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51.
Akio Suzuki Eiji Ohtani Hidenori Terasaki Keisuke Nishida Hiromi Hayashi Tatsuya Sakamaki Yuki Shibazaki Takumi Kikegawa 《Physics and Chemistry of Minerals》2011,38(1):59-64
The viscosity of a silicate melt of composition NaAlSi2O6 was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880°C. We employed in situ falling sphere
viscometry using X-ray radiography. We found that the viscosity of the NaAlSi2O6 melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using
the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow
were calculated to be 3.7 ± 0.4 × 102 and 3.7 ± 0.5 × 102 kJ/mol at 2.2 and 2.9 GPa, respectively. 相似文献
52.
By using the Euler-Lagrangian method, we examine water movements within the layer of minimum oxygen concentration and estimate local oxygen consumption rates for 15 regions of the global ocean. To do this, a number of labeled particles (which represent water parcels) are deployed at the center of a grid with 15 depth levels and tracked backward in time for 50 years in a three-dimensional velocity field. We assume that a particle picks up oxygen when it encounters the point of maximum oxygen concentration along the 50 years segment of its path. We introduce a contribution rate from waters distributed throughout the global ocean to the oxygen concentration of a local layer under consideration. Water parcels which are assumed to pick up oxygen within the oxygen minimum layer of an oceanic region under consideration make a very small contribution to the overall oxygen concentration of this layer. In addition, these parcels move out of the layer and water parcels from the upper layers take their place. The averaged Lagrangian local oxygen consumption rate is 0.033 ml/l/yr for the depth of the oxygen minimum layer, 0.20 ml/l/yr at 100 m depth (euphotic layer), 0.043 ml/l/yr for layers from 150 m to 800 m depth and 0.012 ml/l/yr for deep layers from 800 m to 3000 m. The present Lagrangian numerical experiment produces a maximum difference between observed and calculated concentrations of oxygen and, therefore, a maximum oxygen consumption rate. Although the present method has an ambiguity as to how oxygen is picked up, we nevertheless were able to identify regions in which the water parcels pick up oxygen of maximum concentration. We found that the South Equatorial Current (SEC) transports oxygen of higher concentration to the middle latitude regions of both the North Atlantic and the North Pacific across the equator. 相似文献
53.
We have developed a rapid and accurate method for the determination of Mo, Sb and W in geological samples using isotope dilution inductively coupled plasma-mass spectrometry with a flow injection system (ID-FI-ICP-MS). The chemical procedure requires HF digestion of the sample with a Mo-Sb-W mixed spike, subsequent evaporation and dissolution of Mo, Sb and W from Mg and Ca fluorides with HF. Recovery yields of Mo, Sb and W in the extraction were > 94% for samples of peridotite, basalt and andesite composition, with the exception of W in samples of peridotite composition for which recovery was 81%. No matrix effects were observed in the determination of the isotope ratios of Mo, Sb and W in solutions prepared from peridotite, basalt and andesite samples down to a dilution factor of 100. Detection limits of Mo, Sb and W in silicate materials were at the several ng g−1 level. Analysis of the silicate reference materials PCC-1, DTS-1, BCR-1, BHVO-1, AGV-1 from the US Geological Survey and JP-1, JB-1, -2, -3, JA-1, -2, and -3 from the Geological Survey of Japan as well as the Smithsonian reference Allende powder yielded reliable Mo, Sb and W concentrations. The repeatability in the analysis of basalts and andesites was < 9%. This technique requires only 0.2 ml sample solution, and is therefore suitable for analyzing small and/or precious samples such as meteorites, mantle peridotites and their mineral separates. 相似文献
54.
We have developed a rapid and accurate method to determine Zr, Nb, Hf and Ta (denoted as HFSE) in geological samples by inductively coupled plasma-mass spectrometry fitted with a flow injection system (FI-ICP-MS). The method involves sample decomposition by HF followed by HF dissolution of HFSE coprecipitated with insoluble M and Ca fluoride residues formed during the initial HF attack. This HF solution was directly nebulized into an ICP mass spectrometer. An external calibration curve method and an isotope dilution method (ID) were applied for the determination of Nb and Ta, and of Zr and Hf, respectively. Recovery yields of HFSE were > 96% for peridotite, basalt and andesite compositions, apart from Zr and Hf for peridotite (> 85%). No matrix effects for either signal intensities of HFSE or isotope ratios of Zr and Hf were observed in basalt, andesite and peridotite solutions down to a dilution factor of 100. Detection limits in silicate rocks were 40, 2, 1 and 0.1 ng g-1 for Zr, Nb, Hf and Ta, respectively. This technique required only 0.1 ml of sample solution, and thus is suitable for analysing small and/or precious samples such as meteorites, mantle peridotites and their mineral separates. We also present newly determined data for the Zr, Nb, Hf and Ta concentrations in USGS silicate reference materials DTS-1, PCC-1, BCR-1, BHVO-1 and AGV-1, GSJ reference materials JB-1, -2, -3, JA-1, -2 and -3, and the Smithsonian reference Allende powder. 相似文献
55.
In the chemical evolution of the Galaxy, Type II supernovae (SNe II)have contributed to the early metal enrichment and later
Type Iasupernovae (SNe Ia) have contributed to the delayed enrichment of Fe.In principle, hypothetical pre-galactic population
III objects couldcause the earliest heavy element enrichment. Here we present our twonew findings. 1) The peculiar abundance
pattern among iron peakelements (Cr, Mn, Co, and Fe) in the very metal poor can be reproducedwith SN II nucleosynthesis yields
without invoking the contributionfrom Pop III objects. 2) The observed chemical evolution in the solarneighborhood is well
reproduced with the metallicity dependentoccurrence of SNe Ia, where SNe Ia do not occur if the iron abundanceof the progenitors
is as low as [Fe/H] ≲ -1. We make theprediction that the cosmic SN Ia rate drops at z ∼ 1-2 because ofthe low-iron abundance, which can be observed with the Next GenerationSpace Telescope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
56.
57.
Upper Mantle Velocity Structure Estimated From Ps-Converted Wave Beneath the North-Eastern Japan Arc 总被引:2,自引:0,他引:2
Toru Matsuzawa Norihito Umino Akira Hasegawa Akio Takagi 《Geophysical Journal International》1986,86(3):767-787
Summary. The upper boundary of the descending oceanic plate is located by using PS -waves (converted from P to S at the boundary) in the Tohoku District, the north-eastern part of Honshu, Japan. the observed PS-P time data are well explained by a two-layered oceanic plate model composed of a thin low-velocity upper layer whose thickness is less than 10 km and a thick high-velocity lower layer; the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle. the estimated location of the upper boundary is just above the upper seismic plane of the double-planed deep seismic zone. This result indicates that events in the upper seismic plane, at least in the depth range from 60 to 150 km, occur within the thin low-velocity layer on the surface of the oceanic plate. 相似文献
58.
Tsutomu Ota Katsura Kobayashi Takuya Kunihiro Eizo Nakamura 《Geochimica et cosmochimica acta》2008,72(14):3531-3541
Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in 11B relative to 10B (δ11B = −1.2 to +7.7) and 7Li relative to 6Li (δ7Li = −1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (δ11B = −16.6 to −2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle. 相似文献
59.
60.
We found that the suppression of signals for 88 Sr, 140 Ce and 238 U in rock solution caused by rock matrix in ICP-MS (matrix effects) was reduced at high power operation (1.7 kW) of the ICP. To make the signal suppression by the matrix negligible, minimum dilution factors (DF) of the rock solution for Sr, Ce and U were 600, 400 and 113 at 1.1, 1.4 and 1.7 kW, respectively. Based on these findings, a rapid and precise determination method for Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U using FI (flow injection)-ICP-MS was developed. The amount of the sample solution required for FI-ICP-MS was 0.2 ml, so that 1.8 mg sample was sufficient for analysis with a detection limit of several ng g-1 . Using this method, we determined the trace element concentrations in the USGS rock reference materials, DTS-1, PCC-1, BCR-1 and AGV-1, and the GSJ rock reference materials, JP-1, JB-1, -2, -3, JA-1, -2 and -3. The reproducibilities (RSD %) in replicate analyses (n=5) of BCR-1, AGV-1, JB-1, -2, -3, JA-1, -2, and -3 were < 6 %, and typically 2.5%. The difference between the average concentrations of this study for BCR-1 and those of the reference values were < 2%. Therefore, it was concluded that the method can give reliable data for trace elements in silicate rocks. 相似文献