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121.
Remnant riparian vegetation,sediment and nutrient loads,and river rehabilitation in subtropical Australia
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Jon Olley Joanne Burton Virgilio Hermoso Kate Smolders Joe McMahon Belinda Thomson Andrew Watkinson 《水文研究》2015,29(10):2290-2300
A decline in the ecosystem health of Australia's Moreton Bay, a Ramsar wetland of international significance, has been attributed to sediments and nutrients derived from catchment sources. To address this decline the regional management plan has set the target of reducing the loads by 50%. Reforestation of the channel network has been proposed as the means to achieve this reduction, but the extent of revegetation required is uncertain. Here we test the hypothesis that sediment and nutrient loads from catchments decrease proportionally with the increasing proportion of the stream length draining remnant vegetation. As part of a routine regional water quality monitoring program sediment and nutrient loads were measured in 186 flow events across 22 sub‐catchments with different proportions of remnant woodland. Using multiple linear regression analysis we develop a predictive model for pollutant loads. Of the attributes examined a combination of runoff and the proportion of the stream length draining remnant vegetation was the best predictor. The sediment yield per unit area from a catchment containing no remnant vegetation is predicted to be between 50 and 200 times that of a fully vegetated channel network; total phosphorus between 25 and 60 times; total nitrogen between 1.6 and 4.1 times. There are ~48 000 km of streams in the region of which 32% drain areas of remnant vegetation. Of these 17 095 km are above the region's water storage dams. We estimate that decreasing the sediment and phosphorus loads to Moreton Bay by 50% would involve rehabilitating ~6350 km of the channel network below the dams; halving the total nitrogen load would require almost complete restoration of the channel network. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
122.
123.
R. Muller 《Solar physics》1976,48(1):101-102
It is confirmed that the penumbral bright grains are moving towards the sunspots umbra. At the umbra-penumbra boundary their horizontal velocity is about 0.5 km s–1 and their displacement is inclined downwards with an angle of 5° to 20°. 相似文献
124.
R. Muller 《Solar physics》1983,85(1):113-121
A high resolution time series of pictures, obtained at Pic du Midi Observatory, is used to analyze the dynamical behavior of facular points in the quiet Sun. The following characteristics of the behavior are revealed: (a) relative to the supergranular pattern, facular points appear at the supergranular boundaries, rarely inside the cells; (b) relative to the pattern of the granulation, they appear in spaces at the junction of several granules, never inside a granule nor in a space between two granules only; (c) their mean lifetime is 18 min; (d) they remain in intergranular lanes during their whole life; (e) their observed size never significantly exceeds 0″. 5; (f) they have a strong tendency to appear very close to an already existing facular point; (g) about 15% of them seem to split in two facular points; (h) they disappear simply by fading away in an intergranular space; (i) they never merge with another facular point or with a granule. The formation of facular points in the quiet photosphere is very closely connected to both granular and supergranular patterns. Some possible consequences on the behavior of the associated magnetic flux tubes are discussed. 相似文献
125.
R. Muller 《Solar physics》1973,32(2):409-420
Resumé L'analyse microphotométrique des structures fines de la pénombre d'une tache solaire, photographiée en lumiére blanche au Pic du Midi avec une résolution de l'ordre de 0'.3, permet d'en donner, à 15280, l'image suivante: elle est constituée d'un fond sombre (espaces interfilamentaires) de brillance I/I
d = 0.6 à peu près uniforme, avec un léger gradient radial, sur lequel se détachent des grains brillants alignés en filaments, de brillance moyenne I/I
b = 0.95, de largeur moyenne 0'.36 (270 km) et qui recouvrent 43% de sa surface.
Ce travail a été en grande partie réalisé alors que l'auteur faisait un séjour à l'Universitäts Sternéwarte de Göttingen. 相似文献
The microphotometric analysis of the fine structure of a sunspot penumbra, photographed in white light with the 38 cm refractor of the Pic du Midi Observatory with a resolution very close to 0'.3, allows to give from it, at 5280, the following picture: the penumbra appears to consist of bright grains, lined up in the form of filaments, with an average brightness I/I b = 0.95 of average width 0.36 (270 km) and which cover 43% of its surface, showing up a dark background of brightness I/I d = 0.6 nearly uniform.
Ce travail a été en grande partie réalisé alors que l'auteur faisait un séjour à l'Universitäts Sternéwarte de Göttingen. 相似文献
126.
Solomon Tafesse Joanne M. Robison Fernlund Wenjuan Sun Fredrik Bergholm 《Sedimentology》2013,60(4):1100-1110
Angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits. In the past, visual classification using silhouette charts was widely used to determine particle angularity, but this approach is subjective and time‐consuming. With advances in modern image analysis techniques and low‐cost software packages, it is possible to rapidly quantify particle angularity more objectively than using visual classification methods. This study re‐examines the performance of three existing image analysis methods and one new image analysis procedure, applied to six rock and sediment samples that were visually different in angularity. To facilitate comparison between the angularity results, measurements were reduced to rankings for each aggregate sample. These results show that the four image analysis methods rank the angularity of the samples differently, and that none rank the mean angularity index in the same order as the angularity ranking using visual classification. Therefore, further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely. 相似文献
127.
Joanne S. Johnson Jeremy D. Everest Philip T. Leat Nicholas R. Golledge Dylan H. Rood Finlay M. Stuart 《Quaternary Research》2012,77(2):273-280
Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic 10Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the 10Be ages are in the range 10.2–21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic 3He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes. 相似文献
128.
In 1981 a magnetic and bathymetric survey was carried out over Explorer Seamount located approximately between 48°50′ and
49°30′N and 130°40′ and 131°30′W. During the cruise four pillow fragments were dredged from peaks in this area. Based on the
observed magnetic data, it was identified that the main peak of Explorer Seamount should be of the Bruhnes age while the magnetic
high in the NW of study area would be Gauss. This would yield a spreading rate of about 2 cm per year for the Matuyama epoch.
The results of intensities of remanence measured from the pillow fragments indicate that the ages are less than 106 years. Similarly the Curie temperature is consistent with ages of around 106 years. An attempt was made to model the observed magnetic field using a series of uniformly magnetized NE-SW trending blocks
of alternating polarity. Agreement between the model and observed results is satisfied. Oxidation ratios calculated from measured
samples suggest that the main peak of Explorer Seamount is not far from the present day ridge axis, which agrees with the
younger interpretation from the magnetic profiles.
The results mentioned above strongly, but not conclusively, favour an interpretation in which the southeastern peak of Explorer
Seamount is of the Bruhnes age and the recent spreading is at Explorer trench, then the Sovanco Fracture Zone should be thought
of as a complex triangular area between the northern end of Juan de Fuca Ridge and Explorer Seamount rather than as a simple
transform fault as defined conventionally. 相似文献
129.
Joanne?C.?Bintz Scott?W.?NixonEmail author Betty?A.?Buckley Stephen?L.?Granger 《Estuaries and Coasts》2003,26(3):765-776
We investigated the independent and interactive effects of nutrient loading and summer water temperature on phytoplankton,
drift macroalgae, and eelgrass (Zostera marina) in a coastal lagoon mesocosm experiment conducted from May through August 1999. Temperature treatments consisted of controls
that approximated the 9-yr mean daily temperatures for Ninigret and Point Judith Lagoons in Rhode Island (United States) and
treatments approximately 4°C above and 4°C below the controls. Nutrient treatments consisted of the addition of 6 mmol N m−2d−1 and 0.5 mmol P m−2 d−1 to mesocosms 4°C above and 4°C below the 9-yr daily mean. Nutrient enrichment produced marked phytoplankton blooms in both
cool and warm treatments during early summer. These were replaced after midsummer by dramatic growths of macroalgal mats ofEnteromorpha flexuosa and, to a lesser degree,Cladophora sericea. No phytoplankton blooms were observed in the cool unenriched treatments, but blooms did develop in the mean temperature
and warm mesocosms during the second half of the summer that were similar in intensity, though of shorter duration, than those
observed earlier in the enriched systems. Macroalgal blooms did not occur in the unenriched mesocosms. Sustained warm water
temperatures markedly decreased eelgrass density and belowground production and increased the time interval between the initiation
of new leaves, particuarly when the biomass of macroalgae was high. The negative effect of elevated water temperature on eelgrass
was significantly increased under conditions of elevated inorganic nutrient input. By the end of summer, virtually all of
the measures of eelgrass health declined in rank order from cool, to mean, to cool enriched, to warm, to warm enriched treatments.
It is likely that the marked declines in eelgrass abundance observed during recent decades in the Northeast have resulted
from an interaction of increasing nutrient enrichment combined with increasing summer water temperatures. 相似文献
130.
We study the mean size of granules as a function of distance from the boundaries of the sunspot penumbra. We use for the determination of the mean size two different methods, a visual and a photometric. In all cases the mean diameter of the granules away from the spot was greater than the mean diameter of the granules in the neighbourhood of the penumbra. Our study is based on an excellent sequence of photos, taken at the Pic-du-Midi Observatory on May 11, 1979. 相似文献