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531.
Fukashi Maeno Masashi Nagai Setsuya Nakada Rose E. Burden Samantha Engwell Yuki Suzuki Takayuki Kaneko 《Bulletin of Volcanology》2014,76(6):1-16
Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?106 m3 for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?106 m3 for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?106 kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations. 相似文献
532.
Richard L. Reynolds Jessica S. Mordecai Joseph G. Rosenbaum Michael E. Ketterer Megan K. Walsh Katrina A. Moser 《Journal of Paleolimnology》2010,44(1):161-175
Sediments in Marshall and Hidden Lakes in the Uinta Mountains of northeastern Utah contain records of atmospheric mineral-dust
deposition as revealed by differences in mineralogy and geochemistry of lake sediments relative to Precambrian clastic rocks
in the watersheds. In cores spanning more than a thousand years, the largest changes in composition occurred within the past
approximately 140 years. Many elements associated with ore deposits (Ag, As, Bi, Cd, Cu, In, Mo, Pb, S, Sb, Sn, and Te) increase
in the lake sediments above depths that correspond to about AD 1870. Sources of these metals from mining districts to the
west of the Uinta Mountains are suggested by (1) the absence of mining and smelting of these metals in the Uinta Mountains,
and (2) lower concentrations of most of these elements in post-settlement sediments of Hidden Lake than in those of Marshall
Lake, which is closer to areas of mining and the densely urbanized part of north-central Utah that is termed the Wasatch Front,
and (3) correspondence of Pb isotopic compositions in the sediments with isotopic composition of ores likely to have been
smelted in the Wasatch Front. A major source of Cu in lake sediments may have been the Bingham Canyon open-pit mine 110 km
west of Marshall Lake. Numerous other sources of metals beyond the Wasatch Front are likely, on the basis of the widespread
increases of industrial activities in western United States since about AD 1900. In sediment deposited since ca. AD 1945,
as estimated using 239+240Pu activities, increases in concentrations of Mn, Fe, S, and some other redox-sensitive metals may result partly from diagenesis
related to changes in redox. However, our results indicate that these elemental increases are also related to atmospheric
inputs on the basis of their large increases that are nearly coincident with abrupt increases in silt-sized, titanium-bearing
detrital magnetite. Such magnetite is interpreted as a component of atmospheric dust, because it is absent in catchment bedrock.
Enrichment of P in sediments deposited after ca. AD 1950 appears to be caused largely by atmospheric inputs, perhaps from
agricultural fertilizer along with magnetite-bearing soil. 相似文献
533.
Matthew P. Miller Bailey E. Simone Diane M. McKnight Rose M. Cory Mark W. Williams Elizabeth W. Boyer 《Aquatic Sciences - Research Across Boundaries》2010,72(3):269-275
In their article, “New light on a dark subject: On the use of fluorescence data to deduce redox states of natural organic
matter,” Macalady and Walton-Day (2009) subjected natural organic matter (NOM) samples to oxidation, reduction, and photochemical transformation. Fluorescence spectra
were obtained on samples, which were diluted “to bring maximum uvvisible absorbance values below 1.0.” The spectra were fit
to the Cory and McKnight (2005) parallel factor analysis (PARAFAC) model, and consistent variation in the redox state of quinone-like moieties was not detected.
Based on these results they concluded that fitting fluorescence spectra to the Cory and McKnight (2005) PARAFAC model to obtain information about the redox state of quinone-like moieties in NOM is problematic. Recognizing that
collection and correction of fluorescence spectra requires consideration of many factors, we investigated the potential for
inner-filter effects to obscure the ability of fluorescence spectroscopy to quantify the redox state of quinone-like moieties.
We collected fluorescence spectra on Pony Lake and Suwannee River fulvic acid standards that were diluted to cover a range
of absorbance wavelengths, and fit these spectra to the Cory and McKnight (2005) PARAFAC model. Our results suggest that, in order for the commonly used inner-filter correction to effectively remove inner-filter
effects, samples should be diluted such that the absorbance at 254 nm is less than 0.3 prior to the collection of fluorescence
spectra. This finding indicates that inner-filter effects may have obscured changes in the redox signature of fluorescence
spectra of the highly absorbing samples studied by Macalady and Walton-Day (2009). 相似文献
534.
535.
It is well known that the magnetic field imbedded in the solar wind modulates the production of cosmogenic isotopes by galactic cosmic rays. Power spectral analysis yields evidence for fundamental periods relevant to this study including the Suess, Gleissberg, Hale and Schwabe cycles of ca. 210, 88, 22 and 11 years lengths. There is increasing evidence for an irradiance component accompanying each of these cycles. Assuming this is valid, we model the magnitude of irradiance change associated with these cycles that is compatible with the paleoclimate record. We conclude that the resultant model fit requires less than ±0.8 change in solar irradiance for each of these cycles even if we assume low climate sensitivity (0.5 °C(Wm–2)). Our solar irradiance model accounts for about 18% of 20th century global warming to 1997 and also predicts that the next maximum would occur in ad 2040 and contribute 0.2 °C to 21st century Northern Hemisphere warming. 相似文献
536.
Patricia?A.?TesterEmail author Sabrina?M.?Varnam Mary?E.?Culver David?L.?Eslinger Richard?P.?Stumpf Robert?N.?Swift James?K.?Yungel Megan?D.?Black R.?Wayne?Litaker 《Estuaries and Coasts》2003,26(5):1353-1364
Airborne laser-induced fluorescence measurements were used to detect and monitor ecosystem wide changes in the distribution
and concentration of chlorophyll biomass and colored dissolved organic matter in the Pamlico-Albemarle Sound system, North
Carolina, U.S., following massive flooding caused by a series of three hurricanes in the late summer of 1999. These high-resolution
data provided a significantly more detailed representation of the overall changes occurring in the system than could have
been achieved by synoptic sampling from any other platform. The response time for the distribution of chlorophyll biomass
to resume pre-flood conditions was used as a measure of ecosystem stability. Chlorophyll biomass patterns were reestablished
within four mo of the flooding, whereas higher chlorophylla biomass concentrations persisted for approximately 6 mo. The primary trophic level in the Pamlico-Albemarle Sound system
returned to equilibrium in less than a year of a major perturbation. 相似文献
537.
The pattern and influence of low dissolved oxygen in the Patuxent River,a seasonally hypoxic estuary
Denise?L.?BreitburgEmail author Aaron?Adamack Kenneth?A.?Rose Sarah?E.?Kolesar Beth?Decker Jennifer?E.?Purcell Julie?E.?Keister James?H.?Cowan 《Estuaries and Coasts》2003,26(2):280-297
Increased nutrient loadings have resulted in low dissolved oxygen (DO) concentrations in bottom waters of the Patuxent River,
a tributary of Chesapeake Bay. We synthesize existing and newly collected data to examine spatial and temporal variation in
bottom DO, the prevalence of hypoxia-induced mortality of fishes, the tolerance of Patuxent River biota to low DO, and the
influence of bottom DO on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous
predators and zooplankton prey. We use this information, as well as output from watershed-quality and water-quality models,
to configure a spatially-explicit individual-based model to predict how changing land use within the Patuxent watershed may
affect survival of early life stages of summer breeding fishes through its effect on DO. Bottom waters in much of the mesohaline
Patuxent River are below 50% DO saturation during summer. The system is characterized by high spatial and temporal variation
in DO concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions of organisms and
trophic interactions in the river. Gelatinous zooplankton are among the most tolerant species of hypoxia, while several of
the ecologically and economically important finfish are among the most sensitive. This variation in DO tolerances may make
the Patuxent River, and similar estuaries, particularly susceptible to hypoxia-induced alterations in food web dynamics. Model
simulations consistently predict high mortality of planktonic bay anchovy eggs (Anchoa mitchilli) under current DO, and increasing survival of fish eggs with increasing DO. Changes in land use that reduce nutrient loadings
may either increase or decrease predation mortality of larval fish depending on the baseline DO conditions at any point in
space and time. A precautionary approach towards fisheries and ecosystem management would recommend reducing nutrients to
levels at which low oxygen effects on estuarine habitat are reduced and, where possible, eliminated. 相似文献
538.
Measurements of CO2 fluxes from open-vent volcanos are rare, yet may offer special capabilities for monitoring volcanos and forecasting activity.
The measured fluxes of CO2 and SO2 from Mount St. Helens decreased from July through November 1980, but the record includes variations of CO2/SO2 in the emitted gas and episodes of greatly increased fluxes of CO2. We propose that the CO2 flux variations reflect two gas components: (a) a component whose flux decreased in proportion to 1/ √t with a CO2/SO2 mass ratio of 1.7, and (b) a residual flux of CO2 consisting of short-lived, large peaks with a CO2/SO2 mass ratio of 15. We propose two hypotheses: (a) the 1/ √t dependence was generated by crystallization in a deep magma body at rates governed by diffusion-limited heat transfer, and
(b) the gas component with the higher CO2/SO2 was released from ascending magma, which replenished the same magma body. The separation of the total CO2 flux into contributions from known processes permits quantitative inferences about the replenishment and crystallization
rates of open-system magma bodies beneath volcanos. The flux separations obtained by using two gas sources with distinct CO2/SO2 ratios and a peak minus background approach to obtain the CO2 contributions from an intermittent source and a continuously emitting source are similar. The flux separation results support
the hypothesis that the second component was generated by episodic magma ascent and replenishment of the magma body. The diffusion-limited
crystallization hypothesis is supported by the decay of minimum CO2 and SO2 fluxes with 1/ √t after 1 July 1980. We infer that the magma body at Mount St. Helens was replenished at an average rate (2.8×106 m3 d–1) which varied by less than 5% during July, August, and September 1980. The magma body volume (2.4–3.0 km3) in early 1982 was estimated by integrating a crystallization rate function inferred from CO2 fluxes to maximum times (20±4 years) estimated from the increase of sample crystallinity with time. These new volcanic gas
flux separation methods and the existence of relations among the CO2 flux, crystallization rates, and magma body replenishment rates yield new information about the dynamics of an open-vent,
replenished magma body.
Received: 15 February 1995 / Accepted: 30 March 1996 相似文献
539.
Preliminary shock experiments at approximately 50 and 250 kb have been carried out with lunar soil and with a dispersion of iron in quartz. The lunar soils acquire remanent magnetization in the Earth's field of order of magnitude 10?3 G cm3 g?1. The remanence exhibited considerable stability against AF demagnetization. Remanence appears to be acquired both during the passage of the shock wave through the material and during post shock cool-down. The higher shock range gave rise to an increase in magnetic viscosity and in the saturation magnetization of the soil, which is most readily explained as due to the generation of fine grained iron. 相似文献
540.
The hydrology of a small wet forested region is studied. Catchment discharge, solar radiation, air temperature, humidity, precipitation, soil moisture, and the water elevation in a swamp were monitored for several months in 1973 and 1975. These data are used to investigate various aspects of the catchment's hydrology and in particular to study the catchment's evapotranspirational requirements. The actual evapotranspiration loss is calculated from a water budget approach. The Priestley-Taylor model is used to predict the medium to long-term evapotranspiration from the basin. The predictions based on the model are in very good agreement with the actual evapotranspirational demand. Evapotranspiration is found to play a significant role in the catchment's water balance. 相似文献