全文获取类型
收费全文 | 1511篇 |
免费 | 256篇 |
国内免费 | 116篇 |
专业分类
测绘学 | 115篇 |
大气科学 | 87篇 |
地球物理 | 846篇 |
地质学 | 703篇 |
海洋学 | 39篇 |
天文学 | 18篇 |
综合类 | 49篇 |
自然地理 | 26篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 36篇 |
2019年 | 41篇 |
2018年 | 42篇 |
2017年 | 40篇 |
2016年 | 58篇 |
2015年 | 50篇 |
2014年 | 91篇 |
2013年 | 70篇 |
2012年 | 55篇 |
2011年 | 92篇 |
2010年 | 54篇 |
2009年 | 105篇 |
2008年 | 98篇 |
2007年 | 105篇 |
2006年 | 95篇 |
2005年 | 87篇 |
2004年 | 91篇 |
2003年 | 72篇 |
2002年 | 80篇 |
2001年 | 43篇 |
2000年 | 52篇 |
1999年 | 54篇 |
1998年 | 56篇 |
1997年 | 50篇 |
1996年 | 52篇 |
1995年 | 37篇 |
1994年 | 32篇 |
1993年 | 26篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1883条查询结果,搜索用时 40 毫秒
991.
Hans-Rudolf Wenk Erik Rybacki Georg Dresen Ivan Lonardelli Nathan Barton Hermann Franz Gabriela Gonzalez 《Physics and Chemistry of Minerals》2006,33(10):667-676
Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with time-of-flight neutron diffraction and hard synchrotron X-rays, analyzing diffraction data with the Rietveld method. Similar texture patterns are observed as described previously but the new results establish a profound influence of temperature and document that twinning initiates at stresses less than 50 MPa. Possibilities of using Dauphiné twinning as a paleopiezometer in quartz-bearing rocks are discussed. 相似文献
992.
Comparing geophysical methods for talus slope investigations in the Turtmann valley (Swiss Alps) 总被引:3,自引:1,他引:3
Three geophysical methods, ground penetrating radar, 2D-resistivity and seismic refraction were applied to two landform complexes in a high-alpine valley in Switzerland to investigate their internal structure. Results of the different methods were analysed separately, before conclusions about sediment thickness and geomorphologic implications were drawn. The results from the three methods were compared to focus on the quality of the methods and their field utility, with respect to portability of equipment, required man-power and measurement time. In this study, ground penetrating radar and seismic refraction proved to be the most suitable with respect to the quality and resolution of the subsurface information and the level of field utility. Sediment thicknesses of 15 m on a rectilinear slope and more than 30 m on a talus cone have been measured; a backweathering rate of approximately 700 mm ka− 1 was established. Furthermore, the radar delivered detailed internal sediment structure as well as interfaces between talus and rock glacier. The combined geophysical investigation produced a detailed image of the subsurface composition of the two landform complexes that enhance the understanding of the paraglacial landform evolution in this hanging valley. 相似文献
993.
One of the goals of using the Global Positioning System (GPS) and other geodetic survey techniques in tectonics has been to detect boundaries such as faults or shear zones between rigid or mildly deforming crustal masses. The calculation of infinitesimal strains and rotations with GPS data has been widely used to detect shear zones but it has been largely unsuccessful because infinitesimal strain and rotation, although useful in many other ways, is non-diagnostic of shear zones or faults. Our approach is to work with components of deformation, not strain, and to design specifically a diagnostic method of detecting shear zones. This paper introduces the first part of our method, the detection of two-dimensional, strike-shift shear zones (MODES-2D). The MODES-2D method has three elements: (1) determination of the orientation of a suspected strike-shift shear zone by analyzing components of a deformation tensor derived from a data set of displacements in an arbitrary coordinate system; (2) resolution of the deformation tensor into the coordinate system parallel and normal to the detected shear zone; and (3) exploration of the resolved data set for evidence for a belt of inhomogeneous deformation, which is an essential characteristic of a shear zone. The operation of MODES-2D is illustrated herein with a theoretical survey network across an ideal shear zone developed with a buried dislocation-fault and with a survey network afforded by the crossing of the Kaynaşlı viaduct by the 1999 Düzce–Bolu earthquake rupture in Turkey. 相似文献
994.
易门瓷厂高墙地砖厂主体车间建于残积土地基上,约三分之二的基坑地基土天然强度低,压缩性高。加固处理,通过基坑原位测试,对加固处理前、后的地基土容许承载力进行对比,检查残积土软地基加固处理效果。 相似文献
995.
996.
Modeling decadal timescale interactions between surface water and ground water in the central Everglades, Florida, USA 总被引:1,自引:0,他引:1
Surface-water and ground-water flow are coupled in the central Everglades, although the remoteness of this system has hindered many previous attempts to quantify interactions between surface water and ground water. We modeled flow through a 43,000 ha basin in the central Everglades called Water Conservation Area 2A. The purpose of the model was to quantify recharge and discharge in the basin's vast interior areas. The presence and distribution of tritium in ground water was the principal constraint on the modeling, based on measurements in 25 research wells ranging in depth from 2 to 37 m. In addition to average characteristics of surface-water flow, the model parameters included depth of the layer of ‘interactive’ ground water that is actively exchanged with surface water, average residence time of interactive ground water, and the associated recharge and discharge fluxes across the wetland ground surface. Results indicated that only a relatively thin (8 m) layer of the 60 m deep surfical aquifer actively exchanges surface water and ground water on a decadal timescale. The calculated storage depth of interactive ground water was 3.1 m after adjustment for the porosity of peat and sandy limestone. Modeling of the tritium data yielded an average residence time of 90 years in interactive ground water, with associated recharge and discharge fluxes equal to 0.01 cm d−1. 3H/3He isotopic ratio measurements (which correct for effects of vertical mixing in the aquifer with deeper, tritium-dead water) were available from several wells, and these indicated an average residence time of 25 years, suggesting that residence time was overestimated using tritium measurements alone. Indeed, both residence time and storage depth would be expected to be overestimated due to vertical mixing. The estimate of recharge and discharge (0.01 cm d−1) that resulted from tritium modeling therefore is still considered reliable, because the ratio of residence time and storage depth (used to calculated recharge and discharge) is much less sensitive to vertical mixing compared with residence time alone. We conclude that a small but potentially significant component of flow through the Everglades is recharged to the aquifer and stored there for years to decades before discharged back to surface water. Long-term storage of water and solutes in the ground-water system beneath the wetlands has implications for restoration of Everglades water quality. 相似文献
997.
998.
The deformation characteristics, shear moduli and damping ratios of reconstituted lacustrine carbonate silt samples were investigated in different kinds of laboratory tests. Material from a landslide that occurred in a seismically very active area in Slovenia was used in the tests. The initial values of this material's deformation characteristics and the extent to which these values change due to increasing shear strain depend on a number of factors, such as the degree of saturation, the initial void ratio, over-consolidation, and the effective stresses. The use of a volumetric threshold strain has proved to be the best way of describing the shear modulus reduction curve irrespective of any other factors, and it fits well with the data obtained in the experiments. The critical state and consolidation lines for the investigated material are presented in the paper as deformational characteristics at critical strain levels. The material's liquefaction potential was studied for certain in situ conditions. 相似文献
999.
Federica Riguzzi Grazia Pietrantonio Antonio Piersanti Salah M. Mahmoud 《Journal of Geodynamics》2006,41(5):485-499
We analyze observations from eight GPS campaigns carried out between 1997 and 2005 on a network of 13 sites in the Suez–Sinai area, where separation between the African and the Arabian plates takes place. This is the key area to understand if and in which way Sinai behaves like a sub-plate of the African plate and the role played by seismic and geodetic (long-term) deformation release.Our analysis shows that, on average, the Suez–Sinai area motion, in terms of ITRF00 velocities, matches the African plate motion defined by the NNR-NUVEL-1A model.The horizontal principal strain rate axes estimated separately in the Gulf of Suez area and in the northern Sinai vary from compression across the Gulf (−2.2 ± 1.2) × 10−8 year−1 to NE extension (1.0 ± 1.5) × 10−8 year−1 in the North, showing the presence of two distinct domains, so that in our opinion Sinai cannot be considered simply a unique rigid block.The analysis of GPS baseline length variations shows short-term deformations across the Gulf of Suez, reaching up a maximum value of more than 1 cm in 8 years.Since current geodynamical models do not predict significant tectonic deformation in this area, we work under the hypothesis that a contribute may be expected by post-seismic relaxation effects. Under this hypothesis, we compare the baselines length variations with the post-seismic relaxation field associated with five major local earthquakes occurred in the area, testing two different viscoelastic models. Our results show that the detected short-term deformations are better modeled for viscosity values of 1018 Pa s in the lower crust and 1020 Pa s in the asthenosphere. However, since the modeled post-seismic effect results modest and a certain amount of the detected deformation is not accounted for, we think that an improved modeling should take into account the lateral heterogeneities of crust and upper mantle structures. 相似文献
1000.
The Bardoc Tectonic Zone (BTZ) of the late Archaean Eastern Goldfields Province, Yilgarn Craton, Western Australia, is physically
linked along strike to the Boulder-Lefroy Shear Zone (BLSZ), one of the richest orogenic gold shear systems in the world.
However, gold production in the BTZ has only been one order of magnitude smaller than that of the BLSZ (∼100 t Au vs >1,500 t
Au). The reasons for this difference can be found in the relative timing, distribution and style(s) of deformation that controlled
gold deposition in the two shear systems. Deformation within the BTZ was relatively simple and is associated with tight to
iso-clinal folding and reverse to transpressive shear zones over a <12-km-wide area of high straining, where lithological
contacts have been rotated towards the plane of maximum shortening. These structures control gold mineralisation and also
correspond to the second major shortening phase of the province (D2). In contrast, shearing within the BLSZ is concentrated to narrow shear zones (<2 km wide) cutting through rocks at a range
of orientations that underwent more complex dip- and strike-slip deformation, possibly developed throughout the different
deformation phases recorded in the region (D1–D4). Independent of other physico-chemical factors, these differences provided for effective fluid localisation to host units
with greater competency contrasts during a prolonged mineralisation process in the BLSZ as compared to the more simple structural
history of the BTZ. 相似文献