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排序方式: 共有266条查询结果,搜索用时 15 毫秒
81.
Bruce R. Doe 《Geochimica et cosmochimica acta》1983,47(8):1341-1354
A new major frontier of geological research, which was initiated in the 1970's, involves predicting future geologic trends or events through study of the present and past, rather than trying to understand the past, often using what one knows about the present. Like most scientific frontiers, this one began from practical considerations—environmental concerns. The lack of formal recognition of this frontier results from fragmentation among many Federal agencies and highly focused mission-oriented programs (e.g., earthquake prediction, CO2, nuclear-energy safety, etc.). Most programs aim to predict only the next 50–100 years, but much longer periods of the past need to be studied to do this. Nuclear-waste disposal has sometimes been considered in terms of the next million years, a period of time permitting significant and broad geologic changes. Decreasing public interest in environmental concerns relegates many questions from the realm of applied research back to that of basic research. Most of these questions are so fascinating, however, that the frontier is still worth pursuing. Such questions include whether a phenomenon will or will not take place and the rates at which it can develop (e.g., how fast do rifts form, how fast can a caldera event begin, and how quickly can a glacial maximum arrive?). Common elements of all studies include the historic record, trends in the Quaternary, analogues in various periods of the geologic time scale, and allowance for phenomena never experienced before. Other examples of studies include the Cretaceous as a period of a climatic extreme, an especially interesting time period; establishing the amount of paleocloudiness, a particularly challenging and important research area; acid rain as a possible new phenomenon. Geochemistry has much to contribute to this frontier science. 相似文献
82.
Tanja Barth Sylvi Hiland Per Fotland Kjell Magne Askvik Bent Skaare Pedersen Anna Elisabet Borgund 《Organic Geochemistry》2004,35(11-12):1513
Twelve oil samples have been characterised by titration, FT-IR and chromatographic analysis to determine the differences between the organic acid composition of biodegraded and non-biodegraded oils. The biodegraded oils have higher total acid and total base contents, both by titration and extraction. The molecular weight ranges of the extracted acids are lowest in the biodegraded oils, and the equivalent weight calculations indicate a dominance of multi-functional molecules. Gel permeation chromatography gives a molecular weight range with most of the molecules between 300 and 500 g/mol. FT-IR shows that the extracted acids from biodegraded oils are more carboxylic and aliphatic while the non-degraded oils are more phenolic. Molecular analysis of the derivatised extracts give UCM envelopes for biodegraded oils, and no molecular identification. The results indicate that the acidic constituents in biodegraded oils are a product of the biodegradation, as the composition is very different from the non-biodegraded oils. 相似文献
83.
Early Holocene history of the Baltic Sea, as reflected in coastal sediments in Blekinge, southeastern Sweden 总被引:4,自引:0,他引:4
Bjrn E. Berglund Per Sandgren Lena Barnekow Gina Hannon Hui Jiang Gran Skog Shi-Yong Yu 《Quaternary International》2005,130(1):111
Integrated palaeoecological studies of two fiord sediment sequences in the province of Blekinge, SE Sweden, covering the time span 11,000–5000 cal BP, reveal the timing and the environment for the Ancylus Lake/Littorina Sea transition 9800–8500 cal BP. The first ingression of saline water into the Baltic Sea through the Danish Straits occurred earlier than formerly assumed. New evidence, particularly mineral magnetic and palaeobotanical analyses, demonstrate that on the general trend of the eustatically caused Littorina transgression several minor fluctuations of the water level can be identified between 8500 and 5000 cal years BP. A distinct regression phase around 8100 cal BP is correlated with the Greenland ice-core cold event dated to 8200 ice-core years BP. This is described as a regional climatic catastrophe for the Baltic Sea region. The coastal stratigraphy is compared with the offshore stratigraphy earlier studied. A tentative shore displacement curve for Early and Middle Holocene is presented. 相似文献
84.
Sune G. Nielsen Mark Rehkämper Per Andersson Peter W. Swarzenski Detlef Günther 《Geochimica et cosmochimica acta》2005,69(8):2007-2019
The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols.The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ε205Tl = −2.0 ± 0.3 (ε205Tl represents the deviation of the 205Tl/203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 104). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ±1.5 ε205Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ± 4 ng/kg and ε205Tl = −2.5 ± 1.0, respectively.In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study. 相似文献
85.
This study tests the hypothesis that Fourier-transform infrared spectroscopy (FTIRS) of lake sediments can be used to infer
past changes in tree-line position and total organic carbon (TOC) content of lake water. A training set of 100 lakes from
northern Sweden spanning a broad altitudinal and TOC gradient from 0.7 to 14.9 mg/l was used to assess whether vegetation
zones and TOC can be modelled from FTIR spectra of surface sediments (0–1 cm) using principal component analysis (PCA) and
partial least squares (PLS) regression. Preliminary results show that FTIRS of lake sediments can be used to reconstruct past
changes in tree line and the TOC content of lake water, which is hardly surprising since FTIRS registers the properties of
organic and minerogenic material derived from the water mass and the drainage area. The FTIRS model for TOC gives a root mean
squared error (RMSECV) of calibration of 1.4 mg/l (10% of the gradient) assessed by internal cross-validation (CV) yielding
an Rcv2 of 0.64. This should be compared with a near-infrared spectroscopy (NIRS) and diatom transfer function for TOC from the same
set of lakes, which have a Rcv2 of 0.61 and 0.31, and RMSECV of 1.6 and 2.3 mg/l, respectively. The FTIRS-TOC model was applied to a Holocene sediment core
from a tree-line lake and the results show similar trends as inferences from NIRS and pollen from the same core. Overall,
the results indicate that changes in FTIR spectra from lake sediments reflect differences in catchment vegetation and TOC,
and that FTIRS-models based on surface-sediment samples can be applied to sediment cores for retrospective analysis. 相似文献
86.
Per H. Nielsen Thomas H. Christensen Hans-Jørgen Albrechtsen Robert W. Gillham 《Ground Water Monitoring & Remediation》1996,16(1):130-140
An in situ microcosm (ISM) consists of a stainless steel cylinder isolating about 2 L of the aquifer and is equipped with valves allowing for loading and sampling from the ground surface. During the last five years, this technique has been used frequently to study the degradation of organic chemicals in polluted and pristine aquifers representing different redox environments. The ISM technique has great potential for providing field-relevant degradation potentials and rate constants, but care must be taken in using the equipment and interpreting the results. This paper provides details concerning the installation and operation of an ISM and presents experiences concerning data interpretation and monitoring of redox conditions. 相似文献
87.
David W. Dyrssen Per O. J. Hall Conny Haraldsson Melissa Chierici Jens M. Skei H. Göte östlund 《Aquatic Geochemistry》1996,2(2):111-129
Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.502 + H2S S(colloidal) + H2O. The elemental sulfur, being stabilized with HS–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10–6 m2 s–1 which lies in the range of values given by Fröyland. Finally, the 14C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren. 相似文献
88.
Per Nysten 《Mineralium Deposita》1986,21(2):116-120
The mineralogy of gold from a volcanogenic sulfide deposit in northern Sweden (Långsele) was studied. The enrichment of gold and silver in massive ore occurs associated with an intrusive metadolerite vein which can be traced across the ore. The emplacement of this vein mobilized the precious metals together with galena and Pb-Sb sulfosalts into fractures and low pressure zones. A high mercury content at L»ngsele (average 250 ppm) has influenced the gold mineralogy. Thus, gold occurs as Au-Ag amalgam, native gold and rarely as aurostibite (AuSb2). The results of microprobe analyses of amalgam cluster around Au0.45Ag0.45Hg0.10. The composition of ternary amalgam is discussed in connection with the synthetic Au-Ag-Hg system. Furthermore, native gold was found myrmekitically integrown with stibnite which has been interpreted as a breakdown product of aurostibite at low temperature. 相似文献
89.
Intrinsic biodegradation of toluene coupled with the microbial reduction of ferric iron (Fe(III)) as the terminal electron acceptor was studied by using laboratory column experiments under continuous flow conditions. Columns were packed with contaminated aquifer sediment and N2-purged groundwater taken from the western part of the Gardermoen aquifer. The columns were operated anaerobically at 8 °C (in-situ temperature). Chloride was initially used to characterize flow properties of the columns. Intrinsic biodegradation of toluene, including abiotic loss and biological loss, was estimated by comparing breakthrough curves of toluene for live columns and sterilized control columns based on mass balance in steady-state conditions. The column experiments were run at two different flow velocities. The estimated average intrinsic rate was -0.73 and -0.53 mM day-1 for pore-water velocities of 1.75 and 2.68 cm h-1, respectively, corresponding to -0.27 and -0.22 mM day-1 in biological loss rate. The results indicate that intrinsic biodegradation of toluene could be used as an efficient remediation approach for contaminated groundwater at the Gardermoen fire-fighting training site. 相似文献
90.