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641.
642.
A. V. Roldugin V. G. Vorobjev V. C. Roldugin S. A. Chernouss 《Geomagnetism and Aeronomy》2010,50(1):34-40
The results of the ground-based optical observations of sunlit auroras, performed at Lovozero and Apatity observatories on
April 10 (event 1) and April 27, 2007(event 2), are presented. The observations were performed in the (OI) 557.7 nm emission,
using a new equipment based on a Fabry-Pérot interferometer connected to a PhotonMAX CCD camera. During event 1, the observations
were performed in the Harang discontinuity region at a low magnetic disturbance. It has been indicated that an auroral arc
was located in the polar part of the eastward electrojet, and the arc position coincides with the equatorward boundary of
structured precipitation (b2e). During event 2, auroras were observed within the average statistical boundaries of the auroral
oval and the region of structured precipitation under the conditions of rather high geomagnetic activity. However, during
the period of low geomagnetic activity, discrete auroras were registered at a geomagnetic latitude of ~64° on that day, which
is 3°—4° equatorward of the structured precipitation region. Such a low latitudinal position of auroras can be explained by
the effect of a high solar wind velocity, which was ~580 km/s during the period of observations. 相似文献
643.
644.
F. Delplancke F. Derie F. Paresce A. Glindemann F. Lévy S. Lévêque S. Ménardi 《Astrophysics and Space Science》2003,286(1-2):99-104
The four main scientific objectives of PRIMA – the Phase-Referenced Imaging and Micro-arc second Astrometry facility for the
VLTI – will be described:– extra-solar system characterization with astrometry, to detect planets and evaluate their mass,
and imaging of the dust accretion disk,– galactic center study with astrometry(dynamics of the bulge stars) and imaging at
10μm (piercing the gas and dust clouds surrounding the galactic center),– observations of AGNs and other extra-galactic objects,
too faint to be observed without PRIMA, for which partial imaging is needed to constrain their structuremodels,– micro-gravitational
lensing event resolution (imaging and astrometry of their photo-center) in the Galactic Bulge and Magellanic Clouds, helping
to determine directly the lens mass and distance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
645.
Assessing future risk: quantifying the effects of sea level rise on storm surge risk for the southern shores of Long Island, New York 总被引:1,自引:1,他引:1
Christine C. Shepard Vera N. Agostini Ben Gilmer Tashya Allen Jeff Stone William Brooks Michael W. Beck 《Natural Hazards》2012,60(2):727-745
Sea level rise threatens to increase the impacts of future storms and hurricanes on coastal communities. However, many coastal
hazard mitigation plans do not consider sea level rise when assessing storm surge risk. Here we apply a GIS-based approach
to quantify potential changes in storm surge risk due to sea level rise on Long Island, New York. We demonstrate a method
for combining hazard exposure and community vulnerability to spatially characterize risk for both present and future sea level
conditions using commonly available national data sets. Our results show that sea level rise will likely increase risk in
many coastal areas and will potentially create risk where it was not before. We find that even modest and probable sea level
rise (.5 m by 2080) vastly increases the numbers of people (47% increase) and property loss (73% increase) impacted by storm
surge. In addition, the resulting maps of hazard exposure and community vulnerability provide a clear and useful example of
the visual representation of the spatial distribution of the components of risk that can be helpful for developing targeted
hazard mitigation and climate change adaptation strategies. Our results suggest that coastal agencies tasked with managing
storm surge risk must consider the effects of sea level rise if they are to ensure safe and sustainable coastal communities
in the future. 相似文献
646.
S. Mahmood A. Ahmed A. Hussain M. Athar 《International Journal of Environmental Science and Technology》2005,2(3):193-199
Variability among populations was analyzed in five provenances of Acacia nilotica from spatially variable habitats. Populations of A. nilotica developed in response to their habitat conditions. The level of variability was significantly high among the populations. Phenotypic variability was extremely high for leaf and stipular spine characteristics. The nature of morphological variability for vegetative traits appeared environmentally controlled. The differentiation of leaf and stipular spine expression seems to have an adaptive significance for the species in terms of water economy. Although, seed and pod characteristics are genetically controlled showing a lower proportion of variability but these traits supported r and k-selection that may allow the species to survive under a wide array of contrasting habitats. The study suggested that populations of A. nilotica are differentiated in relation to the heterogeneity of environment. These populations became adapted to their habitat through the variability of morphological expressions. The morphologically differentiated populations of the species had allowed them to maintain themselves in a wide array of environmental situations enabling A. nilotica to occupy ample ecological ranges. 相似文献
647.
John F. Rudge Marian B. Holness Graham C. Smith 《Contributions to Mineralogy and Petrology》2008,156(4):413-429
The spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush, and
in turn is controlled by the rate of crystal growth and accumulation. A predominant non-spherical habit for igneous minerals
brings into question the use of spherical particles in reference packings used for quantification of spatial distribution.
Furthermore, variations of crystal clustering/ordering with length scale require spatial statistics which take into account
the distribution of particles beyond nearest neighbours. Using random close packings of spherocylinders, we demonstrate the
importance of aspect ratio for the aggregation index (usually known as R) and show that packings of spherical particles have more structure than packings of rods. The spatial distribution functions
demonstrate that the plagioclase grains in the colonnade from the Holyoke basalt are clustered on a length scale of 0.5 mm.
Understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques
to well-understood environments. 相似文献
648.
Mirta Garrido Fernando Barra Eduardo Domínguez Joaquin Ruiz Victor A. Valencia 《Mineralium Deposita》2008,43(5):591-597
The La Voluntad porphyry Cu–Mo deposit in Neuquén, Argentina, is one of several poorly known porphyry-type deposits of Paleozoic
to Early Jurassic age in the central and southern Andes. Mineralization at La Voluntad is related to a tonalite porphyry from
the Chachil Plutonic Complex that intruded metasedimentary units of the Piedra Santa Complex. Five new Re–Os molybdenite ages
from four samples representing three different vein types (i.e., quartz–molybdenite, quartz–sericite–molybdenite and quartz–sericite–molybdenite
± chalcopyrite–pyrite) are identical within error and were formed between ~312 to ~316 Ma. Rhenium and Os concentrations range
between 34 to 183 ppm and 112 to 599 ppb, respectively. The new Re–Os ages indicate that the main mineralization event at
La Voluntad, associated to sericitic alteration, was emplaced during a time span of 1.7 ± 3.2 Ma and that the deposit is Carboniferous
in age, not Permian as previously thought. La Voluntad is the oldest porphyry copper deposit so far recognized in the Andes
and indicates the presence of an active magmatic arc, with associated porphyry style mineralization, at the proto-Pacific
margin of Gondwana during the Early Pennsylvanian. 相似文献
649.
Michael A. Carpenter 《Contributions to Mineralogy and Petrology》1982,78(4):433-440
The kinetics of cation disordering in a natural ordered (P2/n) omphacite have been followed at P=18 and 30 kb, T= 750–1,260° C, for times of between 1.5 min and 16 days in a piston-cylinder apparatus. Time-temperature-transformation (TTT) analysis of the experimental data, using the presence or absence of the 11¯1 reflection in single crystal X-ray precession photographs to indicate the extent of reaction, yields an equilibrium order/disorder temperature (T
ord) of 865±10° C, an activation enthalpy (1 bar) of 71±6 kcal mole–1 and an activation volume of 9±4 cm3 mole–1 (plus and minus figures represent the precision of a best fit between experimental data and TTT theory rather than absolute errors). The activation volume is consistent with a vacancy mechanism of cation diffusion. H2O, added in the form of oxalic acid, appears to speed the process up slightly. The overall transformation mechanism is continuous, involving neither the nucleation of a disordered phase nor a change in antiphase-domain distribution. This is consistent with both first- and non-first-order character for the C2/cP2/n transformation, though a range of ordered states below T
ord is indicated by the weakening of h+k=odd reflections. A simple extrapolation of the disordering rates to geological conditions leads to the first estimate of how long disordered omphacites would take to order in nature, ranging from less than one year at T800° C to more than 107 years at T<350° C. 相似文献
650.
Jun Liu Letitia Topor Jianzhong Zhang Alexandra Navrotsky Robert C. Liebermann 《Physics and Chemistry of Minerals》1996,23(1):11-16
High temperature drop-solution calorimetry in molten 2 PbO · B2O3 at 1044 K for coesite and stishovite polymorphs of silica was carried out to determine the enthalpy of the coesite-stishovite transition. These experiments were performed on high-purity, single-phase samples of coesite and stishovite. Our new value for the enthalpy of the coesitestishovite transition (ΔH 298 0 ) is 29.85 ± 0.78 kJ/mol, which is about 35% lower than previously reported by Akaogi and Navrotsky (1984) and Holm et al. (1967), but which compares well with new measurements by Akaogi et al. (1994b). Using these new data, we have calculated the equilibrium phase boundary between coesite and stishovite and obtained a slope, dP/dT=0.0031 (2) GPa/K. This calculated slope is in good agreement with that determined [0.0026 (2) GPa/K] from the in-situ X-ray diffraction study of Zhang et al. (1996). 相似文献