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391.
Barros J Igrejas G Andrade M Radhouani H López M Torres C Poeta P 《Marine pollution bulletin》2011,62(6):1245-1248
Antibiotic resistance in bacteria is a growing problem that is not only restricted to the clinical setting but also to other environments such as marine species that harbor antibiotic resistant bacteria and therefore may serve as reservoirs for antibiotic-resistance genetic determinants. The aim of this study was to evaluate antibiotic resistance phenotypes in enterococci isolated from fecal samples of gilthead seabream and the associated mechanisms of resistance. A collection of 118 samples were analyzed and 73 enterococci were recovered. The strains showed high percentages of resistance to erythromycin and tetracycline (58.9% and 17.8%, respectively). Lower level of resistance (<13%) was detected for quinupristin-dalfopristin, ampicillin, high-level-gentamicin, high-level-streptomycin, high-level-kanamycin, ciprofloxacin and chloramphenicol. The erm(B), tet(L) or tet(M), aac(6′)-aph(2″) and aph(3′)-IIIa genes were shown in isolates resistant to erythromycin, tetracycline, high-level gentamicin and high-level kanamycin, respectively. Antibiotic resistance in natural microbiota is becoming a concern of human and environmental health. 相似文献
392.
Myriam Andrea Rada Torres Vincenzo Costanzo-Álvarez Milagrosa Aldana Nery Suárez Corina Campos Maria Magdalena Mackowiak-Antczak María Carmela Brandt 《Studia Geophysica et Geodaetica》2011,55(4):717-736
Rock magnetic, petrographic and dielectric analyses were carried out, in a number of archeological ceramic potsherds, in order
to characterize the different manufacturing techniques used by Prehistoric Venezuelan Amerindian potters. Samples were excavated
in 7 Venezuelan islands and ascribed to distinct cultural groups on purely stylistic grounds (i.e. Valencioide, Ocumaroide,
Dabajuroide and Unknown). Mean coercivity values were determined through a direct signal analyses (DSA) applied to isothermal
remanent magnetization (IRM) acquisition curves. Logarithmic plots of these mean coercivities are the best quantitative means
to classify diverse ceramics. The mean coercivity values seem to group the samples according to the manufacturing development.
These values also seem to discriminate the samples provenance, indeed, this plot displays a good grouping of data for samples
presumably manufactured by the same culture but excavated at different locations. Thermomagnetic cycles supply helpful information
about original ceramic firing conditions. The irreversibility parameter (IP) for thermomagnetic curves (heating and cooling),
serves as an indicator of the amount of organic matter burnt during original pottery firing. The IP for a number of pottery
samples from Venezuelan islands and mainland, with ages ranging between 300 BC to 1500 AD, might suggest a possible increasing
trend in time towards the complete reversibility line of IP = 0. Most samples, independently of age and cultural group, have
IP values that suggest that most open fires, used by primitive Venezuelan Amerindian potters, had enough ventilation and oxidizing
atmospheres. A scatter plot of maximum current depolarization temperatures versus natural remanent magnetization (NRM) suggests
a complex non-linear relationship between these two parameters most likely due to the fact that both, dielectric and rock
magnetic data, are linked to pore-related features. 相似文献
393.
Miriela María Ulloa Santana Márcia Abrahão Moura Gema R. Olivo Nilson Francisquini Botelho T. Kurtis Kyser Bernhard Bühn 《Mineralium Deposita》2011,46(1):91-104
The Camagüey district, Cuba, is known for its epithermal precious metal deposits in a Cretaceous volcanic arc setting. Recently,
the La Unión prospect was discovered in the southern part of the district, containing gold and minor copper mineralization
interpreted as porphyry type. Mineralization is hosted in a 73.0 ± 1.5 Ma calc–alkaline I-type oxidized porphyry quartz diorite
intrusive within volcanic and volcaniclastic rocks of the early Cretaceous Guáimaro Formation. The porphyry is affected by
propylitic alteration and crosscut by a network of quartz and carbonate veinlets and veins. Chlorite, epidote, sericite, quartz,
and pyrite are the main minerals in the early veins which are cut by late carbonate and zeolite veins. Late barite pseudomorphously
replaces pyrite. Gold is associated with pyrite as disseminations in the altered quartz diorite and in the veins, occurring
as inclusions or filling fractures in pyrite with 4 g/t Au in bulk samples, and up to 900 ppm Au in in pyrite. Fluid inclusion
and oxygen isotope data are consistent with a H2O–NaCl–(KCl) mineralizing fluid, derived from the quartz diorite magma, and trapped at least at 425°C and 1.2 kbar. This primary
fluid unmixed into two fluid phases, a hypersaline aqueous fluid and a low-salinity vapor-rich fluid. Boiling during cooling
may have played an important role in metal precipitation. Pyrite δ34S values for the La Unión prospect range between 0.71‰ and 1.31‰, consistent with a homogeneous magmatic sulfur source. The
fluids in equilibrium with the mineralized rocks have estimated δ18O values from 8‰ to 11.8‰, calculated for a temperature range of 480–505°C. The tectonic environment of the La Unión prospect,
its high gold and low copper contents, the physical–chemical characteristics of the mineralizing fluids and the isotopic signature
of the alteration minerals and fluids indicate that the La Unión gold mineralization is similar to the porphyry gold type,
even though the ore-related epidote–chlorite alteration can be classified as propylitic and not the classic potassic and/or
phyllic alteration. The low copper contents in the prospect could be due to a mineralizing fluid previously saturated in copper,
which is indicated by trapped chalcopyrite crystals in high-temperature fluid inclusions. The low-temperature paragenesis,
represented by carbonate, zeolite and barite, indicates epithermal overprint. The study shows the potential for other gold
porphyry-type deposits in the Cretaceous volcanoplutonic arc of Cuba. 相似文献
394.
Sequential Gaussian simulation is widespread in Earth Science applications to quantify the uncertainty about regionalized
properties. Its practical implementation relies on the screen effect approximation in order to determine the successive conditional
distributions by considering only the information available in the neighborhood of the target location. A methodology is presented
to assess the accuracy of sequential Gaussian simulation, by calculating the theoretical moments (expectation and variance–covariance
matrix) of the simulated random vector and comparing them with the moments of the underlying model. The methodology can be
applied in both the conditional and non-conditional contexts, as well as for univariate or multivariate simulation. It is
helpful to determine appropriate implementation parameters, in particular about the visiting sequence and the design of the
moving neighborhood for selecting relevant conditioning information, prior to performing simulation. 相似文献
395.
A. Fouépé Takounjou J. R. Ndam Ngoupayou J. Riotte G. E. Takem G. Mafany J. C. Maréchal G. E. Ekodeck 《Environmental Earth Sciences》2011,64(1):107-118
A study of environmental chloride and groundwater balance has been carried out in order to estimate their relative value for
measuring average groundwater recharge under a humid climatic environment with a relatively shallow water table. The hybrid
water fluctuation method allowed the split of the hydrologic year into two seasons of recharge (wet season) and no recharge
(dry season) to appraise specific yield during the dry season and, second, to estimate recharge from the water table rise
during the wet season. This well elaborated and suitable method has then been used as a standard to assess the effectiveness
of the chloride method under forest humid climatic environment. Effective specific yield of 0.08 was obtained for the study
area. It reflects an effective basin-wide process and is insensitive to local heterogeneities in the aquifer system. The hybrid
water fluctuation method gives an average recharge value of 87.14 mm/year at the basin scale, which represents 5.7% of the
annual rainfall. Recharge value estimated based on the chloride method varies between 16.24 and 236.95 mm/year with an average
value of 108.45 mm/year. It represents 7% of the mean annual precipitation. The discrepancy observed between recharge value
estimated by the hybrid water fluctuation and the chloride mass balance methods appears to be very important, which could
imply the ineffectiveness of the chloride mass balance method for this present humid environment. 相似文献
396.
Glaciers and rock glaciers’ distribution at 28° SL,Dry Andes of Argentina,and some considerations about their hydrological significance 总被引:1,自引:0,他引:1
The area studied includes a little-known portion on the Dry Andes of the San Juan Frontal Cordillera, Argentina, where the
hydrological significance of glaciers and rock glaciers was earlier never studied. The surveyed sector includes Cerro El Potro
(5,870 m ASL) and nearby mountain chains (28°S). The predominant landforms in these areas were shaped in a periglacial environment
superimposed on an earlier glacial landscape. These regions comprise abundant rock glaciers, a noteworthy rock glacier zone
in the world, of which little is known in South America. This work employs geomorphological mapping to analyze the distribution
of active rock glaciers in relation to altitude, aspect and slope using optical remote sensing techniques with GIS. Statistical
estimation techniques were used based on a Digital Elevation Model (DEM) and aerial photos and Spot images interpretation.
The specific density of rock glaciers’ estimation in the surveyed area (Argentine border) is 1.56% with corresponds to 38
rock glaciers with an area of 5.86 km2 and 0.12 km3 of water equivalent. Furthermore, the analytical results show that elevations >4,270 m ASL, a southeast-facing aspect, and
slope between 2° and 40° favor the existence of rock glaciers, Finally, a comparison with glacier water equivalent, which
covers an area of ~16 km2 and 0.9 km3 of water equivalent, shows that glaciers are the main stores of water at 28°S (Cerro El Potro Glacier). However, the importance
of rock glaciers as water reserves in this portion of Argentina should not be underestimated. 相似文献
397.
Morphology and structure of the Camarinal Sill from high-resolution bathymetry: evidence of fault zones in the Gibraltar Strait 总被引:2,自引:2,他引:0
The Gibraltar Strait is the very narrow neck which connects the Atlantic Ocean and the Mediterranean Sea. The causes and mode
of its opening at the end of the Messinian Salinity Crisis are still a matter of debate, and models based on eustatic rise
and/or topographic lowering due to either erosion or faulting are generally evoked. We investigated the presence of faults
based on a morphological and structural analysis of the Camarinal Sill, the shallowest passage in the Gibraltar Strait (<100 m
water depth in places). This sill connects the Spanish and Moroccan shelves, and probably represents a structural high inherited
from the Miocene compressive tectonics which took place in the external zones of the Betic-Rif orogenic arc. Our high-resolution
bathymetric data enabled us to identify and interpret the origin of major morphological features in the area, including canyons,
channels and a landslide, which we name the Tarifa landslide. Topographic arguments suggest that the Camarinal Sill is crossed
by two main E-W- to ENE-WSW-directed fault zones which bound areas with different distribution, orientation and slopes of
both scarps and crests. We name these the Hercules and Tarik fault zones, north and south of the sill respectively. The Hercules
fault zone probably incorporates a normal movement component, whereas kinematic indicators are poor along the Tarik fault
zone. The age of faulting is poorly constrained in both cases. Together with existing evidence of faults onland, the presence
of these fault zones implies that they could be responsible for, or have contributed to, the opening of the Gibraltar Strait. 相似文献
398.
Macroalgae build biogenic habitats which give shelter and provide a suitable physical environment for a great variety of organisms. Structural complexity of algal substrates may influence the composition of their attached epifauna. The aim of this study is to test whether the taxonomic relatedness of the algal hosts and the functional groups to which they belong influence the species richness and composition of their epifaunal bryozoans. We analysed 36 algal genera from the Atlantic coast of South America between 42°S and Cape Horn. Changes in bryozoan species richness (number of species) among different algal functional groups (filamentous algae, foliose algae, corticated foliose algae, corticated macrophytes) were non-significant. The composition of the epifaunal assemblages differed significantly only between filamentous and foliose algae. Sheet-like bryozoans (i.e. encrusting, pluriserial colonies) were more frequent on foliose than on filamentous algae, while runner-like species (i.e. uniserial stolons) were characteristic epibionts on filamentous thallii. Similarity of bryozoan assemblages increased with increasing taxonomic relatedness of their hosts. As most filamentous seaweeds analysed in this study are members of the Order Ceramiales, the influence of algal taxonomic relatedness and functional groups on the composition of their bryozoan assemblages can be viewed as two different aspects of the same phenomenon. 相似文献
399.
400.
D. Sabina D’Ambrosio Adriana García Analía R. Díaz Allan R. Chivas María C. Claps 《Journal of Paleolimnology》2017,58(2):101-117
Ecological and biogeographical studies of Neotropical non-marine ostracods are rare, although such information is needed to develop reliable paleoecological and paleoclimatic reconstructions for the region. An extensive, yet little explored South American area of paleoclimatic interest, is the arid-semiarid ecotone (Arid Diagonal) that separates arid Patagonia from subtropical/tropical northern South America, and lies at the intersection of the Pacific and Atlantic atmospheric circulation systems. This study focused on the Laguna Llancanelo basin, Argentina, a Ramsar site located within the Arid Diagonal, and was designed to build a modern dataset using ostracods (diversity, spatial distribution, seasonality, habitat preferences) and water chemistry. Cluster and multivariate analysis of the data indicated that salinity is the most significant variable segregating two ostracod groups. Limnocythere aff. staplini is the only species that develops abundant populations in the saline ephemeral Laguna Llancanelo during almost all seasons, and is accompanied by scarce Cypridopsis vidua in summer. The latter species is abundant in freshwater lotic sites, where Ilyocypris ramirezi, Herpetocypris helenae, and Cyprididae indet. are also found in large numbers. Darwinula stevensoni, Penthesilenula incae, Heterocypris incongruens, Chlamydotheca arcuata, Chlamydotheca sp., Herpetocypris helenae, and Potamocypris smaragdina prefer freshwater lentic conditions (springs), with C. arcuata and Chlamydotheca sp. found only in the Carapacho warm spring, which has a year-round constant temperature of ~20 °C. Seasonal sampling was necessary because some taxa display a highly seasonal distribution. Species that were recorded have either subtropical or Patagonian affinities, although a few taxa are endemic or common to both regions. These data can serve as modern analogues for reconstructing the late Quaternary history of the area, and to investigate the extent and position of the arid/semiarid ecotone (Arid Diagonal) during past glacial/interglacial cycles. 相似文献