全文获取类型
收费全文 | 6365篇 |
免费 | 367篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 169篇 |
大气科学 | 695篇 |
地球物理 | 1670篇 |
地质学 | 2518篇 |
海洋学 | 334篇 |
天文学 | 1071篇 |
综合类 | 28篇 |
自然地理 | 278篇 |
出版年
2023年 | 32篇 |
2022年 | 46篇 |
2021年 | 123篇 |
2020年 | 139篇 |
2019年 | 104篇 |
2018年 | 304篇 |
2017年 | 317篇 |
2016年 | 414篇 |
2015年 | 299篇 |
2014年 | 358篇 |
2013年 | 505篇 |
2012年 | 403篇 |
2011年 | 365篇 |
2010年 | 343篇 |
2009年 | 358篇 |
2008年 | 248篇 |
2007年 | 200篇 |
2006年 | 192篇 |
2005年 | 152篇 |
2004年 | 163篇 |
2003年 | 125篇 |
2002年 | 125篇 |
2001年 | 102篇 |
2000年 | 87篇 |
1999年 | 74篇 |
1998年 | 75篇 |
1997年 | 100篇 |
1996年 | 56篇 |
1995年 | 69篇 |
1994年 | 68篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 35篇 |
1990年 | 60篇 |
1989年 | 28篇 |
1988年 | 21篇 |
1987年 | 42篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 38篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 40篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 23篇 |
1975年 | 17篇 |
1974年 | 17篇 |
1973年 | 21篇 |
排序方式: 共有6763条查询结果,搜索用时 125 毫秒
101.
José F. Noguera Lluís Rivero Xavier Font Andrés Navarro Francisco Martínez 《Environmental Geology》2002,41(8):898-905
102.
103.
—?The aim of our study consists of analyzing potentially non-double-couple seismic events recorded at regional distances. In order to define the nature of the seismic source, a moment tensor inversion is carried out as this method is general enough not to initially constrain the source mechanism. In this paper we present an application to a seismic event induced by a mine collapse which occurred near the town of Halle in Germany. Because of its induced nature, many parameters such as the location and geometry of this seismic source are known. This information allows us to test the influence of inadequate propagation modeling on the moment tensor obtained from the inversion. Green's functions have been computed with the reflectivity method in a flat layered medium, using the European model EurID (Du et? al., 1998; Dufumier et al., 1997). From the inversion of P-wave seismograms recorded by the German Regional Seismic Network will, we obtained a source time function which can be decomposed into two subevents. The first one has a large isotropic part and a deviatoric mechanism with near vertical nodal planes. No volume change is observed for the second subevent, but a deviatoric component opposite of the first one. The addition of S-waves does not change the results of the inversion which are stable. Surface waves were not used because of their poor dispersion curves. Based on the moment tensor obtained from these inversions, the physical process at the source is compatible with a large cavity collapse. 相似文献
104.
105.
Arantxa Luzón Angel González Arsenio Muñoz Belén Sánchez-Valverde 《Journal of Paleolimnology》2002,28(4):441-456
The lacustrine facies from two sections (Candasnos and Fraga) ofthe Oligocene-Miocene Torrente de Cinca lithostratigraphic Unit in thecentral part of the Ebro Basin (Spain) have been analysed to determine theinfluence of orbital parameters in lacustrine sedimentation. The unit ispredominantly composed of limestones and marls, and represents a shallowlacustrine freshwater system. The sedimentological features of the faciesstudied demonstrate that the lower part of the Candasnos section representsoffshore lacustrine subenvironments whereas the upper part, and the whole ofthe Fraga section, characterise marginal lacustrine areas. Series of stratalthickness variations of limestone, marl, and limestone/marl couplets fromboth sections have been analysed using spectral analysis. This shows thatinformation corresponding to periodic cycles only appears in the offshorefacies, that is to say, in the lower part of Candasnos section, and disappearsin the marginal facies where non-periodic cycles exist. Furthermore, thespectral analysis of the offshore facies highlights the existence of a peak inthe power spectrum with a period of around 7 (6.8 to 7.8) that can berecognised in the field as shallowing-upward lacustrine sequences.Magnetostratigraphic data from the Candasnos section allow us to establish atime span of 2,808 years for the limestone/marl couplet from the lower partof this section, and between 19,000 and 22,000 years for the periodic cycleidentified, thus representing the climatic precession cycle. Shallowingsequences from marginal areas do not correspond with any periodiccycle. 相似文献
106.
Anne Pelletier Denis Gapais René-Pierre Ménot Jean-Jacques Peucat 《Comptes Rendus Geoscience》2002,334(7):505-511
The Palaeoproterozoic units of Terre Adélie show two types of structural domains associated with HT–LP metamorphic conditions: domes and NS–N340° striking vertical shear zones. Shear zones reflect dextral transpressive motions. Domes reflect sub-vertical shortening and principal stretching subparallel to shear zones. They could partly result from longitudinal flow coeval with transpression. Deformations are comparable to those described along the eastern and western boundaries of the Archean Gawler Craton (South-East Australia), which underlines the continuity between these two areas before opening of the Austral Ocean. To cite this article: A. Pelletier et al., C. R. Geoscience 334 (2002) 505–511. 相似文献
107.
— It is well known that there is no “universal” permeability-porosity relationship valid in all porous media. However, the evolution of permeability and porosity in rocks can be constrained provided that the processes changing the pore space are known. In this paper, we review observations of the relationship between permeability and porosity during rock evolution and interpret them in terms of creation/destruction of effectively and non-effectively conducting pore space. We focus on laboratory processes, namely, plastic compaction of aggregates, elastic-brittle deformation of granular rocks, dilatant and thermal microcracking of dense rocks, chemically driven processes, as a way to approach naturally occurring geological processes. In particular, the chemically driven processes and their corresponding evolution permeability-porosity relationships are discussed in relation to sedimentary rocks diagenesis. 相似文献
108.
— Analytical expressions to predict the enhancement of permeability due to stress-induced microcracking in initially low porosity rock are presented. A fracture mechanical microcrack model is employed to derive integrated effective hydraulic variables as a function of stress, which are then used to calculate the evolution of permeability using the statistically-based Dienes model. The model enables determination of permeability enhancement as a function of two loading parameters and three material parameters. Results are in reasonable agreement with experimental measurements and indicate that appreciable increases in permeability can be anticipated during brittle failure. The analytical nature of the model makes it easily incorporatable into numerical models that require quantification of the permeability evolution as a function of stress, for which there is currently no law. 相似文献
109.
A method of visualizing structures in closed chaotic flows out of homogenous particle distributions is presented in the example of models of a meandering jet. To this end, the system will be leaked or opened up by defining a region of the flow, so that a particle is considered to be escaped if it leaves this region. By applying this method to an ensemble of nonescaped tracers, we are able to characterize mixing processes by visualizing the converging and stretching filamentations (stable and unstable manifolds) in the flow without using additional mathematical tools. The possibility of applying the algorithm to analyze buoy data, and a comparison with the finite time manifolds are discussed. 相似文献
110.
Failure Mode and Spatial Distribution of Damage in Rothbach Sandstone in the Brittle-ductile Transition 总被引:4,自引:0,他引:4
— To elucidate the spatial complexity of damage and evolution of localized failure in the transitional regime from brittle faulting to cataclastic ductile flow in a porous sandstone, we performed a series of triaxial compression experiments on Rothbach sandstone (20% porosity). Quantitative microstructural analysis and X-ray computed tomography (CT) imaging were conducted on deformed samples. Localized failure was observed in samples at effective pressures ranging from 5 MPa to 130 MPa. In the brittle faulting regime, dilating shear bands were observed. The CT images and stereological measurements reveal the geometric complexity and spatial heterogeneity of damage in the failed samples. In the transitional regime (at effective pressures between 45 MPa and 130 MPa), compacting shear bands at high angles and compaction bands perpendicular to the maximum compression direction were observed. The laboratory results suggest that these complex localized features can be pervasive in sandstone formations, not just limited to the very porous aeolian sandstone in which they were first documented. The microstructural observations are in qualitative agreement with theoretical predictions of bifurcation analyses, except for the occurrence of compaction bands in the sample deformed at effective pressure of 130 MPa. The bifurcation analysis with the constitutive model used in this paper is nonadequate to predict compaction band formation, may be due to the neglect of bedding anisotropy of the rock and multiple yield mechanisms in the constitutive model. 相似文献