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61.
Laura Gaggero Laura Buzzi Ivan Haydoutov Luciano Cortesogno 《International Journal of Earth Sciences》2009,98(8):1853-1877
Eclogitic rocks were sampled from two zones in the basement of the Sredna Gora terrane (central western Bulgaria): (1) partially
retrogressed eclogites and amphibolites embedded in sillimanite-bearing garnet-micaschists with kyanite relics and migmatites
and (2) banded amphibolites associated with muscovite-bearing metagranites within two-mica paragneisses. Rutile relics and
oligoclase + green hornblende + epidote ± biotite pseudomorphs after garnet suggest an eclogite facies event. A tholeiitic,
transitional affinity was determined for the protoliths, suggesting a continental rift environment, consistent with several
eclogite-bearing complexes in the eastern segments of the Variscan belt that arose from the Cambro-Ordovician Gondwana break-up.
Decreasing pressure after the eclogite overprint was demonstrated by (a) diopside-albite symplectite, and (b) plagioclase
+ red–brown to green amphibole kelyphite. The early static re-equilibration, dated to 398 ± 5.2 Ma by 40Ar–39Ar technique, was followed by an amphibolite facies foliation, which was pervasive in amphibolites, gneisses and micaschists,
and poorly developed in eclogites. The lithospheric PT paths corresponding to higher and lower metamorphic gradients reflect
the juxtaposition of crustal and lithospheric mantle units, respectively. In the build-up of the basement of the Balkan orogen,
the physical properties of the lithological complexes might have influenced the collisional pattern of involved microplates. 相似文献
62.
Ian Lewis Michael Balogh Roberto De Propris Warrick Couch Richard Bower Alison Offer Joss Bland-Hawthorn Ivan K. Baldry Carlton Baugh Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Nicholas Cross Gavin Dalton Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,334(3):673-683
63.
Very Long Baseline Interferometry (VLBI) is one of the new techniques which will probably dominate geodesy and geophysics
in the near future. Its main advantage lies in the fact that it brings the accuracy of direction measurements to a level previously
possible only for range measurements. This closes the gap between powerful range determination techniques such as laser ranging
and the much less accurate determination of directions through photographic tracking of artificial earth satellites.
The technique is geometric in the sense that the relevant observations are independent of the gravity field of the earth.
However, the “orbits” of the observed extragalactic radio sources with respect to an earth-fixed system are dominated and
perturbed by the rotation of the earth with respect to inertial frame. This allows the determination of polar motion, precession-nutation
and length-of-the-day variations, and the technique becomes also “dynamic” in this respect.
The capability of determining the geometry of a network of stations within a short time interval and with a centimeter level
accuracy also allows the study of the variation of network geometry with time caused by earth tides and other periodic or
secular station drifts.
The main objective of the present work is the exploration of the capabilities of VLBI for the recovery of earth rotation and
network geometry parameters. For this purpose, a number of characteristic experimental designs based on present and candidate
for the near future station locations is chosen. The results from the analysis of simulated observations for each particular
design are presented in the paper.
Presented at IAG International Symposium on “Optimization of Design and Computation of Control Networks”, Sopron, Hungary,
4–10 July 1977. 相似文献
64.
Ivan Cupal 《Studia Geophysica et Geodaetica》1970,14(1):51-66
Zusammenfassung Den Hauptgegenstand des Artikels bildet die Auswahl von Geschwindigkeiten für ein kinematisches Modell eines hydromagnetischen
Dynamos. Die Ergebnisse der theoretischen Analyse betreffend die M?glichkeit der Entwicklung des magnetischen Feldes werden
durch die Angaben über die Oberfl?chenstr?mung an der Grenze zwischen dem Erdkern und dem Mantel erg?rzt, die man aus der
beobachteten sekul?ren ?nderung des magnetischen Feldes der Erde erwcrben hat. Das dreidimensionale Geschwindigkeitsfeld wurde
in der Weise gew?hlt, damit die notwendige Bedingung der Entwicklung, d.i. das Nichtverschwinden des Braginskischen Entwicklungskoeffizienten,
erfüllt werde und damit der Charakter von Str?mung auf der Kernoberfl?che den aus der sekul?ren ?nderung gewonnenen Angaben
entspreche. Eine m?glichen Form des dreidimensionalen Geschwindigkeitsfeldes wird im Modell des hydromagnetischen Dynamos
angewendet, das durch ein System von Integralgleichungen dargestellt wird. Die vorausgesetzte numerische L?sung ist nicht
durchgeführt.
Address: Boční II, Praha 4-Spořilov. 相似文献
Address: Boční II, Praha 4-Spořilov. 相似文献
65.
Laurence Le Callonnec Alain Person Maurice Renard René Létolle Nathalie Nebout Leila Ben Khelifa Ivan Rubanov 《Comptes Rendus Geoscience》2005,337(12):1035-1044
The withdrawal of the Aral Sea tributaries (Amu and Syr Daria) for cultures has led to significant falls of its level and an important increase in its salinity. During the Holocene, a succession of low and high water inputs occurred. Silty deposits correspond to the high levels and carbonates to the low levels. This study makes a distinction between the Syr Daria and the Amu Daria water inputs during low-level periods by using mineralogical and chemical compositions of the carbonates deposits. Waters from the Syr Daria are more sulphatic and have a low iron content in comparison with that of the Amu Daria. The Syr Daria was the major tributary around 7500, 4956 and 970 yr?BP, whereas around 6200 and 3610 yr?BP, inflow also from the Amu Daria is observed. To cite this article: L. Le Callonnec et al., C. R. Geoscience 337 (2005). 相似文献
66.
The long-wave outgoing radiation, effective cloudiness equal to the product of the total cloud amount by their optical density,
and the sea-surface temperature determined from the satellites are used to determine the annual course of the components of
external heat balance on the sea surface whose climatic anomalies, parallel with the meridional heat and water transfer in
the ocean-atmosphere system, specify the intraannual and interannual large-scale variations of weather in different regions
of the Earth. The development of these studies is connected with the progress of satellite hydrophysics because the data obtained
from the space become sufficiently exact, regular, and global. The increase in the existing data array on the external heat
balance of the oceans from ∼15–20 to 100 yr and more would promote the solution of the problem of oscillations of Earth's
climate. We present examples of coordinated numerical analysis of the heat balance of the upper (0–100 m ) layer of the Black
Sea performed on the basis of the shipborne and satellite data.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 59–75, November–December, 2007. 相似文献
67.
正1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom sediments of the lakes contain detailed geochemical information on 相似文献
68.
3C454.3是近几年引起广泛注意的一个强活动射电类星体,它有毫角秒尺度的核——喷流结构,其核在1981年的一次流量密度大爆发之后,显示出“超光速增亮”现象,在6厘米波长,用包括欧洲、美国及南非的9个射电望远镜,于1983年10月对3C454.3进行了甚长基线干涉网观测。观测结果除了证实其核——喷流结构,显示了从毫角秒到角秒尺度上该类星体结构的系统弯曲外,还清楚地揭示了“超光速增亮”所预期的,在1981年8月到1983年1月期间,核的超光速膨胀现象。 相似文献
69.
Nenad Marić Sanja Mrazovac Kurilić Ivan Matić Stanko Sorajić Jelena Zarić 《Environmental Earth Sciences》2014,72(2):525-534
This paper provides insight into the quality of groundwater used for public water supply on the territory of Kikinda municipality (Vojvodina, Serbia) and main processes which control it. The following parameters were measured: color, turbidity, pH, KMnO4 consumption, TDS, EC, NH4 +, Cl?, NO2 ?, NO3 ?, Fe, Mn, total hardness, Ca2+, Mg2+, SO4 2+, HCO3 ?, K+, Na+, As. The correlations and ratios among parameters that define the chemical composition were determined aiming to identify main processes that control the formation of the chemical composition of the analyzed waters. Groundwater from 11 analyzed sources is Na–HCO3 type. Intense color and elevated organic matter content of these waters originate from humic substances. The importance of organic matter decay is assumed by positive correlation between organic matter content and TDS, HCO3 content. There is no evidence that groundwater chemistry is determined by the depth of captured aquifer interval. The main processes that control the chemistry of all analyzed water are cation exchange and feldspar weathering. 相似文献
70.
Jennifer Hauxwell James McClelland Peter J. Behr Ivan Valiela 《Estuaries and Coasts》1998,21(2):347-360
Macroalgal biomass and competitive interactions among primary producers in coastal ecosystems may be controlled by bottom-up processes such as nutrient supply and top-down processes such as grazing, as well as other environmental factors. To determine the relative importance of bottom-up and top-down processes under different nutrient loading conditions, we estimated potential amphipod and isopod grazer impact on a dominant macroalgal species in three estuaries in Waquoit Bay, Cape Cod, Massachusetts, that are subject to different nitrogen loading rates. We calculated growth increases and grazing losses in each estuary based on monthly benthic survey data of macrophyte biomass and herbivore abundance, field grazing rates of amphipods (Microdeutopus gryllotalpa andCymadusa compta) and an isopod (Idotea baltica) on the preferred and most abundant macroalga (Cladophora vagabunda) and laboratory grazing rates for the remaining species, and in situ macroalgal growth rates. As nitrogen loading rates increased, macroalgal biomass increased (3×), eelgrass (Zostera marina) was lost, and herbivore abundance decreased (1/4×). Grazing rates increased with relative size of grazer (I. baltica > C. compta > M. gryllotalpa) and, for two of the three species investigated, were faster on algae from the high-nitrogen estuary in comparison to the low-nitrogen estuary, paralleting the increased macroalgal tissue percent nitrogen with nitrogen load. Macroalgal growth rates increased (2×) with increasing nitrogen loading rate. The comparison between estimated growth increases versus losses ofC. vagabunda biomass to grazing suggested first, that grazers could lower macroalgal biomass in midsummer, but only in estuaries subject to lower nitrogen loads. Second, the impact of grazing decreased as nitrogen loading rate increased as a result of the increased macroalgal growth rates and biomass, plus the diminished abundance of grazers. This study suggests the relative impact of top-down and bottom-up controls on primary producers varies depending on rate of nitrogen loading, and specifically, that the impact of herbivory on macroalgal biomass decreases with increasing nitrogen load to estuaries. 相似文献