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121.
To distinguish the manner of spread of upwelling effects in the Cook Strait/Taranaki Bight (New Zealand) region, nitrogen uptake and the distribution of nutrients and chlorophyll a are described. NO3 concentrations were closely linked to upwelled water, but this was distributed irregularly and not necessarily with the upwelling focus. NH4, SRP, and chlorophyll a showed varying degrees of association with recycling processes, but linear correlations were not present. NO3 uptake was strongly inhibited by ambient NH4, but not completely. There was no evidence of either N or P limitation of total planktonic biomass, and there was indirect evidence from C/N uptake and cellular ratios that a high growth rate prevailed. N uptake increased with irradiance (= decreasing depth) similar to photosynthesis, but without high light inhibition, and could be related to light by a simple equation. The irregularity of distribution of features suggests that future modelling of the phytoplankton biomass in the region could benefit from analysis of event occurrence rather than of evenly progressive changes. 相似文献
122.
In the last 50 years, there have been many incidences of failure of gravity quay walls. These failures are often associated with significant deformation of liquefiable soil deposits. Gravity quay wall failures have stimulated great progress in the development of deformation-based design methods for geotechnical structures. In this paper, the effective-stress analysis method has been used in conjunction with a generalised elasto-plasticity constitutive model implemented into a finite element procedure. Various monotonic and cyclic triaxial paths are simulated in order to demonstrate the capabilities of the constitutive model. The FEM is validated by back analysis of a typical Port Island PC1 caisson type quay wall, which was damaged during the 1995 Hyogoken-Nanbu earthquake. The numerical results are compared with the observed data obtained consisting of seaward displacement, settlement and tilting. In addition, both the influence of permeability, on the generation of pore water pressure and the influence of the relative density of the backfill and foundation layers, on the residual deformation of gravity quay walls are investigated. 相似文献
123.
M.A. Woods C.J. Wood I.P. Wilkinson G.K. Lott 《Proceedings of the Geologists' Association. Geologists' Association》2009,120(2-3):108-120
Re-examination of the classic exposures of the Eggardon Grit (topmost Upper Greensand Formation) at Eggardon Hill, Dorset shows that the upper part of this unit has a more complex stratigraphy than has been previously recognised. The Eggardon Grit Member, as described herein, is capped by a hardground and associated conglomerate, and is entirely of Late Albian age. The hardground is probably the lateral equivalent of the Small Cove Hardground, which marks the top of the Upper Greensand succession in southeast Devon. The conglomerate is overlain by a thin sandy limestone containing Early Cenomanian ammonites. This limestone is almost certainly the horizon of the Early Cenomanian ammonite fauna that has previously been attributed to the top of the Eggardon Grit. The limestone is regarded as a thin lateral equivalent of the Beer Head Limestone Formation (formerly Cenomanian Limestone) exposed on the southeast Devon coast. The fauna of the limestone at Eggardon suggests that it is probably the age equivalent to the two lowest subdivisions of the Beer Head Limestone in southeast Devon, with a remanié fauna of the Pounds Pool Sandy Limestone Member combined with indigenous macrofossils of the Hooken Nodular Limestone Member. The next highest subdivision of the Beer Head Limestone in southeast Devon (Little Beach Bioclastic Limestone Member), equates with the ammonite-rich phosphatic conglomerate of the ‘Chalk Basement Bed’, which caps the Beer Head Limestone at Eggardon, and which was previously regarded as the base of the Chalk Group on Eggardon Hill.Petrographic analysis of the Eggardon Grit shows that lithologically it should more correctly be described as a sandy limestone rather than sandstone. The original stratigraphical definition of the unit should probably be modified to exclude the softer, nodular calcareous sandstones that have traditionally been included in the lower part of the member.Without the apparently clear evidence of unbroken sedimentation across the Albian–Cenomanian boundary, suggested by the previous interpretation of the Eggardon succession, it is harder to argue for this being a prevalent feature of Upper Greensand stratigraphy in southwest England. Correlation of the Eggardon succession with successions in Dorset and southeast Devon reveals a widespread regional break in sedimentation at the Albian–Cenomanian boundary. The sand-rich facies above this unconformity represent the true base of the Chalk Group, rather than the ‘Chalk Basement Bed’ of previous interpretations.Selected elements of regionally important Upper Greensand ammonite faunas previously reported from Shapwick Quarry, near Lyme Regis, and Babcombe Copse, near Newton Abbot, are newly figured herein. 相似文献
124.
Historical changes in bioavailable Zn concentrations of the surface waters of Lake Geneva were assessed by analyzing the zinc content of fossil diatoms. The measured ratios of Zn to Si in the opal ((Zn/Si)opal) were consistent with both data obtained for cultured freshwater diatoms that were representative of lake Geneva and with field data. Reconstructed variations suggested that increased Zn uptake by phytoplankton occurred in the period from 1960–1980 resulting from an increased loading of Zn to the lake. Nonetheless, observed concentrations were sufficiently low that no adverse effects were expected on the pelagic community. The data presented here suggest that (Zn/Si)opal records may become a valuable tool to assess past changes in bioavailable Zn concentrations in freshwater systems. 相似文献
125.
Alan R. Duffy Richard A. Battye Rod D. Davies Adam Moss Peter N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2008,383(1):150-160
We discuss the possibility of performing a substantial spectroscopic galaxy redshift survey selected via the 21-cm emission from neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope (FAST) to be built in China. We consider issues related to the estimation of the source counts and optimizations of the survey, and discuss the constraints on cosmological models that such a survey could provide. We find that a survey taking around two years could detect ∼107 galaxies with an average redshift of ∼0.15 making the survey complementary to those already carried out at optical wavelengths. These conservative estimates have used the z = 0 H i mass function and have ignored the possibility of evolution. The results could be used to constrain Γ=Ωm h to 5 per cent and the spectral index, n s , to 7 per cent independent of cosmic microwave background data. If we also use simulated power spectra from the Planck satellite, we can constrain w to be within 5 per cent of −1. 相似文献
126.
L.?S.?CampbellEmail author W.?Compston K.?N.?Sircombe C.?C.?Wilkinson 《Contributions to Mineralogy and Petrology》2014,168(2):1041
Extremely U-depleted (<1 ppm) zircons from H8 banded ores in the East Orebody of the Bayan Obo REE–Nb–Fe deposit are presented, with mineral compositions, textures, 232Th–208Pb SHRIMP ages and petrological context. Cores of East Orebody zircon contain up to 7 wt% HfO2 and are zoned, depicting bipyramidal crystal forms. A distinct generation of patchy, epitaxial rim zircon, similarly depleted in U, is intergrown with rare earth ore minerals (bastnäsite, parisite, monazite). Overprinting aegirine textures indicate paragenetically late, reactive Na-rich fluids. Chondrite-normalized REE patterns without Eu anomalies match closely with those from the Mud Tank and Kovdor carbonatitic zircons. Increased HREE in rims ((Lu/Gd)N 43–112) relative to cores ((Lu/Gd)N 6–7.5) and the localized presence of xenotime are attributable to reactive, mineralizing fluid compositions enriched in Y, REE and P. Cathodoluminescence further reveals HREE fractionation in rims, evidenced by a narrow-band Er3+ emission at 405 nm. The extreme depletion of U in core and rim zircon is characteristic for this mineral deposit and is indicative of a persistent common source. U depletion is also a characteristic for zircons from carbonatitic or kimberlitic systems. 232Th–208Pb (SHRIMP II) geochronological data reveal the age of zircon cores as 1,325 ± 60 Ma and a rim-alteration event as 455.6 ± 28.27 Ma. The combined findings are consistent with a protolithic igneous origin for zircon cores, from a period of intrusive, alkaline–carbonatitic magmatism. Fluid processes responsible for the REE–Nb mineralizations affected zircon rim growth and degradation during the widely reported Caledonian events, providing a new example in a localized context of HREE enrichment processes. 相似文献
127.
Katya Dimitrova-Petrova Josie Geris Mark E. Wilkinson Allan Lilly Chris Soulsby 《水文研究》2020,34(4):972-990
Tracer studies have been key to unravelling catchment hydrological processes, yet most insights have been gained in environments with relatively low human impact. We investigated the spatial variability of stream isotopes and water ages to infer dominant flow paths in a ~10-km2 nested catchment in a disturbed, predominantly agricultural environment in Scotland. We collected long-term (>5 years) stable isotope data of precipitation, artificial drainage, and four streams with varying soil and land use types in their catchment areas. Using a gamma model, Mean Transit Times (MTTs) were then estimated in order to understand the spatial variability of controls on water ages. Despite contrasting catchment characteristics, we found that MTTs in the streams were generally very similar and short (<1 year). MTTs of water in artificial drains were even shorter, ranging between 1 to 10 months for a typical field drain and <0.5 to 1 month for a country road drain. At the catchment scale, lack of heterogeneity in the response could be explained by the extensive artificial surface and subsurface drainage, “short-circuiting” younger water to the streams during storms. Under such conditions, additional intense disturbance associated with highway construction during the study period had no major effect on the stream isotope dynamics. Supplementary short-term (~14 months) sampling of mobile soil water in dominant soil-land use units also revealed that agricultural practices (ploughing of poorly draining soils and soil compaction due to grazing on freely draining soils) resulted in subtle MTT variations in soil water in the upper profile. Overall, the isotope dynamics and inferred MTTs suggest that the evolution of stream water ages in such a complex human-influenced environment are largely related to near-surface soil processes and the dominant soil management practices. This has direct implications for understanding and managing flood risk and contaminant transport in such environments. 相似文献
128.
129.
I. A.Bond F.Abe R. J.Dodd J. B.Hearnshaw P. M.Kilmartin K.Masuda Y.Matsubara Y.Muraki S.Noda O. K. L.Petterson N. J.Rattenbury M.Reid To.Saito Y.Saito T.Sako J.Skuljan D. J.Sullivan T.Sumi S.Wilkinson R.Yamada T.Yanagisawa P. C. M.Yock 《Monthly notices of the Royal Astronomical Society》2002,331(2):L19-L23
Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002. 相似文献
130.