全文获取类型
收费全文 | 724篇 |
免费 | 142篇 |
国内免费 | 278篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 81篇 |
地球物理 | 173篇 |
地质学 | 600篇 |
海洋学 | 144篇 |
天文学 | 10篇 |
综合类 | 49篇 |
自然地理 | 77篇 |
出版年
2024年 | 6篇 |
2023年 | 17篇 |
2022年 | 33篇 |
2021年 | 30篇 |
2020年 | 30篇 |
2019年 | 47篇 |
2018年 | 24篇 |
2017年 | 47篇 |
2016年 | 27篇 |
2015年 | 29篇 |
2014年 | 50篇 |
2013年 | 59篇 |
2012年 | 47篇 |
2011年 | 36篇 |
2010年 | 35篇 |
2009年 | 50篇 |
2008年 | 50篇 |
2007年 | 55篇 |
2006年 | 65篇 |
2005年 | 50篇 |
2004年 | 41篇 |
2003年 | 34篇 |
2002年 | 29篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 31篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 26篇 |
1995年 | 17篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有1144条查询结果,搜索用时 15 毫秒
221.
Alessandro Morbmelli Jacques Henrard 《Celestial Mechanics and Dynamical Astronomy》1991,51(2):131-167
In this paper a theoretical perturbation approach to the problem of the dynamics in secular resonance is exposed. This approach avoids any expansion of the main term of the Hamiltonian (linear term in the masses) with respect to the eccentricity or the inclination of the asteroid, in order to achieve results valid for any value of these variables. Moreover suitable action-angle variables are introduced to take properly into account the dynamics related to the motion of the argument of perihelion of the asteroid, which is relevant at high inclination. A class of secular resonances wider than that usually considered is found. An explicit computation of the location of the main secular resonances, estimating also the contribution of the quadratic term in the masses by means of classical series expansion, is reported in the last sections. The accuracy of computations obtained by series expansion is discussed in the paper. 相似文献
222.
金刚石绳索取心钻进要求冲洗液有良好的流变性、泥皮薄而韧,能有效防止钻杆内壁结垢,有利于内管通过。ST-1无固相冲洗液主要南ST-1高分子防塌剂组成,具有吸附在孔壁岩层粘土矿物,抑制粘土岩、泥岩水化膨胀的优点.其线型长链卷曲成团状物,渗析于孔壁表面或孔隙内,减少或阻止冲洗液向孔壁内渗透,具有絮凝劣质土、岩屑而不絮凝优质土的功能,把冲洗液中的岩屑携带到地面及时絮凝聚沉,从而降低冲洗液的同相含量,保持冲洗液的低比重、低粘度。详细介绍了该冲洗液的配制方法以及在不同地层中的应用,经过生产试验证实该冲液在预防钻杆内壁结垢,使孔壁园滑.防塌防缩径方面具有很好的效果。 相似文献
223.
Andrea Brogi 《International Journal of Earth Sciences》2008,97(4):677-703
The tectonic evolution of the Mt Amiata volcano-geothermal area is under discussion. Some authors state that this region,
as well as the hinterland of the Northern Apennines, were affected by compression from the Cretaceous to the Quaternary. In
contrast, most authors believe that extension drove the tectonic evolution of the Northern Apennines from the Early Miocene
to the Quaternary. Field data, seismic analyses and borehole logs have been integrated in order to better define the structural
features of the continental crust in the Mt Amiata geothermal area. In this paper I propose the hypothesis that the structure
of the crust in the Mt Amiata volcano-geothermal area derives from two main geological processes: (1) contractional tectonics
related to the stacking of the Northern Apennines (Cretaceous–Early Miocene), (2) subsequent extensional collapse of the hinterland
of the mountain chain, and related opening of the Northern Tyrrhenian Sea (Early Miocene–Quaternary). Compressional and extensional
structures characterise the Mt Amiata region, although extensional structures dominate its geological framework. In particular
the extension produced: (a) Middle-Late Miocene boudinage of the previously stacked tectonic units; (b) Pliocene–Quaternary
normal faulting which favoured the emplacement of a magmatic body in the middle-upper crust; and (c) the eruption of the Mt
Amiata volcano, which gave rise to an acid and intermediate volcanic complex (0.3–0.19 Ma). The extension produced the space
necessary to accommodate the Middle-Late Miocene marine and continental sediments. Pliocene and Quaternary normal and transtensional
faults dissected the previous structures and influenced the Early Middle Pliocene marine sedimentation within the structural
depressions neighbouring the Mt Amiata volcano. The magmatic body was emplaced at depth (about 6–7 km) during the Pliocene
extension, and produced the eruption of the Mt Amiata volcano during the Late Pleistocene. This gave rise to local uplift,
presently reaching about 3,000 m, as well as a negative Bouguer anomaly (−16 mgal), both centred on the Mt Amiata area. The
crustal dome shows a good correspondence with the convex shape of the regional seismic marker known as the K-horizon, which
corresponds to the 450°C isotherm, and the areas with greatest heat flow. This is probably a consequence of the above-cited
magmatic body presently in the process of solidification. A Late Pleistocene eruption occurred along a crustal fissure striking
N50° (Mt Amiata Fault), which crosscuts the crustal dome. Hydrothermal circulation, proven by the occurrence of thermal springs
and gas vents (mainly CO2 and H2S), mainly occurs along the Mt Amiata Fault both in the northeastern ans southwestern sides of the volcano. 相似文献
224.
锆石中钛温度计在鲁西—苏北地区中生代侵入杂岩中的应用 总被引:4,自引:1,他引:3
利用锆石中钛地质温度计对鲁西—苏北地区出露的8个中生代侵入杂岩的岩浆岩结晶温度进行计算,结果表明研究区斑井岩体的平均岩浆结晶温度为715~716℃,蔡山岩体为653℃,丰山岩体为697℃,夹沟岩体为711℃,利国岩体为737℃,铁铜沟岩体为766℃,上峪岩体为889℃,金岭岩体为770℃。岩体的岩浆结晶温度沿侵入杂岩带展布方向,从S到N依次增高,暗示其岩浆起源深度逐渐加大。岩浆结晶温度计算结果大致限定了各岩体的岩浆源区深度范围,结合锆石寄主岩石和寄主岩石中的深源包体的研究表明研究区中生代侵入杂岩体的母岩浆起源于上地幔和/或下地壳。 相似文献
225.
Michael J. Toplis William L. Brown Elsa Pupier 《Contributions to Mineralogy and Petrology》2008,155(3):329-340
The anorthite content of plagioclase grains (XAn) in 12 rocks from the layered series of the Skaergaard intrusion has been studied by electron microprobe (typically ∼30 core
and ∼70 rim analyses per thin section). Mean core compositions vary continuously from An66 at the base of the layered series (LZa) to An32–30 at the top. On the other hand, crystal rims are of approximately constant composition (An50 ± 1) from the LZa to the lower Middle Zone (MZ). Above the MZ, core and rim compositions generally overlap. Profiles across individual
plagioclase grains from the lower zone show that most crystals have an external zone buffered at XAn ∼50 ± 1. The simplest explanation for these features is that during postcumulus crystallization in the lower zone, interstitial
liquids passed through a density maximum. This interpretation is consistent with proposed liquid lines of descent that predict
silica enrichment of the liquid associated with the appearance of cumulus magnetite. 相似文献
226.
Sebastiano Imposa 《Environmental Geology》2008,55(5):1061-1073
In this study 50 seismic events, preceding and accompanying the eruptions occurring in 1981 and 1983, have been considered.
Seismic moments, fault radii, stress drops and seismic energies have been calculated using Brune’s model (J Geophys Res 75:4997–5009,
1970; J Geophys Res 76:5002, 1971); site, anelastic attenuation along the propagation path, geometrical spreading and interaction with the free surface effects
are taken into account. For each event we have also estimated the equivalent Wood–Anderson magnitude (MWAeq) (Scherbaum and
Stoll in Bull Seism Soc Am 73:1321–1343, 1983); relations among all these source parameters have been determined. Furthermore, the hypothesis of self-similarity (Aki in
J Geophys Res 72:1217–1231, 1967) is not verified for events with seismic moments <1012 N-m: in fact the relationship between log-stress drop and log-moment is linear up to a moment of 1012 N-m (events of 1981 eruption), while for higher moments (events of 1983 eruption) the slope of the regression line is not
significantly different from zero. We suppose that such a behaviour is related to a heterogeneous medium with barriers on
the faults. Finally, the main conclusion is that eruptions of 1981 and 1983 differ from one another both in eruptive and seismic
aspects; analysis of seismic energies indicates an increase in Mt. Etna’s activity, confirmed by studies performed on the
following lateral eruption of 1991–1993 (Patanè et al. in Bull Volcanol 47:941–952, 1995), occurring on the same structural trend. 相似文献
227.
地震主应力方向的附加潮汐应力计算及其对发震断层的作用方式研究 总被引:4,自引:0,他引:4
通过对地震震源处沿主压应力P轴和主张应力T轴方向的附加潮汐应力分量的计算,在岩石力学莫尔-库化准则的基础上分析了附加潮汐应力对发震断层的作用方式。分析和计算表明,对发震断层有促滑作用的附加潮汐应力作用方式分增压型和减压型,增压型潮汐应力增大断层面上的正压力和剪应力,促使断层达到破裂滑动条件,减压型潮汐应力在一定条件下能降低断层面上的破裂滑动强度,同样能促使断层的运动。计算实例显示,大部分发震断层受到了附加潮汐应力的增压型或减压型促滑作用。 相似文献
228.
1989年7月26日,贡嘎山东坡南关沟发生了一场典型的冰雪雨水泥石流。它下行30多公里后堵塞大渡河,造成直接经济损失245万元。这场泥石流历时约3小时,持续流动时间2小时。到达大渡河时的流速9.4米/秒,最大流量6768.0立方米/秒,总径流量1716.4万立方米,总输沙量627.0万立方米,残留沉积物总方量310.4万立方米(其中泥石流堵塞大渡河的扇形地方量30.0万立方米),弯道爬高15.5—16.5米。输往堵河扇形地下游方的固体物质方量是扇形地方量的19.9倍,泥石流尾流作用强烈。 相似文献
229.
本文提出可以用平均限制性变分原理来研究非均匀基流中地形对Rossby波的影响。所得到的结果与用多重尺度法相一致,但却避免了多重尺度法中的冗繁运算,而且物理意义更加清楚,诸如波作用量密度、波能密度等物理量的定义也更自然、合理。 相似文献
230.
Described half a century ago, the Galiléia tonalite represents a milestone in the discovery of plate margin magmatic arcs in the Araçuaí-Ribeira orogenic system (southeastern Brazil). In the 1990's, analytical studies on the Galiléia tonalite finally revealed the existence of a Late Neoproterozoic calc-alkaline magmatic arc in the Araçuaí orogen. Meanwhile, the name Rio Doce magmatic arc was applied to calc-alkaline plutons found in the Araçuaí-Ribeira boundary. After those pioneer studies, the calc-alkaline plutons showing a pre-collisional volcanic arc signature and age between 630 Ma and 585 Ma have been grouped in the G1 supersuite, corresponding to the Rio Doce arc infrastructure. Here, we revisit the Rio Doce arc with our solid field knowledge of the region and a robust analytical database (277 lithochemical analyses, and 47 U–Pb, 53 Sm–Nd, 25 87Sr/86Sr and 7 Lu–Hf datasets). The G1 supersuite consists of regionally deformed, tonalitic to granodioritic batholiths and stocks, generally rich in melanocratic to mesocratic enclaves and minor gabbroic to dioritic plutons. Gabbroic to dioritic enclaves show evidence of magma mixing processes. The lithochemical and isotopic signatures clearly reveal a volcanic arc formed on a continental margin setting. Melts from a Rhyacian basement form the bulk of the magma produced, whilst gabbroic plutons and enclaves record involvement of mantle magmas in the arc development. Tonalitic stocks (U–Pb age: 618–575 Ma, εNd(t): −5.7 to −7.8, Nd TDM ages: 1.28–1.68 Ga, 87Sr/86Sr(t): 0.7059–0.7118, and εHf(t): −5.2 to −11.7) form the northernmost segment of the Rio Doce arc, which dies out in the ensialic sector of the Araçuaí orogen. At arc eastern and central zones, several batholiths (e.g., Alto Capim, Baixo Guandu, Galiléia, Muniz Freire, São Vítor) record a long-lasting magmatic history (632–580 Ma; εNd(t): −5.6 to −13.3; Nd TDM age: 1.35–1.80 Ga; 87Sr/86Sr(t): 0.7091–0.7123). At arc western border, the magmatic evolution started with gabbro-dioritic and tonalitic plutons (e.g., Chaves pluton, U–Pb age: 599 ± 15 Ma, εNd(t): −4.8 to −6.8, Nd TDM ages: 1.48–1.68 Ga, 87Sr/86Sr(t): 0.7062–0.7068, and εHf(t): −4.3 to −9.7; and Brasilândia pluton, U–Pb age: 581 ± 11 Ma, εNd(t): −8.2 to −10.2, Nd TDM ages: 1.63–1.68 Ga, 87Sr/86Sr(t): 0.7088–0.7112, εHf(t): −12.3 to −14.9), followed by late granodioritic intrusions (e.g., Guarataia pluton, U–Pb age: 576 ± 9 Ma, εNd(t): −12.52 to −13.11, Nd TDM age: 1.74–2.06 Ga, 87Sr/86Sr(t): 0.7104–0.7110, εHf(t): −12.9 to −21.6). The Muriaé batholith (U–Pb age: 620–592 Ma, εNd(t): −8.2 to −13.6, Nd TDM age: 1.41–1.88 Ga) and the Conceição da Boa Vista (586 ± 7 Ma) and Serra do Valentim (605 ± 8 Ma) stocks represent a segment of the Rio Doce arc correlated to the Serra da Bolívia and Marceleza complexes, making the link between the Araçuaí and Ribeira orogenic domains. We suggest three phases of arc development: i) eastward migration of arc front (632–605 Ma), ii) widespread magma production in the whole arc (605–585 Ma), and iii) late plutonism in the western arc region (585–575 Ma). Usual processes of volcanic arc development, like subduction of oceanic lithosphere under a continental margin, followed by asthenosphere ascent related to slab retreating and break-off may explain the Rio Doce arc evolution. 相似文献