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1.
Richard A Shakesby David J Boakes Celeste de OA Coelho AJ Bento Gonçalves Rory PD Walsh 《Applied geography (Sevenoaks, England)》1996,16(4):337-355
In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed. 相似文献
2.
BA Maree PD Cowley TF Næsje A-R Childs AI Terörde EB Thorstad 《African Journal of Marine Science》2016,38(2):171-180
Long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii and the distribution of their dominant prey, the sandprawn Callichirus kraussi, were investigated in the intermittently open East Kleinemonde Estuary, South Africa. In addition, the effects of fish length, diel cycle, season and other abiotic factors on home range and area use were examined. Nine adult spotted grunter (326–489?mm total length) were tagged with acoustic transmitters, and their movements were studied by manual tracking on six consecutive days and nights during each of five tracking sessions from March to November 2004. In addition, movement patterns were recorded by stationary data-logging receivers. Kernel home ranges (95% utilised distribution) varied in size (mean: 76 797?m2?, range: 26 296–165 321?m2), but were all located in the lower one-third of the 3.6 km-long estuary. There was no effect of season, the diel cycle or fish length on the home-range estimates. However, the distribution of prey corresponded with the home-range distribution of tagged fish. Although sandprawn distribution was highly variable within and among transects and depth classes, sandprawns were most abundant in the lower region of the estuary, which corresponded to the home-range distribution of spotted grunter. Spatial distribution of prey appears to be a dominant factor influencing home-range parameters of this species within an intermittently open estuary. 相似文献
3.
PD Jones 《Climate Dynamics》1987,1(2):63-75
Reconstructions of monthly mean sea-level grid-point pressure from station pressure data over the Arctic region using an objective technique have revealed two serious errors in the gridded data. First, all gridded data (from the U.S. Historical Weather Map series) for the Arctic Ocean area away from the North Atlantic sector appears to be between 4 and 6 mb too high before about 1931. The semi-permanent Arctic high produced in the early historical map series was the result of a lack of basic station data, and the belief amongst many North American meteorologists of the 1920s and 1930s of the existence of a polar or glacial anticyclone. The second error affects only north-western North America for the years 1899–1909. Here pressure is again too high compared with reconstructed data. The cause of this error is not immediately apparent, but is probably the result of an erroneous correction to sea level for stations in the region. Both errors seriously affect the homogeneity of the gridded Arctic series. The objective scheme used to reveal the errors, can also be used to derive correction factors for the gridded data prior to 1931. 相似文献
4.
PD Dr. Kolumban Hutter 《Aquatic Sciences - Research Across Boundaries》1983,45(1):101-144
Density distribution and temperature and current data which were measured in Lake of Zürich and Lake of Lugano in two summer field programs are scrutinized and interpreted by means of hydrodynamic models. Barotropic surface seiches and baroclinic internal seiches are studied using a one-and two-layer model and measured data permit identification of the respective resonant periods. Wind induced barotropic and baroclinic circulation dynamics is also studied by means of three-dimensional finite difference models of the hydrodynamic viscous equations on the rotating earth. In general the predictions of these models agree favorably with observed data. 相似文献
5.
In this paper, the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode decomposition combined with the Hilbert transform are employed to process various non-stationary signals (strong ground motions and structural responses). The efficacy of these two adaptive techniques for capturing the temporal evolution of the frequency content of specific seismic signals is assessed. In this respect, two near-field and two far-field seismic accelerograms are analyzed. Further, a similar analysis is performed for records pertaining to the response of a 20-story steel frame benchmark building excited by one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. It is shown that the derived joint time–frequency representations of the response time histories capture quite effectively the influence of non-linearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event; in this context, tracing the mean instantaneous frequency of records of critical structural responses is adopted.The study suggests, overall, that the aforementioned techniques are quite viable tools for detecting and monitoring damage to constructed facilities exposed to seismic excitations. 相似文献
6.
RH Bennett PD Cowley A-R Childs CG Attwood L Swart TF Næsje 《African Journal of Marine Science》2017,39(4):475-489
Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r2 = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery. 相似文献
7.
MH Dames PD Cowley A-R Childs RH Bennett EB Thorstad TF Næsje 《African Journal of Marine Science》2017,39(1):111-120
Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ~529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity. 相似文献
8.
The Biomass Expansion Factor (BEF) and the Root-to-Shoot Ratio (R) are variables used to quantify carbon stock in forests.
They are often considered as constant or species/area specific values in most studies. This study aimed at showing tree size
and age dependence upon BEF and R and proposed equations to improve forest biomass and carbon stock. Data from 70 sample Pinus spp. grown in southern Brazil trees in different diameter classes and ages were used to demonstrate the correlation between
BEF and R, and forest inventory data, such as DBH, tree height and age. Total dry biomass, carbon stock and CO2 equivalent were simulated using the IPCC default values of BEF and R, corresponding average calculated from data used in
this study, as well as the values estimated by regression equations. The mean values of BEF and R calculated in this study
were 1.47 and 0.17, respectively. The relationship between BEF and R and the tree measurement variables were inversely related
with negative exponential behavior. Simulations indicated that use of fixed values of BEF and R, either IPCC default or current
average data, may lead to unreliable estimates of carbon stock inventories and CDM projects. It was concluded that accounting
for the variations in BEF and R and using regression equations to relate them to DBH, tree height and age, is fundamental
in obtaining reliable estimates of forest tree biomass, carbon sink and CO2 equivalent. 相似文献
9.
A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a design seismic spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power spectrum which is compatible in a stochastic sense with a given design spectrum. This power spectrum is then treated as the excitation spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) design spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic design spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of nonstationary EC8 design spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic design of structures under severe seismic excitations specified in terms of a design spectrum. 相似文献
10.
PD. Dr. E. A. Thomas 《Aquatic Sciences - Research Across Boundaries》1960,22(1):320-329
Zusammenfassung Die vorliegende Studie gibt Aufschluss über die vertikale Verteilung von gr?sseren Salzmengen, die im Sommer in gel?ster Form
ins Oberfl?chenwasser eines Sees eingebracht werden, sowie über die dabei auftretenden Milieuver?nderungen und deren Einflüsse
auf das Plankton innerhalb von Test-Loten. In praktischer Beziehung sind solche Studien bei entsprechender Anpassung an die
?rtlichen Verh?ltnisse von Interesse für die Kenntnis der Ausbreitung von in Seen eingeleiteten Abw?ssern oder von Düngstoffen
bei Teichdüngung, sowie für das Einbringen bestimmter Stoffe für die Bek?mpfung von Algen (Cladophora oder Planktonalgen) oder tierischen Organismen (zum Beispiel Cercarien).
Weitere Versuche mit geringen Mengen von biologisch inaktiven Substanzen sind erwünscht. Ferner soll sp?ter berichtet werden
über Teilchenwanderungen, bei denen eine Markierung durch radioaktive Substanzen erfolgte. 相似文献