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81.
Robert Bolhar Balz S. Kamber Martin J. Whitehouse 《Geochimica et cosmochimica acta》2005,69(6):1555-1573
New and published major and trace element abundances of clastic metasediments (mainly garnet-biotite-plagioclase schists) from the ∼3.8 Ga Isua Greenstone Belt (IGB), southern West Greenland, are used in an attempt to identify the compositional characteristics of the protoliths of these sediments. Compositionally, the metasediments are heterogeneous with enrichment of LREE (La/Smchond = 1.1-3.9) and variable enrichment and depletion of HREE (Gd/Ybchond = 0.8-4.3). Chondrite-normalized Eu is also variable, spanning a range from relative Eu depletion to enrichment (Eu/Eu* = 0.6-1.3). A series of geochemical and geological criteria provides conclusive evidence for a sedimentary origin, in disagreement with some previous studies that questioned the presence of genuine clastic metasediments. In particular, trace element systematics of IGB metasediments show strong resemblance to other well-documented Archaean clastic sediments, and are consistent with a provenance consisting of ultramafic, mafic and felsic igneous rocks. Two schists, identified as metasomatized mafic igneous rocks from petrographic and field evidence, show distinct compositional differences to the metasediments.Major element systematics document incipient-to-moderate source weathering in the majority of metasediments, while signs of secondary K-addition are rare. Detailed inspection of Eu/Eu*, Fe2O3 and CIW (chemical index of weathering) relationships reveals that elevated iron contents (when compared to averages for continental crust) and strong relative enrichment in Eu may be due to precipitation of marine Fe-oxyhydroxides during deposition or diagenesis on the seafloor.Some of the IGB metasediments have yielded anomalous 142Nd and 182W isotopic compositions that were respectively interpreted in terms of early mantle differentiation processes and the presence of a meteorite component. Alternatively, W and possibly Nd isotopes could have been affected by thermal neutron capture on the Hadean surface. The latter process was tested in this study by analysis of Sm isotope compositions, which serve as an effective monitor for neutron capture effects. As no anomalous variation from terrestrial values was detected, we infer that isotope systematics (including 182W and 142Nd) of IGB metasediments were not affected by neutron capture, but reflect decay of radioactive parent isotopes. 相似文献
82.
Brian Whitehouse 《Estuarine, Coastal and Shelf Science》1985,20(4):393-402
The partitioning of six polynuclear aromatic hydrocarbons into aqueous solutions containing dissolved organic matter from various coastal environments was investigated by liquid chromatography. Specific hydrocarbon-organic matter interactions were observed. The greatest interactions occurred with the very low solubility hydrocarbons and with organic matter of terrestrial origin. Ultrafiltration experiments suggested that it was the relatively high (greater than approximately 500) molecular weight organic matter that was interacting with the hydrocarbons. 相似文献
83.
Several subcropping anorthosite–mangerite–charnockite–granite (AMCG) plutonic suites are aligned along E–W trending lineaments in the Lithuanian part of the East European Craton. The Rukai quartz monzodiorite from the Nemunas suite yields a zircon U–Pb intrusion age of 1447 ± 5 Ma, and the Geluva granite an age of 1445 ± 8 Ma, both obtained using secondary ion mass spectrometry. These rocks are 50 Myr younger than the 1.53–1.50 Ga Mazury AMCG complex in southern Lithuania and northern Poland. The Nemunas and Geluva AMCG rocks correlate in age with Bornholm granitoids in the Baltic Sea and Blekinge granites in southern Sweden, and are similarly aligned along E–W trending lineaments. This regional 1.45 Ga magmatic event across the Baltic Sea may be regarded as an inboard manifestation of the accretionary 1.50 Ga Danopolonian orogeny (cf. Pol. Mineral. Soc. Spec. Publ., 2005, 26: 18) farther west. 相似文献
84.
Pentti Hoelttae Victor Balagansky Adam A. Garde Satu Mertanen Petri Peltonen Alexander Slabunov Peter Sorjonen-Ward Martin Whitehouse 《《幕》》2008,31(1):13-19
The North Atlantic craton in southern West Greenland mainly consists of a tectonic collage of Mesoarchean continental crustal terranes, which were amalgamated at c. 2.7 Ga and are currently exposed at mid-crustal amphibolite to granulite facies levels. Tonalitic orthogneisses predominate, intercalated with slightly older tholeiitic to andesitic metavolcanic rocks and associated gabbro-anorthosite intrusive complexes. The North Atlantic craton also contains enclaves of Eoarchean, c. 3.86-3.6 Ga orthogneisses and supracrustal rocks including the Isua greenstone (or supracrustal) belt. This is the oldest known assemblage of rocks deposited at the surface of the Earth, comprising mafic pillow lavas, banded iron formations and metasedimentary schists with local disseminated graphite of possible biogenic origin. Eoarchean rocks have not been found in Kola and Karelia in Fennoscandia where most rocks are 2.9-2.7 Ga tonalitic-trondhjemitic-granodioritic orthogneisses with intercalated coeval greenstone belts and amphibolites. Mesoarchean 3.0-3.2 Ga rocks are found in the eastern and western parts of the Karelian province. Subduction-related rocks like the Iringora supra-subduction type ophiolite and basalt-andesite-dacite-rhyolite series volcanic rocks in many greenstone belts, as well as eclogites are found in the Archean of Fennoscandia. A clear distinction between Greenland and Fennoscandia is the abundance of 2.75-2.65 Ga igneous rocks in Fennoscandia which indicates that these two cratons had a separate evolution during the Neoarchean. 相似文献
85.
86.
The nature of scour development and scour protection at offshore windfarm foundations 总被引:1,自引:0,他引:1
Analysis and interpretation of monitoring data for the seabed bathymetry local to offshore windfarm foundations has shown how the scour develops in time and highlighted variations between sites with different seabed sediment characteristics, i.e. sands and clays. Results from European offshore windfarms have generated a unique dataset for comparison with previously published data. Where surficial sediment is underlain by a marine clay the scour (to date) has been limited, whilst those with unconstrained depths of sandy sediments show scour as deep as 1.38 times the monopile diameter. Scour protection has been installed at some sites for structural stability of the foundation or for cable protection. The flow interaction with the protection causes edge scour or secondary scour in the seabed around the protection. In some cases this scour is deeper than the unprotected case. The analysis has resulted in an improved evidence base for scour in the marine environment. 相似文献
87.
Janelidze N Jaiani E Lashkhi N Tskhvediani A Kokashvili T Gvarishvili T Jgenti D Mikashavidze E Diasamidze R Narodny S Obiso R Whitehouse CA Huq A Tediashvili M 《Marine pollution bulletin》2011,62(3):573-580
From 2006 to 2008, microbial water quality was monitored along the Georgian coast of the Black Sea. Temperature, pH, salinity, and dissolved oxygen were measured, along with a variety of aquatic microbial parameters, including heterotrophic plate count (HPC), total culturable bacterial count (TCBC), and chlorophyll a (Chl-a) concentration. Total and fecal coliforms and total enterococci counts were recorded as indicators of fecal pollution. Vibrio bacteria, and Escherichia coli- and Vibrio-specific bacteriophages were isolated and enumerated to determine their relationships to standard marine pollution indicators.Persistent microbial pollution was observed, particularly in the summer months, with a higher rate of contamination in estuaries. Microbial indicators generally showed seasonal dependence, suggesting that temperature may influence bacterial dynamics in this environment. No correlation was apparent between fecal pollution indicators and physical-chemical and aquatic microbial parameters, although there were significant relationships amongst the indicators themselves, as well as with the prevalence of Vibrio bacteria and phage. 相似文献
88.
Whitehouse M. J. Kusiak M. A. Wirth R. Ravindra Kumar G. R. 《Mineralogy and Petrology》2017,111(4):467-474
Mineralogy and Petrology - A transmission electron microscope (TEM) study of Paleoproterozoic zircon that has experienced ultra-high temperature (UHT) metamorphism at ca. 570 Ma in the... 相似文献
89.
90.
Y. Be’eri-Shlevin Y. Katzir J. Blichert-Toft I. C. Kleinhanns M. J. Whitehouse 《Contributions to Mineralogy and Petrology》2010,160(2):181-201
Multi-isotope study including whole-rock Nd–Sr, single zircon Hf, and SIMS δ18O analyses of zircons sheds light on magma sources in the northernmost Arabian–Nubian Shield (ANS) during ~820–570 Ma. Reconnaissance
initial Nd and Sr isotope data for the older rocks (~820–740 Ma) reaffirms previous estimates that early crustal evolution
in this part of the shield involved some crustal contamination by pre-ANS material. Prominent isotope provinciality is displayed
by post-collisional calc-alkaline and alkaline igneous rocks of ~635–570 Ma across a NW-SE transect across basement of the
Sinai Peninsula (Egypt) and southern Israel. Silicic rocks of the NW-region are characterized by lower εNd(T)–εHf(T) and higher
Sri and δ18O compared with rocks of the SE-region, and the transition between the regions is gradual. Within each region isotope ratios
are independent of the extent of magma fractionation, and zircon cores and rims yield similar δ18O values. Comparison with southern segments of the ANS shows that the source for most ~635–570 Ma rocks can be modeled as
the isotopically aged lower-intermediate crust in the ANS core (SE-region) and its northern, more contaminated ANS margins
(NW-region). Nevertheless, Nd–Sr isotope enrichment of the lithospheric mantle is indicated by some basic magmas of the NW-region
displaying the most enriched Nd–Sr isotope compositions. Comparison of Nd and Hf depleted mantle model ages for rocks of the
SE-region may indicate that crustal formation events in the ANS geographical core took place at 1.1–1.2 Ga and were followed
by crustal differentiation starting at ~0.9 Ga. 相似文献