全文获取类型
收费全文 | 2640篇 |
免费 | 606篇 |
国内免费 | 236篇 |
专业分类
测绘学 | 180篇 |
大气科学 | 208篇 |
地球物理 | 1952篇 |
地质学 | 332篇 |
海洋学 | 301篇 |
天文学 | 259篇 |
综合类 | 118篇 |
自然地理 | 132篇 |
出版年
2024年 | 13篇 |
2023年 | 42篇 |
2022年 | 65篇 |
2021年 | 97篇 |
2020年 | 100篇 |
2019年 | 100篇 |
2018年 | 105篇 |
2017年 | 99篇 |
2016年 | 87篇 |
2015年 | 109篇 |
2014年 | 128篇 |
2013年 | 120篇 |
2012年 | 110篇 |
2011年 | 137篇 |
2010年 | 134篇 |
2009年 | 132篇 |
2008年 | 144篇 |
2007年 | 163篇 |
2006年 | 159篇 |
2005年 | 157篇 |
2004年 | 162篇 |
2003年 | 162篇 |
2002年 | 132篇 |
2001年 | 96篇 |
2000年 | 105篇 |
1999年 | 90篇 |
1998年 | 86篇 |
1997年 | 68篇 |
1996年 | 68篇 |
1995年 | 71篇 |
1994年 | 44篇 |
1993年 | 51篇 |
1992年 | 37篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3482条查询结果,搜索用时 31 毫秒
991.
F. Pacor D. Bindi L. Luzi S. Parolai S. Marzorati G. Monachesi 《Bulletin of Earthquake Engineering》2007,5(1):27-43
Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that
strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys
et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly
exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and
discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters,
such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface
waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect
to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects
on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface
waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal
and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable
to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a
preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization,
exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the
basin. 相似文献
992.
Kaja Pietsch Paweł Marzec Marcin Kobylarski Tomasz Danek Andrzej Leśniak Artur Tatarata Edward Gruszczyk 《Acta Geophysica》2007,55(2):191-208
The thin-layer build of the Carpathian Foredeep Miocene formations and large petrophysical parameter variation cause seismic
images of gas-saturated zones to be ambiguous, and the location of prospection wells on the basis of anomalous seismic record
is risky. A method that assists reservoir interpretation of standard recorded seismic profiles (P waves) can be a converted wave recording (PS waves).
This paper presents the results of application of a multicomponent seismic survey for the reservoir interpretation over the
Chałupki Dębniańskie gas deposit, carried out for the first time in Poland by Geofizyka Kraków Ltd. for the Polish Oil and
Gas Company. Seismic modeling was applied as the basic research tool, using the SeisMod program based on the finite-difference
solution of the acoustic wave equation and equations of motion. Seismogeological models for P waves were developed using Acoustic Logs; S-wave model (records only from part of the well) was developed on the basis of theoretical curves calculated by means of the
Estymacja program calibrated with average S-velocities, calculated by correlation of recorded P and PS wavefields with 1D modeling.
The conformity between theoretical and recorded wavefields makes it possible to apply the criteria established on the basis
of modeling for reservoir interpretation. Direct hydrocarbon indicators (bright spots, phase change, time sag) unambiguously
identify gas-prone layers within the ChD-2 prospect. A partial range of the indicators observed in the SW part of the studied
profile (bright spot that covers a single, anticlinally bent seismic horizon) points to saturation of the horizon. The proposed
location is confirmed by criteria determined for converted waves (continuous seismic horizons with constant, high amplitude)
despite poorer agreement between theoretical and recorded wavefields. 相似文献
993.
A unified criterion for initiation of sediment motion and inception of sheet flow under water waves 总被引:1,自引:0,他引:1
A unified criterion is developed for initiation of non‐cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, Uo = 2πC[1 + 5(TR/T)2]?1/4, where Uo is the onset velocity of sediment motion or sheet flow, T is wave period, and C and TR are the coefficients. It is found that for a given sediment, Uo initially increases sharply with wave period, then gradually approaches the maximum onset velocity Uo = 2πC and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion. 相似文献
994.
Michael F. Goodchild 《Mathematical Geology》1988,20(6):615-630
A class of stochastic processes known as fractional Brownian motion (fBm) provides strikingly realistic simulations of certain types of terrain, particularly those which appear to be unmodified by geomorphological and geological processes. In addition to their less serious applications in video games and science fiction movies, fractal terrain simulations have proven useful in a number of areas of spatial analysis. For example, they can provide sample data sets for testing the efficiency of data structures and algorithms designed for topographic applications. Previous work has shown that stream networks simulated on fBm surfaces show the same deviations from accepted theories of channel network topology as do real stream networks, implying that such deviations originate in the geometrical constraints of packing channels onto surfaces, rather than from geological or other environmental controls. In effect, this work demonstrates the usefulness of fBm as a null hypothesis for terrain. One difficulty, however, stems from the abundant pits which occur in the simulations, because peaks and pits are equally likely. Flooding of pits on fBm surfaces was simulated to obtain lakes. Lake-rich stream networks were extracted and represented with a suitable integer code. The relative frequencies of various network topologies and groups of topologies were compared to known characteristics of channel networks on real lake-rich landscapes. Lake-string topologies are significantly less abundant than in glaciated landscapes. Lake areas show good fits to hyperbolic distributions, but lake in-degrees do not fit the negative binomial model. fBm surfaces are appropriate null hypotheses of scale-free, lake-rich landscapes.This paper was presented at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987. 相似文献
995.
漠滨金矿的可见金中,有一种呈聚集式乳滴状结构的自然金集合体。本文就其形成机理进行了探讨。这种结构显示的自然金的运动趋势和历史,为原生粗粒金的形成提供了一种可以探讨的途径。 相似文献
996.
Representation of near-fault pulse-type ground motions 总被引:7,自引:3,他引:4
Near-fault ground motions with long-period pulses have been identified as critical in the design of structures. To aid in the representation of this special type of motion, eight simple pulses that characterize the effects of either the fling-step or forward-directivity are considered. Relationships between pulse amplitudes and velocity pulse period for different pulses are discussed. Representative ratios and peak acceleration amplification can exhibit distinctive features depending on variations in pulse duration, amplitude and the selected acceleration pulse shape. Additionally, response spectral characteristics for the equivalent pulses are identified and compared in terms of fixed PGA and PGV, respectively. Response spectra are strongly affected by the duration of pulses and the shape of the basic pulses. Finally, dynamic time history response features of a damped SDOF system subjected to pulse excitations are examined. These special aspects of pulse waveforms and their response spectra should be taken into account in the estimation of ground motions for a project site close to a fault. 相似文献
997.
A family of symplectic integrators adapted for the integration of perturbed Hamiltonian systems of the form H=A+B was given in (McLachlan, 1995). We give here a constructive proof that for all integer p, such integrator exists, with only positive steps, and with a remainder of order O(p + 22), where is the stepsize of the integrator. Moreover, we compute the analytical expressions of the leading terms of the remainders at all orders. We show also that for a large class of systems, a corrector step can be performed such that the remainder becomes O(p +42). The performances of these integrators are compared for the simple pendulum and the planetary three-body problem of Sun–Jupiter–Saturn. 相似文献
998.
Dong-Soo Kim Choong-Ki Chung Chang-Guk Sun Eun-Seok Bang 《Soil Dynamics and Earthquake Engineering》2002,22(5):358
The earthquake hazard has been evaluated for 10 km×10 km area around Kyeongju. The ground motion potentials were determined based on equivalent linear analysis by using the data obtained from in situ and laboratory tests. In situ tests include 16 boring investigations, 4 crosshole, 12 downhole, 26 spectral analysis of surface waves tests, and in the laboratory, resonant column tests were performed. The peak ground accelerations range between 0.141g and 0.299g on collapse level earthquake and between 0.050g and 0.120g on operation level earthquake, respectively, showing the high potential of amplification in the deep alluvial layer in Kyeongju area. Distribution maps of site amplification for the peak acceleration, amplification factors (Fa and Fv) and dominant site period of Kyeongju are constructed using geographic information system tools. The amplification factor based on the Korean seismic design guide underestimated the motion in short range and overestimated the motion in mid-period range in Kyeongju. The importance of site-specific analysis and the need for the improved site characterization method are introduced. 相似文献
999.
Ronan Pavic Martin G. Koller Pierre-Yves Bard Corinne Lacave-Lachet 《Journal of Seismology》2000,4(1):59-77
An assessment of uncertainties for ground motion predictions with the aid of the empirical Green's function (EGF) technique is presented. The main input parameters were identified, and their respective uncertainties were assessed by means of an international expert inquiry. The repercussion of these input uncertainties on the final ground motion estimates were investigated by means of the Latin Hypercube Sampling technique. The mean ground motion estimates (response spectra) and their standard deviations were compared with results obtained from empirical attenuation laws. The most sensitive input parameter turned out to be the seismic moment corresponding to the EGF. In general, if the source parameters are well determined, equivalent uncertainties, statistically speaking, can be expected from the EGF technique and from the application of attenuation laws. Therefore, if EGFs with well known source parameters are available, the EGF technique seems to be preferable: site effects are automatically taken into account, and physically realistic acceleration time histories can be obtained. However, further investigations on the reliability of the EGF technique should be performed, and finally, it is recalled that the EGF technique is based on the assumption of linearity. If conditions are such that this assumption cannot be maintained, the EGF technique should be combined with non-linear geotechnical methods. 相似文献
1000.