全文获取类型
收费全文 | 220篇 |
免费 | 43篇 |
国内免费 | 218篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 7篇 |
地球物理 | 48篇 |
地质学 | 360篇 |
海洋学 | 11篇 |
天文学 | 1篇 |
综合类 | 10篇 |
自然地理 | 18篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2018年 | 19篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 19篇 |
2014年 | 29篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 21篇 |
2005年 | 15篇 |
2004年 | 33篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有481条查询结果,搜索用时 312 毫秒
121.
盾构偏航引起的地表位移预测 总被引:2,自引:1,他引:2
对于盾构隧道的设计和施工,解析方法预测地表沉降,具有使用简便、物理意义明确的特点。在Sagaseta提出的基于由地层损失引起的地表沉降理论基础上,结合工程实际情况,提出了模拟盾构推进过程的三维地层损失模式,并推导了相应的地表位移计算解析公式,对实际工程具有参考价值。 相似文献
122.
123.
The Tin Zebane dyke swarm was emplaced at the end of the Pan-African orogeny along a mega-shear zone separating two contrasting terranes of the Tuareg shield. It is located along the western boundary of the Archaean In Ouzzal rigid terrane, but inside the adjacent Tassendjanet terrane, strongly remobilized at the end of the Precambrian. The Tin Zebane swarm was emplaced during post-collisional sinistral movements along the shear zone at 592.2±5.8 Ma (19WR Rb–Sr isochron). It is a dyke-on-dyke system consisting of dykes and stocks of gabbros and dykes of metaluminous and peralkaline granites. All rock types have Sr and Nd isotopic initial ratios (Sri=0.7028 and Nd=+6.2) typical of a depleted mantle source, similar to the prevalent mantle (PREMA) at that period. No crustal contamination occurred in the genesis of the Tin Zebane swarm. Even the samples showing evidence of fluid interaction (essentially alkali mobility) have the same isotopic signature. The peralkaline granites have peculiar geochemical characteristics that mimic subduction-related granites: this geochemical signature is interpreted in terms of extensive differentiation effects due to late cumulates comprising aegirine, zircon, titanite, allanite and possibly fergusonite, separated from the liquid in the swarm itself due to magmatic flow turbulence. The Tin Zebane dyke swarm is thus of paramount importance for constraining the differentiation of mantle products to generate highly evolved alkaline granites without continental crust participation, in a post-collisional setting. 相似文献
124.
盾构隧道衬砌结构受力分析的梁—弹簧系统模型 总被引:44,自引:6,他引:38
盾构隧道衬砌结构由若干管片及其间的连接螺栓组成。在其断面受力的工程设计中,目前普遍采用梁-弹簧系统模型来模拟其受力性态。其中,梁可分成直梁和曲梁两类。本文在考虑弹簧刚度的轴向、切向和转动效应的同时,从卡氏(Castigliano)第二定理出发,给出了梁-弹簧模型的矩阵式,并论证了直梁-弹簧模型与曲梁-弹簧模型的一致性关系。在数值模拟计算过程中,还考虑了地层反作用力非线性情形和管片接头转动刚度正、负弯矩时的非对称性问题。 相似文献
125.
盾构施工地面长期沉降的神经网络预测 总被引:1,自引:0,他引:1
基于逆传播人工神经网络方法,建立了盾构施工地面长期沉降的非线性预测模型,建立了沉降与诸多影响因素:所处位置、时间、上覆土性参数及盾构施工参数等的关系模型。通过在上海地铁2号线龙东路一中央公园站区间资料的验证,发现与实际比较吻合。 相似文献
126.
The rare earth element patterns of the gneisses of Bastar and Bundelkhand are marked by LREE enrichment and HREE depletion
with or without Eu anomaly. The spidergram patterns for the gneisses are characterized by marked enrichment in LILE with negative
anomalies for Ba, P and Ti. The geochemical characteristics exhibited by the gneisses are generally interpreted as melts generated
by partial melting of a subducting slab. The style of subduction was flat subduction, which was most common in the Archean.
The rare earth patterns and the multi-element diagrams with marked enrichment in LILE and negative anomalies for Ba, P and
Ti of the granitoids of both the cratons indicate interaction between slab derived melts and the mantle wedge. The subduction
angle was high in the Proterozoic. Considering the age of emplacement of the gneisses and granitoids that differs by ∼ 1 Ga,
it can be assumed that these are linked to two independent subduction events: one during Archaean (flat subduction) that generated
the precursor melts for the gneisses and the other during the Proterozoic (high angle subduction) that produced the melts
for the granitoids. The high values of Mg #, Ni, Cr, Sr and low values of SiO2 in the granitoids of Bastar and Bundelkhand cratons compared to the gneisses of both the cratons indicate melt-mantle interaction
in the generation of the granitoids. The low values of Mg#, Ni, Cr, Sr and high values of SiO2 in the gneisses in turn overrules such melt-mantle interaction. 相似文献
127.
The N–S trending Tuludimtu Belt in the extreme west of Ethiopia has been subdivided into five lithotectonic domains, from east to west, the Didesa, Kemashi, Dengi, Sirkole and Daka domains. The Kemashi, Dengi and Sirkole Domains, forming the core of the belt, contain volcano-sedimentary successions, whilst the Didesa and Daka Domains are gneiss terranes, interpreted to represent the eastern and western forelands of the Tuludimtu Belt. The Kemashi Domain, which consists of an ophiolitic sequence of ultramafic and mafic volcanic and plutonic rocks together with sedimentary rocks of oceanic affinity, is interpreted as oceanic crust and is considered to represent an arc-continent suture zone. The Dengi Domain, composed of mafic to felsic volcanic and plutonic rocks, and a sequence of volcanoclastic, volcanogenic, and carbonate sediments, is interpreted as a volcanic arc. The Sirkole Domain consists of alternating gneiss and volcano-sedimentary sequences, interpreted as an imbricated basement-cover thrust-nappe complex. All the domains are intruded by syn- and post-kinematic Neoproterozoic granitoids. Structural analysis within the Didesa and Daka Domains indicate the presence of pre-Pan African structures, upon which Neoproterozoic deformation has been superimposed. The gneissic rocks of these two domains are regarded as pre-Pan African continental fragments amalgamated to West Gondwana during Neoproterozoic collision events. Unconformably overlying all of the above are a series of tilted but internally undeformed conglomerate–sandstone–shale sequences, regarded as post-accretionary molasse-type deposits, formed during gravitational collapse of the Tuludimtu Belt. The Tuludimtu Belt is interpreted as a collision orogenic belt formed during the assembly of West Gondwana prior to final closure of the Mozambique Ocean. 相似文献
128.
Introduction A lot of work has been done in studying geological problems in terms of finite-element method (FEM). Assuming the material of fault as a perfect plastic one, WANG, et al (1980, 1982) simulated the transference of the larger earthquakes in North China by elasto-plastic FEM, the earthquakes are simulated by reducing frictional coefficients of the fault. YIN and ZHANG (1982) investigated the instability of earthquakes by FEM with strain-softening material model. WANG and C… 相似文献
129.
130.
Additives for Slurry Shields in Highly Permeable Ground 总被引:2,自引:0,他引:2
P. Fritz 《Rock Mechanics and Rock Engineering》2007,40(1):81-95
Summary. For tunneling projects in saturated soils tunnel boring machines (TBMs) with slurry shields are widely used. However, in coarse,
highly permeable soils the suspension penetrates the ground and the required support pressure cannot be built up. For the
Zimmerberg Base Tunnel near Zurich permeabilities much greater than 10−3 m/s were expected. This value is usually considered as the critical limit for the applicability of slurry shields. Therefore
it was aimed to find additives for the bentonite suspension which would allow it to attain a higher suspension pressure.
For these investigations an apparatus has been developed. It allows the maximum attainable support pressure for a given suspension
and a ground to be determined. It reflects the real situation, produces reproducible results and is insensitive to the inevitable
variation of individual parameters.
In the tests the additives polymer, sand and vermiculite were studied and their effects on the attainable maximum suspension
pressure investigated. For the best combination, i.e. with a well defined proportion of the individual components, suspension
pressures could be attained which were about 10 to 20 times higher than those with an ordinary bentonite suspension. Successful
excavation of the Zimmerberg Base Tunnel proved the validity of the laboratory tests containing 200 kg bentonite per m3 water. 相似文献