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161.
Precipitation stable isotope variability and subcloud evaporation processes in a semi‐arid region
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The stable isotopic (2H/1H and 18O/16O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ 18O of precipitation was with local surface relative humidity. The reduced major axis precipitation weighted local meteoric water line was δ 2H = 7.20 δ 18O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ 2H ? 8 δ 18O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water. Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were 18O and 2H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean. The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd. 相似文献
162.
163.
Feldspar-bearing lherzolite xenoliths in alkali basalts from Hamar-Daban,southern Baikal region,Russia 总被引:4,自引:0,他引:4
D. A. Ionov Suzanne Y. O'Reilly Igor V. Ashchepkov 《Contributions to Mineralogy and Petrology》1995,122(1-2):174-190
Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range in southern Siberia provide
sampling of the mantle close to the axis of the Baikal rift. These anhydrous spinel lherzolites commonly have foliated fabrics
and spongy rims around clinopyroxene, and many contain accessory feldspar. The feldspar occurs in reaction zones adjacent
to spinel and orthopyroxene (where it appears to have been formed by the reaction: spl+opx+cpx+fluid →fs+ol) and less commonly
as thin, irregular veins. The feldspars have variable compositions but are generally alkali-rich; their K2O content ranges from 0.3 to 11.2% and is much higher than in plagioclase from orogenic lherzolites (usually <0.1% K2O). The temperature range for the Hamar-Daban xenolith suite (950–1010° C) is more restricted than for spinel peridotite xenoliths
from other occurrences in the Baikal area. The feldspar-bearing lherzolites yield equilibration temperatures similar to or
slightly lower than feldspar-free ones. The majority of the Hamar-Daban lherzolites are fertile and clinopyroxene-rich, as
for most other occurrences in the Baikal region. Trace element compositions of selected xenoliths and their clinopyroxenes
were determined by ICP-MS, INAA and proton microprobe. Feldspar-bearing xenoliths are enriched in alkalies indicating that
feldspar formation is associated with addition of material and is not simply due to isochemical phase changes. Most xenoliths
and their clinopyroxenes studied are depleted in light REE and have contents of Sr, Zr and Y common for fertile or moderately
depleted mantle peridotites. Few are moderately enriched in LREE, Sr, Th and U. Sr-Nd isotope compositions of clinopyroxenes
indicate long-term depletion in incompatible elements similar to unmetasomatised xenoliths from other occurrences south and
east of Lake Baikal. The formation of feldspar and of spongy aggregates after clinopyroxene, and the enrichment in alkalies
appear to be recent phenomena related to infiltration of an alkali-rich, H2O-poor fluid into spinel peridotites.
Received: 20 March 1995 / Accepted: 26 June 1995 相似文献
164.
Warren HP Bookbinder JA Forbes TG Golub L Hudson HS Reeves K Warshall A 《The Astrophysical journal》1999,527(2):L121-L124
The ability of the Transition Region and Coronal Explorer (TRACE) to image solar plasma over a wide range of temperatures (Te approximately 104-107 K) at high spatial resolution (0&farcs;5 pixels) makes it a unique instrument for observing solar flares. We present TRACE and Yohkoh observations of an M2.4 two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We observe impulsive footpoint brightenings that are followed by the formation of high-temperature plasma (Te greater, similar10 MK) in the corona. After an interval of about 1300 s, cooler loops (Te<2 MK) form below the hot plasma. Thus, the evolution of the event supports the qualitative aspects of the standard reconnection model of solar flares. The TRACE and Yohkoh data show that the bulk of the flare emission is at or below 10 MK. The TRACE data are also consistent with the Yohkoh observations of hotter plasma (Te approximately 15-20 MK) existing at the top of the arcade. The cooling time inferred from these observations is consistent with a hybrid cooling time based on thermal conduction and radiative cooling. 相似文献
165.
SummaryOptimizing the Control of Rock Failure in Servo-Controlled Laboratory Tests Recent studies of rock failure have been made with a closed loop servo-controlled testing machine. Feedback from the failing specimen is electronically compared with a pre-determined program and the hydraulic system is continuously and automatically adjusted to ensure that feedback and program are coincident. It is suggested that optimum control of rock failure in any laboratory test is achieved when the closed loop feedback represents the most sensitive indicator of failure. Any required experimental output can then be independently monitored. This method was applied to a variety of rock specimens loaded in uniaxial compression using lateral displacement as feedback. It was possible to control the failure of some rocks which had failed explosively in previous tests where the axial displacement had been programmed to increase monotonically.
With 5 Figures 相似文献
ZusammenfassungOptimale Aufzeichnung des Bruchablaufes von Gestein in servo-gesteuerten Laborversuchen Studien zum Bruch von Gesteinsproben wurden kürzlich mit einem elektronisch geregelten Belastungssystem vorgenommen. Bei diesem System werden Meßdaten der über die maximale Bruchverformung hinaus deformierten Probe mit einem vorgegebenen Verformungs-Programm elektronisch verglichen und das hydraulische Belastungs-System wird dementsprechend kontinuierlich geregelt.Ein optimaler Ablauf des Bruchvorganges wird gewährleistet, wenn das Regelsystem durch möglichst feinstufige Meßdaten der Bruchverformung gesteuert wird. Jede gewünschte zusätzliche physikalische Größe kann dann unabhängig davon gemessen werden.Die Meßmethode wurde bei einachsigen Belastungsversuchen von verschiedenen Gesteinsproben angewendet, wobei zur Steuerung des Regelsystems die gemessene Verformung normal zur Belastungsrichtung gewählt wurde. Dabei war es möglich, auch den Bruch solcher Gesteinsproben zu beherrschen, welche bei früheren Versuchen, bei denen der Vorgang aufgrund der Verformung in Belastungsrichtung mit stetigem Verlauf programmiert wurde, explosionsartig geborsten waren.
RésuméPour un meilleur contrôle de la rupture des roches dans les essais de laboratoire sur machines asservies Des études récentes sur la rupture des roches ont fait usage de machines d'essai asservies.La réponse de l'éprouvette en cours de rupture est comparée électroniquement à un programme fixé à l'avance, et le système hydraulique est ajusté continuellement et automatiquement pour faire coïncider la réponse avec le programme.On suggère que le meilleur contrôle sera obtenu, quel que soit l'essai, si le signal utilisé représente l'indicateur le plus sensible de la progression de la rupture. Toute autre grandeur physique qui est jugée nécessaire peut alors être enregistrée indépendamment.Cette méthode a été appliquée à la compression monoaxiale de diverses roches, en employant comme signal la déformation transversale. On a pu ainsi régulariser la rupture de certaines roches, qui était explosive dans des essais antérieurs où la déformation axiale augmentait suivant un programme monotone.(Dans cet article, la rupture est un processus, comportant notamment la naissance et le développement de fissures, qui ne peut être observé, avec les machines d'essai classiques, à cause de l'explosion due à une libération brutale de l'énergie de déformation emmaganisée dans la presse. Le contrôle de la rupture, au sens anglais, correspond à une régularisation de ce processus. Note de la Rédaction.)
With 5 Figures 相似文献
166.
K. B. Matthews A. MacDonald R. J. Aspinall G. Hudson A. N. R. Law E. Paterson 《Climatic change》1994,28(3):273-287
This paper discusses a GIS based implementation of a model for soil droughtiness assessment evaluating the impact of possible climate change. It focuses, in particular, on the development of a methodology for mapping Available Water Capacity. An assessment of the Soil Drought Susceptibility for Scotland in the year 2030 is made and illustrated with maps and derived statistics. 相似文献
167.
Chromian valleriite occurs as a replacement product of chrome spinel in the Nepean and Perseverance nickel-iron sulphide deposits of Western Australia. Compositions determined for chromian valleriites are variable due to intergrowth with spinel and to substitution of Fe and Ni for Cu. At Perseverance, valleriite, with minor admixed chrome spinel, has a composition expressed by the formula Fe1.18Cu0.81Ni0.01S2.00·2.03[Mg0.50Cr0.37Mn0.08Fe0.03Ti0.01Al0.01(OH)2.00]. Nepean valleriites are similarly intergrown with spinel, with the purest chromian valleriites varying in composition from a nickel-poor Fe1.21Cu0.78Ni0.01S2.00·1-46.[Mg0.43Cr0.18Mn0.05Fe0.30(OH)2] to Fe1.58Cu0.28Ni0.15S2.00·1.79[Mg0.51Cr0.30Fe0.16Ti0.03(OH)2]. Conversion of chrome spinel to valleriite is attributed to addition of Cu and S from the breakdown of chalcopyrite, addition of Mg from serpentinising olivine and limited addition of Ni from the breakdown of pentlandite to mackinawite. These processes are thought to occur as post-metamorphic hydrothermal reactions in nickel sulphide ores that have been subjected to high grade regional metamorphism. 相似文献
168.
Sbil Seitzinger Scott Nixon Michael E.Q. Pilson Suzanne Burke 《Geochimica et cosmochimica acta》1980,44(11):1853-1860
Methods were developed for determining rates of denitrification in coastal marine sediments by measuring the production of N2 from undisturbed cores incubated in gas-tight chambers. Denitrification rates at summer temperatures (23°C) in sediment cores from Narragansett Bay, Rhode Island, were about 50μmol N2m?2 hr?1. This nitrogen flux is equal to approximately one-half of the NH+4flux from the sediments at this temperature and is of the magnitude necessary to account for the anomalously low N/P and anomalously high O/N ratios often reported for benthic nutrient fluxes. The loss of fixed nitrogen as N2 during the benthic remineralization of organic matter, coupled with the importance of benthic remineralization processes in shallow coastal waters may help to explain why the availability of fixed nitrogen is a major factor limiting primary production in these areas. Narragansett Bay sediments are also a source of N2O, but the amount of nitrogen involved was only about 0.2 μmol m?2 hr?1 at 23°C. 相似文献
169.
Walter K. Conrad Suzanne M. Kay Robert W. Kay 《Journal of Volcanology and Geothermal Research》1983,18(1-4)
The complexity of igneous processes in the Aleutian calc-alkaline magma series can be inferred from study of xenolithic fragments. Composite xenoliths and cognate inclusions provide direct evidence for magma—magma and wall-rock—magma mixing processes. Using distributions of Cr in clinopyroxene, compositional endmembers involved in mixing are identified within the xenoliths. The basaltic mixing endmember is more mafic than calc-alkaline lavas in the arc. Magma mixing and wall-rock assimilation within calc-alkaline basaltic to andesitic magmas is identified in phenocrystic assemblages as well as in xenoliths, and appears to be a widespread phenomenon in Aleutian calc-alkaline magmas. 相似文献
170.