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41.
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中更新世气候转型与100ka周期研究 总被引:6,自引:0,他引:6
中更新世气候转型是第四纪气候变化中最重要的特征之一,它是指全球气候的主导周期在中更新世时从41ka转变为100ka,且气候波动的幅度也加大。经典的Milankovitch假说不能完全解释中更新世气候转型的原因以及100ka周期在气候记录中的强烈表现,因为太阳辐射与气候记录之间存在着相当的差异,尤其是二者在变化幅度上不匹配。近年来围绕这一转型过程的时代和原因获得了一些新的进展,主要是针对中更新世气候转型的时间、对气候记录中100ka周期的重新检讨以及非太阳辐射因素在这一转型过程中所起的作用。其它可能的转型原因包括大冰盖、温室气体、地球轨道面倾角、冰盖基底、构造隆升等。 相似文献
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Phase Equilibria of Hornblende‐Bearing Eclogite in the Western Dabie Mountain,Central China 总被引:1,自引:0,他引:1
The high-pressure (HP) eclogite in the western Dabie Mountain encloses numerous hornblendes, mostly barroisite. Opinions on the peak metamorphic P-T condition, PT path and mineral paragenesis of it are still in dispute. Generally, HP eclogite involves garnet, omphacite, hornblendes and quartz, with or without glaucophane, zoisite and phengite. The garnet has compositional zoning with XMg increase, XCa and XMn decrease from core to rim, which indicates a progressive metamorphism. The phase equilibria of the HP eclogite modeled by the P-T pseudosection method developed recently showed the following: (1) the growth zonation of garnet records a progressive metamorphic PT path from pre-peak condition of 1.9–2.1 GPa at 508°C–514°C to a peak one of 2.3–2.5 GPa at 528°C–531°C for the HP eclogite; (2) the peak mineral assemblage is garnet+omphacite+glaucophane+quartz±phengite, likely paragenetic with lawsonite; (3) the extensive hornblendes derive mainly from glaucophane, partial omphacite and even a little garnet due to the decompression with some heating during the post-peak stage, mostly representing the conditions of about 1.4–1.6 GPa and 580°C–640°C, and their growth is favored by the dehydration of lawsonite into zoisite or epidote, but most of the garnet, omphacite or phengite in the HP eclogite still preserve their compositions at peak condition, and they are not obviously equilibrious with the hornblendes. 相似文献
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W. H. Berger 《International Journal of Earth Sciences》1999,88(2):305-316
The ice-age hypothesis of Muller and MacDonald (1995, 1997a, 1997b) has two parts: (a) The 100-kyr cycle does not owe its
existence to Milankovitch forcing; and (b) variations in inclination of Earth's orbit (i.e., the orbit's angle with the solar
system invariable plane) provide the mechanism sought. In support of the first proposition, Muller and MacDonald point to
the paradox that the spectrum of oxygen isotope series from deep-sea sediments contains no power for two prominent eccentricity
cycles, 125 and 400 kyr. In support of the second proposition, they offer a match between the SPECMAP record (Imbrie et al.
1984) and a plot of the amplitude of orbital inclination, shifted by 33 kyr. The hypothesis of Muller and MacDonald is rejected
in both parts, although an influence of inclination forcing is not precluded entirely. The paradox of the missing eccentricity
cycles (125 and 400 kyr) is explained by suppression of the two longer cycles, and enhancement of the one near 96 kyr, as
a result of internal oscillation. A Muller–MacDonald machine for making the 100-kyr ice-age cycles, however conceived, would
have to have a memory near 30 kyr to provide for phase shift between input and output. Precisely this amount of memory is
sufficient to produce the needed oscillation in Milankovitch machine here applied; thus, there is no advantage, from the point
of view of either necessity or simplicity, in replacing Milankovitch forcing, with its precise phasing (despite the fuzzy
physics), with inclination forcing, and with its severe problems in phasing (and, thus far, no physics at all).
Received: 10 June 1998 / Accepted: 2 February 1999 相似文献
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利用1993年4—6月共4次南京降雨过程中取到的GBPP-100资料与滤纸斑点法所取资料,通过对应资料的雨滴谱基本参量的计算分析,研究GBPP-100用于外场观测的可行性。结果表明:在瞬时雨强度变化缓慢且雨强小于160mm·h-1的阵性降水和非阵性降水过程中,GBPP-100完全可代替滤纸斑点法用于外场观测,对雨强变化迅速阵性降水GBPP-100与滤纸斑点法取样结果差异较大,其原因还有待进一步研究。 相似文献
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