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831.
The radiative damping of trapped gravity waves in an optically thin atmosphere is studied for a stratified Boussinesq fluid. The character of the atmospheric eigenmodes depends on the distribution of the Brunt-Väisälä frequency N and the radiative relaxation time . The calculations for simple layer models show that if N is large over some finite fraction of the trapping region, then modes of long lifetime can exist. In order to suppress gravity waves entirely, it is necessary that N < 1 over the entire trapping region. Qualitative application of the results to the solar atmosphere leads to the conclusion that gravity wave eigenmodes of the solar atmosphere, although damped, are by no means eliminated by radiative effects. 相似文献
832.
833.
Alfred Grund 《Mineralogy and Petrology》1955,5(3):227-230
Zusammenfassung BeSO4 kristallisiert im BPO4-Typ, der sich von der Cristobalitstruktur herleitet. a=4·49 A, c=6·90 A, c/a=1·536. Die Atomabstände sind: S–O=1·50 A, Be–O=1·56 A. 相似文献
834.
835.
836.
Marianna?PastuszakEmail author Klaus?Nagel Alfred?Grelowski Volker?Mohrholz Mariusz?Zalewski 《Estuaries and Coasts》2003,26(5):1238-1254
The Pomeranian Bay is a coastal region fed by the Oder River, one of the seven largest Baltic rivers, whose waters flow through
a large and complex estuarine system before entering the bay. Nutrients (NO3
−, NO2
−, NH4
+, Ntot, PO4
3−, Ptot, DSi), chlorophylla concentrations, oxygen content, salinity, and temperature were measured in the Pomeranian Bay in nine seasonally distributed
cruises during 1993–1997. Strong spatial and temporal patterns were observed and they were governed by: the seasonally variable
riverine water-nutrient discharges, the seasonally variable uptake of nutrients and their cycling in the river estuary and
the Bay, the character of water exchange between the Pomeranian Bay and the Szczecin Lagoon, and the water flow patterns in
the Bay that are dominated by wind-driven circulation. Easterly winds resulted in water and nutrient transport along the German
coastline, while westerly winds confined the nutrient rich riverine waters to the Polish coast and transported them eastward
beyond the study area. Two water masses, coastal and open, characterized by different chemical and physical parameters and
chla content were found in the Bay independently of the season. The role of the Oder estuary in nutrient transformation, as well
as the role of temperature in transformation processes is stressed in the paper. The DIN:DIP:DSi ratio indicated that phosphorus
most probably played a limiting role in phytoplankton production in the Bay in spring, while nitrogen did the same in summer.
During the spring bloom, predominated by diatoms, the DSi:DIN ratio dropped to 0.1 in the coastal waters and to 0.6 in the
open bay waters, pointing to silicon limitation of diatom growth, similar to what is being observed in other Baltic regions. 相似文献
837.
Transport of terrestrial organic carbon to the oceans by rivers: re-estimating flux- and burial rates 总被引:5,自引:0,他引:5
This study re-estimates one important component in the global carbon cycle: the modern global fluviatile organic carbon discharge-
and burial rates. According to these results, approximately 430×1012 g of terrestrial organic carbon are transported to the ocean in modern times. This amount is higher than the latest estimates
but takes into account new data from Oceania not previously considered in global flux studies. However, only the minor amount
of 10% or approximately 43×1012 gC year–1 is most likely buried in marine sediments. This amount is similar to the burial of marine organic carbon in the coastal ocean
(55×1012 gC year–1). Adding both estimates gives approximately 100×1012 gC year–1, which is the value calculated by Berner (1982) for "terrestrial" deltaic-shelf sediments. However, the results in this study
suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but
a mixture of nearly equal amounts of marine and terrestrial organic carbon. The major part of the terrestrial organic carbon
that enters the ocean by rivers (approximately 400×1012 gC year–1) seems to be either (a) remineralised in the ocean, whereas the mechanism by which the terrestrial organic carbon is oxidised
in the ocean are unknown; or (b) is dispersed throughout the oceans and accumulates in pelagic sediments.
Received: 9 November 1998 / Accepted: 25 May 1999 相似文献
838.
The problem of a one-dimensional, nonlinear, circularly polarized wave in a collisionless plasma is solved for the case in which the group velocity of the localized wave is zero relative to the plasma frame.For an electron-positron plasma the ponderomotive potential is repulsive, and both small and large amplitude waves in the presence of reflected and transmitted particles is discussed.The inclusion of an external magnetic field such that the cyclotron frequency is smaller than the wave frequency does not alter qualitatively the results of the fieldless case, except for the fact that an electrostatic potential is generated.For the case in which the cyclotron frequency is larger than the wave frequency, the resulting potential is attractive, and it is shown that no localized waves can coexist with confined and transmitted particles. If, however, an ionic component is presnt in the electron-positron plasma, such as may be the case in pulsar magnetospheres, localized waves may again be possible. 相似文献
839.
840.
Synneusis of Kilauea Iki olivines 总被引:1,自引:1,他引:0
Kathleen R. Schwindinger Alfred T. Anderson Jr 《Contributions to Mineralogy and Petrology》1989,103(2):187-198
Olivine phenocrysts in the picritic scoria that erupted from Kilauea Iki in 1959 occur as glomeroporphyritic aggregates of 2–16 crystals. The compositions and three-dimensional textures of the olivines vary within an aggregate and within individual lapilli. The attachment of crystals from different environments indicates that these aggregates formed by synneusis — the swimming together of crystals. Most of the crystals are attached along faces with their a crystallographic axes parallel and their c axes either parallel or perpendicular, so that the structural mismatch and interfacial energy are minimized. Observed facial attachments are consistent with fluid dynamical interactions of crystals falling with their large {010} faces horizontal. The aggregates formed in a liquid-rich magma. Rough computations suggest that the minimum aggregation time could be on the order of minutes. Aggregation of very small crystals suggests that the yield strength was less than 3 dynes cm–2. The textures of the aggregates are similar to those of cumulate peridotites. 相似文献