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91.
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93.
The acute toxicity of Kepone in freshwater was determined with three fish species,Ictalurus punctatus (channel catfish),Lepomis macrochirus (bluegills), andAnguilla rostrata (American eel). Elvers ofA. rostrata were most sensitive with a 96 h lethal concentration for 50% of the animals tested (LC50) of 35 μg per. 1. Bluegills were slightly less sensitive with a 96 h LC50 of 50 μg per 1. Catfish were most tolerant with a 96 h LC50 of 514 μg per l. Bluegills and catfish exposed to comparable concentrations of Kepone accumulated equivalent amounts in 96 h. This observation in conjunction with the markedly different 96 h LC50's for these species suggest a difference in the ways these fish cope with Kepone. 相似文献
94.
Richard V. Morris 《Geochimica et cosmochimica acta》1975,39(5):621-634
Electron paramagnetic resonance (EPR) measurements were made on Gd3+ and Eu2+ ions in polycrystalline samples to determine the nature of the sites occupied by those ions in mineral structures. Both Gd3+ and Eu2+ ions were incorporated at Ca2+ structural sites in β-Ca2SiO4, pseudo-CaSiO3, CaMgSiO4, CaMgSi2O6, hex-CaAl2Si2O8, CaAl2O4, and Ca3Al2O6. For tri-CaAl2Si2O8, Eu2+ was incorporated at a Ca2+ site and Gd3+ was incorporated at a site where the crystalline electric field was disordered. That difference in behavior may contribute to the anomalous behavior of Eu in plagioclase feldspar. Both Gd3+ and Eu2+ were incorporated as aggregates or clusters of those ions in Mg2SiO4 and clino-MgSiO3. 相似文献
95.
Joel S. Steward Robert W. Virnstein Lori J. Morris Edgar F. Lowe 《Estuaries and Coasts》2005,28(6):923-935
Seagrass protection and restoration in Florida’s Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs.
These programs require, the establishment of management targets indicative of seagrass recovery and health. We used three
metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the
IRLS’s spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments.
Our method consisted of two steps: mapping the union of seagrass coverages from all availabe mapping years (1943, 1986, 1989,
1992, 1994, 1996, and 1999) to delineate wherever seagrass had been mapped and determining the distribution of depth limits
based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution
of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth
limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among
segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively.Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using
a 10-yr record of light data (1990–1999) and the union coverage depth limit distributions from the most temporally stable
seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 ± 17%
of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions,
is 20 ± 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 ± 13%). Variation
in depth limits and light requirements, is probably due to factors other than light that influence the depth limit of seagrasses
(e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data
sets and can be applied to other estuaries where grass beds are routinely monitored and mapped. 相似文献
96.
Apatite fission track analyses of 21 samples from the central and eastern Pyrenees are modelled to generate time–temperature plots for the post 110±10 °C cooling history over the 40–10 Ma time interval. Modelled thermal histories have been converted into exhumation plots through the application of the present-day geothermal gradient in the Pyrenees. The documented geology of the Pyrenees allows us to assume no significant extensional unroofing and subvertical exhumation trajectories, thus enabling exhumation to be translated into erosional denudation. Maps of denudation have been constructed for six, 5-Myr time intervals. Denudation varied with a 20–50-km length scale, and does not appear to have been related to the major structural zones of the mountain belt. Spatially averaged denudation rates for the six time intervals ranged from 34 to 61 mm kyr?1 assuming the present-day geothermal gradient. Maximum rates of 240 mm kyr?1 occurred in the interval 35–30 Ma, in the region of the Querigut-Millas massif. Assuming the denudation resulted primarily from erosion, the denudation maps can be used to calculate sediment discharge through time to the neighbouring foreland basins. Using a series of rectangular drainage basins with a 2:1 aspect ratio (based on modern linear mountain belts) and a location of the main drainage divide based on the mean present-day position, it is possible to evaluate the potential for spatial and temporal variations in sediment discharge as a function of denudation. The results show along-strike variations in sediment discharge between drainage basins of 500%, and temporal variations from individual basins of >300%. A comparison of total sediment discharge per year to the Ebro and Aquitaine basins, assuming a fixed drainage divide, shows that the discharge to the south is likely to have been between 1.5 and 2.8 times greater than to the north. 相似文献
97.
98.
Landon L. Morris Marty J. McVey Robert A. Lohnes C.Phillip Baumel 《Engineering Geology》1996,43(4):255-264
In the beginning of the 20th century, many streams in western Iowa were channelized to reduce flooding and to open swamp land to cultivation. Channel straightening accomplished its goal. However, it resulted in greater streamflow velocities, causing stream channels to degrade. This degradation has resulted in significant loss of land and damage to transportation and communications infrastructure in western Iowa and in several states in the United States. Baumel et al. (1994; Impact of Degrading Western Iowa Streams on Private and Public Infrastructure Costs. Final Report Iowa DOT HR-352, Stream Stabilization in Western Iowa) estimated the historical cost of this degradation on land loss and damage to transportation and communications infrastructure in western Iowa. The purpose of this paper is to extend the Baumel et al. analysis to estimate future degradation costs on 141 streams in western Iowa. It also presents two types of degradation cost estimates. One is a time neutral cost that does not consider the dates on which the degradation costs are incurred. The second is a time value cost which considers the dates on which the costs are incurred and then discounts these costs back to 1992 dollars. The time value costs are the more accurate estimates of the cost of future degradation in 1992 dollars and should be used to evaluate stream stabilization project proposals. 相似文献
99.
A resident wild dolphin is reported to avoid the discharge plume from the Red River which empties into the northern end of St Ives Bay. The river effluent is found to contain a high load of finely divided metalliferous particles rich in iron but also containing significant amounts of Sn, As, Cu and Zn. It is suggested that the echo-location system and/or chemosensory system of the dolphin may be affected by this discharge causing the animal to avoid the area of the effluent. 相似文献
100.