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41.
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The paper reports the results of the textural and mineralogical studying of clast Kaidun #d6A. The principal minerals of the clast are phyllosilicates, carbonates, and sulfides, but the clast contains no anhydrous silicates. The clast is characterized by extremely high concentration of inclusions, which broadly vary in size, composition, and texture, from completely remelted to practically unchanged when brought to the parent body. The latter group includes two inclusions having a concentrically zonal texture, which have never before been found in meteorites. One of the inclusions consists of serpentine replaced by talc in the margins. The inclusion was formed in relation to silification under the effect of silicon-bearing aqueous fluid at a temperature of more than 300°C. The other inclusion consists of alternating Ca carbonate and phyllosilicate zones. The texture and composition of the inclusion suggest that its genesis was related to the metasomatic alteration of carbonates under the effect of silicon- and alumina-bearing aqueous fluids at temperatures of about 400–500°C. These processes are typical of large differentiated planets, and there are no reasons to expect them in the parent bodies of carbonaceous chondrites, such as Kaidun. Our results obtained on clast #d6A are in good agreement with the hypothesis that the parent body of the Kaidun meteorite was Phobos [1]. Correspondingly, inclusions #d6Aa and #d6Ab likely originated from Mars, as previously examined alkali-rich clasts did. The clast described in this publication seems to originate from the surface regolith of Phobos, which was compacted in the process of the aqueous alteration of the material and subsequently buried at a greater depth.  相似文献   
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Study of biogeochemical processes in water and sediments of the Chukchi Sea in August 2004 revealed atypical maximums of the concentration of biogenic elements (N, P, and Si) and the rate of microbial sulfate reduction in the surface layer (0–3 cm) of marine sediments. The C: N: P ratio in the organic matter (OM) of this layer does not fit the Redfield-Richards stoichiometric model. Specific features of biogeochemical processes in sea are likely related to the complex dynamics of water, high primary productivity (110–1400 mg C/(m2 day)), low depth of basin (<50 m in 60% of the water area), reduced food chain due to low population of zooplankton, high density of zoobenthos (up to 4230 g m?2), and high activity of microbial processes. Drastic decrease in the concentration of biogenic elements, iodine, total alkalinity (Alk), and population of microorganisms beneath the 0–3 cm layer testify to a large-scale OM decay at the water-seafloor barrier. Our original experimental data support the high annual rate of OM mineralization at the bottom of the Chukchi Sea.  相似文献   
45.
The application of the Sm-Nd isotope system of scheelite to dating of low-sulfide, quartz-vein hosted Au mineralization is still under discussion. In the present work, new Sm-Nd and Rb-Sr data for scheelite from the giant Muruntau/Myutenbai Au deposit (Kyzylkum, Western Uzbekistan) are discussed. Based on the geological relationship, mineralogical properties, and trace element characteristics, two types of scheelite can be distinguished within the deposit. The first one is represented by early bluish luminescent and weakly coloured scheelite (generation 1) found within strongly deformed flat quartz veins. The apparent isochron defined by this scheelite (351ᆪ Ma) is interpreted as a mixing line. Typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins (generation 2) defines a Sm-Nd isochron age of 279ᆦ Ma ()Nd=-9.5ǂ.3; MSWD: 1.5). No evidence for mixing or disturbance by late alteration were found for these scheelites. This Sm-Nd isochron age agrees with the Rb-Sr and K-Ar age range for wall rock alteration in this deposit reported previously. The age of 280 Ma is interpreted to date the high-grade ore formation in the Muruntau deposit. There are currently no reliable age data available on the magmatic events in the Muruntau region. Probably, there is some overlap in time of the Hercynian gold deposition with the intrusion of lamprophyric dykes. The Nd and Sr isotopic signatures of scheelite define the wall rocks (mainly metasiltstones and metasandstones) as the most probable sources for these elements in scheelite.  相似文献   
46.
Direct observation of active emission of fluids and mud from a submarine mud volcano were made for the first time in an extensive field of mud diapirs and mud volcanoes on the Mediterranean Ridge using a video camera towed 2 m above the seafloor in 1800 m of water. This recent research using both long range and deep-towed sidescan sonar systems indicates also that diapirism and eruption of mud along the crest of the ridge is more common than previously thought. The southwards increase in age of rock fragments carried within the erupted mud supports the hypothesis that the fluid mud becomes overpressured within a southward-dipping backthrust from the Inner Deformation Front of this accretionary prism.  相似文献   
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An analysis is presented which seeks to reveal the possible causes for discrepancy in the results on the dependence of Cepheid amplitudes on star positions in the instability strip noted by different investigators.A comparison of the data used in two of these investigations—that of Yakimova (1970) and that of Sandage and Tammann (1971)—shows that it is most unlikely to be able to explain completely the conflicting results obtained in these studies. But if we analyse the data of Sandage and Tammann following the approach of Yakimova — namely, by considering the Cepheids in only one stellar system and taking into account the stellar colours in maximum light — we obtain Yakimova's result: the light amplitude is the larger, the nearer to the low temperature edge of the instability strip a Cepheid is. Therefore, it appears that differences between the various approaches contribute greatly to the different results of Sandage and Tammann and Yakimova (and the other investigators).  相似文献   
49.
It is shown that the size-frequency distribution (SFD) of a time-averaged projectile population derived from the lunar crater SFD of Neukum and Ivanov (in Hazards Due to Comets and Asteroids (T. Gehrels, Ed.), 1994, pp. 359-416, Univ. of Arizona Press, Tucson) provides a convincing fit to the SFD of the current near-Earth asteroid (NEA) population, as deduced from the results of asteroid search programs. Our results suggest that the shape of the SFD of the impactor flux has remained in a steady state since the late heavy bombardment, so that the current NEA population can be viewed as a snapshot of the flux of impactors on the Moon. The number of bodies in the projectile population with diameters of 1 km or more is 700±130, which is in good agreement with recent estimates of the total number of NEAs in this size range. Our results imply that the contribution to the projectile flux from comets is small for diameters below 10 km.  相似文献   
50.
Attention is paid to the generation of the Katrine hurricane with destructive consequences during the geomagnetic extrastorm of August 24, 2005, at a repeated crossing of the strongly disturbed IMF sector boundary. This fact is discussed in the light of the Eigenson-Usmanov hypothesis that solar activity can affect generation of hurricanes. According to the law of enhancement, solar activity and corresponding geomagnetic disturbances increase baric contrasts in the lower atmosphere over oceans on the Earth’s dayside hemisphere and decrease background pressure at tropical latitudes. It has been assumed that this can be one of the factors facilitating triggering of the positive feedback mechanisms necessary for generation and maintenance of hurricanes according to the Golitsyn [1999] model.  相似文献   
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