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91.
Soil evolution and subalpine ecosystem changes in the French Alps inferred from geochemical analysis of lacustrine sediments 总被引:1,自引:0,他引:1
Brice Mourier Jerome Poulenard Christopher Carcaillet David Williamson 《Journal of Paleolimnology》2010,44(2):571-587
This study aimed to reconstruct the history of soil development, ecosystem changes and associated erosional processes in a
small mountain lacustrine basin at the decennial to millennial scale. Geochemical proxies of soil evolution were analysed
in the Holocene lacustrine sediments and peats from Thyl Lake, Maurienne Valley, French Alps. Podzolization and chemical weathering
processes were assessed using secondary Al- and Fe-bearing phases together with major and Rare Earth Elements (REE). The resulting
proxy records, spanning ca. 4,400 years between 8.6 and 4.2 cal ka BP, indicate that progressive pedogenesis occurred after deglaciation in a relatively
stable subalpine ecosystem. As shown by the associated increase in Al- and Fe-bearing phases and some REE fractions, the establishment
of a mixed cembra pine ecosystem from ca. 7.2–6.5 ka BP was associated with enhanced podzolisation processes in the catchment. The progressive soil development was
followed by a rapid transformation of the local environment and plant cover (the open waters of the lake were replaced by
a confined peat environment) together with changes in forest fire regimes from ca. 6.8 ka BP. Depleted REE patterns, associated with low contents of secondary Al and Fe, suggest a decrease in chemical weathering
and podzolization in the catchment at that time, possibly associated with local intensification of weathering and drainage
processes in a relatively acidic peat environment. The higher variability of cembra pine and the increased abundance of sedge
and other herbaceous plant remains in the lake sediment indicate semi-open vegetation environments from 5.7 cal ka BP onwards.
Whereas fire events and plant cover appear to be significantly related, the soil processes seem primarily linked to vegetation
composition, and secondarily to changes in fire regime. 相似文献
92.
Farooq Ahmad Dar Jerome Perrin Shakeel Ahmed Allu China Narayana 《Hydrogeology Journal》2014,22(7):1493-1506
About 3 % of India’s total land surface is occupied by carbonate rocks which are mostly karstified and constitute a significant source of groundwater. The groundwater drawn from these aquifers matches the water demand of ~35 million people living in 106 districts of the country and also the water needs of livestock, irrigation and industry. The studies on karst in India carried out so far have mostly addressed geology, hydrology and groundwater contamination. A literature survey suggests that there is a need for detailed research, applying new approaches and techniques for proper carbonate aquifer identification, characterization and management. Such specific approaches will improve modeling, exploitation and protection of karst groundwater. An overview of the research carried out on groundwater resources of karst formations in India is presented, which also throws light on the protection of karst aquifers from existing anthropogenic activities such as mining and groundwater over-exploitation. 相似文献
93.
Impact‐related noncoaxial deformation in the Pułtusk H chondrite inferred from petrofabric analysis
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Agata Krzesińska Jérôme Gattacceca Jon M. Friedrich Pierre Rochette 《Meteoritics & planetary science》2015,50(3):401-417
Petrofabrics in chondrites have the potential to yield important information on the impact evolution of chondritic parent asteroids, but studies involving chondritic petrofabrics are scarce. We undertook an analysis of the Pu?tusk H chondrite regolith breccia. Measurements of anisotropy of magnetic susceptibility and quantitative tomographic examination of metal grains are presented here and the results are compared with petrographic observations. The major fabric elements are in Pu?tusk shear fractures cutting the light‐colored chondritic clasts as well as brittly and semibrittly deformed, cataclased fragments in dark matrix of regolith breccia. Cataclasis is accompanied by rotation of silicate grains and frictional melting. Fabric of metal grains in chondrite is well defined and coherently oriented over the breccia, both in the clasts and in the cataclastic matrix. Metal grains have prolate shapes and they are arranged into foliation plane and lineation direction, both of which are spatially related and kinematically compatible to shear‐dominated deformational features. We argue that the fabric of Pu?tusk was formed in response to impact‐related noncoaxial shear strain. Deformation promoted brittle cataclastic processes and shearing of silicates, and, simultaneously, allowed for ductile metal to develop foliation and lineation. We suggest that plastic flow is the most probable mechanism for the deformation of metal grains in the shear‐dominated strain field. The process led also to the formation of large metal nodules and bands in the dark matrix of breccia. 相似文献
94.
The effects of geological heterogeneities and piezometric fluctuations on groundwater flow and chemistry in a hard-rock aquifer, southern India 总被引:1,自引:0,他引:1
Crystalline aquifers of semi-arid southern India represent a vital water resource for farming communities. A field study is described that characterizes the hydrodynamic functioning of intensively exploited crystalline aquifers at local scale based on detailed well monitoring during one hydrological year. The main results show large water-table fluctuations caused by monsoon recharge and pumping, high spatial variability in well discharges, and a decrease of well yields as the water table decreases. Groundwater chemistry is also spatially variable with the existence of aquifer compartments within which mixing occurs. The observed variability and compartmentalization is explained by geological heterogeneities which play a major role in controlling groundwater flow and connectivity in the aquifer. The position of the water table within the fracture network will determine the degree of connectivity between aquifer compartments and well discharge. The presented aquifer conceptual model suggests several consequences: (1) over-exploitation leads to a drop in well discharge, (2) intensive pumping may contribute to the hydraulic containment of contaminants, (3) groundwater quality is highly variable even at local scale, (4) geological discontinuities may be used to assist in the location of drinking-supply wells, (5) modeling should integrate threshold effects due to water-table fluctuations. 相似文献
95.
Jérôme Gattacceca Roger H. Hewins Jean‐Pierre Lorand Pierre Rochette France Lagroix Cécile Cournède Minoru Uehara Sylvain Pont Violaine Sautter Rosa. B. Scorzelli Chrystel Hombourger Pablo Munayco Brigitte Zanda Hasnaa Chennaoui Ludovic Ferrière 《Meteoritics & planetary science》2013,48(10):1919-1936
96.
Jerome E. Dobson 《Geographical review》2014,104(2):123-138
The author proposes scientific recognition of an existing, previously undefined and unnamed global feature. Aquaterra is suggested as the new name for the lands that were alternately exposed and inundated as ice sheets advanced and retreated over the past 120,000 years. The vertical amplitude of sea level change amounts to 130 meters, and the aggregate global area of aquaterra equates to the continent of North America. The time period coincides with the total span during which modern humans are known to have existed. 相似文献
97.
98.
Lattice Boltzmann simulation of turbulence-induced flocculation of cohesive sediment 总被引:1,自引:0,他引:1
Jin-Feng Zhang Qing-He Zhang Jerome P.-Y. Maa Guang-Quan Qiao 《Ocean Dynamics》2013,63(9-10):1123-1135
Both the floc formation and floc breakup of cohesive sediment are affected by turbulent shear which is recognized as one of the most important parameters, and thus, on the settling and transport of cohesive sediment. In this study, the development of floc characteristics at early stage and steady-state of flocculation were investigated via a three-dimensional lattice Boltzmann numerical model for turbulence-induced flocculation. Simulations for collision and aggregation of various size particles, floc growth, and breakup in isotropic and homogenous turbulent flows with different shear stresses were conducted. Model results for the temporal evolution of floc size distribution show that the normalized floc size distributions is time-independent during early stage of flocculation, and at steady-state, shear rate has no effect on the shape of normalized floc size distribution. Furthermore, the size, settling velocity, and effective density of flocs at the non-equilibrium flocculation stage do not change significantly for shear stresses in the range 0–0.4 N m?2. The relationships between floc size and settling velocity established during floc growth stages and that during steady-states are different. 相似文献
99.
100.
Particulate contribution to extinction of visible radiation: Pollution, haze, and fog 总被引:2,自引:0,他引:2
Thierry Elias Martial Haeffelin Philippe Drobinski Laurent Gomes Jerome Rangognio Thierry Bergot Patrick Chazette Jean-Christophe Raut Michle Colomb 《Atmospheric Research》2009,92(4):443-454
A data set acquired by eight particle-dedicated instruments set up on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, which is French for Instrumented Site for Atmospheric Remote Sensing Research) during the ParisFog field campaign are exploited to document microphysical properties of particles contributing to extinction of visible radiation in variable situations. The study focuses on a 48-hour period when atmospheric conditions are highly variable: relative humidity changes between 50 and 100%, visibility ranges between 65 and 35 000 m, the site is either downwind the Paris area either under maritime influence. A dense and homogeneous fog formed during the night by radiative cooling. In 6 h, visibility decreased down from 30 000 m in the clear-sky regime to 65 m within the fog, because of advected urban pollution (factor 3 to 4 in visibility reduction), aerosol hydration (factor 20) and aerosol activation (factor 6). Computations of aerosol optical properties, based on Mie theory, show that extinction in clear-sky regime is due equally to the ultrafine modes and to the accumulation mode. Extinction by haze is due to hydrated aerosol particles distributed in the accumulation mode, defined by a geometric mean diameter of 0.6 μm and a geometric standard deviation of 1.4. These hydrated aerosol particles still contribute by 20 ± 10% to extinction in the fog. The complementary extinction is due to fog droplets distributed around the geometric mean diameter of 3.2 μm with a geometric standard deviation of 1.5 during the first fog development stage. The study also shows that the experimental set-up could not count all fog droplets during the second and third fog development stages. 相似文献