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91.
Gilbert Mille Jan Yu Chen Henri Dou Edgar Azoulay Maryse Colin Jean-Claude Bertrand 《Marine environmental research》1985,17(1):65-80
Coastal Mediterranean sediments highly polluted by refinery effluents have been studied for their hydrocarbon content and bacterial activity. The study has taken into account both the distance from the refinery and depth of sampling. Very high hydrocarbon concentrations have been found (1–250 g/kg dry sediment). Micro-organisms in the sediments have a high bacterial activity and a good correlation exists between hydrocarbon concentrations and bacteria able to use these substrates as a carbon and energy source. 相似文献
92.
93.
Spatio‐temporal changes in bog pool bottom topography – temperature effect and its influence on pool development: an example from a raised bog in Estonia
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Increases in pool water and peat temperature in summer accelerate peat decomposition and production of biogenic gases, which can be trapped in peat pores and cause oscillation of peatland surfaces and the rise of peat from the bottom of bog pools. Associated changes in peat water conductivity, holding capacity and transpiration also affect bog hydrology. Our multi‐year study is the first to show in detail the extent and dynamics of changes in bog pool depth and bottom topography associated with changes in temperature, peat type and other factors. The true seasonal rise of peat from the pool bottom begins once the water temperature at the pool bottom exceeds 13–14 °C, although the speed and extent of the rise depends on peat properties, making the rise more erratic than its subsequent descent. The more rapid descent occurs after the first large drop in the temperature of the pool's surface water at the end of summer, resulting from the combination of reduced methane production and increased gas solubility with less influence by peat properties. Much higher dissolved organic carbon concentrations (216 ± 26 mg l?1) in the pore water of peat risen from the bottom to the pool surface compared with that in the same type of peat at the pool bottom (62 ± 20 mg l?1) indicate an acceleration of peat decomposition at the warmer pool surface. We show the extent and character of changes in pool depth and bottom topography and how annual differences relate to temperature. Only a few degrees' increase in pool water temperature could induce the pool bottom to rise faster and more extensively for a longer period and enhance decomposition in the peat at the pool surface. This should be evaluated in greater detail to assess the effects of temperature increase on the carbon budget and hydrology of peatlands. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
94.
The presence of geochemical anomalies, defining haloes around hydrothermal ore deposits, can be used to vector towards mineralization, or identify ore bodies buried at depth. Several important types of ore deposits, including skarn deposits, are often hosted within carbonate-rich sedimentary rocks. Identifying anomalous trace-element concentrations in carbonate rocks is complicated by variable lithology (i.e. siliciclastic component) and volume loss during hydrothermal alteration. In this study of the world-class Antamina skarn deposit in Peru, we use the ratio of metals:immobile elements (e.g. La, Al2O3) to differentiate genuine and false geochemical anomalies in limestones and marbles surrounding the skarn deposit. Unaltered limestones are used to define threshold values for metal:immobile element ratios (through use of the median value ± 2 median absolute deviations). Genuine anomalies are identified when metal concentrations exceed those predicted using median + 2 median absolute deviations. In addition, comparison of “four acid” and lithium-borate fusion analytical techniques reveals that the lower cost four-acid techniques give reliable results. Our approach can be used to identify geochemical anomalies and halos related to hydrothermal alteration of carbonate-rich rocks, which have direct application to skarn deposits. 相似文献
95.
Vladimir Escalante Christophe Morisset 《Monthly notices of the Royal Astronomical Society》2005,361(3):813-823
The predicted emission spectrum of N ii is compared with observations of permitted lines in the Orion nebula. Conventional nebular models show that the intensities of the more intense lines can be explained by fluorescence of starlight absorption with a N abundance that is consistent with forbidden lines. Lines excited mostly by recombination, on the other hand, predict high N abundances. The effects of stellar and nebular parameters and of the atomic data on the predicted intensities are examined. 相似文献
96.
M. de Val-Borro R. G. Edgar P. Artymowicz P. Ciecielag P. Cresswell G. D'Angelo E. J. Delgado-Donate G. Dirksen S. Fromang A. Gawryszczak H. Klahr W. Kley W. Lyra F. Masset G. Mellema R. P. Nelson S.-J. Paardekooper A. Peplinski A. Pierens T. Plewa K. Rice C. Schäfer R. Speith 《Monthly notices of the Royal Astronomical Society》2006,370(2):529-558
97.
98.
Summary Supra-solidus phase relations at temperatures and pressures ranging from 800 to 1700 °C and 2 to 6.4 GPa have been determined
experimentally for three silica-rich lamproites: hyalo-leucite phlogopite lamproite (Oscar, West Kimberley); sanidine richterite
lamproite (Cancarix, Murcia-Almeria); and phlogopite transitional madupitic lamproite (Middle Table Mountain, Wyoming). All
samples have extended melting intervals (500–600 °C). Bulk composition has a significant control on the nature of the initial
liquidus phases, with orthopyroxene occurring at low pressures (<4 GPa) in the relatively calcium-poor Oscar and Cancarix
lamproites. At higher pressure (>6 GPa) orthopyroxene is replaced by garnet plus clinopyroxene as near-liquidus phases in
the Oscar lamproite and by orthopyroxene plus clinopyroxene in the Cancarix sample. Clinopyroxene is a near-liquidus phase
at all pressures in the Middle Table Mountain lamproite. Near-solidus phase assemblages at high pressure (>5 GPa) are: clinopyroxene + phlogopite + coesite + rutile + garnet
(Oscar); clinopyroxene + garnet + coesite + K–Ti-silicate (Cancarix); clinopyroxene + phlogopite + apatite + K–Ti-silicate
(Middle Table Mountain). In all compositions olivine is never found as a liquidus phase at any of the temperatures or pressures
studied here. The phase relationships are interpreted to suggest that silica-rich lamproites cannot be derived by the partial
melting of lherzolitic sources. Their genesis is considered to involve high degrees of partial melting of ancient metasomatic
veins within a harzburgitic-lherzolitic lithospheric substrate mantle. The veins are considered in their mineralogy to be
similar to the experimentally-observed, high pressure, near-solidus phase assemblages. The composition of silica-rich primary
lamproite magmas differs between cratons as a consequence of differing mineralogical modes of the source veins and different
relative contributions from the veins and wall-rocks to the partial melts.
Received February 21, 2000; revised version accepted July 3, 2001 相似文献
99.
Edgar L. Andreas 《Boundary-Layer Meteorology》2011,141(3):333-347
A common parametrization over snow-covered surfaces that are undergoing saltation is that the aerodynamic roughness length
for wind speed (z
0) scales as au*2/g{\alpha u_\ast^2/g}, where u
* is the friction velocity, g is the acceleration of gravity, and α is an empirical constant. Data analyses seem to support this scaling: many published plots of z
0 measured over snow demonstrate proportionality to u*2{u_\ast^2 }. In fact, I show similar plots here that are based on two large eddy-covariance datasets: one collected over snow-covered
Arctic sea ice; another collected over snow-covered Antarctic sea ice. But in these and in most such plots from the literature,
the independent variable, u
*, was used to compute z
0 in the first place; the plots thus suffer from fictitious correlation that causes z
0 to unavoidably increase with u
* without any intervening physics. For these two datasets, when I plot z
0 against u
* derived from a bulk flux algorithm—and thus minimize the fictitious correlation—z
0 is independent of u
* in the drifting snow region, u
* ≥ 0.30 ms−1. I conclude that the relation z0 = au*2/g{z_0 = \alpha u_\ast^2/g} when snow is drifting is a fallacy fostered by analyses that suffer from fictitious correlation. 相似文献
100.
Rodolfo Silva Casarin Gabriel Ruiz Martinez Ismael Mariño‐Tapia Gregorio Posada Vanegas Edgar Mendoza Baldwin Edgar Escalante Mancera 《洁净——土壤、空气、水》2012,40(9):911-919
Climate change and resultant coastal erosion and flooding have been the focus of many recent analyses. Often these studies overlook the effects of manmade modifications to the coastline which have reduced its resilience to storm events. In this investigation, we integrate previous reports, historical photo analysis, field work, and the application of numerical models to better understand the effects of Wilma, the most destructive hurricane to affect Cancun, Mexico. Huge waves (of significant height, >12 m), long mean wave periods (>12 s), devastating winds (>250 km/h), and powerful currents (>2 m/s) removed >7 million cubic meters of sand from the Cancun beach system, leaving 68% of the sub‐aerial beach as bedrock, and the rest considerably eroded. Numerical simulations show that the modifications to the barrier island imposed by tourist infrastructure have considerably increased the rigidity of the system, increasing the potential erosion of the beach under extreme conditions. If there were no structural barriers, a series of breaches could occur along the beach, allowing exchange of water and alleviating storm surge on other sections of the beach. If the effects caused by anthropogenic changes to Cancun are ignored, the analysis is inaccurate and misleading. 相似文献