全文获取类型
收费全文 | 1194篇 |
免费 | 74篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 86篇 |
地球物理 | 320篇 |
地质学 | 568篇 |
海洋学 | 91篇 |
天文学 | 136篇 |
综合类 | 5篇 |
自然地理 | 45篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 58篇 |
2017年 | 60篇 |
2016年 | 63篇 |
2015年 | 55篇 |
2014年 | 75篇 |
2013年 | 114篇 |
2012年 | 44篇 |
2011年 | 85篇 |
2010年 | 73篇 |
2009年 | 79篇 |
2008年 | 54篇 |
2007年 | 49篇 |
2006年 | 36篇 |
2005年 | 23篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 19篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 10篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1962年 | 2篇 |
排序方式: 共有1274条查询结果,搜索用时 250 毫秒
221.
Stress sensitivity of stylolite morphology 总被引:1,自引:0,他引:1
Marcus Ebner Daniel Koehn Renaud Toussaint François Renard Jean Schmittbuhl 《Earth and Planetary Science Letters》2009,277(3-4):394-398
Stylolites are rough surfaces that form by localized stress-induced dissolution. Using a set of limestone rock samples collected at different depths from a vertical section in Cirque de Navacelles (France), we study the influence of the lithostatic stress on the stylolites morphology on the basis of a recent morphogenesis model. We measured the roughness of a series of bedding-parallel stylolites and show that their morphology exhibits a scaling invariance with two self-affine scaling regimes separated by a crossover-length (L) at the millimeter scale consistent with previous studies. The importance of the present contribution is to estimate the stylolite formation stress σ from the sample position in the stratigraphic series and compare it to the crossover-length L using the expected relationship: L ~ σ ?2. We obtained a successful prediction of the crossover behavior and reasonable absolute stress magnitude estimates using relevant parameters: depth of stylolite formation between 300 to 600 m with corresponding normal stress in the range of 10–18 MPa. Accordingly, the stylolite morphology contains a signature of the stress field during formation and we thus suggest that stylolites could be used as paleo-stress gauges of deformation processes in the upper crust. 相似文献
222.
Climate modelers have recognized the possibility of abrupt climate changes caused by a reorganization of the North Atlantic's current pattern (technically known as a thermohaline circulation collapse). This circulation system now warms north-western Europe and transports carbon dioxide to the deep oceans. The posited collapse of this system could produce severe cooling in northwestern Europe, even when general global warming is in progress. In this paper we use a simple integrated assessment model to investigate the optimal policy response to this risk. Adding the constraint of avoiding a thermohaline circulation collapse would significantly reduce the allowable greenhouse gas emissions in the long run along an optimal path. Our analysis implies that relatively small damages associated with a collapse (less than 1% of gross world product) would justify a considerable reduction of future carbon dioxide emissions. 相似文献
223.
Mário E. C. Vieira 《Estuaries and Coasts》2000,23(2):199-207
Current meter data were acquired in Long Island Sound over a period of about 6 mo in 1988 at six different transects. The
averages of the low-passed residuals represent the contributions from tidal steering and density forcing. It is found that
the long-term residual circulation starts out with a classical estuarine pattern at the Race. The flows into and out of the
Sound are vertically partitioned by Long Sand Shoal; they gradually revert back to classical vertically layered estuarine
circulation as the Central Basin is traversed. Further west, the bottom oceanic water becomes a westward flowing swift jet
close to the Connecticut shore, while the East River water is constrained to flow eastward along the Long Island coast. Counterclockwise
gyres, identified in the Eastern Narrows and Western Basin, may increase residence times of polluted East River water in the
western Long Island Sound. 相似文献
224.
Marine Geophysical Research - 相似文献
225.
André Burnol Francis Garrido Philippe Baranger Catherine Joulian Marie-Christine Dictor Françoise Bodénan Guillaume Morin Laurent Charlet 《Geochemical transactions》2007,8(1):12
High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the
release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis.
Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted.
Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The
biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and
genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing
bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase
amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant
after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant,
or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial
solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst
X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction
revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results.
The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high
Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically
more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more
weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully
applied to recent experimental results on the release of arsenic from Bengal delta sediments. 相似文献
226.
François Farges 《Physics and Chemistry of Minerals》2009,36(8):463-481
Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO4 2? moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses. 相似文献
227.
Trace Metal Solid State Speciation in Aerosols of the Northern Levantine Basin,East Mediterranean 总被引:3,自引:0,他引:3
Mustafa Koçak Nilgun Kubilay Barak Herut Malcolm Nimmo 《Journal of Atmospheric Chemistry》2007,56(3):239-257
An established three stage sequential leach scheme was applied to a series of selected high volume aerosol samples (n = 35) collected from the Turkish Eastern Mediterranean coastline (Erdemli). Samples were selected according to their air
mass back trajectory history to reflect the contrasting mixtures of aerosol material present in the Eastern Mediterranean
marine aerosol. Two populations were adopted, those samples which were classed as “anthropogenic” and those which were “Saharan”
dominated aerosol populations. Applying the three stage leach it was possible to define the proportion for each of the considered
metals (Al, Fe, Cu, Pb, Cd, Zn and Mn) present in the (a) “exchangeable” (b) “carbonate / oxide” and (c) “refractory” phases,
representing novel solid state aerosol speciation data for this marine system. Clear trends were established, conforming with
data from previous studies with mainly crustal derived metals (Al and Fe) being present in the refractory phases (Al > 88%;
Fe > 84%) and those influenced by anthropogenic sources being dominating in the exchangeable phase, although for these metals
the variability was comparatively high (12–64%; 19–85%; 40–100% for Zn, Pb and Cd, respectively). For the majority, greater
exchangeable fractions were present the lower the crustal source contribution to the aerosol population, whereas the “refractory”
fraction exhibited contrasting behaviour. This was illustrated by the novel application of the mixing diagram, presenting
each of the three speciation stages against the corresponding percent anthropogenic contribution to each collected sample.
Zn, Pb and Cd all illustrated progressive decrease in the percent exchangeable with increasing crustal contribution to the
aerosol population. The percent exchangeable was discussed in terms of its use to represent the upper limit of the bioavailable
fraction of metal associated with the aerosol, post deposition. The mixing diagram approach enabled the prediction of the
residual fractions for Cd, Pb and Zn (41 ± 4%; 62 ± 4% and 82 ± 5%, respectively,) in Saharan end-member material. 相似文献
228.
The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection 总被引:3,自引:11,他引:3
Frédéric Hourdin Ionela Musat Sandrine Bony Pascale Braconnot Francis Codron Jean-Louis Dufresne Laurent Fairhead Marie-Angèle Filiberti Pierre Friedlingstein Jean-Yves Grandpeix Gerhard Krinner Phu LeVan Zhao-Xin Li François Lott 《Climate Dynamics》2006,27(7-8):787-813
The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model. 相似文献
229.
A climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric
General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity
waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved
waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects
of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model’s
ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the
stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation
(AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the
parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents
much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the
downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the
surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal
from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used
tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic
AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this
result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment
of the model parameters that affect the tropospheric variability. 相似文献
230.