全文获取类型
收费全文 | 8204篇 |
免费 | 1453篇 |
国内免费 | 1589篇 |
专业分类
测绘学 | 856篇 |
大气科学 | 740篇 |
地球物理 | 3406篇 |
地质学 | 3250篇 |
海洋学 | 795篇 |
天文学 | 1278篇 |
综合类 | 432篇 |
自然地理 | 489篇 |
出版年
2024年 | 44篇 |
2023年 | 138篇 |
2022年 | 233篇 |
2021年 | 308篇 |
2020年 | 303篇 |
2019年 | 373篇 |
2018年 | 304篇 |
2017年 | 301篇 |
2016年 | 375篇 |
2015年 | 435篇 |
2014年 | 484篇 |
2013年 | 445篇 |
2012年 | 444篇 |
2011年 | 455篇 |
2010年 | 443篇 |
2009年 | 554篇 |
2008年 | 513篇 |
2007年 | 613篇 |
2006年 | 562篇 |
2005年 | 485篇 |
2004年 | 517篇 |
2003年 | 449篇 |
2002年 | 371篇 |
2001年 | 309篇 |
2000年 | 283篇 |
1999年 | 267篇 |
1998年 | 234篇 |
1997年 | 160篇 |
1996年 | 164篇 |
1995年 | 127篇 |
1994年 | 89篇 |
1993年 | 121篇 |
1992年 | 70篇 |
1991年 | 60篇 |
1990年 | 57篇 |
1989年 | 49篇 |
1988年 | 40篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Seismic Hazard for Selected Sites in Greece: A Bayesian Estimate of Seismic Peak Ground Acceleration 总被引:1,自引:1,他引:1
A procedure for estimating maximum values of seismic peak ground accelerationat the examined site and quantiles of its probabilistic distribution in a future timeinterval of a given length is considered. The input information for the method areseismic catalog and regression relation between peak seismic acceleration at a givenpoint and magnitude and distance from the site to epicenter (seismic attenuation law).The method is based on Bayesian approach, which simply accounts for influenceof uncertainties of seismic acceleration values. The main assumptions for the method are Poissonian character of seismic events flow and distribution law of Gutenberg-Richter's type. The method is applied to seismic hazard estimation in six selected sitesin Greece. 相似文献
82.
83.
Horizontal and vertical components of earthquake ground motions at liquefiable sites 总被引:1,自引:0,他引:1
Field observations on ground motions from recent earthquakes imply that current knowledge is limited with regard to relating vertical and horizontal motions at liquefiable sites. This paper describes a study with the purpose of clarifying this emerging issue to some extent. A series of numerical analyses is carried out on a liquefiable soil deposit with a verified, fully coupled, nonlinear procedure. It is shown that the transformation of vertical motions in the deposit differs considerably from the transformation of horizontal motions. Both the amplitude and frequency content of the horizontal motions are strongly dependent on the shaking level or the associated nonlinear soil behavior. The transfer function for vertical motions is however likely to be independent of the intensity of input motions; no reduction in the amplitude occurs even in the case of strong shaking. The results are shown to be in consistence with the laboratory observations on shaking table tests and recent field observations that less nonlinearity exists for vertical motions. It is also shown that the possibility exists for using information on spectral ratios between the horizontal and vertical surface motions to quickly identify in situ soil behavior and liquefaction that are not readily covered by conventional field or laboratory experimentation procedures. 相似文献
84.
J. J. Bommer M. B. Benito M. Ciudad-Real A. Lemoine M. A. Lpez-Menjívar R. Madariaga J. Mankelow P. Mndez de Hasbun W. Murphy M. Nieto-Lovo C. E. Rodríguez-Pineda H. Rosa 《Soil Dynamics and Earthquake Engineering》2002,22(5)
The small Central American republic of El Salvador has experienced, on average, one destructive earthquake per decade during the last hundred years. The latest events occurred on 13 January and 13 February 2001, with magnitudes Mw 7.7 and 6.6, respectively. The two events, which were of different tectonic origin, follow the patterns of the seismicity of the region although neither event has a known precedent in the earthquake catalogue in terms of size and location. The earthquakes caused damage to thousands of traditionally built houses and triggered hundreds of landslides, which were the main causes of fatalities. The earthquakes have clearly demonstrated trends of increasing seismic risk in El Salvador due to rapid population expansion in areas of high shaking and landslide hazard, exacerbated by deforestation and uncontrolled urbanisation. The institutional mechanisms required for the control of land use and building practice are very weak and present a major obstacle to risk mitigation. 相似文献
85.
Uniform models for the Earth–ionosphere cavity are considered with particular attention to the physical properties of the ionosphere for the extremely low frequency (ELF) range. Two consistent features have long been recognized for the range: the presence of two distinct altitude layers of maximum energy dissipation within the lower ionosphere, and a “knee”-like change in the vertical conductivity profile representing a transition in dominance from ion-dominated to electron-dominated conductivity. A simplified two-exponential version of the Greifinger and Greifinger (1978) technique widely used in ELF work identifies two slopes in the conductivity profile and, providing accurate results in the ELF communication band (45–75 Hz), simulates too flat a frequency dependence of the quality factor within the Schumann resonance frequency range (5–40 Hz). The problem is traced to the upward migration, with frequency increasing, of the lower dissipation layer through the “knee” region resulting in a pronounced decrease of the effective scale height for conductivity. To overcome this shortcoming of the two-exponential approximation and still retain valuable model analyticity, a more general approach (but still based on the Greifinger and Greifinger formalism) is presented in the form of a “knee” model whose predictions for the modal frequencies, the wave phase velocities and the quality factors reasonably represent observations in the Schumann resonance frequency range. 相似文献
86.
Spatial variation of earthquake ground motion is an important phenomenon that cannot be ignored in the design and safety of strategic structures. Several models have been developed to describe this variation using statistical, mathematical or physical approaches. The latter approach is not specific to an event. A recent contribution, which uses such an approach and called complete stochastic deamplification approach (CSDA), was developed [1]. The aim of this paper is to analyze the spatial variation of earthquake motion induced by the propagation of body waves using the CSDA. Coherency functions are evaluated for the cases of SH–SV–P waves propagating through stratified soil. Results obtained show that the variation of the coherency function is not the same for vertical and horizontal components and that the motion is more coherent at depth than at the free surface. In fact, we found that the rate of decrease with frequency and distance is not the same if P–SV waves propagate through stratified soil. 相似文献
87.
大型维歇特地震仪自德国引进南京地震台已近70年。本文简要叙述了该仪器的性能;并以南京地震台的大型维歇特地震仪的记录为例,介绍了该仪器在300-2000km范围内的记录特征,回顾了该仪器在地震速报中所起的历史作用。 相似文献
88.
液化场地桩-土-桥梁结构动力相互作用振动台试验研究进展 总被引:20,自引:3,他引:20
本文在全面归纳与总结液化场地桩-土-桥梁结构动力相互作用振动台试验及与之相关领域的国内外研究进展基础上,直接针对我国桥梁工程中的主要震害问题,提出在我国开展液化场地桩-土-桥梁结构动力相互作用振动台试验研究的必要性,并阐述作者对液化场地桩-土-张桥梁结构动力相互作用振动台试验中若干问题的认识。 相似文献
89.
90.
David K. Keefer 《Surveys in Geophysics》2002,23(6):473-510
Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides. This paper traces thehistorical development of knowledge derived from these investigations. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. For example, the number of landslides triggered by a given event is almost always greatly underestimated. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. Techniques have also been developed for performing ``retrospective' analyses years or decades after an earthquake that attempt to reconstruct the distribution of landslides triggered by the event. The additional use of Geographic Information System (GIS) processing and digital mapping since about 1989 has greatly facilitated the level of analysis that can applied to mapped distributions of landslides. Beginning in 1984, syntheses of worldwide and national data on earthquake-induced landslides have defined their general characteristics and relations between their occurrence and various geologic and seismic parameters. However, the number of comprehensive post-earthquake studies of landslides is still relatively small, and one of the most pressing needs in this area of research is for the complete documentation of landslides triggered by many more earthquakes in a wider variety of environments. 相似文献