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61.
62.
Andrey A. Grachev Edgar L Andreas Christopher W. Fairall Peter S. Guest P. Ola G. Persson 《Boundary-Layer Meteorology》2007,124(3):315-333
Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used
to examine the profile stability functions of momentum, φ
m
, and sensible heat, φ
h
, in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover
different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five
levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φ
m
and φ
h
in detail and includes ample data for the very stable case. New parameterizations for φ
m
(ζ) and φ
h
(ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter
ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ
m
follows a ζ 1/3 dependence, whereas φ
h
initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects
of self-correlation, which occur in plots of φ
m
and φ
h
versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging. 相似文献
63.
Effect of moisture content on ammonia emissions from broiler litter: A laboratory study 总被引:3,自引:0,他引:3
Zifei Liu Lingjuan Wang David Beasley Edgar Oviedo 《Journal of Atmospheric Chemistry》2007,58(1):41-53
A dynamic flow-through chamber system was designed to measure ammonia emissions from broiler litter and to investigate the
responses of ammonia emissions to litter moisture content under laboratory-controlled conditions. It was observed that ammonia
emissions from litter were very sensitive to litter moisture content. As water was added to the litter, the total ammoniac
nitrogen content (TAN) in the litter increased, and can potentially increase ammonia emissions. However, measurements of ammonia
concentrations in the chamber and total nitrogen losses from litter samples all suggested that water applied to the litter
also had an effect of suppressing ammonia emissions for a short time. After enough time (1 to 2 weeks) was allowed, higher
moisture content in litter eventually resulted in higher ammonia emissions. It was also noticed that, at very high litter
moisture content, even when more time was allowed, ammonia concentrations began to decrease as moisture content further increased. 相似文献
64.
65.
66.
67.
We formulate a method for determining the smallest time interval Tover which a turbulence time series can be averaged to decompose it intoinstantaneous mean and random components. From the random part the method defines the optimal interval (or averaging window) AW over which this part should be averaged to obtain the instantaneous spectrum. Both T and AW vary randomly with time and depend on physical properties of the turbulence. T also depends on the accuracy of the measurements and is thus independent of AW. Interesting features of the method are its real-time capability and the non-equality between AW and T. 相似文献
68.
We present new results on the recently discovered 69 ms X-ray pulsar AXS J161730-505505, the sixth youngest example of a rotation-powered pulsar. We have undertaken a comprehensive X-ray-observing campaign of AXS J161730-505505 with the ASCA, BeppoSAX, and RXTE observatories and follow its long-term spin-down history between 1989 and 1999 using these observations and archival Ginga and ASCA data sets. The spin-down is not simply described by a linear function as originally thought, but instead we find evidence of a giant glitch (DeltaP&solm0;P greater, similar10-6) between 1993 August and 1997 September, perhaps the largest yet observed from a young pulsar. The glitch is well described by steps in P and P&d2; accompanied by a persistent P&d3; similar to those seen in the Vela pulsar. The pulse profile of AXS J161730-505505 presents a single asymmetric peak that is maintained over all observation epochs. The energy spectrum is also steady over time, characterized by a highly absorbed power law with a photon index Gamma=1.4+/-0.2, consistent with that found for other young rotation powered pulsars. 相似文献
69.
Andrey A. Grachev P. Ola G. Persson Edgar L. Andreas Peter S. Guest 《Boundary-Layer Meteorology》2005,116(2):201-235
Turbulent and mean meteorological data collected at five levels on a 20-m tower over the Arctic pack ice during the Surface
Heat Budget of the Arctic Ocean experiment (SHEBA) are analyzed to examine different regimes of the stable boundary layer
(SBL). Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime
to very stable stratification. Scaling arguments and our analysis show that the SBL can be classified into four major regimes:
(i) surface-layer scaling regime (weakly stable case), (ii) transition regime, (iii) turbulent Ekman layer, and (iv) intermittently
turbulent Ekman layer (supercritical stable regime). These four regimes may be considered as the basic states of the traditional
SBL. Sometimes these regimes, especially the last two, can be markedly perturbed by gravity waves, detached elevated turbulence
(‘upside down SBL’), and inertial oscillations. Traditional Monin–Obukhov similarity theory works well in the weakly stable
regime. In the transition regime, Businger–Dyer formulations work if scaling variables are re-defined in terms of local fluxes,
although stability function estimates expressed in these terms include more scatter compared to the surface-layer scaling.
As stability increases, the near-surface turbulence is affected by the turning effects of the Coriolis force (the turbulent
Ekman layer). In this regime, the surface layer, where the turbulence is continuous, may be very shallow (< 5 m). Turbulent
transfer near the critical Richardson number is characterized by small but still significant heat flux and negligible stress.
The supercritical stable regime, where the Richardson number exceeds a critical value, is associated with collapsed turbulence
and the strong influence of the earth’s rotation even near the surface. In the limit of very strong stability, the stress
is no longer a primary scaling parameter. 相似文献
70.
Edgar L Andreas Kerry J. Claffy Aleksandr P. Makshtas 《Boundary-Layer Meteorology》2000,97(3):459-486
For four months in the fall and earlywinter of 1992, as Ice Station Weddell (ISW) driftednorthward through the ice-covered western Weddell Sea,ice station personnel profiled the atmosphericboundary layer (ABL) with radiosondes. These showedthat the ABL was virtually always stably stratifiedduring this season: 96% of the soundings found anear-surface inversion layer. Forty-four percent ofthese inversions were surface-based. Eighty percentof the soundings that yielded unambiguous windprofiles showed an atmospheric jet with speeds as highas 14 m s-1 in a core below an altitude of 425 m. This paper documents the features of these inversionsand low-level jets. Because the inversion statistics,in particular, are like those reported in and aroundthe Arctic Ocean, similar local processes seem tocontrol the ABL over sea ice regions in bothhemispheres. A simple two-layer model, in which anelevated layer becomes frictionally decoupled from thesurface, does well in explaining the ISW jetstatistics. This model also implies a new geostrophicdrag parameterization for sea-ice regions that dependson the magnitude of the geostrophic wind, the 10-mdrag coefficient CDN10, and the ABL height, butnot explicitly on any stratification parameter. 相似文献