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791.
Plagioclase preferred orientation, Foreshore Group metasediments, Bluff, New Zealand 总被引:1,自引:0,他引:1
David Shelley 《Tectonophysics》1979,58(3-4)
Recrystallised plagioclase in volcanic metasediments of the Foreshore Group (hornblende-hornfels facies) has a strong preferred orientation with crystal a-axes [100] lying parallel to bedding and with a maximum parallel to a lineation (= maximum principal strain axis or axis of greatest elongation); composition varies widely from bed to bed from oligoclase to anorthite. The preferred orientation is interpreted to result from the mechanical rotation of elongate plagioclase ejecta in the original unconsolidated tuff during strain caused by intrusion of the adjacent Bluff igneous complex. Evidence for such an orienting mechanism is found in the preferred orientation of large unrecrystallised plagioclase ejecta. Matrix plagioclase is generally recrystallised to form granoblastic mosaics; this texture represents a mimetic recrystallisation which reduced grainboundary energy in the fine-grained matrix during the thermal event immediately succeeding deformation. 相似文献
792.
793.
David J. Des Marais J.M. Mitchell W.G. Meinschein J.M. Hayes 《Geochimica et cosmochimica acta》1980,44(12):2075-2086
The structures and 13C contents of individual alkanes extracted from bat guano found in the Carlsbad region of New Mexico can be related to both the photosynthetic pathways of the local plants and the feeding habits of the insects that support the bats.Carbon isotopic analyses show that equivalent numbers of C3 and C4 native plant species occupy the Pecos River Valley, a very significant feeding area for the Carlsbad bats. During the seasons when bats frequent the area, the agricultural crops consist principally of alfalfa and cotton, both C3 plants.The molecular composition of the bat guano hydrocarbons is fully consistent with an insect origin. Two isotopically distinct groups of insect branched alkanes were discerned. These two groups of alkanes derived from two chemotaxonomically distinct populations of insects possessing distinctly different feeding habits. It is possible that one population grazes predominantly on crops whereas the other population prefers native vegetation. This and other isotopic evidence suggests that crop pests constitute a major percentage of the bats' diet.Because the guano sample was less than 40 years old, this material reflects the present day plant community in the Pecos River Valley. Future studies of more ancient guano deposits should reveal a measurable influence of both natural and man-induced vegetative changes with time upon the 13C content of the bat guano hydrocarbons. 相似文献
794.
Joachim Hoefs Gunter Faure David H. Elliot 《Contributions to Mineralogy and Petrology》1980,75(3):199-203
Theδ18O (SMOW) values of the Kirkpatrick Basalt (Jurassic) on Mt. Falla, Queen Alexandra Range, vary between +6.3‰ and +8.6‰ The apparent enrichment of these rocks in18O excludes the possibility that they were altered by interaction with aqueous solutions of meteoric origin. Theδ18O values of the flows correlate significantly with the initial87Sr/86Sr ratios and all major elements. These correlations confirm the hypothesis that the basalt magma was contaminated by rocks of the continental crust through which it was extruded. Estimates of the chemical composition of the basalt magma and the contaminant, based on extrapolations of the new oxygen data, generally confirm earlier estimates based on extrapolations of initial87Sr/86Sr ratios. The87Sr/86Sr ratio of the uncontaminated basalt was 0.7093 which indicates that magma may have originated by melting either in old Rb-enriched lithospheric mantle under Antarctica or in the overlying crust, or both. 相似文献
795.
Heat generation and heat flow were determined for the Bohus granite massif in western Sweden. This is the start of a major program concerning geothermal energy in Sweden. Neutron activation analyses, temperature measurements, thermal conductivity measurements have been carried out. As was expected the result, 76 mW m−2, shows that even old Precambrian shields locally exhibit much higher values than normal. 相似文献
796.
797.
Melt density and the average composition of basalt 总被引:9,自引:0,他引:9
Densities of residual liquids produced by low pressure fractionation of olivine-rich melts pass through a minimum when pyroxene and plagioclase joint the crystallization sequence. The observation that erupted basalt compositions cluster around the degree of fractionation from picritic liquids corresponding to the density minimum in the liquid line of descent may thus suggest that the earth's crust imposes a density filter on the liquids that pass through it, favoring the eruption of the light liquids at the density minimum over the eruption of denser more fractionated and less fractionated liquids. 相似文献
798.
Twenty-seven colonies of wild scyphistomae ofChrysaora quinquecirrha were observed for a period of ten weeks during the summer. Asexual activities of individual organisms were recorded several times each week. Polyps most often proceeded to strobilate in mid-June and then strobilate a second time 18 days later. They then detached and changed position by means of stolons and then produced podocysts. Initial cysts first excysted and the resulting polyps then strobilated. A second strobilation was not generally observed. The developmental implications of these activities are discussed. 相似文献
799.
An extensive ancient archeologic site containing lithic artifacts and associated with mammoth remains was reported at Chinitna Bay, southern Alaska in 1943. The presence of such a site adjacent to the continental shelf at the base of the rugged Aleutian Range suggested that humans may have inhabited the inner shelf environment during the late Pleistocene at times of lowered sea level. Because of the site's potential significance, an interdisciplinary research team relocated and reinvestigated the area in 1978, but failed to find evidence of prehistoric human habitation. Geologic studies and radiocarbon dating indicate that the strata reported at the site are intertidal in origin, very late Holocene in age, and have undergone significant tectonic movement in the recent past. These observations indicate that the previously published observations of the Chinitna Bay site are probably invalid. 相似文献
800.
A 1950–1994 data set of major weather losses developed by the property insurance industry was examined to assess its potential utility in climate change research and use in assessing the relevance of recent extreme losses in the United States. A process for adjusting these historical storm losses to ever-changing factors including dollar values, amount of insurance coverage per area, and the sensitivity of society to damaging storms was developed by the industry. Analysis of the temporal frequency and losses of these adjusted weather catastrophes revealed differences according to the amount of loss. Temporal changes since 1975 in the catastrophes causing $35 to $100 million in loss were strongly related to changes in U.S. population, whereas catastrophes that created insured losses greater than $100 million appear related to both shifting weather conditions and to regional population changes. This evaluation revealed that the industry's catastrophe adjustment technique did not adequately allow for changes in various demographic and social factors affecting damage; however, results suggest use of population values for normalizing the adjusted catastrophe database to allow meaningful studies of their temporal variability. 相似文献