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481.
Andrés S. Rigual-Hernández Thomas W. Trull Kevin McCartney Anne-Marie Ballegeer Kelly-Anne Lawler Stephen G. Bray Leanne K. Armand 《Geo-Marine Letters》2016,36(4):271-280
This study reports detailed silicoflagellate assemblage composition and annual seasonal flux from sediment traps at four locations along a transect across the Southern Ocean frontal systems. The four traps sampled the central Subantarctic Zone (SAZ, 47°S site), the Subantarctic Front (SAF, 51°S site), the Polar Frontal Zone (54°S site) and the Antarctic Zone (61°S site) across the 140°E longitude. Annual silicoflagellate fluxes to the deep ocean exhibited a similar latitudinal trend to those of diatom fluxes reported in previous work, with maxima in the Antarctic Zone and minima in the Subantarctic Zone. The data suggest that, along with diatoms, silicoflagellates are important contributors to biogenic silica export at all sites, particularly in the Subantarctic Zone. Two main silicoflagellate genera were observed, with Stephanocha sp. (previously known as Distephanus) dominating polar waters and Dictyocha sp. important in sub-polar waters. This is consistent with previous use of the Dictyocha / Stephanocha ratio to infer paleotemperatures and monitor shifts in the position of the Polar Frontal Zone in the sedimentary record. It appears possible to further refine the application of this approach by using the ratio between two Dictyocha species, because Dictyocha aculeata dominated at the Subantarctic Front, while Dictyocha stapedia dominated in the central Subantarctic Front. Given the well-defined environmental affinities of both species, a new SAF silicoflagellate index (SAF-SI) based on this ratio is proposed as a useful diagnostic for SAF and SAZ water mass signatures in the Plio-Pleistocene and Holocene sedimentary record. 相似文献
482.
Malcolm Luxton 《新西兰海洋与淡水研究杂志》2013,47(3):497-504
Tangaroellus porosus, gen. nov., sp. nov., is described from three coastal localities in New Zealand. Its affinities with the family Rhodacaridae are discussed. 相似文献
483.
Malcolm E. Forster 《新西兰海洋与淡水研究杂志》2013,47(1):85-90
Patterns of ventilation, oxygen consumption (VO2), blood gas tensions (PaO2 and PaCO2) and pH were determined in shortfin eels (Anguilla australis schmidtii (Phillips)). At rest, shortfin eels (average weight 646.5 ± 64.5 g) had a VO2 of 20.4 ± 1.2 ml. kg‐1.h‐1 (n = 13) at 17.5 ± 0.2°c, with smaller fish having the highest metabolic rates. The frequency of ventilation was inversely proportional to body weight in both A. australis schmidtii and A. dieffenbachii. In air‐saturated water 10 eels exhibited periodic apnoea (mean duration 3.59 min); periods of ventilation were more variable in duration (mean 4.92 min). After 2.62 min of apnoea, the PaO2 of dorsal aortic blood had fallen from 9.12 to 1.91 kPa. Thus, although the blood has a high affinity for oxygen and the haemoglobins are 30% oxygen‐saturated at this low PaO2, the eel allows its blood to be significantly depleted in oxygen during apnoeic pauses at rest. When ventilating its gills at rest, PaO2 does not approach the PO2 of the inspired water. It is suggested that these features of respiration in eels result in a saving of metabolic costs involved in ventilation. The results are discussed in terms of the eel's ability to withstand hypoxic conditions. 相似文献
484.
John A. Bray 《Marine Geodesy》2013,36(2):177-197
Geodetic survey records for a meridional chain of first‐order leveling spanning 50 latitude degrees are available at the Defense Mapping Agency Topographic Center (DMATC) for the Pacific coast of South America. The coastal route from Talara, Peru, to Puerto Montt, Chile (37° of latitude or 4,100 kilometers of arc), has been analyzed to evaluate the accuracy of the leveling and to determine whether or not “mean water level” (MWL) has a slope relative to the equipotential surface passing through Talara. A provisional meridional, sea‐level profile is discussed in terms of the magnitudes of the different kinds of measurement uncertainties. 相似文献
485.
Tsuyoshi Iizuka Malcolm T. McCulloch Tsuyoshi Komiya Takazo Shibuya Kenji Ohta Haruka Ozawa Emiko Sugimura Kenneth D. Collerson 《Contributions to Mineralogy and Petrology》2010,160(6):803-823
Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are
of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance
of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical
data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer
meta-sediments during tectonothermal events, including metamorphism at ~3.3–3.2 and 2.7–2.6 Ga. These results set a new minimum
age of 3.2 Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and ~2.7 Ga. Despite the significant
metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This
is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet.
In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism
in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3 Ga
granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older
than 3.65 Ga have been identified, implying either that the source rocks of >3.65 Ga detrital zircons in the sediments contained
little monazite, or that >3.65 Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary
recycling, resulting in the complete dissolution or recrystallization of monazite. 相似文献
486.
Wind Modulation of Dissolved Oxygen in Chesapeake Bay 总被引:1,自引:0,他引:1
Malcolm E. Scully 《Estuaries and Coasts》2010,33(5):1164-1175
A numerical circulation model with a simplified dissolved oxygen module is used to examine the importance of wind-driven ventilation
of hypoxic waters in Chesapeake Bay. The model demonstrates that the interaction between wind-driven lateral circulation and
enhanced vertical mixing over shoal regions is the dominant mechanism for providing oxygen to hypoxic sub-pycnocline waters.
The effectiveness of this mechanism is strongly influenced by the direction of the wind forcing. Winds from the south are
most effective at supplying oxygen to hypoxic regions, and winds from the west are shown to be least effective. Simple numerical
simulations demonstrate that the volume of hypoxia in the bay is nearly 2.5 times bigger when the mean wind is from the southwest
as compared to the southeast. These results provide support for a recent analysis that suggests much of the long-term variability
of hypoxia in Chesapeake Bay can be explained by variations in the summertime wind direction. 相似文献
487.
Garnet compositions and their use as indicators of peraluminous granitoid petrogenesis — southeastern Arabian Shield 总被引:1,自引:0,他引:1
Edward A. du Bray 《Contributions to Mineralogy and Petrology》1988,100(2):205-212
Garnet, an uncommon accessory mineral in igneous rocks, occurs in seven small peraluminous granitoid plutons in the southeastern Arabian Shield; textural equilibrium between garnet and other host granitoid minerals indicates that the garnets crystallized from their host magmas. Compositions of the garnets form three groups that reflect host-granitoid compositions, which in turn reflect source compositions and tectonic regimes in which the host magmas were generated. Garnets from the seven plutons have almandine-rich cores and spessartine-rich rims. This reverse zoning depicts host magma compositional evolution; i.e. rimward spessartine enrichment resulted from progressive, host-magma manganese enrichment. The garnets are heavy rare-earth element enriched; (Lu/La)
N
ranges from 13 to 355 and one of the garnets contains spectacularly elevated abundances of Y, Ta, Th, U, Zn, Zr, Hf, Sn, and Nb. Involvement of garnets with these trace element characteristics in magma genesis or evolution can have dramatic effects on trace element signatures of the resulting magmas. Other researchers suggest that Mn-enriched magmas are most conducive to garnet nucleation. Although the garnetiferous granitoids discussed here are slightly Mn enriched, other genetically similar peraluminous Arabian granitoids lack garnet; Mn enrichment alone does not guarantee garnet nucleation. The presence of excess alumina in the magma may be a prerequisite for garnet nucleation. 相似文献
488.
Detrimental effects of engineering works on the coast and a wish to conserve parts of the coastline have increased realization among coastal managers of the need to examine shoreline problems and proposals for protection in a wider spatial context than the site itself and over a longer time scale than the past few years. This paper outlines the approach taken in one region of the United Kingdom, the central south coast of England, to provide that wider perspective. Authorities responsible for coastal protection and sea defenses formed a coastal group, which, among other activities, commissioned research aimed at providing a greater understanding on which to base shoreline management decisions. A major project undertaken was a sediment transport study in which all existing information relating to coastal sediment processes in the region was collated and analyzed. All inputs, flows, and outputs of sediment were documented. Links between processes were examined for each part of the region. Finally, nine littoral cells of sediment circulation were identified and were suggested as forming a framework for shoreline management. The methods of compilation and analysis are outlined here and are exemplified for one area in the region. The approach is recommended as a cost-effective basis for strategic management of the coast in developed regions. 相似文献