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291.
292.
The possible discovery of three new -ray pulsars PSR 0656+14, PSR 0950+08, and PSR 1822-09 (Ma, Lu, Yu, and Young, 1993) in data obtained with the COS-B experiment is reinvestigated using a refined technique for pulsar light curve analysis. The results of this study do not confirm the previously claimed -ray pulsar nature of any of these pulsars. Even when using the standard epoch folding technique in conjunction with energy-dependent acceptance cones, we do not detect pulsed -ray emission from these sources. We suspect that insufficient position accuracy is the cause for the discrepancy between our results and those of Maet al. (1993). We do not rule out that any one of the three candidates, or all of them, is in fact a -ray pulsar, but their spin properties must differ from those derived by Maet al. (1993). More work is needed to determine the correct high-energy properties of these three sources.  相似文献   
293.
The Mariner 6 and 7 infrared spectrometers provided data which, in principle, determine upper limits on the possible atmospheric abundance of every gaseous substance that was undetected but which has recognized absorptions in the accessible spectral region, 1.9 to 14.4 μ. Through supporting laboratory determinations of curves of growth under pressure broadening conditions appropriate to Mars, upper limits can be specified (expressed first in cm-atm, STP, for a vertical column and then in parts per million) for the following gases: NO2 (<0.0016, 0.23); NH3 (<0.0031, 0.44); C3O2 (<0.0032, 0.45); SO2 (?0.0037, 0.52); OCS (<0.0040, 0.56); NO (<0.0050, 0.70); O3 (<0.0061, 0.86); CH4 (<0.026, 3.7); N2O (<0.13, 18); HCl (<3.7, 520); HBr (?8.2, 1150); H2S (<27, 3800). In addition, considerations of band contours, moments of inertia, and experimental absorption coefficients permit us to place useful upper limits on twenty-seven additional substances that were not detected and for which curves of growth have not been measured: less than 1.0ppm (or, <0.0071cm-atm); SF6, NF3, Cl2CO, CF4, CHF3, Br2CO, SiF4; less than 6.0ppm (or, <0.035 cm-atm); C2F6, CO3, F2CO, C2H4, BF3, CS2, CHCl3, C2H6, H2CO, CH3F, C6H6, CH2I2; less than 50ppm (or, <0.35 cm-atm): C2H2, HCN, CH2Br2, CH2Cl2, CH3Br, PH3, CH3I, and CH3Cl. These upper limits are compared to earlier limits based upon terrestrial measurements. The present limits placed upon the possible atmospheric content of the molecules C3O2 and CO3 are of particular interest because of their relevance to the photochemistry of the Martian atmosphere.  相似文献   
294.
We discuss recent results from near-infrared bispectrum speckle interferometry observations of the young outflow sources in the S140 and Mon R2 star forming regions. With spatial resolutions down to 0.075'', our data represent the highest resolution images obtained so far for these objects and exhibit previously unseen complex structures in the immediate vicinity of the young stellar objects. We discuss the relation of these structures to the jets and outflows.  相似文献   
295.
Abstract— The suevite breccia of the Chicxulub impact crater, Yucatàn, Mexico, is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters. Detailed studies (microscope, electron microprobe, SEM, XRF) have been carried out on a noncontinuous set of samples from the drill hole Yucatàn 6 (Y6) located 50 km SW from the center of the impact structure. Three subunits can be distinguished in the suevite: the upper unit is a fine‐grained carbonate‐rich suevite breccia with few shocked basement clasts, mostly altered melt fragments, and formerly melted carbonate material; the middle suevite is a coarse‐grained suevite with shocked basement clasts and altered silicate melt fragments; the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts. The matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene. The composition of the upper members of the suevite is dominated by the sedimentary cover of the Yucatàn target rock. With depth in well Y6, the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly. Even at the thin section scale, melt phases of different chemistry can be identified, showing that no widespread homogenization of the melt took place. The melt compositions also reflect the heterogeneity of the deep Yucatàn basement. Calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt. The proportion of carbonate to evaporite clasts is less than 5:1, except in the lower suevite where large evaporite clasts are present. This proportion constrains the amount of CO2 and SOX released by the impact event.  相似文献   
296.
Bacterial spores (Bacillus subtilis), cyanobacteria (Chroococcidiopsis sp.), and lichen (Xanthoria elegans) embedded in martian analogue rock (gabbro) were exposed to shock pressures between 5 and 50 GPa which is the range of pressures observed in martian meteorites. The survival of Bacillus subtilis and Xanthoria elegans up to 45 GPa and of Chroococcidiopsis sp. up to 10 GPa supports the possibility of transfer of life inside meteoroids between Mars and Earth and it implies the potential for the transfer of life from any Mars-like planet to other habitable planets in the same stellar system.  相似文献   
297.
Zusammenfassung Der starke Süßwassereintrag im Sommer 1987 führte in der Deutschen Bucht zu erhöhten Konzentrationen der anorganischen Stickstoffverbindungen. Keine Konzentrationserhöhung gegenüber den Sommer 1986 zeigte sich beim anorganischen gelösten Phosphat. Wie die im Vergleich zu normalen Sommern in Oberflächennähe hohen Nährstoffkonzentrationen und niedrigen pH-Werte zeigen, führte das erhöhte Nährstoffangebot nicht zu einer verstärkten Primäproduktion. Dies und eine wetterbedingte stärkere Wasserdurchmischung verhinderten ungünstige Auswirkungen auf den Sauerstoffhaushalt in der Deutschen Bucht.
Increased concentrations of the inorganic nitrogen compounds in the German Bight during the rainy summer 1987
Summary Due to the strong freshwater input during spring and summer 1987, increased concentrations of inorganic nitrogen were measured in the German Bight. Compared to 1986, no change was found in the concentration of dissolved inorganic phosphate. Relatively high nutrient concentrations and low pH values in the upper water layer indicate, that the increased nutrient supply was not utilized for primary production. Therefore, and due to a weak stratification no oxygen deficiency occured in the German Bight.
  相似文献   
298.

Editorial

Formation of island ecosystems and genetic change after colonization  相似文献   
299.
Abstract— The chemical composition of suevites, displaced Cretaceous target rocks, and impact‐generated dikes within these rocks from the Yaxcopoil‐1 (Yax‐1) drill core, Chicxulub impact crater, Mexico, is reported and compared with the data from the Yucatán 6 (Y6) samples. Within the six suevite subunits of Yax‐1, four units with different chemical compositions can be distinguished: a) upper/lower sorted and upper suevite (depth of 795–846 m); b) middle suevite (depth of 846–861 m); c) brecciated impact melt rock (depth of 861–885 m); and d) lower suevite (depth of 885–895 m). The suevite sequence (a), (b), and (d) display an increase of the CaO content and a decrease of the silicate basement component from top to bottom. In contrast, the suevite of Y6 shows an inverse trend. The different distances of the Yax‐1 and Y6 drilling sites from the crater center (~60, and ~47 km, respectively) lead to different suevite sequences. Within the Cretaceous rocks of Yax‐1, a suevitic dike (depth of ~916 m) does not display chemical differences when compared with the suevite, while an impact melt rock dike (depth of ~1348 m) is significantly enriched in immobile elements. A clastic breccia dike (depth of ~1316 m) is dominated by material derived locally from the host rock, while the silicate‐rich component is similar to that found in the suevite. Significant enrichments of the K2O content were observed in the Yax‐1 suevite and the impact‐generated dikes. All impactites of Yax‐1 and Y6 are mixtures of a crystalline basement and a carbonate component from the sedimentary cover. An anhydrite component in the impactites is missing (Yax‐1) or negligible (Y6).  相似文献   
300.
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