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381.
382.
Experiments have been conducted to investigate the effects of temperature on the interfacial surface area and on the rate of oxygen transfer from air bubbles dispersed in aqueous NaCl solutions. Tests were also conducted to estimate the effects of salt concentration on the size of the bubbles. In addition to NaCl solutions, seawater was used in some tests. The temperature effects were investigated at 5, 10, 15, 20, 25, and 30°C. The results showed a pronounced effect of the salt on the size of the bubbles, which first decreased sharply with increasing concentration, but showed no further drop when the concentration was increased beyond 0.6 M. Both in seawater and in the 0.6 M solution, the mass transfer rate, KLA, increased almost linearly when temperature was increased within the range from 5 to 25°C. The salt solution, as well as the seawater, showed an increase of KLA of 60–70% over that in pure water at the same temperatures. This effect was the result of increased surface area of bubbles because of decreased coalescence. The increase in surface area was strongly temperature dependent, especially between 15 and 20°C. Contrary to this behavior the surface area in pure water showed, practically, no temperature dependence. The results are explained and discussed on the basis of ion-water interactions. 相似文献
383.
The Arctic as a trigger for glacial terminations 总被引:1,自引:0,他引:1
We propose a hypothesis to explain the very abrupt terminations that end most of the glacial episodes. During the last glaciation,
the buildup and southerly expansion of large continental ice-sheets in the Northern Hemisphere and extensive cover of sea
ice in the N. Pacific and the N. Atlantic imposed a much more zonal climatic circulation system than exists today. We hypothesize
that this, in combination with the frigid (dry) polar air led to a significant decrease in freshwater runoff into the Arctic
Ocean. In addition the freshwater contribution of the fresher Pacific water was completely eliminated by the emergence of
the Bering Strait (sill depth 50 m). As the Arctic freshwater input was depleted, regions of the Arctic Ocean lost surface
stability and eventually overturned, bringing warmer deep water to the surface where it melted the overlying sea ice. This
upwelled water was quickly cooled and sank as newly formed deep water. For sustained overturn events, such as might have occurred
during the peak of very large glacial periods (i.e. the last glacial maximum), the voluminous deep water formed would eventually
overflow into the Nordic Seas and North Atlantic necessitating an equally voluminous rate of return flow of warmer surface
waters from the North Atlantic thus breaking down the Arctic's zonal isolation, melting the expansive NA sea ice cover and
initiating oceanic heating of the atmosphere over the ice-sheets bordering the NA. We suggest that the combined effect of
these overturn-induced events in concert with a Milankovitch warming cycle, was sufficient to drive the system to a termination.
We elaborate on this proposed sequence of events, using the model for the formation of the Weddell Sea polynya as proposed
by Martinson et al. (1981) and various, albeit sparse, data sets from the circum-Arctic region to apply and evaluate this
hypothesis to the problem of glacial terminations. 相似文献
384.
Christopher J. Conselice & John S. Gallagher III 《Monthly notices of the Royal Astronomical Society》1998,297(2):L34-L38
We present evidence for a new morphologically defined form of small-scale substructure in the Coma cluster, which we call galaxy aggregates. Aggregates are dominated by a central galaxy, which is on average 5 mag brighter than the smaller aggregate members, nearly all of which lie to one side of the central galaxy. We have found three such galaxy aggregates: two dominated by the S0 galaxies RB 55 and RB 60, and one by the starbursting SBb NGC 4858. RB 55 and 60 are both equidistant between the two dominant D galaxies NGC 4874 and 4889, while NGC 4858 is located near the large E0 galaxy NGC 4860. All three central galaxies have redshifts consistent with Coma cluster membership. We describe the spatial structures of these unique objects, and suggest several possible mechanisms to explain their origin. These include: chance superpositions from background galaxies, interactions between other galaxies and with the cluster gravitational potential, and ram pressure. We conclude that the most probable scenario of creation is an interaction with the cluster through its gravitational potential. 相似文献
385.
386.
Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA 总被引:1,自引:0,他引:1
John M. Ferry Sorena S. Sorensen Douglas Rumble III. 《Contributions to Mineralogy and Petrology》1998,130(3-4):358-378
The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and
amount of fluid flow during contact metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite
(Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically.
At the peak of metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward.
Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope
composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point
at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (<1615 mol/cm2). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm2. The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic
model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from
the fluid source along contacts between limestone and more siliceous rocks point to strong control of flow geometry at the
0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict
correctly fundamental aspects of contact metamorphic fluid flow.
Received: 27 January 1997 / Accepted: 2 October 1997 相似文献
387.
Summary A system of miniature radio interferometer terminals is proposed for the measurement of vector baselines with uncertainties
ranging from the millimeter to the centimeter level for baseline lengths ranging, respectively, from a few to a few hundred
kilometers. Each terminal would have no moving parts, could be packaged in a volume of less than 0.1 m3, and could operate unattended. These units would receive radio signals from low-power (<10 w) transmitters on Earth-orbiting
satellites. The baselines between units could be determined virtually instantaneously and monitored continuously as long as
at least four satellites were visible simultaneously. Acquisition of the satellite signals by each terminal would require
about one minute, but less than a second of signal integration, and the collection of only a few kilobits of data from two
receiving units would suffice to determine a baseline. Different baseline lengths, weather conditions, and desired accuracies
would, in general, dictate different integration times. 相似文献
388.
389.
The abundance and distribution of the California poppy (Eschscholtzia mexicana) correlates closely with the copper-rich outcrop of a small porphyry-type deposit in Arizona. Chemical factors are probably more important than physical factors in determining why this species is sometimes found as a copper indicator plant. 相似文献
390.