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91.
Open-marsh water management (OMWM) manipulates selected areas of an estuarine marsh by constructing narrow, deep ditches that harbor resident populations of predators of mosquito larvae. It does not, however, alter the surrounding vegetation by deposition of spoil mounds. We censused the summer (breeding and nonbreeding) bird populations in two adjacent salt marsh sites on Topsail Island, North Carolina, for two summers before OMWM ditching occurred and for four seasons postditching. A total of 53 nonbreeding species and five breeding species of birds were encountered on the study sites. None of the interannual changes in bird populations can be attributed to OMWM. 相似文献
92.
U-Pb isotope analyses, rare earth and trace element analyses, and petrographic observations are presented for monazites from
the Wepawaug Schist in southern Connecticut, USA. Two samples of kyanite zone schist were collected less than a meter apart.
Each sample contains a different variety of monazite with distinct morphology, chemistry, and Pb isotopic composition. One
sample preserves a largely amphibolite facies mineralogy, including kyanite, staurolite, garnet, biotite, and chlorite, with
little textural evidence of later shearing. Monazites from this sample are xenoblastic with about 1 wt% ThO2, 0.3 wt% CaO, and a more LREE enriched pattern than monazites from the second sample. These xenoblastic monazites preserve
textural evidence of a retrograde reaction to apatite which involves chlorite, indicating that these monazites became unstable
during retrograde chloritization of biotite. These monazites give strongly discordant U-Pb ages which fit a chord with an
upper intercept age of 411±18 Ma, interpreted as the minimum growth age of these xenoblastic monazites, perhaps during amphibolite
facies metamorphism. The second sample contains S-C banding, evidence of dynamic recrystallization, and abundant retrograde
chlorite. This sample contains idioblastic monazites with about 3 wt% ThO2, 0.8 wt% CaO, and with less fractionated REE patterns. These monazites give close to concordant U-Pb ages with a mean 207Pb*/206Pb* age of 388 ± 2 Ma. This age is interpreted as probably representing the time of monazite growth during retrogression of
the sample from an amphibolite to greenschist facies mineralogy.
Received: 26 June 1995/Accepted: 25 May 1996 相似文献
93.
Stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3-m dolerite sill have been studied by gas chromatography-mass spectrometry (GC-MS). The steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17β(H), 21β(H) configuration at some distance from the intrusion, to one dominated by the thermally more stable 17α(H), 21β(H) and 17β(H), 21α(H) configurating in the immediate vicinity of the intrusion. In addition, severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism, and high concentrations of extractable organic matter were observed below the intrusion. Characterization of the kerogens by Curie-point pyrolysis has enabled the effects of the intrusion on the shales to be monitored. 相似文献
94.
95.
The probability of setting global temperature records is reconsidered in light of cooling due to the Mt. Pinatubo eruption. The cooling resets temperature by moving it away from the top of its 100-year range. Depending on the statistical model for temperature, this reset can lead to a much lower probability for a record in the next few years. The exercise illustrates how record setting depends on the underlying model, the current record value, and - if there is serial correlation- the current temperature. 相似文献
96.
97.
I.S. Spooner D. Mazzucchi G. Osborn R. Gilbert I. Larocque 《Journal of Paleolimnology》2002,28(4):419-431
A stratigraphic record from a lake in the Central Plateau Regionof northern British Columbia reveals changes in environment and inferredclimate during the Holocene. Upon deglaciation (ca. 11500 BP), Skinny Lakebecame an embayment of an ice-dammed lake. High clastic sedimentationrates, an unstable landscape, and cool, possibly wet conditions likelypersisted until the early Holocene (ca. 9000 BP). From ca. 9000–8300 BPdeclining lake levels coupled with warm and dry conditions resulted in theformation of a prominent marl bed. A colonizing shrub and herb assemblagepersisted from 9000 BP until about 8300 BP when it was replaced by a spruce(Picea) and subalpine fir (Abieslasiocarpa) forest under slightly cooler and moister conditions. Themiddle Holocene was warmer-than-present, however, decreasingtemperature and increasing precipitation trends characterize the period fromca. 6000 BP–3000 BP. The transition to modern climate at 3000 BP isevident primarily in the lithostratigraphic record and corresponds with theinitiation of the Tiedemann glacial advance (ca. 3300 BP) in thesouth-coastal mountains of British Columbia. A significant change infossil pollen occurs at ca. 2400 BP and is characterised by an increase in pinepollen accompanied by decreases in alder (Alnus), spruceand fir. This also coincides with an increase in west-sourced exoticwestern hemlock (Tsuga heterophylla) and cedar type(Cupressaceae) pollen possibly transported by regional changes in air masscirculation patterns associated with Aleutian Low dynamics. This studydemonstrates that both lithostratigraphic and biotic proxies are helpful inreconstructing the timing and nature of climate change and that each may havevarying sensitivities to a particular type of change. 相似文献
98.
Abigail McQuatters-Gollop Alison J. Gilbert Laurence D. Mee Jan E. Vermaat Yuri Artioli Christoph Humborg Fred Wulff 《Estuarine, Coastal and Shelf Science》2009,82(4):583-596
Anthropogenic eutrophication affects the Mediterranean, Black, North and Baltic Seas to various extents. Responses to nutrient loading and methods of monitoring relevant indicators vary regionally, hindering interpretation of ecosystem state changes and preventing a straightforward pan-European assessment of eutrophication symptoms. Here we summarize responses to nutrient enrichment in Europe's seas, comparing existing time-series of selected pelagic (phytoplankton biomass and community composition, turbidity, N:P ratio) and benthic (macro flora and faunal communities, bottom oxygen condition) indicators based on their effectiveness in assessing eutrophication effects. Our results suggest that the Black Sea and Northern Adriatic appear to be recovering from eutrophication due to economic reorganization in the Black Sea catchment and nutrient abatement measures in the case of the Northern Adriatic. The Baltic is most strongly impacted by eutrophication due to its limited exchange and the prevalence of nutrient recycling. Eutrophication in the North Sea is primarily a coastal problem, but may be exacerbated by climatic changes. Indicator interpretation is strongly dependent on sea-specific knowledge of ecosystem characteristics, and no single indicator can be employed to adequately compare eutrophication state between European seas. Communicating eutrophication-related information to policy-makers could be facilitated through the use of consistent indicator selection and monitoring methodologies across European seas. This work is discussed in the context of the European Commission's recently published Marine Strategy Directive. 相似文献
99.
Prey importance and ontogenetic transitions in the diet of stocked and wild mulloway (Argyrosomus japonicus) were compared between a southeast Australian reverine estuary and a coastal lagoon. Stomach content analysis of fish captured
from these estuaries in 1997–1979, 1997–1998, and 2003–2005 revealed size-specific and estuary-specific diets. Mysid shrimp
were most common in diets of fish <250 mm total length (TL), and prawns were common in diets of fish measuring 301–450 mm.
Forage fish were most abundant in diets of mulloway >500 mm. Index of Relative Importance (IRI) of forage fish increased with
TL, while IRI of mysids decreased with TL. Prawn IRI was greatest for fish 150–600 mm TL. Comparisons between benthic resources
and dietary composition revealed that Georges River mulloway consumed prey categories in proportions similar to those in their
environment. No mysid shrimp were detected in the coastal lagoon or in the diet of mulloway captured there; growth was comparable
to the Georges River. Hatchery-reared fish fed<16 d after stocking, indicating normal behavioural adaptation after release.
Dietary information can be used to optimize stocking locations, times, and densities, as well as estimate potential effects
of mulloway on potential prey and wild conspecifics. 相似文献
100.