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71.
Paul Bishop 《The Professional geographer》1980,32(3):310-315
Many “sociological”factors can account for the initial acceptance and continued persistence of W. M. Davis's Geographical Cycle. Such factors include Davis's attractive and forceful presentation of the cycle and the role of the cycle as a unifier of the discipline of physical geography, to name two. An analysis of the scientific character of the cycle, in the light of Karl Popper's criteria for demarcating between science and non-science, suggests that persistence of the cycle can also be attributed to a “logical”factor, the irrefutability of the central concept, stage. 相似文献
72.
Scale-dependent analysis of satellite imagery for characterization of glacier surfaces in the Karakoram Himalaya 总被引:1,自引:0,他引:1
Information regarding process-structure relationships and change in the Karakoram Himalaya is of great importance in studying glacier hydrollogy, mass balance, and dynamic environmental change. Such information is not readily available. Detailed spatio-temporal assessment requires field investigation coupled with quantitative remote sensing studies. We conducted an investigation of the large Batura Glacier in Pakistan to determine if spectral variability can be quantified and used to characterize glacier surfaces. Specifically, SPOT Panchromatic satellite data were evaluated for differentiating features of glacier structure resulting from ice movement, ablation, and supraglacial fluvial action. Image semivariogram analysis was conducted. for assessing spectral variability patterns and fractal analysis was used to examine scale-dependent variation in the data. Results indicate that spectral variability from fields of ice seracs can exhibit fractal characteristics, although most surface features on the glacier exhibit a change in the fractal dimension over different ranges in scale. The fractal dimension was found to be useful for differentiating between glacier surfaces such as white ice and debris-covered ice. Characteristics of the debris-load and the scale-dependent nature of calculating the fractal dimension ultimately determined the potential of class separability. 相似文献
73.
Nearby catchments in the same landscape are often assumed to have similar specific discharge (runoff per unit catchment area). Five years of streamflow from 14 nested catchments in a 68 km2 landscape was used to test this assumption, with the hypothesis that the spatial variability in specific discharge is smaller than the uncertainties in the measurement. The median spatial variability of specific discharge, defined as subcatchment deviation from the catchment outlet, was 33% at the daily scale. This declined to 24% at a monthly scale and 19% at an annual scale. These specific discharge differences are on the same order of magnitude as predicted for major land‐use conversions or a century of climate change. Spatial variability remained when considering uncertainties in specific discharge, and systematic seasonal patterns in specific discharge variation further provide confidence that these differences are more than just errors in the analysis of catchment area, rainfall variability or gauging. Assuming similar specific discharge in nearby catchments can thus lead to spurious conclusions about the effects of disturbance on hydrological and biogeochemical processes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
74.
75.
Alistair Becker Laurie J.B. Laurenson Kylie Bishop 《Estuarine, Coastal and Shelf Science》2009,82(4):566-572
Fish kills are not uncommon within estuaries in many regions of the world. In seasonally open systems, which are common in temperate areas, they are often associated with mouth openings. Such a kill occurred in July 2005 in the Surrey Estuary following a closed mouth period of seven months resulting in the loss of many thousands of fish. At the time the fish community within the estuary was under investigation which provided comprehensive data of this population prior to the kill. Monthly water quality monitoring was also being conducted prior to the kill and also carried out on a daily basis following the mouth opening. The Surrey was stratified during the closed mouth phase, isolated waters below the halocline had stagnated and become anoxic. As a result only waters above the halocline contained oxygen concentrations capable of sustaining most fish. It appears that if a mouth opening happens under low flow conditions, a shearing effect occurs within the water column where surface waters flow out to sea leaving deeper waters behind. This resulted in only anoxic waters being present for in excess of six days and was responsible for the fish kill. Fish sampling of the Surrey Estuary was conducted three and six months following the kill and those data were compared to that collected in the 12 months prior to the event. Three months after the kill few fish were collected within the estuary and included marine opportunists near the mouth and estuarine resident species in the far upper reaches of the system. However six months following the kill large numbers of estuarine resident species were collected throughout the Surrey Estuary. As many species were euryhaline, it is believed that some individuals migrated into freshwater reaches of the Surrey to escape the anoxic conditions within the estuary. As conditions improved they recolonised the Surrey Estuary. The high fecundity and rapid growth of these small, short lived species probably aided in their re-establishing populations within the estuary. It is clear from this research that artificial openings of estuaries should be avoided during low flow periods when oxygen concentrations are low. It also appears that many of the small estuarine resident species common in seasonally open estuaries are capable of recolonising estuaries following fish kills. The effects on larger, longer lived resident species are not known but likely to be more detrimental due to longer time required for them to reach sexual maturity. 相似文献
76.
Mario Parente Heather D. Makarewicz Janice L. Bishop 《Planetary and Space Science》2011,59(5-6):423-442
This study advances curve-fitting modeling of absorption bands of reflectance spectra and applies this new model to spectra of Martian meteorites ALH 84001 and EETA 79001 and data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). This study also details a recently introduced automated parameter initialization technique. We assess the performance of this automated procedure by comparing it to the currently available initialization method and perform a sensitivity analysis of the fit results to variation in initial guesses. We explore the issues related to the removal of the continuum, offer guidelines for continuum removal when modeling the absorptions and explore different continuum-removal techniques. We further evaluate the suitability of curve fitting techniques using Gaussians/Modified Gaussians to decompose spectra into individual end-member bands. We show that nonlinear least squares techniques such as the Levenberg–Marquardt algorithm achieve comparable results to the MGM model (Sunshine and Pieters, 1993, Sunshine et al., 1990) for meteorite spectra. Finally we use Gaussian modeling to fit CRISM spectra of pyroxene and olivine-rich terrains on Mars. Analysis of CRISM spectra of two regions show that the pyroxene-dominated rock spectra measured at Juventae Chasma were modeled well with low Ca pyroxene, while the pyroxene-rich spectra acquired at Libya Montes required both low-Ca and high-Ca pyroxene for a good fit. 相似文献
77.
A. F. Velegrakis D. Michel M. B. Collins R. Lafite E. K. Oikonomou J. P. Dupont M. F. Huault M. Lecouturier J. C. Salomon C. Bishop 《Continental Shelf Research》1999,19(15-16)
Seasonal observations on the nature and concentration of suspended particulate matter (SPM) are presented for a cross-section of the English Channel, between the Isle of Wight (UK) and Cotentin peninsula (France) i.e. the western boundary of the eastern English Channel. The highest concentrations of suspended material are found adjacent to the English coastline, whereas the offshore waters are associated with low concentrations. Seasonal variations in the concentration and nature of suspended material are identified, with highest concentrations in winter. At this time, the suspended particles are characterised generally by peaked grain size spectra and an enrichment in coarse silt particles; in summer, the distributions are generally flat. The diatom communities found within the suspended matter indicate that material resuspended in the coastal zone and the estuarine environments is transported offshore. SPM fluxes (based upon the observed SPM concentrations and the output from a 2-D hydrodynamic model) from the western Channel through the Wight–Cotentin Section, ranged between 2 and 71×106 t a−1 with a mean of around 20×106 t a−1 over the period of the observations (1994–1995). These fluxes are comparable to the order of magnitude and mean value reported as output through the Dover Strait. Therefore, it is possible that the eastern English Channel may be characterised as an area of fine-grained sediment ‘bypass'. This interpretation is corroborated by: (a) the absence of fine-grained sediment deposits over the area; and (b) correlation between the potential resuspension time of the fine particles and the seabed sediment distribution. 相似文献
78.
John D. Robinson Edgardo Diaz-Ferguson Monica F. Poelchau Steven Pennings Thomas Dale Bishop John Wares 《Estuaries and Coasts》2010,33(4):865-877
Factors that maintain genetic and species diversity may act in concert in natural ecosystems. Here, we investigate correlations
between genetic diversity (in eight salt marsh species) and community species diversity. A significant positive correlation
existed between genetic diversity and species richness, although the relationship was not significant for any species individually.
Nonetheless, four of the eight comparisons showed strong positive relationships between genetic and species diversity. Additionally,
several abiotic variables were used in a model selection procedure to determine what site-level characteristics might drive
differences in genetic diversity in this system. The rate of larval influx, as measured by barnacle abundance on Spartina alterniflora, was the strongest predictor of site-level genetic diversity in our samples. Our results suggest that estuarine management
efforts should consider recruitment rates when selecting areas for protection. 相似文献
79.
T. Dale Bishop Harlan L. MillerIII Randal L. Walker Dorset H. Hurley Theron Menken Charles E. Tilburg 《Estuaries and Coasts》2010,33(3):688-698
The blue crab, Callinectes sapidus Rathbun, 1896, represents the second most important fishery for coastal Georgia; yet, little is known about environmental
forces that affect planktonic postlarval settlement in the region. Here, we describe a study to examine the physical mechanisms
responsible for blue crab settlement in the extensive salt marsh system of coastal Georgia. Bottom and surface samplers were
placed at three sites along a salinity gradient from a low-salinity site in the Altamaha River to a high-salinity area of
the Duplin River, Sapelo Island, GA, USA during 2005. Megalopae and juvenile monitoring occurred from July through December.
The majority of both megalopae (86.8%) and juvenile (89.3%) blue crabs were recovered in bottom samplers at the low-salinity
Altamaha River site during August and early September. Few megalopae were collected at the surface of the Altamaha River or
at the two higher-salinity sites in the Duplin and North Rivers. Downwelling winds were unable to explain all settlement events;
however, winds with an onshore component regularly preceded settlement events. The use of a multiple-regression model revealed
a lagged relationship (r = 0.5461, $ lag = 0–2 days $ lag = 0–2 days ) between wind events, temperature, salinity, maximum tidal height, and settlement. 相似文献
80.
Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to estuarine ecosystems. In laboratory and field experiments, naïve calcifying organisms that are exposed for even short periods (1–2 mo) to runoff from ASS suffer 80% mortality and slowed growth. Based on these observations we expected that sampling of wild oyster, gastropod and crab populations at sites close to and away from drains discharging ASS runoff would reveal more depauperate populations, of sparser and smaller-sized individuals at the more acidified sites. Sampling within three estuaries of New South Wales, Australia, confirmed that the oyster Saccostrea glomerata and gastropods (primarily Bembicium auratum) were less abundant at ASS-affected than reference sites. Nevertheless, crab abundances did not differ between the acidified and reference sites and impacts to bivalves and gastropods were far smaller than predicted. Although at ASS-affected sites gastropod populations were dominated by smaller individuals than at reference sites, oyster populations were skewed towards larger individuals. Even at ASS-affected sites, oyster and gastropod abundances were within the range encountered in estuaries that are not influenced by ASS runoff. Behaviour, long-term physiological acclimation or genetic selection may be responsible for differences in the responses of wild and naïve macroinvertebrates to acidification. Alternatively, wild populations may exhibit some recovery between the rainfall events that transport ASS runoff into estuaries, despite the persistently lower pH near outflow drains. Irrespective, this study suggests that at the population level, calcifying organisms display a certain degree of natural resistance to recurrent disturbance from ASS runoff. 相似文献