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451.
Agnès Bouchez Noémie Pascault Cècile Chardon Marc Bouvy Philippe Cecchi Luc Lambs Mélanie Herteman François Fromard Patrice Got Christophe Leboulanger 《Marine pollution bulletin》2013,66(1-2):39-46
Mangroves are threatened ecosystems that provide numerous ecosystem services, especially through their wide biodiversity, and their bioremediation capacity is a challenging question in tropical areas. In a mangrove in Mayotte, we studied the potential role of microbial biofilm communities in removing nutrient loads from pre-treated wastewater. Microbial community samples were collected from tree roots, sediments, water, and from a colonization device, and their structure and dynamics were compared in two areas: one exposed to sewage and the other not. The samples from the colonization devices accurately reflected the natural communities in terms of diversity. Communities in the zone exposed to sewage were characterized by more green algae and diatoms, higher bacteria densities, as well as different compositions. In the area exposed to sewage, the higher cell densities associated with specific diversity patterns highlighted adapted communities that may play a significant role in the fate of nutrients. 相似文献
452.
Mathieu Duval Christophe Falguères Jean-Jacques Bahain Rainer Grün Qingfeng Shao Maxime Aubert Jean-Michel Dolo Jordi Agustí Bienvenido Martínez-Navarro Paul Palmqvist Isidro Toro-Moyano 《Quaternary Research》2012,77(3):482-491
The combined U-series/electron spin resonance (ESR) dating method was applied to nine teeth from two Early Pleistocene archaeological sites located in the Orce area (Guadix-Baza Basin, Southern Spain): Fuente Nueva-3 (FN-3) and Barranco León (BL). The combination of biostratigraphy and magnetostratigraphy places both sites between the Olduvai and Jaramillo subchrons (1.78–1.07 Ma).Our results highlight the difficulty of dating such old sites and point out the limits of the combined U-series/ESR dating method based on the US model. We identified several sources of uncertainties that may lead to inaccurate age estimates. Seven samples could not be dated because the dental tissues had (230Th/234U) activity ratios higher than equilibrium, indicating that uranium had probably leached from these tissues. It was however possible to calculate numerical estimates for two of the teeth, both from FN-3. One yielded a Middle Pleistocene age that seems to be strongly underestimated; the other provided an age of 1.19 ± 0.21 Ma, in agreement with data obtained from independent methods. The latter result gives encouragement that there are samples that can be used for routine dating of old sites. 相似文献
453.
7000 years of paleostorm activity in the NW Mediterranean Sea in response to Holocene climate events
Pierre Sabatier Laurent Dezileau Christophe Colin Louis Briqueu Frédéric Bouchette Philippe Martinez Giuseppe Siani Olivier Raynal Ulrich Von Grafenstein 《Quaternary Research》2012,77(1):1-11
A high-resolution record of paleostorm events along the French Mediterranean coast over the past 7000 years was established from a lagoonal sediment core in the Gulf of Lions. Integrating grain size, faunal analysis, clay mineralogy and geochemistry data with a chronology derived from radiocarbon dating, we recorded seven periods of increased storm activity at 6300–6100, 5650–5400, 4400–4050, 3650–3200, 2800–2600, 1950–1400 and 400–50 cal yr BP (in the Little Ice Age). In contrast, our results show that the Medieval Climate Anomaly (1150–650 cal yr BP) was characterised by low storm activity.The evidence for high storm activity in the NW Mediterranean Sea is in agreement with the changes in coastal hydrodynamics observed over the Eastern North Atlantic and seems to correspond to Holocene cooling in the North Atlantic. Periods of low SSTs there may have led to a stronger meridional temperature gradient and a southward migration of the westerlies. We hypothesise that the increase in storm activity during Holocene cold events over the North Atlantic and Mediterranean regions was probably due to an increase in the thermal gradient that led to an enhanced lower tropospheric baroclinicity over a large Central Atlantic–European domain. 相似文献
454.
455.
Aurélien Royer Christophe Lécuyer Sophie Montuire Jérôme Primault François Fourel Marcel Jeannet 《Quaternary Research》2014
The oxygen isotope composition of phosphate from tooth enamel of rodents (δ18Op) constitutes a valuable proxy to reconstruct past air temperatures in continental environments. This method has been applied to rodent dental remains from three genera, Arvicola sp., Microtus sp. and Dicrostonyx sp., coming from Taillis-des-Coteaux, Vienne, France. This archaeological site contains an exceptionally preserved sedimentary sequence spanning almost the whole Upper Palaeolithic, including seven stratigraphic layers dated from 35 to 17 cal ka BP. The abundant presence of rodent remains offers the opportunity to quantify the climatic fluctuations coeval of the various stages of human occupation of the site. Differences between δ18Op values of Arvicola sp. and Microtus sp. teeth are interpreted as the result of heterochrony in tooth formation as well as differences in ecology. Mean δ18Op values of Microtus sp. are preferentially used to reconstruct summer air temperatures, which range from 16.0 ± 3.7 to 19.1 ± 3.1°C throughout the sedimentary sequence; however, the highest variability is observed during the last glacial maximum. 相似文献
456.
Nadjinangar Gotoum Christophe Nkem Kamel Hammami M. Ahamat?Charfadine L. C. Owono?Owono Nejm-Eddine Jaidane 《Astrophysics and Space Science》2011,332(1):209-217
We report on the calculation of collision induced rotational excitation cross sections and rate coefficients of AlF by He
atom at low temperature. These quantities were obtained by first computing the interaction potential energy surface (PES)
of the AlF(X
1Σ+)-He(1
S) van der Waals complex at the ab initio Coupled Cluster with Single and Double and perturbative Triple excitations [CCSD(T)] level of theory. The aug-cc-pVQZ Gaussian
basis, to which was added a set of bond functions, was used for that purpose. The calculations account for basis set superposition
errors (BSSE). The interaction potential presents a minimum of ∼24 cm−1 below the AlF-He dissociation limit. The PES was fitted on a basis of Legendre polynomial functions to allow for the calculation
of cross sections in the close-coupling (CC) approach. By averaging these cross sections over a Maxwell-Boltzmann velocity
distribution, rate coefficients were inferred at low temperatures (T≤300 K). From our computations, a propensity towards ΔJ=1 transitions is observed. 相似文献
457.
Maarten Haest Jens Schneider Christophe Cloquet Kris Latruwe Frank Vanhaecke Philippe Muchez 《Mineralium Deposita》2010,45(4):393-410
Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed
during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago)
in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic
composition (206Pb/204Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides
were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a
chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of
lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the 207Pb/204Pb vs. 206Pb/204Pb diagram (206Pb/204Pb = 18.66–23.65; 207Pb/204Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead
and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation
also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided
Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides,
whereas the U most likely originated from external sources. Local metal sources are also suggested by the 208Pb/204Pb–206Pb/204Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate
host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu
Plateau clearly record a diachronous evolution. 相似文献
458.
Christophe Lécuyer Vincent Balter François Fourel Romain Amiot Olga Otero Gérard Panczer Rossana Martini 《Geochimica et cosmochimica acta》2010,74(7):2072-584
The oxygen isotope fractionation between the structural carbonate of inorganically precipitated hydroxyapatite (HAP) and water was determined in the range 10-37 °C. Values of 1000 ln α() are linearly correlated with inverse temperature (K) according to the following equation: 1000 ln α() = 25.19 (±0.53)·T−1 − 56.47 (±1.81) (R2 = 0.998). This fractionation equation has a slightly steeper slope than those already established between calcite and water (
[O’Neil et al., 1969] and [Kim and O’Neil, 1997]) even though measured fractionations are of comparable amplitude in the temperature range of these experimental studies. It is consequently observed that the oxygen isotope fractionation between apatite carbonate and phosphate increases from about 7.5‰ up to 9.1‰ with decreasing temperature from 37 °C to 10 °C. A compilation of δ18O values of both phosphate and carbonate from modern mammal teeth and bones confirms that both variables are linearly correlated, despite a significant scattering up to 3.5‰, with a slope close to 1 and an intercept corresponding to a 1000 ln α() value of 8.1‰. This apparent fractionation factor is slightly higher or close to the fractionation factor expected to be in the range 7-8‰ at the body temperature of mammals. 相似文献
459.
Catherine Larose Aurélien Dommergue Martine De Angelis Bernard Averty Nicolas Soumis Christophe Ferrari 《Geochimica et cosmochimica acta》2010,74(22):6263-6275
Seasonal snow is an active media and an important climate factor that governs nutrient transfer in Arctic ecosystems. Since the snow stores and transforms nutrients and contaminants, it is of crucial importance to gain a better understanding of the dynamics of contaminant cycling within the snowpack and its subsequent release to catchments via meltwater. Over the course of a two-month field study in the spring of 2008, we collected snow and meltwater samples from a seasonal snowpack in Ny-Ålesund, Norway (78°56′N, 11°52′E), which were analyzed for major inorganic ions and some organic acids, as well as total, dissolved, bioavailable mercury (THg, DHg, BioHg, respectively) and monomethylmercury (MMHg) species. We observe a seasonal gradient for ion concentrations, with surface samples becoming less concentrated as the season progressed. A significant negative correlation between BioHg and MMHg was observed in the snowpack. MMHg was positively and significantly correlated to methanesulfonate concentrations. Based on these results, we propose a new model for aerobic methylation of mercury involving species in the dimethylsulfoniopropionate cycle. 相似文献
460.
Gert Finger Frank Eisenhauer Reinhard Genzel Christopher Mandla Ian Baker Domingo Alvarez Antonio Amorim Wolfgang Brandner Christophe Dupuy Casey Deen Derek Ives Leander Mehrgan Manfred Meyer Karin Perraut Guy Perrin Jörg Stegmeier Christian Straubmeier Harald J. Weller Vincent Isgar 《Astronomische Nachrichten》2023,344(8-9):e20230069
Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e−APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is mk = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10−3 e−/s have been demonstrated with 1Kx1K e−APD arrays and 2Kx2K e−APD arrays have already been developed, the possibilities and adaptations of e−APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed. 相似文献