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排序方式: 共有347条查询结果,搜索用时 15 毫秒
71.
72.
Gary R. Huss Elizabeth Koeman‐Shields Amy J. G. Jurewicz Donald S. Burnett Kazuhide Nagashima Ryan Ogliore Chad T. Olinger 《Meteoritics & planetary science》2020,55(2):326-351
NASA's Genesis mission was flown to capture samples of the solar wind and return them to the Earth for measurement. The purpose of the mission was to determine the chemical and isotopic composition of the Sun with significantly better precision than known before. Abundance data are now available for noble gases, magnesium, sodium, calcium, potassium, aluminum, chromium, iron, and other elements. Here, we report abundance data for hydrogen in four solar wind regimes collected by the Genesis mission (bulk solar wind, interstream low‐energy wind, coronal hole high‐energy wind, and coronal mass ejections). The mission was not designed to collect hydrogen, and in order to measure it, we had to overcome a variety of technical problems, as described herein. The relative hydrogen fluences among the four regimes should be accurate to better than ±5–6%, and the absolute fluences should be accurate to ±10%. We use the data to investigate elemental fractionations due to the first ionization potential during acceleration of the solar wind. We also use our data, combined with regime data for neon and argon, to estimate the solar neon and argon abundances, elements that cannot be measured spectroscopically in the solar photosphere. 相似文献
73.
Brian N. Tissot Barbara A. Best Eric H. Borneman Andrew W. Bruckner Cara H. Cooper Heather D’Agnes Timothy P. Fitzgerald Amanda Leland Susan Lieberman Amy Mathews Amos Rashid Sumaila Teresa M. Telecky Frazer McGilvray Brian J. Plankis Andrew L. Rhyne Glynnis G. Roberts Benjamin Starkhouse Todd C. Stevenson 《Marine Policy》2010
As the world’s largest importer of marine ornamental species for the aquaria, curio, home décor, and jewelry industries, the United States has an opportunity to leverage its considerable market power to promote more sustainable trade and reduce the effects of ornamental trade stress on coral reefs worldwide. Evidence indicates that collection of some coral reef animals for these trades has caused virtual elimination of local populations, major changes in age structure, and promotion of collection practices that destroy reef habitats. Management and enforcement of collection activities in major source countries such as Indonesia and the Philippines remain weak. Strengthening US trade laws and enforcement capabilities combined with increasing consumer and industry demand for responsible conservation can create strong incentives for improving management in source countries. This is particularly important in light of the March 2010 failure of the parties to the Convention on International Trade in Endangered Species (CITES) to take action on key groups of corals. 相似文献
74.
Amy E. Draut Patrick E. Hart Thomas D. Lorenson Holly F. Ryan Florence L. Wong Ray W. Sliter James E. Conrad 《Marine Geophysical Researches》2009,30(3):193-206
Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine
sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely
sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara–Ventura
coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary
climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection
data over >570 km2 of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River
deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor
controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment
5–20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed
at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment
deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80%
of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara
Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation.
Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial
quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental
margins, and for inferring the distribution of hydrocarbon resources in relict shelf deposits. 相似文献
75.
John Ryks Jonathan Kilgour Jesse Whitehead Amy Whetu James Whetu 《New Zealand geographer》2019,75(3):152-162
During the 1990s, the township of Pōkeno was held up as an example of a declining rural Aotearoa/New Zealand. By‐passed from the national state highway, it lost its status as a service hub and drastic measures were introduced to revitalise the town, including renaming the town “ Jenniferann.com .” Pōkeno has since undergone an unlikely transformation, with foreign investment and its location within an extended Auckland commuter zone meaning that the township has grown exponentially. This article describes the transformation of Pōkeno and uncovers what has been missing from discussions about Pōkeno's reinvention, namely, the place of mana whenua. 相似文献
76.
A stepwise stalagmite sample screening process was applied in order to select a stalagmite as a sensitive recorder of recent tropical cyclone rainfall events near Belize. Field and laboratory criteria were combined in series, to screen out candidate stalagmites whose characteristics indicated lower sensitivity to stormwater infiltration. The approach described here was designed to increase the likelihood that selected stalagmites would increase the signal:noise ratio of the target phenomenon in the resulting proxy records. This four-stage method for sample selection may be an important methodological consideration for researchers attempting to use speleothems for stable isotope paleotempestology. Hallmarks of this approach include: (1) establishing a priori scientific targets, (2) applying sample criteria in the form of contra-indicators, and (3) organizing the sample screening protocol into a series of practical stages. The overall approach to stalagmite selection presented here supports cave conservation, and can be adapted readily by others in support of different scientific goals. It is hoped that other investigators will also publish field and laboratory sample selection schemes, as increased transparency will provide new information invaluable to replication efforts and to advancing the field of speleothem paleo-environmental studies. 相似文献
77.
A fundamental question in ecology is how biological interactions and biogeographic processes interact to determine the biodiversity
of local sites. We quantified patterns of plant species diversity on transects across elevation at 59 salt marsh sites in
Georgia and 49 sites in Texas. Although these regions have similar climates and floras, we anticipated that diversity might
differ because of differences in tidal regime. Diversity was measured at global, regional, site, and plot scales to consider
processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and
plot scales, suggesting that processes occurring at the site scale differed. The greater diversity of Texas sites and plots
was associated with wider distributions of individual species across the marsh landscape and proportionally more middle marsh
(a high diversity zone) and less low marsh (a low diversity zone) than in Georgia marshes. Preliminary data suggested that
these differences were not due to differences in salinity regime or standing biomass between regions, leaving differences
in tidal regime as the most plausible hypothesis accounting for differences in plant diversity. We speculate that the less-predictable
tidal regime in Texas leads to temporal variation in abiotic conditions that limit the ability of any one species to competitively
exclude others from particular marsh zones. 相似文献
78.
Tectonostratigraphic and geochronologic constraints on evolution of the northeast Paleotethys from the Songpan-Ganzi complex, central China 总被引:1,自引:0,他引:1
Amy L. Weislogel 《Tectonophysics》2008,451(1-4):331-345
The Middle to Late Triassic deep-water deposits that form the Songpan-Ganzi complex (SGC) of central China comprise an estimated ~ 2.0 × 106 km3 of detrital material that accumulated in the northeasternmost branch of the Paleotethys. A review of existing data demonstrates significant spatial and temporal variations in the stratigraphic and petrologic character of these turbidites. These variations are used to divide the complex into different depocenters: a northeastern depocenter (SGC-NE), a eastern–central depocenter (SGC-EC) and a northwestern depocenter (SGC-NW). Turbidite strata of the SGC-NE and SGC-EC zones of the Songpan-Ganzi complex are linked to the collision of the North China and South China blocks, whereas turbidite strata of the SGC-NW area are likely to be more closely affiliated with evolution of the Kunlun deformation belt. To test the validity of the Songpan-Ganzi stratigraphic framework and interpretations of its tectonostratigraphic evolution, sixty-eight U–Pb zircon ages were determined from five samples of felsic intrusive igneous rock, two samples from felsic plutonic rock of the adjacent Yidun arc complex, and one sample of volcanic rock interbedded with Middle Triassic turbidites of the SGC using the Sensitive High Resolution Ion Microprobe-Reverse Geometry (SHRIMP-RG). Together these data indicate primarily Late Triassic (~ 214–211 Ma) felsic magmatism in the SGC, with some indication of magmatic activity beginning as early as Middle Triassic (220 Ma). Zircon ages from the Yidun arc complex support Middle–Late Triassic magmatism from 225–215 Ma, prior to deformation of the SGC, suggesting deformation of the SGC was not related to subduction of the SGC substrate southwestward beneath the Yidun arc. Inherited Neoproterozoic (880–740 Ma) zircon ages found in two samples from the SGC-EC indicate either inheritance of zircon crystals from the surrounding SGC turbidite strata or possibly involvement of South China basement during crustal thickening and magma genesis. 相似文献
79.
In the United States, there is a growing awareness of the implications of our globalized food system, a system that incorporates all manner of agriculture, food distribution, food processing and transformation, and consumption. The ever increasing distance between where our food is produced and where it is consumed has helped spur a movement to develop a system of place based foods. Right now multiple models are in play, including farmers markets, community supported agriculture, and the localvore movement. This article will do a close examination of another model from France, the French system of appellation d’origine contrôlée (AOC); nationally regulated by the French Ministry of Agriculture it supports and protects foods and drinks with unique links to particular territories. The AOC system is based on geographically distinct and historically specific food and drink found throughout France. By closely examining one AOC product—Comté cheese produced in the rural agricultural region in Jura—the authors consider the possibilities for an AOC-style system in the United States. 相似文献
80.