全文获取类型
收费全文 | 1619篇 |
免费 | 61篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 115篇 |
地球物理 | 409篇 |
地质学 | 657篇 |
海洋学 | 131篇 |
天文学 | 227篇 |
综合类 | 5篇 |
自然地理 | 121篇 |
出版年
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 33篇 |
2017年 | 35篇 |
2016年 | 60篇 |
2015年 | 42篇 |
2014年 | 43篇 |
2013年 | 95篇 |
2012年 | 57篇 |
2011年 | 89篇 |
2010年 | 90篇 |
2009年 | 98篇 |
2008年 | 73篇 |
2007年 | 85篇 |
2006年 | 72篇 |
2005年 | 93篇 |
2004年 | 73篇 |
2003年 | 51篇 |
2002年 | 56篇 |
2001年 | 41篇 |
2000年 | 26篇 |
1999年 | 33篇 |
1998年 | 32篇 |
1997年 | 12篇 |
1996年 | 22篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1975年 | 6篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1972年 | 5篇 |
排序方式: 共有1700条查询结果,搜索用时 46 毫秒
991.
Michel Monzier Claude Robin Pablo Samaniego Minard L. Hall Jo Cotten Patricia Mothes Nicolas Arnaud 《Journal of Volcanology and Geothermal Research》1999,90(1-2)
Sangay (5230 m), the southernmost active volcano of the Andean Northern Volcanic Zone (NVZ), sits 130 km above a >32-Ma-old slab, close to a major tear that separates two distinct subducting oceanic crusts. Southwards, Quaternary volcanism is absent along a 1600-km-long segment of the Andes. Three successive edifices of decreasing volume have formed the Sangay volcanic complex during the last 500 ka. Two former cones (Sangay I and II) have been largely destroyed by sector collapses that resulted in large debris avalanches that flowed out upon the Amazon plain. Sangay III, being constructed within the last avalanche amphitheater, has been active at least since 14 ka BP. Only the largest eruptions with unusually high Plinian columns are likely to represent a major hazard for the inhabited areas located 30 to 100 km west of the volcano. However, given the volcano's relief and unbuttressed eastern side, a future collapse must be considered, that would seriously affect an area of present-day colonization in the Amazon plain, 30 km east of the summit. Andesites greatly predominate at Sangay, there being few dacites and basalts. In order to explain the unusual characteristics of the Sangay suite—highest content of incompatible elements (except Y and HREE) of any NVZ suite, low Y and HREE values in the andesites and dacites, and high Nb/La of the only basalt found—a preliminary five-step model is proposed: (1) an enriched mantle (in comparison with an MORB source), or maybe a variably enriched mantle, at the site of the Sangay, prior to Quaternary volcanism; (2) metasomatism of this mantle by important volumes of slab-derived fluids enriched in soluble incompatible elements, due to the subduction of major oceanic fracture zones; (3) partial melting of this metasomatized mantle and generation of primitive basaltic melts with Nb/La values typical of the NVZ, which are parental to the entire Sangay suite but apparently never reach the surface and subordinate production of high Nb/La basaltic melts, maybe by lower degrees of melting at the periphery of the main site of magma formation, that only infrequently reach the surface; (4) AFC processes at the base of a 50-km-thick crust, where parental melts pond and fractionate while assimilating remelts of similar basaltic material previously underplated, producing andesites with low Y and HREE contents, due to garnet stability at this depth; (5) low-pressure fractionation and mixing processes higher in the crust. Both an enriched mantle under Sangay prior to volcanism and an important slab-derived input of fluids enriched in soluble incompatible elements, two parameters certainly related to the unique setting of the volcano at the southern termination of the NVZ, apparently account for the exceptionally high contents of incompatible elements of the Sangay suite. In addition, the low Cr/Ni values of the entire suite—another unique characteristic of the NVZ—also requires unusual fractionation processes involving Cr-spinel and/or clinopyroxene, either in the upper mantle or at the base of the crust. 相似文献
992.
Current activities and recent progress on constructive approximation and numerical analysis in physical geodesy are reported
upon. Two major topics of interest are focused upon, namely trial systems for purposes of global and local approximation and
methods for adequate geodetic application. A fundamental tool is an uncertainty principle, which gives appropriate bounds
for the quantification of space and momentum localization of trial functions. The essential outcome is a better understanding
of constructive approximation in terms of radial basis functions such as splines and wavelets.
Received: 4 May 1999 / Accepted: 21 May 1999 相似文献
993.
Observation of a 3d Magnetic Null Point in the Solar Corona 总被引:3,自引:0,他引:3
A saddle-like structure is clearly discerned in SOHO EIT images in the Fe wavebands in the active region NOAA 8113, from 6 to 10 December 1997, when the active region reached the solar limb. It appears after the emergence of a small patch of parasitic polarity near the footpoints of the loops forming the outer boundary of an arcade. There is a 3D null point in the center of the saddle. The height of the null is in good agreement with the relationship between the parasitic flux and the background magnetic field. In spite of the fact that a saddle-like or hyperbolic magnetic configuration is usually assumed as the necessary condition for magnetic field-line reconnection and magnetic energy release, no additional heating is observed inside the saddle structure. Moreover, interior parts of the saddle seem to be darker than the neighbouring loops of the arcade. 相似文献
994.
Physical properties, spectral reflectance and thickness development of first year fast ice in Kongsfjorden, Svalbard 总被引:2,自引:0,他引:2
Sebastian Gerland Jan-Gunnar Winther Jon Børre Ørbæk Boris V. Ivanov 《Polar research》1999,18(2):275-282
A ground truth study was performed on first year fast ice in Kongsfjorden, Svalbard, during spring 1997 and 1998. The survey included sea ice thickness monitoring as well as observation of surface albedo, attenuation of optical radiation in the ice, physical properties and texture of snow and sea ice. The average total sea ice thickness in May was about 0.9 m, including a 0.2 m thick snow layer on top. Within a few weeks in both years, the snow melted almost completely, whereas the ice thickness decreased by not more than 0.05 m. During spring, the lower part of the snow refroze into a solid layer. The sea ice became more porous. Temperatures in the sea ice increased and the measurable salinity of the sea ice decreased with time. Due to snow cover thinning and snow grain growth, maximum surface albedo decreased from 0.96 to 0.74. Texture analysis on cores showed columnar ice with large crystals (max. crystal lenght > 0.1 m) below a 0.11 m thick mixed surface layer of granular ice with smaller crystals. In both years, we observed sea ice algae at the bottom part of the ice. This layer has a significant effect on the radiation transmissivity. 相似文献
995.
Jean-Jacques Schott Michel Roussignol Michel Menvielle & Flavien R. Nomenjahanary 《Geophysical Journal International》1999,138(3):769-783
In this paper, we will report on the application of Bayesian inference to DC resistivity inversion for 1-D multilayer models. The posterior probability distribution is explored through a Markov process based upon a Gibbs's sampler. The process would lead to unrealistic estimates without additional prior information, which takes the form of a second Markov chain where the transition kernel corresponds to a smoothness constraint. The outcomes are posterior marginal probabilites for each parameter, as well as, if required, joint probabilities for pairs of parameters. We will discuss the main properties of the method in the light of a theoretical example and illustrate its capabilities with some field examples taken from various contexts. 相似文献
996.
Vincent Bichet Michel Campy Jean-Franois Buoncristiani Christian Digiovanni Michel Meybeck Herv Richard 《Quaternary Research》1999,51(3):267
The Upper Doubs River Valley is a 910-km2watershed feeding into Lake Chaillexon. The lake was formed by a natural rockfall at the end of the Bølling Chronozone (around 14,250 cal yr B.P.) and since then has trapped material eroded from the watershed. The filling process and variations in sediment yield have been investigated by mechanical coring, seismic surveys, and electric soundings. The detrital sediment yield of the upstream watershed can be calculated by quantifying the sedimentary stocks for each climatic stage of the Late-Glacial period and Holocene Epoch and estimating the lake's entrapment capacity. This enables us to determine the intensity of the erosion processes in relation to climate and environmental factors. The Bølling–Allerød Interstade produced the greatest yields with mean values of 19,500 metric tons per calendar year (t/yr). The Younger Dryas Chronozone saw a sharp fall (8900 t/yr) that continued into the Preboreal (2100 t/yr). Clastic supply increased during the Boreal (4500 t/yr) before declining again in the Early Atlantic (2400 t/yr). Since then, yields have risen from 4500 t/yr in the Late Atlantic to 6800 t/yr in the Subboreal and 11,100 t/yr in the Subatlantic. Comparison of quantitative data with the qualitative analysis of the deposits and with the paleohydrologic curve of the watershed based on level fluctuations in lakes around Chaillexon shows that climate was the controlling factor of sediment yield until the Late Atlantic. From the Late Atlantic–Subboreal around 5400 cal yr B.P. (470014C yr B.P.) and especially from the end of the Subboreal Chronozone and during the Subatlantic Chronozone (2770 cal yr B.P./270014C yr B.P.–present) climatic constraints have been compounded by human activity related to forest clearing and land use. 相似文献
997.
Plomerová Jaroslava Granet Michel Judenherc Sebasten Achauer Ulrich Babuška Vladislav Jedlička Petr Kouba Daniel Vecsey Luděk 《Studia Geophysica et Geodaetica》2000,44(2):195-209
We present the first results of a comparison of deep lithosphere structure of three Variscan massifs - the Armorican Massif, French Massif Central and Bohemian Massif, as revealed by recent tomographic studies of seismic anisotropy. The data originate from several field measurements made in temporary arrays of stations equipped with both short-period and broadband seismometers with digital recording. The study is based on teleseismic body waves and a joint inversion of anisotropic data (P-residual spheres, the fast shear-wave polarizations and split times) and demonstrates that the three Variscan massifs appear to consist of at least two parts with different orientation of large-scale fabric derived from seismic anisotropy. The boundaries of anisotropic lithospheric domains are related to prominent tectonic features recognised on the surface as sutures, shear zones or transfer fault zones, as well as grabens, thus indicating that some of them extend deep through the entire lithosphere. 相似文献
998.
Judith Sippel Aline Saintot Michel Heeremans Magdalena Scheck-Wenderoth 《Marine and Petroleum Geology》2010
The geodynamic history of a region is archived in its geologic record which, in turn, may reflect deformation patterns that causally can be related to certain configurations of paleostresses. In the Oslo Region, the exposed geological record ranges from Precambrian high-grade metamorphic rocks through Cambro-Silurian sedimentary rocks to Permo-Carboniferous sedimentary and magmatic rocks, the latter being related to the development of the Oslo rift system. We investigate the kinematics of outcrop-scale faults to derive the diversity of paleostress states responsible for the observed strain. For this purpose, we combine different graphical and numerical approaches to separate heterogeneous fault-slip data sets and estimate the associated reduced stress tensors. A reduced stress tensor consists of the directions of the three principal stress axes with σ1 ≥ σ2 ≥ σ3 and the ratio of principal stress differences, R = (σ2 − σ3)/(σ1 − σ3). 相似文献
999.
Succint results of recent geomorphological research conducted by a Canadian team from Université Laval (Quebec city) in the Khabur valley of northeastern Syria confirms the hypothesis put forward by one of the authors concerning the function of the tell 'Atij site during the Early Bronze Age period (3000–2500 B. C.). The detailed study of a stratigraphically controlled cross section of 25 m × 6 m, on the abrupt western side of the main tell of the site, combined with observations made in a trench linking the principal tell to the secondary one showed that these two tells, now forming 'Atij, were small islands on the ancient Khabur River. At the time of their occupation, i. e., the first half of the 3rd millenium, the Khabur was wider, deeper and navigable. Another investigation trench, 400 m N. E. of the main tell, disproved the suggested existence of an ancient irrigation canal in the area. © 1994 John Wiley & Sons, Inc. 相似文献
1000.
Valérie Ballu Jérome Ammann Olivier Pot Olivier de Viron Glenn S. Sasagawa Gilles Reverdin Marie-Noelle Bouin Mathilde Cannat Christine Deplus Sébastien Deroussi Marcia Maia Michel Diament 《Journal of Geodesy》2009,83(2):147-159
Decades of cruise-based exploration have provided excellent snapshots of the structure of mid-ocean ridges and have revealed
that accretion is a mixture of steady-state and quantum events. Observatory-type studies are now needed to quantify the temporal
evolution of these systems. A multi-disciplinary seafloor observatory site is currently being set up at the Lucky Strike volcano,
in the axial valley of the slow spreading Mid-Atlantic ridge as a part of the MoMAR (monitoring of the Mid-Atlantic Ridge)
initiative. The aim of this observatory is to better understand the dynamics of the volcano and the hydrothermal vents hosted
at its summit as well as their plumbing systems. In August 2006, the GRAVILUCK cruise initiated an experiment to monitor the
deformation of Lucky Strike volcano. A geodetic network was installed, and seafloor pressure, gravity and magnetic data were
collected. In this paper, we present the method used to monitor volcanic deformation, which involves measuring relative depth
difference between points within a seafloor geodesy network. We show that, taking into account oceanographic variability and
measurement noise, the network should be able to detect vertical deformations of the order of 1 cm. 相似文献