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西南低涡是对流层下层的中尺度扰动。本文在零级近似条件下,采用p坐标系的基本方程组,在边界层内设计两层模式。通过一定的简化方程组后,得到:当Z≤1/2[kL~2/(μ~2Knu~*)] 时,摩擦效应具有二重性,一方面使扰动减弱;另一方面使扰动增强,而前者的影响略大于后者,最终使扰动消失。频率随高度Z的降低而增加。当Z>1/2[kL~2/(μ~2Knμ~*)]时,摩擦作用甚微,几乎可以忽略不计。频率虽然有两个值,但随高度Z的增加,他们趋于一个常值。 相似文献
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The cumulative probability distributions for stream order, stream length, contributing area, and energy dissipation per unit length of channel are derived, for an ordered drainage system, from Horton's laws of network composition. It is shown how these distributions can be related to the fractal nature of single rivers and river networks. Finally, it is shown that the structure proposed here for these probability distributions is able to fit the observed frequency distributions, and their deviations from straight lines in a log-log plot. 相似文献
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C. La Dous 《Astrophysics and Space Science》1987,130(1-2):337-340
Spectra of accretion disks in dwarf novae and some novalike stars have been computed. Many simplifications to the general model of the nature of a cataclysmic variable are needed to make the system numerically tractable. The necessity, justification, and implications of such simplifications are discussed together with the influences of some system parameters on the disk radiation.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
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Åke Fagereng Chris Harris Mandy La Grange Gary Stevens 《Contributions to Mineralogy and Petrology》2008,155(1):63-78
The Vredefort dome in the Kaapvaal Craton was formed as a result of the impact of a large meteorite at 2.02 Ga. The central
core of Archaean granitic basement rocks is surrounded by a collar of uplifted and overturned strata of the Witwatersrand
Supergroup, exposing a substantial depth section of the Archaean crust. Orthogneisses of the core show little variation in
whole-rock δ
18O value, with the majority being between 8 and 10‰, with a mean of 9.2‰ (n = 35). Quartz and feldspar have per mil differences that are consistent with O-isotope equilibrium at high temperatures,
suggesting minimal interaction with fluids during subsequent cooling. These data refute previous suggestions that the Outer
Granite Gneiss (OGG) and Inlandsee Leucogranofels (ILG) of the core represent middle and lower crust, respectively. Granulite-facies
greenstone remnants from the ILG have δ
18O values that are on average 1.5‰ higher than the ILG host rocks and are unlikely, therefore, to represent the residuum from
the partial melting event that formed the host rock. Witwatersrand Supergroup sedimentary rocks of the collar, which were
metamorphosed at greenschist-to amphibolite-facies conditions, generally have lower δ
18O values than the core rocks with a mean value for metapelites of 7.7‰ (n = 45). Overall, through an ∼20 km thick section of crust, there is a general increase in whole-rock δ
18O value with increasing depth. This is the reverse of what is normal in the crust, largely because the collar rocks have δ
18O values that are unusually low in comparison with metamorphosed sedimentary rocks worldwide. The collar rocks have δD values ranging from −35 to −115‰ (average −62‰, n = 29), which are consistent with interaction with water of meteoric origin, having a δD of about −25 to −45‰. We suggest that fluid movement through the collar rocks was enhanced by impact-induced secondary permeability
in the dome structure.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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The Newtonian viscosity of synthetic rhyolitic liquids with 0.15-5.24 wt% dissolved water was determined in the interval between 580 and 1640 °C and pressures of 1 atm and 5-25 kbar. Measurements were performed by combining static and accelerated (up to 1000g) falling sphere experiments on water-bearing samples, with high temperature concentric cylinder experiments on 0.15 wt% H2O melts. These methods allowed viscosity determinations between 102 and 107 Pa s, and cover the complete range of naturally occurring magmatic temperatures, pressures, and H2O-contents for rhyolites.Our viscosity data, combined with those from previous studies, were modeled by an expression based on the empirical Vogel-Fulcher-Tammann equation, which describes viscosities and derivative properties (glass transition temperature Tg, fragility m, and activation volume of viscous flow Va) of silicic liquids as a function of P-T-X(H2O). The fitted expressions do not account for composition-dependent parameters other than X(H2O) and reproduce the entire viscosity database for silicic liquids to within 3.0% average relative error on log η (i.e. std. error of estimate of 0.26 log units).The results yield the expected strong decrease of viscosity with temperature and water content, but show variable pressure dependencies. Viscosity results to be strongly affected by pressure at low pressures; an effect amplified at low temperatures and water contents. Fragility, as a measure for the deviation from Arrhenian behavior, decreases with H2O-content but is insensitive to pressure. Activation volumes are always largely negative (e.g., less than −10 cm3/mol) and increase strongly with H2O-content. Variations in melt structure that may account for the observed property variations are discussed. 相似文献
8.
Abstract. During the austral summer 1997–98, within the framework of the activities of the Climatic Long-term Interaction for the Massbalance in Antarctica (CLIMA) Project of the Italian National Program for Antarctic Research (PNRA) in the Ross Sea, measurements were conducted to focus on the role of dissolved iron, copper and manganese as micronutrients, and on their distribution in suspended particulate matter in different water masses. Sampling was carried out in two selected shelf areas, both important for formation and mixing processes of the water bodies.
Metal data were evaluated together with physical measurements and classical chemical parameters such as oxygen and nutrients.
In both the studied areas, the distribution of dissolved metals along the waste column confirmed their micronutrient behaviour, showing depletion where phytoplanktonic activities occurred.
The trend of particulate metals underlined the scavenging phenomena along the water column and presented an interesting correlation at intermediate depths with the amount and origin of suspended matter. 相似文献
Metal data were evaluated together with physical measurements and classical chemical parameters such as oxygen and nutrients.
In both the studied areas, the distribution of dissolved metals along the waste column confirmed their micronutrient behaviour, showing depletion where phytoplanktonic activities occurred.
The trend of particulate metals underlined the scavenging phenomena along the water column and presented an interesting correlation at intermediate depths with the amount and origin of suspended matter. 相似文献
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Kastens Kim Bonatti Enrico Caress David Carrara Gabriela Dauteuil Olivier Frueh-Green Gretchen Ligi Marco Tartarotti Paola 《Marine Geophysical Researches》1998,20(6):533-556
Transverse ridges are elongate reliefs running parallel and adjacent to transform/fracture zones offsetting mid-ocean ridges. A major transverse ridge runs adjacent to the Vema transform (Central Atlantic), that offsets the Mid-Atlantic Ridge by 320 km. Multibeam morphobathymetric coverage of the entire Vema Transverse ridge shows it is an elongated (300 km), narrow (<30 km at the base) relief that constitutes a topographic anomaly rising up to 4 km above the predicted thermal contraction level. Morphology and lithology suggest that the Vema Transverse ridge is an uplifted sliver of oceanic lithosphere. Topographic and lithological asymmetry indicate that the transverse ridge was formed by flexure of a lithospheric sliver, uncoupled on its northern side by the transform fault. The transverse ridge can be subdivided in segments bound by topographic discontinuities that are probably fault-controlled, suggesting some differential uplift and/or tilting of the different segments. Two of the segments are capped by shallow water carbonate platforms, that formed about 3–4 m.y. ago, at which time the crust of the transverse ridge was close to sea level. Sampling by submersible and dredging indicates that a relatively undisturbed section of oceanic lithosphere is exposed on the northern slope of the transverse ridge. Preliminary studies of mantle-derived ultramafic rocks from this section suggest temporal variations in mantle composition. An inactive fracture zone scarp (Lema fracture zone) was mapped south of the Vema Transverse ridge. Based on morphology, a fossil RTI was identified about 80 km west of the presently active RTI, suggesting that a ridge jump might have occurred about 2.2 m.a. Most probable causes for the formation of the Vema Transverse ridge are vertical motions of lithospheric slivers due to small changes in the direction of spreading of the plates bordering the Vema Fracture Zone. 相似文献