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131.
Possibility of a persistent structure of source free pure magnetic field contained by the curvature of a static cylindrically
symmetric space-time associated with its own strength of energy density in five dimensional Kaluza-Klein space-time is investigated.
It may be considered as the generalization of Melvin's 4D ‘magnetic universe’ in five dimensional K-K space-time. Time like
and null geodesics are studied in order to investigate the nature of gravitation produced by it and are found not to deviate
much from those noted in Melvin's spacetime. It is further interesting to note that near the axis of symmetry our 5D space-time
exhibits the conical defect similar to that in the case of a string.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
132.
133.
Lynn Margulis Elso S. Barghoorn Debra Ashendorf Sumana Banerjee David Chase Susan Francis Stephen Giovannoni John Stolz 《Precambrian Research》1980,11(2):93-123
In the hypersaline lagoon at Laguna Figueroa vertically stratified diverse communities of microorganisms thrive. The modern sediments of Baja California at Laguna Figueroa contain cyanobacterial communities and sedimentary structures produced by these blue greens that have already been studied by Horodyski and his colleagues. This paper provides an introduction to the complex microbial communities, primarily those that underlie the laminated Microcoleus mats. They are composed of anaerobic photosynthetic and heterotrophic bacteria.The following genera of cyanobacteria at least are components of these mat communities: Lyngbya, Microcoleus, Entophysalis, Phormidium, Pseudoanabaena, Anabaena and Schizothrix. Among the photosynthetic bacteria several species of Thiocapsa-like microbes formed major surface components of certain mats and scums; rhodospirilli, rhodopseudomonads, chromatis and others were seen.The following nonphotosynthetic bacteria were identified: Nocardia sp., three types of spirilli, two types of Spirochaeta sp., two types of Desulfovibria sp., a new strain of red Beneckea and four distinctive unidentified coccoid and filamentous bacteria. Reasons are given for believing several of the species are new to science and that the microbial diversity is far greater than the approximately twenty species reported here. Eukaryotes are extremely rare. Only one species of animal, a herpachtechoid copepod, was ever seen in the 8-km long microbial communities of the hypersaline basin. Dunaliella salina, a chlorophyte and Aspergillus sydowi, an ascomycetous fungus were the only eukaryotes that were observed to be regular components of mat communities. Ciliates, amoebae (including a chrysarchnion-like microbe) and diatom tests, mostly empty, were the only other eukaryotes observed. Attempts to enrich for eukaryotic microorganisms were not successful whereas attempts to enrich for bacteria, especially anaerobes led to such a profusion of forms that to continue detailed study of them was beyond our means. Unidentified small rods and cocci constituted the largest fraction of individuals in the subsurface community. The microbes isolated from mats are adapted for alternating dry and wet conditions as well as high concentrations of salt and low concentrations of oxygen. 相似文献
134.
Exact solutions are obtained in (4+1) dimensions for plane symmetric and cylindrically symmetric inhomogeneous spacetimes. In the former case the three space depends on time only while the metric corresponding to the extra dimension is dependent on space as well as time coordinates. The cylindrically symmetric nonstatic solutions for the perfect fluid have no singularity near the axis, but show big bang type of singularity in the finite past. One of the classes of such solutions satisfies the barotropic equation of state of the form =p. Static solutions with cylindrically symmetric solutions are also obtained in 5 dimensions. 相似文献
135.
We have observed natural remanent magnetizations (NRM), ranging from 10−3 to 10−5 Gauss cm3/g, at least two orders of magnitude greater than 10−7, the noise level of our spinner magnetometer, in the carbonaceous chondrites, Orgueil, Cold Bokkeveld, Nogoya and Mighei. Preliminary alternating field demagnetization of two samples of Orgueil showed a moderate sized stable component of 10−4 Gauss cm3/g. Microscopic study reveals that a grey spinel oxide, Ni-Fe and an Fe sulphide are the principal opaque minerals in both Cold Bokkeveld and Orgueil; the oxide phase predominates in both, while the Ni-Fe is more visible in the former. Coercive force determinations in Orgueil and Cold Bokkeveld indicate single domain particles as the NRM carrier. These meteorites are suitable for the determination of the magnetic field intensity in the primary solar nebula. 相似文献
136.
137.
P. K. Banerjee 《Geo-Marine Letters》1993,13(1):56-60
Along the coast of East and South India, a slow and minor sea level fall as an immediate response to the Last Glacial Maximum (LGM) followed by strong aridity and fast retreat of the sea to the outer shelf are indicated by coastal ironstones, traces of channels in nearshore shallow seismic reflectors, and submerged, structureless, multimineral placer sands. Nearshore peat beds and inland beach ridges reflect perturbations during Early to Mid-Holocene sea level rise. The Little Ice Age witnessed shifts in littoral sediment budget, possibly as a result of reduced transport of sediments from the Himalaya to the Bay of Bengal. 相似文献
138.
Mineral chemical analyses of transitional basalts from the Carlsberg Ridge show plagioclase (An ~ 87 mole %), phenocrysts, and microphenocrysts have a K2O depletion as compared to the laths (An ~ 79 mole %). Olivine (Fo ~ 91 mole %) are few and rarely zoned. The composition of plagioclase and olivine indicate low pressure equilibrium crystallization. The basalts were probably derived through fractional crystallization at shallow depths under low partial melting conditions. Morphology of plagioclase phenocrysts and bulk rock chemistry suggest magma mixing and fractional crystallization for the origin of these basalts. (Detailed chemical analyses can be obtained from the authors.) 相似文献
139.
Study of precipitation chemistry over an industrial city 总被引:2,自引:2,他引:0
The growing trend of industrialization has marked impact on the atmospheric chemistry around the globe. Such impacts are also predicted for developing countries like India. Acid precipitation due to secondary pollutants is one of them. The present investigation was conducted with an aim of studying the precipitation chemistry over Asansol city, India during the monsoon season. The rain water samples, collected on event basis during the period of June to September 2006, were analyzed for HCO3 ?, Cl?, SO4 2?, NO3 ?, NH4 +, K+, Na+, Mg2+, Ca2+ and pH using standard procedures. The study revealed that the precipitation was alkaline in nature with mean pH value of 6.08. Dominant anion in rain water samples was HCO3 ? (36 %), whereas Ca2+ was highest among the cations (53 %). The observed acidic events, based on pH value, were only 17 %, indicating the alkaline components effectively neutralize rain water over the area. This was also supported by the total alkaline to acid ion ration of 1.05. The ratio of (NO3-?+Cl?) and SO4 2? was >1, indicating that acidic properties were influenced by HNO3 and HCl. In the ratio between (Ca2++NH4 +) and (NO3 ?+SO4 2?), values >1 were obtained, indicating significant alkaline influence, which effectively prevented acid depositions in the area. 相似文献
140.
Konstantin Kröniger Frederik De Roo Peter Brugger Sadiq Huq Tirtha Banerjee Judith Zinsser Eyal Rotenberg Dan Yakir Shani Rohatyn Matthias Mauder 《Boundary-Layer Meteorology》2018,169(2):209-232
Afforestation in semi-arid regions can potentially enhance the global carbon sink by increasing the terrestrial biomass. However, the survival of planted forests under such extreme environmental conditions is not guaranteed a priori, and critically depends on the surface–atmosphere exchange of energy. We investigate the pine forest Yatir in Israel, an example of a man-made semi-arid ecosystem, by means of large-eddy simulations. We focus on the interaction between surface–atmosphere exchange and secondary circulations that couple the isolated forest to the surrounding shrubland. The large-eddy simulations feature a grid resolution that resolves the forest canopy in several layers, and are initialized by satellite data and Doppler lidar, eddy-covariance and radiosonde measurements. We perform three large-eddy simulations with different geostrophic wind speeds to investigate the influence of those wind speeds on the surface–atmosphere exchange. We reproduce the measured mean updrafts above the forest and mean downdrafts above the shrubland, which increase in strength with decreasing geostrophic wind speed. The largest updrafts emerge above the older, denser part of the forest, triggering secondary circulations. The spatial extent of these circulations does not cover the entire forest area, although we observe a reduced aerodynamic resistance in the regions of updraft. Our simulations indicate that the enhanced surface–atmosphere exchange of the Yatir forest is not sufficient to compensate for the increased net radiation, due to the lower albedo of the forest with respect to the surroundings, resulting in higher air temperatures inside the forest. However, the difference between the forest and shrubland temperatures decreases with increasing geostrophic wind speed due to reduction in the aerodynamic resistance. 相似文献