level up‐crossings and a measure of the bandwidth, all expressed as functions of time. Post‐processing by a second filter assures zero residual velocity and displacement, and improves the match to response spectral ordinates for long periods. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
914.
915.
应用小波伽略金方法,对Maxwell方程进行离散化,导出了DB2-MRTD算法的探地雷达3D差分公式、数值稳定性条件.在此基础上,开发了探地雷达MRTD(multi-resolution time domain)法正演模拟程序,该程序极大地提高了运算速度,改善了三维探地雷达正演方法,并利用该自制程序,对三角形金属体模型进行了正演模拟,得到了其相应的正演合成三维剖视图及切片图,通过对这些模拟结果进行分析,可以加深对三维雷达反射特征的认识,提高探地雷达探测的可靠性、准确度,同时也说明时域多分辨率法在探地雷达三维正演模拟中的有效性. 相似文献
916.
The Wenchuan earthquake of 12 May 2008 is the most destructive earthquake in China in the past 30 years in terms of property
damage and human losses. In order to understand the earthquake process and the geo-morphological factors affecting the seismic
hazard, we simulated the strong ground motion caused by the earthquake, incorporating three-dimensional (3D) earth structure,
finite-fault rupture, and realistic surface topography. The simulated ground motions reveal that the fault rupture and basin
structure control the overall pattern of the peak ground shaking. Large peak ground velocity (PGV) is distributed in two narrow
areas: one with the largest PGV values is above the hanging wall of the fault and attributed to the locations of fault asperities
and rupture directivity; the other is along the northwestern margin of the Sichuan Basin and caused by both the directivity
of fault rupture and the amplification in the thick sediment basin. Rough topography above the rupture fault causes wave scattering,
resulting in significantly larger peak ground motion on the apex of topographic relief than in the valley. Topography and
scattering also reduce the wave energy in the forward direction of fault rupture but increase the PGV in other parts of the
basin. These results suggest the need for a localized hazard assessment in places of rough topography that takes the topographic
effects into account. Finally, had the earthquake started at the northeast end of the fault zone and ruptured to the southwest,
Chengdu would have suffered a much stronger shaking than it experienced on 12 May, 2008.
Supported by the U.S. National Science Foundation (Grant Nos. EAR 0738779 and OCE 0727919), the National Basic Research Program
of China (Grant No. 2004CB418404), and partially by the National Nature Science Foundation of China (Grant No. 40521002) 相似文献
917.
Tomotaka Iwata Takao Kagawa Anatoly Petukhin Yoshihiro Ohnishi 《Journal of Seismology》2008,12(2):223-234
We constructed a prototype of the basin and crustal structure model for the Kinki area, southwest of Japan, for the simulation
of strong ground motions of hypothetical crustal and subduction earthquakes. We collected results of the deep seismic velocity
profiles obtained by the reflection experiments and seismic imaging results, which were conducted in the Kinki area. The obtained
profiles give underground velocity structures of the crust, from the surface to the subducting slab. We also gather the basin
velocity structure information of the Osaka, Kyoto, Nara, and Ohmi basins. To examine the applicability of the constructed
velocity structure model to the ground motion simulation, we simulated waveforms of an intermediate size event occurred near
the source area of the hypothetical subduction earthquakes. Simulated ground motions using the basin and crustal velocity
structure model are fairly well reproducing the observations at most of stations, and the constructed basin and crustal velocity
structure model is applicable for the long-period ground motion simulations. 相似文献
918.
Probabilistic aftershock hazard assessment II: application of strong ground motion simulations 总被引:1,自引:1,他引:0
Probabilistic aftershock hazard assessment (PAHA) has been introduced by Wiemer (Geophys Res Lett 27:3405–3408, 2000). The method, in its original form, utilizes attenuation relations in evaluating peak ground velocity (PGV) exceedence probability.
We substitute the attenuation relations together with their uncertainties by strong ground motion simulations for a set of
scenarios. The main advantage of such an approach is that the simulations account for specific details of the aftershock source
effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGVs and their standard deviations
are retrieved from the simulation results obtained by the new hybrid k-squared source model, and they are used for the PAHA analysis at a station under study. The model chosen for the testing
purposes is inspired by the Izmit A25 aftershock (M
w
= 5.8) that occurred 26 days after the mainshock. The PAHA maps are compared with (1) those obtained by the use of attenuation
relations and (2) the peak values of ten selected strong-motion recordings written by the aftershock at epicentral distances
<50 km. We conclude that, although the overall hazard decay with increasing fault distance is similar, the PAHA maps obtained
by the use of simulations exhibit remanent radiation pattern effect and prolongation in the strike direction due to the directivity
effect pronounced for some of the scenarios. As regard the comparison with real data, we conclude that the PAHA maps agree
with observed peak values due to appropriate attenuation model adopted in the analysis. 相似文献
919.
Haruko Sekiguchi Masayuki Yoshimi Haruo Horikawa Kunikazu Yoshida Sunao Kunimatsu Kenji Satake 《Journal of Seismology》2008,12(2):185-195
We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of
sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband
ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most
severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models
based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which
long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function
method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary
basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long
predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with
an approximate evaluation by 4 H/V
s where H and V
s are the thickness of the sediment and the average S wave velocity, respectively. 相似文献
920.
A seismological overview of long-period ground motion 总被引:1,自引:1,他引:0
Long-period ground motion has become an increasingly important consideration because of the recent rapid increase in the number
of large-scale structures, such as high-rise buildings and oil storage tanks. Large subduction-zone earthquakes and moderate
to large crustal earthquakes can generate far-source long-period ground motions in distant sedimentary basins with the help
of path effects. Near-fault long-period ground motions are generated, for the most part, by the source effects of forward
rupture directivity. Far-source long-period ground motions consist primarily of surface waves with longer durations than near-fault
long-period ground motions. They were first recognized in the seismograms of the 1968 Tokachi-oki and 1966 Parkfield earthquakes,
and their identification has been applied to the 1964 Niigata earthquake and earlier earthquakes. Even if there is no seismogram,
we can identify far-source long-period ground motions through the investigation of tank damage by liquid sloshing. 相似文献