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551.
Elena Terlevich Angeles I. Díaz Roberto Terlevich 《Astrophysics and Space Science》1989,157(1-2):15-21
The IR Caii triplet at 8498, 8542, 8662 Å, relatively easy to observe and measure and free from atmospheric absorption bands, is a powerful tool for the study of the stellar populations in galaxies, provided that we can understand its behaviour with the stellar parameters: effective temperature, surface gravity and metal content. We present here the results of CCD spectroscopic observations for a sample of 86 stars covering a wide range in luminosity, effective temperature and metallicity (from subdwarfs to supergiants and –2.70[F3/H]0.43), in order to establish the dependence of the IR Caii triplet on stellar atmosphere parameters. We do not confirm previous results giving the main dependence on surface gravity. We find instead a bi-parametric dependence on metallicity and surface gravity, and no dependence on effective temperature. 相似文献
552.
Flooding mine tailings to limit the oxidation of sulfides provides a habitat for aquatic organisms, such as plants, plankton,
insects, and fish, which can uptake metals and, thus, threats for local ecosystems and influence the cycling of elements in
biogeocenosis. An aquatic ecosystem developed naturally in sulphide tailing ponds containing cyanidation wastes of the Salair
ore-refining plant (SORP), Russia, was studied. The objectives of this research were to: (i) reveal the level of contamination
of living organisms in the tailing ponds compared to a natural control site and (ii) calculate the weight of metals in aquatic
biomass to estimate the amount of metals transferring from the tailing ponds into the biogechemical cycle. The concentration
of Cu, Zn, Cd, and Pb in the sediments of the tailing ponds is significantly higher than from the control site. Concentrations
of Cu, Zn, Cd, and Pb in plant shoots were significantly higher than in the control and accumulated mainly in cell envelopes
and membranes. The concentration of Pb in fish liver and eggs were 41 and 7.5 times higher, respectively, than maximum allowable
concentrations.
The biomass distribution between producers and consumers of the tailing pond ecosystem is similar to those of natural pond
ecosystems. However, the weights of Cu, Zn, Cd, and Pb in all trophic levels per hectare of the tailing pond are orders of
magnitude higher than those for Lake Baikal. The largest portion of metal circulates within the ecosystem of the Dyukov Ravine
Pond with a maximum of 5 to 13% of this amount transferred into the surrounding environment through the food chains. 相似文献
553.
Giovanni Scicchitano Fabrizio Antonioli Elena Flavia Castagnino Berlinghieri Andrea Dutton Carmelo Monaco 《Quaternary Research》2008,70(1):26-39
Precise measurements of submerged archaeological markers in the Siracusa coast (Southeastern Sicily, Italy) provide new data on relative sea-level change during the late Holocene. Four submerged archaeological sites have been studied and investigated through direct observations. Two of them are Greek archaic in age (2.5–2.7 ka) and are now 0.98–1.48 m below sea level; the other two developed during the Bronze age (3.2–3.8 ka) and are now 1.03–1.97 m below sea level. These archaeological data have been integrated with information derived from a submerged speleothem collected in a cave located along the Siracusa coast at − 20 m depth. The positions of the archaeological markers have been measured with respect to present sea level, corrected for tide and pressure at the time of surveys. These data were compared with predicted sea-level rise curves for the Holocene using a glacio-hydro-isostatic model. The comparison with the curve for the southeastern Sicily coast yields a tectonic component of relative sea-level change related to regional uplift. Uplift rates between 0.3 and 0.8 mm/yr have been estimated. 相似文献
554.
The Tree Shelter site dates to the Early to Mid-Holocene (8000 to 4900 14C yr BP). Present conditions around the site are hyperarid, but charcoal remains indicate less severe aridity at the time of its occupation. The environment around the site then supported a rich wadi vegetation, which allowed hunting during the Epipaleolithic and herding during the Neolithic occupation. Although more favorable than today, the environmental conditions also displayed a desert character and seem to have limited the range of domestic herbivores introduced in the area. 相似文献
555.
Elena Ortu Odile Peyron Amandine Bordon Jacques Louis de Beaulieu Consolata Siniscalco Rosanna Caramiello 《Quaternary International》2008,190(1):71
The high topographic complexity of the Alpine region is the origin of important climate differences that characterise the different areas of the Alps. These differences might have had a strong influence on vegetation and on migrations of human populations in the past. Based on an improved database containing about 3000 modern pollen samples, the standard “Modern Analogue Technique” has been applied to five pollen sequences from the subalpine belt of the South-western Italian Alps (Laghi dell’Orgials, 2240 m, Lago delle Fate, 2130 m, Torbiera del Biecai, 1920 m, Rifugio Mondovì, 1760 m, Pian Marchisio, 1624 m) to provide quantitative climate estimates for the Lateglacial and Holocene periods. Consistent climate trends are reconstructed for the different sequences. Sites recorded in detail the climate variations when they were located at the limit of two ecotones. Sites above the tree line recorded lower temperature values and less important variations. Climate was cold and dry during the Oldest and Younger Dryas and close to present-day values during the Bølling/Allerød interstadial. At the beginning of the Holocene, climate changed to warmer and moister conditions; a high number of climate fluctuations are recorded at several sites. A climate optimum is recorded in the Atlantic period, which caused a development of fir above its present-day altitudinal distribution. Climatic differences recorded at the various sites are discussed taking into account the limits of the method. 相似文献
556.
We analyze the Wolf number daily series WN (1849 to present) as well as two other related series characterizing solar activity. Our analysis consists in computing the
amplitude of a given Fourier component in a sliding time window and examining its long-term evolution. We start with the well-known
27.03- and 27.6-day periods and observe strong decadal variations of this amplitude as well as a sharp increase of the average
value starting around 1905. We then consider a packet of 31 lines with periods from 25.743 to 28.453 days, which is shown
to be a better representation of the synodic solar rotation. We first examine the temporal evolution of individual lines,
then the energy of the packet. The energy of the packet increases sharply at the beginning of the 20th century, leading by
more than two decades the well-known increase of the Wolf number. The nonaxisymmetry of sunspots increases before the total
increase of activity and may be considered as a precursor. We discuss briefly and tentatively this observation in terms of
solar dynamo theory. 相似文献
557.
A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian
distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence
of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes
in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities
of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results
can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one
can be significant. 相似文献
558.
559.
A hydrochemical facies evolution diagram (HFE‐D) is a multirectangular diagram, which is a useful tool in the interpretation of sea water intrusion processes. This method note describes a simple method for generating an HFE‐D plot using the spreadsheet software package, Microsoft Excel. The code was applied to groundwater from the alluvial coastal plain of Grosseto (Tuscany, Italy), which is characterized by a complex salinization process in which sea water mixes with sulfate or bicarbonate recharge water. 相似文献