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101.
Philip M. Ross Ian D. Hogg Conrad A. Pilditch Carolyn J. Lundquist Richard J. Wilkins 《Estuaries and Coasts》2012,35(1):143-154
We examined the population genetic structure of the New Zealand endemic clam, Austrovenus stutchburyi, to determine (1) whether populations of this estuarine taxon are genetically subdivided and (2) if the locations of genetic
boundaries were congruent with known biogeographic break points. We obtained sequences of the mitochondrial gene cytochrome
c oxidase I for 372 A. stutchburyi from 29 New Zealand estuaries and conducted analyses to identify population genetic structure. We detected a pattern of genetic
isolation by distance and identified six A. stutchburyi subpopulations, a greater number of subpopulations than reported for much of New Zealand’s open coast benthos. Although these
data indicate that long distance dispersal may be less frequent in estuarine than in open coast taxa, partial congruence between
genetic and biogeographic boundaries suggests that historical events and natural selection may also contribute to the observed
population genetic structure. 相似文献
102.
Randall J. Schaetzl Helen Enander Michael D. Luehmann David P. Lusch Carolyn Fish Michael Bigsby 《自然地理学》2013,34(1):2-39
Abstract We present a new physiographic map of Michigan, that is also available interactively, online. Only four, small-scale physiographic maps of Michigan had been previously published. Our mapping project made use of a wide variety of spatial data, in a GIS environment, to visualize and delineate the physical landscape in more detail than has been done previously. We also examined many of the unit boundaries in the field, using a GIS running on a GPS-enabled laptop. Unlike previous physiographic maps, the online version of the map enables users to query the criteria used to define each of the 224 boundaries of its 10 major and 91 minor physiographic units. The interactive nature of the online version of the map is a unique enhancement to physiographic maps and mapping. Our study also provides data on the number and types of criteria used to define each of the 224 unit boundaries within the map. Most of our unit boundaries are based on data derived from 10-m raster elevation data and NRCS soils data, e.g., relief, soil wetness, escarpments, landscape fabric, and parent material characteristics. Data gleaned from NRCS SSURGO county-scale soil maps were a strength of the project. [Key words: Michigan, physiography, landforms, soils, GIS, mapping] 相似文献
103.
104.
Carolyn Kousky 《Climatic change》2014,124(1-2):9-20
As sea level rises, coastal communities will face increased risks of flooding, storm surge, and inundation. In some areas, structural protective measures will be built, and for some properties, accommodation to sea level rise may be possible. For other areas, however, some form of retreat will be either preferred on economic or sociopolitical grounds or required given fiscal constraints. This paper considers how society can proactively manage shoreline retreat in those locations where it is deemed the preferable policy. A three-part strategy is proposed: (1) reduce new development in the highest-risk areas; (2) adopt policies that allow for expected and orderly removal or modification of development as inundation occurs; and (3) take advantage of disasters to implement managed retreat approaches. Specific policies are recommended and the challenges of institutional change discussed. 相似文献
105.
No-take marine protected areas (MPAs), where all fishing is prohibited, have been shown to provide benefits that include greater productivity of fish stocks due to increased densities, average sizes, and reproductive output. A critical component of this success is the effective management of MPAs to ensure that only those activities deemed permissible, are allowed to occur. As of 2008, 161 MPAs had been designated on the Pacific coast of Canada by federal, provincial or municipal authorities. The objective of this study was to discover how many of these MPAs are intended to provide full protection to habitats and species from commercial fishing and whether management measures were put in place to actualize this conservation intent. The comprehensive spatial dataset was built illustrating commercial fisheries closures and this was overlaid with MPA locations in a GIS. The majority of MPAs were designated as IUCN Strict Nature Reserve (Type Ia), Wilderness Area (Type Ib), and National Park (Type II) marine reserves, which are intended to be free from exploitation. It was found that 160 of the 161 MPAs are open to some commercial harvesting within their bounds. One small municipal MPA and portions of three other MPAs are not open to commercial harvesting. The incongruence between management intent and fisheries permitted suggests a management failure between designation of MPAs and implementation of fisheries management regulations. 相似文献
106.
C. C. Kuranz R. P. Drake D. R. Leibrandt E. C. Harding H. F. Robey A. R. Miles B. E. Blue J. F. Hansen H. Louis M. Bono J. Knauer D. Arnett C. A. Meakin 《Astrophysics and Space Science》2005,298(1-2):9-16
Recent results from an ongoing series of Rayleigh-Taylor instability experiments being conducted on the Omega Laser are described.
The goal of these experiments is to study, in a controlled laboratory setting, the mixing that occurs at an unstable interface
subjected to an acceleration history similar to the explosion phase of a core-collapse supernova. In a supernova, the Reynolds
number characterizing this mixing is extremely large (Re > 1010) and is more than sufficient to produce a turbulent flow at the interface. In the laboratory experiment, by contrast, the
spatial scales are much smaller, but are still sufficiently large (Re > 105) to support a turbulent flow and therefore recreate the conditions relevant to the supernova problem. The data from these
experiments will be used to validate astrophysical codes as well as to better understand the transition to turbulence in such
high energy density systems. The experimental results to date using two-dimensional initial perturbations demonstrate a clear
visual transition from a well-ordered perturbation structure consisting of only a few modes to one with considerable modal
content. Analysis of these results, however, indicates that while a turbulent spectrum visually appears to be forming, the
layer has not yet reached the asymptotic growth rate characteristic of a fully turbulent layer. Recent advances in both target
fabrication and diagnostic techniques are discussed as well. These advances will allow for the study of well-controlled 3D
perturbations, increasing our ability to recreate the conditions occurring in the supernova. 相似文献
107.
James H. Roberts Eliezer G. Kahn Olivier S. Barnouin Carolyn M. Ernst Louise M. Prockter Robert W. Gaskell 《Meteoritics & planetary science》2014,49(10):1735-1748
NEAR‐Shoemaker Multi‐Spectral Imager data reveal several hundred “ponds” on 433 Eros: smooth deposits that sharply embay the bounding depressions in which they lie, and whose spectra appear blue relative to that of the surrounding terrain. We investigate the topography of these ponds on Eros using a new shape model derived from stereophotoclinometric analysis, and validated against altimetry from the NEAR Laser Rangefinder, to constrain the mode of pond formation from three existing models. We update the locations of 55 pond candidates identified in images registered to the new shape model. We classify the flatness of these features according to the behavior of the first and second derivatives of the topography. We find that less than half of pond candidates have clearly flat floors. Based on the pond topography, we favor an external origin for the ponds' deposits. We suggest that fine dust may be transported into bounding depressions by electrostatic levitation, but may adhere to slopes, and that seismic shaking may not be sufficient to bring the deposits to an equipotential surface. Disaggregation of a central boulder should result in an obvious break in slope, such a variation is only observed in roughly half the pond candidates. 相似文献
108.
Ulyana A. Dyudina Andrew P. Ingersoll Carolyn C. Porco William Kurth Anthony Del Genio Joseph Ferrier 《Icarus》2007,190(2):545-555
We report on Cassini Imaging Science Subsystem (ISS) data correlated with Radio and Plasma Wave Science (RPWS) observations, which indicate lightning on Saturn. A rare bright cloud erupt at ∼35° South planetocentric latitude when radio emissions (Saturn Electrostatic Discharges, or SEDs) occur. The cloud consisting of few consecutive eruptions typically lasts for several weeks, and then both the cloud and the SEDs disappear. They may reappear again after several months or may stay inactive for a year. Possibly, all the clouds are produced by the same atmospheric disturbance which drifts West at 0.45 °/day. As of March 2007, four such correlated visible and radio storms have been observed since Cassini Saturn Orbit Insertion (July 2004). In all four cases the SEDs are periodic with roughly Saturn's rotation rate (h10m39), and show correlated phase relative to the times when the clouds are seen on the spacecraft-facing side of the planet, as had been shown for the 2004 storms in [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The 2000-km-scale storm clouds erupt to unusually high altitudes and then slowly fade at high altitudes and spread at low altitudes. The onset time of individual eruptions is less than a day during which time the SEDs reach their maximum rates. This suggests vigorous atmospheric updrafts accompanied by strong precipitation and lightning. Unlike lightning on Earth and Jupiter, where considerable lightning activity is known to exist, only one latitude on Saturn has produced lightning strong enough to be detected during the two and a half years of Cassini observations. This may partly be a detection issue. 相似文献
109.
M. J. Grosskopf R. P. Drake C. C. Kuranz A. R. Miles J. F. Hansen T. Plewa N. Hearn D. Arnett J. C. Wheeler 《Astrophysics and Space Science》2009,322(1-4):57-63
The National Ignition Facility (NIF) will soon provide experiments with far more than ten times the energy than has been previously available on laser facilities. In the context of supernova-relevant hydrodynamics, this will enable experiments in which hydrodynamic instabilities develop from multiple, coupled interfaces in a diverging explosion. This paper discusses the design of such blast-wave-driven explosions in which the relative masses of the layers are scaled to those within the star. It reports scaling simulations with CALE to model the global dynamics of such an experiment. CALE is a hybrid, Arbitrary Lagrangian-Eulerian code. The simulations probed the instability growth and multi-interface interactions in mass-scaled systems using different materials. The simulations assist in the target design process and in developing an experiment that can be diagnosed. 相似文献
110.
James?D.?HagyEmail author Walter?R.?Boynton Carolyn?W.?Keefe Kathryn?V.?Wood 《Estuaries and Coasts》2004,27(4):634-658
A 52-yr record of dissolved oxygen in Chesapeake Bay (1950–2001) and a record of nitrate (NO3
−) loading by the Susquehanna River spanning a longer period (1903, 1945–2001) were assembled to describe the long-term pattern
of hypoxia and anoxia in Chesapeake Bay and its relationship to NO3
− loading. The effect of freshwater inflow on NO3
− loading and hypoxia was also examined to characterize its effect at internannual and longer time scales. Year to year variability
in river flow accounted for some of the observed changes in hypoxic volume, but the long-term increase was not due to increased
river flow. From 1950–2001, the volume of hypoxic water in mid summer increased substantially and at an accelerating rate.
Predicted anoxic volume (DO<0.2 mg I−1) at average river flow increased from zero in 1950 to 3.6×109 m3 in 2001. Severe hypoxia (DO<1.0 mg I−1) increased from 1.6×109 to 6.5×109 m3 over the same period, while mild hypoxia (DO<2.0 mg I−1) increased from 3.4×109 to 9.2×109 m3. NO3
− concentrations in the Susquehanna River at Harrisburg, Pennsylvania, increased up to 3-fold from 1945 to a 1989 maximum and
declined through 2001. On a decadal average basis, the superposition of changes in river flow on the long-term increase in
NO3
− resulted in a 2-fold increase in NO3
− loading from the Susquehanna River during the 1960s to 1970s. Decadal average loads were subsequently stable through the
1990s. Hypoxia was positively correlated with NO3
− loading, but more extensive hypoxia was observed in recent years than would be expected from the observed relationship. The
results suggested that the Bay may have become more susceptible to NO3
− loading. To eliminate or greatly reduce anoxia will require reducing average annual total nitrogen loading to the Maryland
mainstem Bay to 50×106 kg yr−1, a reduction of 40% from recent levels. 相似文献