全文获取类型
收费全文 | 600篇 |
免费 | 86篇 |
国内免费 | 79篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 86篇 |
地球物理 | 154篇 |
地质学 | 217篇 |
海洋学 | 58篇 |
天文学 | 56篇 |
综合类 | 52篇 |
自然地理 | 107篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 18篇 |
2021年 | 10篇 |
2020年 | 19篇 |
2019年 | 12篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 27篇 |
2015年 | 16篇 |
2014年 | 25篇 |
2013年 | 35篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 65篇 |
2007年 | 37篇 |
2006年 | 45篇 |
2005年 | 29篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 22篇 |
2000年 | 13篇 |
1999年 | 19篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有765条查询结果,搜索用时 15 毫秒
691.
Jesús Carrera Xavier Sánchez-Vila Inmaculada Benet Agustín Medina Germán Galarza Jordi Guimerà 《Hydrogeology Journal》1998,6(1):178-190
Matrix diffusion has become widely recognized as an important transport mechanism. Unfortunately, accounting for matrix diffusion
complicates solute-transport simulations. This problem has led to simplified formulations, partly motivated by the solution
method. As a result, some confusion has been generated about how to properly pose the problem. One of the objectives of this
work is to find some unity among existing formulations and solution methods. In doing so, some asymptotic properties of matrix
diffusion are derived. Specifically, early-time behavior (short tests) depends only on φ
m
2
R
m
D
m
/ L
m
2, whereas late-time behavior (long tracer tests) depends only on φ
m
R
m
, and not on matrix diffusion coefficient or block size and shape. The latter is always true for mean arrival time. These
properties help in: (a) analyzing the qualitative behavior of matrix diffusion; (b) explaining one paradox of solute transport
through fractured rocks (the apparent dependence of porosity on travel time); (c) discriminating between matrix diffusion
and other problems (such as kinetic sorption or heterogeneity); and (d) describing identifiability problems and ways to overcome
them.
Received, October 1997 · Revised, November 1997 · Accepted, December 1997 相似文献
692.
693.
694.
695.
Earthquake swarms in California are often localized to areas within dextral offsets in the linear trend in active fault strands, suggesting a relation between earthquake swarms and local crustal spreading. Local crustal spereading is required by the geometry of dextral offsets when, as in the San Andreas system, faults have dominantly strike-slip motion with right-lateral displacement. Three clear examples of this relation occur in the Imperial Valley, Coso Hot Springs, and the Danville region, all in California. The first two of these areas are known for their Holocene volcanism and geothermal potential, which is consistent with crustal spreading and magmatic intrusion. The third example, however, shows no evidence for volcanism or geothermal activity at the surface. 相似文献
696.
Summary Focal mechanisms of 74 shallow and 16 intermediate earthquakes (1964–1970) in the Kamchatka-Commander region are discussed. Regional stress systems and the nature of faulting are analyzed. Complex stress fields in the Kamchatka-Commander region and variable aftershock processes of strong Kamchatka earthquakes show the existence of heterogeneities of the active seismic zone in the Region. 相似文献
697.
Mashael M. Al-Saud 《Arabian Journal of Geosciences》2008,1(1):49-61
Makkah and central Red Sea regions have been re-evaluated from recent earthquake data analysis. Epicenters of recent seismic
activity are concentrated in three local seismic zones. These are Ad Damm fault (NE), Nu’man–Makkah–Fatima (NW), and Jeddah-Red
Sea (NW) seismic zones. Moreover, an extended seismic zone along the central part of Red Sea is observed. Most of these epicenters
are distributed along tectonic faults, as indicated from the subsurface structure analysis of the aeromagnetic anomaly map.
Some epicenters of small magnitudes are inaccurately located. The study indicates the existence of large active structural
basin south of Makkah region, which traverse Ad Damm fault zone with the Red Sea transform faults. Slip vector analyses were
carried out for 50 available earthquake focal mechanisms around Makkah region. In Nu’man, Makkah, and Fatima structural zones,
the slip vectors generally trend NW and NNW. However, in the southern part at the Ad Dam structure zone, the slip vector trends
NE–SW. These may result from the current complicated drifting motion of Arabian plate away from African plate combined with
the opening of the Red Sea rift. 相似文献
698.
Francisco Javier Muñoz-Almaraz Emilio Freire Jorge Galan-Vioque Andre Vanderbauwhede 《Celestial Mechanics and Dynamical Astronomy》2007,97(1):17-47
In this paper we introduce the concept of a quasi-submersive mapping between two finite-dimensional spaces, we obtain the
main properties of such mappings, and we introduce “normality conditions” under which a particular class of so-called “constrained
mappings” are quasi-submersive at their zeros. Our main application is concerned with the continuation properties of normal
doubly symmetric orbits in time-reversible systems with one or more first integrals. As examples we study the continuation
of the figure-eight and the supereight choreographies in the N-body problem. 相似文献
699.
700.
Based on analysis of background of geological tectonic movement and strong earthquake activity, we first obtained the focal mechanism solutions using amplitude ratio and CAP method, then determined the characteristic of average stress field of the study area by inversion of the stress field. On this basis, we selected the source mechanism consistency parameter as the inspection index to obtain the latest changes of stress field in Hetao seismic zone based on its temporal and spatial analysis. Two methods were used in the stress field inversion for comparison and analysis, which are average stress axis tensor and LSIB(Linear stress inversion bootstrap, LSIB). According to the geological tectonic movement and focal mechanism solutions of MS≥4.0 earthquakes from 1970, we judge that the stress field evolution process of Hetao seismic belt is controlled jointly by vertical difference movement and horizontal shear movement, resulting in that the normal fault and strike-slip fault mechanisms are dominating.Taking into account the station layout of the study area, and in order to ensure the accuracy of calculation, we calculated 224 earthquakes focal mechanism solutions by using amplitude ratio and CAP method, including 164 earthquakes with 2.8≤ML<3.5, 42 earthquakes with 3.5≤ML<4.0, and 18 earthquakes with ML≥4.0; The statistical results on type of focal mechanisms show that, there are 142 strike-slip earthquakes(63.4%), 50 normal fault earthquakes(22.3%)and 32 thrust fault earthquakes(14.3%). In this study period(from 2001 to 2012), most earthquakes had a strike-slip mechanism in Hetao seismic belt, this is one of the inherent characteristics of the stress field.The result of average stress axis tensor and LSIB shows that, the azimuth of maximum compressional stress is 47°~52°, direction is NE-SW; The azimuth of minimum compressional stress is 313°~322°, direction is NW-SE; This indicates that, the stress field characteristics of Hetao seismic belt and its sub-block are not completely consistent. Linhe Basin exhibits coordinated stress field characteristics with Hetao seismic belt, but Hubao Basin exhibits regional differences, direction of compressive stress has clockwise deflection in Baotou area, and the compressive stress direction is NEE. This heteropical character of stress field is also confirmed by horizontal projection distribution of stress axis of historical strong earthquakes and recent moderate and small earthquakes. Since 2003, the temporal sequence curve of consistency parameter of Hetao seismic belt had a downward trend, this change was caused by focal mechanism consistency parameter of Linhe to Wuhai area, which indicates that this structural position is possible to be a priority area for stress accumulation and accelerated release in future. 相似文献