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991.
Vinícius dos Santos Marcelo Dias de Oliveira Jan Boll Ricardo Snchez‐Murillo Amauri Antonio Menegrio Luiz Felippe Gozzo Didier Gastmans 《水文研究》2019,33(4):647-660
Equatorial Pacific sea surface temperature variations interact with processes of atmospheric circulation, creating conditions for the occurrence of El Niño–Southern Oscillation (ENSO). ENSO events represent the most important interannual phenomena affecting climate patterns worldwide and causing significant socio‐economic impacts. In the Brazilian territory, ENSO leads to an increase in drought episodes in the north‐eastern region and an increase in precipitation in the southern region, whereas the effects over the south‐east region are yet not well understood. The main goal of this study is to compare variations of isotopic composition in precipitation across the south‐east portion of the Brazilian territory during two very strong ENSO events: 1997–1998 (ENSO 1) and 2014–2016 (ENSO 2). Daily isotopic records, available from the Global Network of Isotopes in Precipitation database for ENSO 1, and samples collected during ENSO 2 were used to compare the influence of both events on the isotopic composition of precipitation. Seasonal variations indicated more depleted precipitation during the wet seasons (δ18O = ?5.4 ± 4.0‰) and enriched precipitation during the dry seasons (δ18O = ?2.8 ± 2.3‰). Observed rainfall variations were associated with atmospheric large‐scale processes and moisture transport from the Amazon region, whereas extreme values (enriched or depleted) appear to be associated with particular convective and stratiform precipitation events. Overall, more depleted isotopic composition of precipitation (δ18O = ?4.60‰) and higher d‐excess (up to +15‰) were observed during the dry season of ENSO 1 when compared with ENSO 2 dry season (δ18O‰ = ?2.80‰, d‐excess lower than +14‰). The latter is explained by greater atmospheric moisture content, particularly associated with recycling of transpiration fluxes from the Amazon region, during dry season of ENSO 1. No significant differences for δ18O and δ2H were observed during the wet season; however, d‐excess from ENSO 2 was greater than ENSO 1, due to the slightly greater atmospheric moisture content and very strong upward motion observed. Our findings highlight the opportunity that environmental isotopes offer towards understanding hydrometeorological processes, particularly, the evolution of extreme climatic events of global resonance such as ENSO. 相似文献
992.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2010,326(2):159-162
The product of two empirical constants, the dimensionless fine-structure constant (α) and the von Klitzing constant (R
k, an electrical resistance), turns out to be an exact dimensionless number. Then the accuracy and cosmological time variation
(if any) of these two constants can be tied together. Also this product defines a natural unit of the electrical resistance,
the inverse of a quantum of conductance. When the speed of light c is taken away from α, as has been shown elsewhere, the constancy of α implies the constancy of the ratio e
2/h (the inverse of the von Klitzing constant), e being the charge of the electron and h the Planck constant. This forces the charge of the electron e to be constant as long as the action h (an angular momentum) is a true constant too. From the constancy of the Rydberg constant the Compton wavelength, h/mc, is then a true constant and consequently there is no expansion at the quantum mechanical level. The momentum mc is also a true constant and then general relativity predicts that the universe is not expanding, as shown elsewhere. The
time variation of the speed of light explains the observed Hubble red shift. And there is a mass-boom effect. From this a
coherent cosmological system of constant units can be defined. 相似文献
993.
Antonio Gamboa Suárez Daniel Hestroffer David Farrelly 《Celestial Mechanics and Dynamical Astronomy》2010,106(3):245-259
Binaries in the Kuiper-belt are unlike all other known binaries in the Solar System. Both their physical and orbital properties
are highly unusual and, because these objects are thought to be relics dating back to the earliest days of the Solar System,
understanding how they formed may provide valuable insight into the conditions which then prevailed. A number of different
mechanisms for the formation of Kuiper-belt binaries (KBBs) have been proposed including; two-body collisions inside the Hill
sphere of a larger body; strong dynamical friction; exchange reactions; and chaos assisted capture. So far, no clear consensus
has emerged as to which of these mechanisms (if any) can best explain the observed population of KBBs. Indeed, the recent
characterization of the mutual orbit of the symmetric (i.e., roughly equal mass) KBB 2001 QW322 has only served to complicate the picture because its orbit does not seem readily explicable by any of the available models.
The binary 2001 QW322 stands out even among the already unusual population of KBBs for the following reasons: its mutual orbit is extremely large
(≈105 km or about 30% of the Hill sphere radius), retrograde, it is inclined ≈120° from the ecliptic and has very low eccentricity, i.e., e ≤ 0.4 (and possibly e ≤ 0.05). Here we propose a hybrid formation mechanism for this object which combines aspects of several of the mechanisms
already proposed. Initially two objects are temporarily trapped in a long-living chaotic orbit that lies close to a retrograde
periodic orbit in the three-dimensional Hill problem. This is followed by capture through gravitational scattering with a
small intruder object. Finally, weak dynamical friction gradually switches the original orbit “adiabatically” into a large,
almost circular, retrograde orbit similar to that actually observed. 相似文献
994.
José Antonio de Freitas Pacheco 《中国天文和天体物理学报》2010,10(11)
Large ground-based laser beam interferometers are presently in operation both in the USA(LIGO) and in Europe(VIRGO) and potential sources that might be detected by these instruments are revisited.The present generation of detectors does not have a sensitivity high enough to probe a significant volume of the universe and,consequently,predicted event rates are very low.The planned advanced generation of interferometers will probably be able to detect,for the first time,a gravitational signal.Advanced LIGO and... 相似文献
995.
Juan-Carlos Ciscar László Szabó Denise van Regemorter Antonio Soria 《Climatic change》2012,112(1):127-142
The PESETA project has estimated the physical effects of climate change in Europe for the following impact categories with
a market valuation: agriculture, river floods, coastal systems and tourism. Four alternative scenarios of future climate change
have been considered. The computable general equilibrium (CGE) GEM-E3 model for Europe has been used to integrate the PESETA
damages under a consistent economic framework. The approach followed has been to assess the effects of future climate (as
of 2080s) on today’s economy. This article details the way each sectoral impact has been integrated into the CGE model. The
EU welfare loss is estimated to be in a range of 0.2% to 1%, depending on the climate future and the projected sea level rise.
Results show that the Southern Europe region appears as the most vulnerable area to climate change. Impacts in coastal systems,
agriculture and river floods determine the overall and regional pattern of impacts within Europe. 相似文献
996.
Antonio García-Alix Gonzalo Jiménez-Moreno R. Scott Anderson Francisco J. Jiménez Espejo Antonio Delgado Huertas 《Journal of Paleolimnology》2012,48(3):471-484
Small lakes and wetlands from high elevation within the Sierra Nevada Range (southern Spain) preserve a complete post-glacial Holocene record. Isotopic, TOC and C/N analyses, carried out on a sediment core, show various stages in the evolution of the Borreguiles de la Virgen, which today constitute a small bog at about 2,950?m above sea level. Glacial erosion generated a cirque depression, which became a small lake during the first phase of infilling (from?8,200 to 5,100?cal?yr BP), as suggested by sedimentary evidence, including an atomic C/N ratio generally below 20, low TOC values and the highest ??13C and ??15N values of the record. These results imply significant algal productivity, which is confirmed by the microscopic algal remains. Drier conditions became established progressively in this area from?5,100 to 3,700?cal?yr BP. Subsequently, the lake evolved into a bog as shown by geochemical evidence (C/N ratios above 20, high TOC content and low ??13C values). Unstable conditions prevailed from?3,600 to 700?cal?yr BP; an extremely low sedimentation rate and scarcity of data from this period do not allow us to make a coherent interpretation. Fluctuating conditions were recorded during the last?~700?cal?yr BP, with wetter conditions prevailing during the first part of the interval (with C/N rate below 20) up to 350?years ago. In general, a gradual trend toward more arid conditions occurred since?~6,900?cal?yr BP, with a further increase in aridity since?~5,100?cal?yr BP. This evidence is consistent with other contemporaneous peri-Mediterranean records. 相似文献
997.
Mónica Fernández-Perea Manuela Vidal-Dasilva Juan Ignacio Larruquert José Antonio Méndez José Antonio Aznárez 《Astrophysics and Space Science》2009,320(1-3):243-246
GOLD (Grupo de Óptica de Láminas Delgadas) is devoted to the development of novel coatings with challenging performance in the far and the extreme ultraviolet (FUV-EUV, 50–200 nm). One of the main goals of this research is to provide the communities of astronomy, solar physics and atmospheric physics with coatings with high reflectance or transmittance at a target wavelength or band, and high rejection of the out-of-band at this complicated spectral range. Above the transparency cutoff of MgF2 (115 nm), transmittance filters based on Al/MgF2 multilayers have been developed peaked at wavelengths as short as 124 nm, with a peak transmittance of 27% and a FWHM of 12 nm for a non-aged coating. Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peaked at the 83.4 nm OII spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14 nm have been obtained. Furthermore, the peak reflectance wavelength of these filters can be tuned by rotation. A filter peaked at 83 nm at normal incidence will shift to ~73 nm at 30 deg from the normal and to ~58 nm at 45 deg. These novel reflective filters based on Al, Yb and SiO must still demonstrate stability over time. 相似文献
998.
Antonio Giorgilli Ugo Locatelli Marco Sansottera 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):159-173
We investigate the long time stability in Nekhoroshev’s sense for the Sun– Jupiter–Saturn problem in the framework of the problem of three bodies. Using computer algebra in order to perform huge perturbation expansions we show that the stability for a time comparable with the age of the universe is actually reached, but with some strong truncations on the perturbation expansion of the Hamiltonian at some stage. An improvement of such results is currently under investigation. 相似文献
999.
Jos A. Lpez-Sez Antonio Blanco-Gonzlez Lourdes Lpez-Merino M. Blanca Ruiz-Zapata Miriam Dorado-Valio Sebastin Prez-Díaz Ana Valdeolmillos Francesc Burjachs 《Quaternary International》2009,200(1-2):90
Correlations between ecological and cultural changes occurred during a short period between the end of Subboreal and the beginning of Subatlantic in the Amblés Valley (Ávila, central Spain) are analyzed, taking into account palaeopalynological and archaeological data. Plant dynamics from pollen analyses, both from archaeological sites and peat bogs, have been interpreted in relation to human settlements and the transformation of economic practices. These provided a comprehensive hypothesis on human/climate interactions at the beginning of the 1st millennium cal BC. There was an ecological crisis in the region that lasted for a century (ca. 850–760 cal BC). This was especially sharp due to both the geographical constraints of the area and its previous agrarian history. This event implied a sudden and abrupt climatic change from xeric and warm conditions (Subboreal) to more humid and cooler ones (Subatlantic). Environmental stress derived from climatic crisis could be an important factor in the explanation of the historical process, whose main consequences were both the origin of the Iron Age peasant villages and the end of the ‘dehesa’ type landscape. 相似文献
1000.
Hydrogeology of the Nurra Region, Sardinia (Italy): basement-cover influences on groundwater occurrence and hydrogeochemistry 总被引:2,自引:0,他引:2
Giorgio Ghiglieri Giacomo Oggiano Maria Dolores Fidelibus Tamiru Alemayehu Giulio Barbieri Antonio Vernier 《Hydrogeology Journal》2009,17(2):447-466
The Nurra district in the Island of Sardinia (Italy) has a Palaeozoic basement and covers, consisting of Mesozoic carbonates, Cenozoic pyroclastic rocks and Quaternary, mainly clastic, sediments. The faulting and folding affecting the covers predominantly control the geomorphology. The morphology of the southern part is controlled by the Tertiary volcanic activity that generated a stack of pyroclastic flows. Geological structures and lithology exert the main control on recharge and groundwater circulation, as well as its availability and quality. The watershed divides do not fit the groundwater divide; the latter is conditioned by open folds and by faults. The Mesozoic folded carbonate sequences contain appreciable amounts of groundwater, particularly where structural lows are generated by synclines and normal faults. The regional groundwater flow has been defined. The investigated groundwater shows relatively high TDS and chloride concentrations which, along with other hydrogeochemical evidence, rules out sea-water intrusion as the cause of high salinity. The high chloride and sulphate concentrations can be related to deep hydrothermal circuits and to Triassic evaporites, respectively. The source water chemistry has been modified by various geochemical processes due to the groundwater–rock interaction, including ion exchange with hydrothermal minerals and clays, incongruent solution of dolomite, and sulphate reduction. 相似文献