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991.
992.
993.
Hendrik Vogel Bernd Wagner Giovanni Zanchetta Roberto Sulpizio Peter Rosén 《Journal of Paleolimnology》2010,44(1):295-310
Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes
during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical
proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology
and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between
ca. 97.6 and 81.7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction
of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake.
Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus
and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic
matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods,
high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced
changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for
short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the
potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean. 相似文献
994.
Armand Hernández Santiago Giralt Roberto Bao Alberto Sáez Melanie J. Leng Philip A. Barker 《Journal of Paleolimnology》2010,44(2):413-429
The late glacial-Holocene transition from the Lago Chungará sedimentary record in northern Chilean Altiplano (18°S) is made up of laminated sediments composed of light-white and dark-green pluriannual couplets of diatomaceous ooze. Light-white sediment laminae accumulated during short-term extraordinary diatom blooms whereas dark-green sediment laminae represent the baseline limnological conditions during several years of deposition. Diatom oxygen isotope ratios (δ18Odiatom) from 40 consecutive dark-green laminae, ranging from 11,990 to 11,450 cal year BP, show that a series of decadal-to-centennial dry–wet oscillations occurred. Dry periods are marked by relatively high isotope values whereas wet episodes are indicated by lower values. This interpretation agrees with the reconstructions of terrigenous inputs and regional effective moisture availability carried out in the lake but there is a systematic temporal disagreement between them owing to the non-linear response of the lacustrine ecosystem to environmental forcings. Furthermore, the δ18Odiatom record tracks effective moisture changes at a centennial scale. Three major phases have been established (11,990–11,800, 11,800–11,550, and 11,550–11,450 cal year BP). Each phase is defined by an increasing isotope trend followed by a sudden depletion. In addition, several wet and dry events at a decadal scale are superimposed onto these major trends. Spectral analyses of the δ18Odiatom values suggest that cycles and events could have been triggered by both El Niño-Southern Oscillation (ENSO) and solar activity. Significant ENSO frequencies of 7–9 years and 15–17 years, and periodicities of the solar activity cycles such as 11 years (Schwabe), 23 years (Hale) and 35 years (Brückner) have been recognised in the oxygen isotope time series. Time–frequency analysis shows that although solar and ENSO forcing were present at the onset of the Holocene, they were more intense during the late glacial period. The early Holocene might have been mainly governed by La Niña-like conditions that correspond to wet conditions over the Andean Altiplano. 相似文献
995.
Roberto Oyarzun Paloma Cubas Pablo Higueras Javier Lillo Willians Llanos 《Environmental Geology》2009,58(4):761-777
The Rodalquilar mineral deposits (SE Spain) were formed in Miocene time in relation to caldera volcanic episodes and dome
emplacement phenomena. Two types of ore deposits are recognized: (1) the El Cinto epithermal, Au–As high sulphidation vein
and breccia type; and (2) peripheral low sulphidation epithermal Pb–Zn–Cu–(Au) veins. The first metallurgical plants for gold
extraction were set up in the 1920s and used amalgamation. Cyanide leaching began in the 1930s and the operations lasted until
the mid 1960s. The latter left a huge pile of ~900,000–1,250,000 m3 of abandoned As-rich tailings adjacent to the town of Rodalquilar. A frustrated initiative to reactivate the El Cinto mines
took place in the late 1980s and left a heap leaching pile of ~120,000 m3. Adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and
sediments, whereas mining and metallurgical operations considerably aggravated contamination. We present geochemical data
for soils, tailings and wild plant species. Compared to world and local baselines, both the tailings and soils of Rodalquilar
are highly enriched in As (mean concentrations of 950 and 180 μg g−1, respectively). Regarding plants, only the concentrations of As, Bi and Sb in Asparagus horridus, Launaea arborescens, Salsola genistoides, and Stipa tenacissima are above the local baselines. Bioaccumulation factors in these species are generally lower in the tailings, which may be
related to an exclusion strategy for metal tolerance. The statistical analysis of geochemical data from soils and plants allows
recognition of two well-differentiated clusters of elements (As–Bi–Sb–Se–Sn–Te and Cd–Cu–Hg–Pb–Zn), which ultimately reflect
the strong chemical influence of both El Cinto and peripheral deposits mineral assemblages. 相似文献
996.
997.
Giovanna T. Sapienza Marco Scambelluri Roberto Braga 《Contributions to Mineralogy and Petrology》2009,158(3):401-420
We document the presence of dolomite ± apatite in orogenic peridotites from the Ulten Zone (UZ, Italian Alps), the remnants
of a Variscan mantle wedge tectonically coupled with eclogitized continental crust. These dolomite peridotites are associated
with dominant carbonate-free amphibole peridotites, which formed in response to infiltration of aqueous subduction fluids
lost by the associated crustal rocks during high-pressure (HP) metamorphism and retrogression. Dolomite-free and dolomite-bearing
peridotites share the same metamorphic evolution, from garnet- (HP) to spinel-facies (low-pressure, LP) conditions. Dolomite
and the texturally coexisting phases display equilibrium redistribution of rare earth elements and of incompatible trace elements
during HP and LP metamorphism; clinopyroxene and amphiboles from carbonate-free and carbonate-bearing peridotites have quite
similar compositions. These features indicate that the UZ mantle rocks equilibrated with the same metasomatic agents: aqueous
CO2-bearing fluids enriched in incompatible elements released by the crust. The P–T crystallization conditions of the dolomite peridotites (outside the field of carbonatite melt + amphibole peridotite coexistence),
a lack of textures indicating quench of carbonic melts, a lack of increase in modal clinopyroxene by reaction with such melts
and the observed amphibole increase at the expense of clinopyroxene, all suggest that dolomite formation was assisted by aqueous
CO2-bearing fluids. A comparison of the trace element compositions of carbonates and amphiboles from the UZ peridotites and from
peridotites metasomatized by carbonatite and/or carbon-bearing silicate melts does not help to unambiguously discriminate
between the different agents (fluids or melts). The few observed differences (lower trace element contents in the fluid-related
dolomite) may ultimately depend on the solute content of the metasomatic agent (CO2-bearing fluid versus carbonatite melt). This study provides strong evidence that C–O–H subduction fluids can produce ‘carbonatite-like’
assemblages in mantle rocks, thus being effective C carriers from the slab to the mantle wedge at relatively low P–T. If transported beyond the carbonate and amphibole solidus by further subduction, dolomite-bearing garnet + amphibole peridotites
like the ones from Ulten can become sources of carbonatite and/or C-bearing silicate melts in the mantle wedge.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
In memory of Lauro Morten 1941–2006. 相似文献
998.
Guillermo F. Hägele † Ángeles I. Díaz ‡ Elena Terlevich § Roberto Terlevich ‡ Enrique Pérez-Montero ¶ Mónica V. Cardaci 《Monthly notices of the Royal Astronomical Society》2008,383(1):209-229
We present high signal-to-noise ratio spectrophotometric observations of seven luminous H ii galaxies. The observations have been made with the use of a double-arm spectrograph which provides spectra with a wide wavelength coverage, from 3400 to 10 400 Å free of second-order effects, of exactly the same region as that of a given galaxy. These observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionized gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects, errors of 1 per cent in t e ([O iii ]), 3 per cent in t e ([O ii ]) and 5 per cent in t e ([S iii ]) are achieved with a resulting accuracy of 7 per cent in total oxygen abundances, O/H.
The ionization structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other – the η and η' plots. The combination of both is shown to provide a means to test photoionization model sequences presently applied to derive elemental abundances in H ii galaxies. 相似文献
The ionization structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other – the η and η' plots. The combination of both is shown to provide a means to test photoionization model sequences presently applied to derive elemental abundances in H ii galaxies. 相似文献
999.
The intertidal copeopod Tigriopus japonicus, which is abundant and widely distributed along the coasts of Western Pacific, has been suggested to be a good marine ecotoxicity testing organism. In this study, a series of experiments were conducted to investigate the reproducibility and variability of copper (Cu) sensitivity of T. japonicus so as to evaluate its potential to serve as an appropriate test species. To understand the seasonal variation of Cu sensitivity, individuals of T. japonicus were collected from the field in summer and winter, and subjected to standard 96 h acute (static renewal) toxicity tests. 96 h-LC50 values of T. japonicus collected from the two seasons were marginally different (p = 0.05), with an overall coefficient of variation (CV) of 33%. Most importantly, our results indicated that chronic Cu sensitivity of T. japonicus was highly reproducible. The CVs of intrinsic rates of increase in the population of the control and Cu treatment (10 microg Cu l(-1)) groups were only 10-11% between 10 runs of a standardised complete life-cycle test. Moreover, different Cu(II) salts generally resulted in a similar 96 h-LC50 value while Cu(I) chloride was consistently slightly less toxic than Cu(II) salts. Given such a high reproducibility of toxic responses, it is advocated to use T. japonicus as a routine testing organism. 相似文献
1000.
Mara Monica Tiberti Stefano Lorito Roberto Basili Vanja Kastelic Alessio Piatanesi Gianluca Valensise 《Pure and Applied Geophysics》2008,165(11-12):2117-2142
We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact. We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wavefields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum water height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat. We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies. 相似文献