全文获取类型
收费全文 | 1727篇 |
免费 | 551篇 |
国内免费 | 215篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 23篇 |
地球物理 | 1207篇 |
地质学 | 1055篇 |
海洋学 | 95篇 |
天文学 | 9篇 |
综合类 | 41篇 |
自然地理 | 49篇 |
出版年
2023年 | 12篇 |
2022年 | 36篇 |
2021年 | 38篇 |
2020年 | 49篇 |
2019年 | 76篇 |
2018年 | 88篇 |
2017年 | 79篇 |
2016年 | 108篇 |
2015年 | 86篇 |
2014年 | 128篇 |
2013年 | 142篇 |
2012年 | 75篇 |
2011年 | 115篇 |
2010年 | 58篇 |
2009年 | 123篇 |
2008年 | 112篇 |
2007年 | 115篇 |
2006年 | 106篇 |
2005年 | 79篇 |
2004年 | 89篇 |
2003年 | 77篇 |
2002年 | 62篇 |
2001年 | 69篇 |
2000年 | 56篇 |
1999年 | 56篇 |
1998年 | 55篇 |
1997年 | 46篇 |
1996年 | 60篇 |
1995年 | 56篇 |
1994年 | 54篇 |
1993年 | 43篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2493条查询结果,搜索用时 609 毫秒
981.
982.
珠江三角洲的新构造运动及其与三角洲演化的关系 总被引:4,自引:0,他引:4
综合已有资料。重新对珠江三角洲的新构造运动进行了系统的分析.分析结果表明该地区的新构造运动以断裂活动和断块差异升降运动为主要特征.这些特征在珠江三角洲的演化过程中起着非常重要的作用。大多数在第四纪形成或重新活化的基底断裂把三角洲切割成一系列的断块,并且在垂直运动上以沉降为主导,为珠江三角洲的第四系沉积创造了空间。另外,第四系两期河流相砂砾层分布的差异反映了古河道在晚更新世海侵后、全新世海侵前所发生的变迁。这主要是断裂活动的结果。因此,在珠江三角洲的形成和演化过程中。新构造运动既影响着三角洲的沉积又控制着河道的变迁. 相似文献
983.
984.
在讨论矿区构造变形序列、变形期次、深度层次、构造组合及变形机制的基础上,重点对马鞍桥金矿的控矿韧性剪切带类型及其与成矿关系进行了研究,根据剪切带的几何要素,用作图法求出矿带的东延方向,综合其他找矿标志,预测出清水河处矿体可能出现的部位。 相似文献
985.
The rheological properties of mantle materials are being investigated up to pressures of 16 GPa and temperatures of 1600°C for times up to 24 h, using a new sample assembly for the 6–8 multi-anvil apparatus. Al2O3 pistons, together with a liquid confining medium, are used to generate deviatoric stress in the specimen. Strain rates are estimated by monitoring the relative displacement of the guide blocks of the multi-anvil apparatus, scaled to the total axial strain of the sample. The applied stress on the sample is estimated using grain size piezometry. Strain rates and flow stresses of approximately 10–4 to 10–6 s–1 and 50 to 250 MPa respectively, are presently attainable.Preliminary results on San Carlos olivine single crystals, partially dynamically recrystallized to a grain size of 10 to 300 m, indicate that the effective viscosity of polycrystalline olivine is consistent with values obtained from olivine single crystal creep laws. Assuming a dislocation creep mechanism (n3.5) with (010)[001] as the dominant slip system, the data are best fit using a creep activation volume of 5 to 10×10–6 m3 mol–1. 相似文献
986.
Chris Marone 《Pure and Applied Geophysics》1991,137(4):409-419
Theoretical constraints on the stress-dilation relation for a deforming Coulomb material requirev ifC=0 andv sin-1(
m
/
m
) always, wherev is the dilation angle, is the friction angle,C is cohesion,
m
is the maximum shear stress, and
m
is the mean effective stress. Recent laboratory measurements of friction and dilatancy of simulated fault gouge show that small amplitude shear-load cycling causes compaction and consolidation. Comparison of the data with theory indicates that such load cycling produces: (1) increased coefficient of friction (or friction angle), (2) increased cohesion, and (3) increased dilatancy rate (or dilation angle). Under certain conditions of load cycling without significant plastic shear strain accumulation (
p
<0.005) we find thatv exceeds both and, in contrast to theory, sin-1(
m
/
m
). This result is interpreted in terms of enhanced cohesion and overconsolidation, which lead to residual stresses within the gouge. An analogy is drawn between these special loading conditions and those extant on natural faults. In particular, our results imply that jostling and minor stress variations associated with microearthquakes may produce strengthening of fault gouge and changes in the fault zone's stress-dilatancy relation. Hence, compaction associated with microseismicity may lead to subsequent dilation of fault gouge, even for faults with large displacement rates and large net offsets (e.g., San Andreas). In regions where such dilation persists over sufficient displacements (on the order of the critical slip distance for seismic faulting) it may tend to inhibit unstable slip. 相似文献
987.
Agust Gudmundsson 《Bulletin of Volcanology》1998,60(3):160-170
The ring fractures that form most collapse calderas are steeply inward-dipping shear fractures, i.e., normal faults. At the
surface of the volcano within which the caldera fault forms, the tensile and shear stresses that generate the normal-fault
caldera must peak at a certain radial distance from the surface point above the center of the source magma chamber of the
volcano. Numerical results indicate that normal-fault calderas may initiate as a result of doming of an area containing a
shallow sill-like magma chamber, provided that the area of doming is much larger than the cross-sectional area of the chamber
and that the internal excess pressure in the chamber is smaller than that responsible for doming. This model is supported
by the observation that many caldera collapses are preceded by a long period of doming over an area much larger than that
of the subsequently formed caldera. When the caldera fault does not slip, eruptions from calderas are normally small. Nearly
all large explosive eruptions, however, are associated with slip on caldera faults. During dip slip on, and doming of, a normal-fault
caldera, the vertical stress on part of the underlying chamber suddenly decreases. This may lead to explosive bubble growth
in this part of the magma chamber, provided its magma is gas rich. This bubble growth can generate an excess fluid pressure
that is sufficiently high to drive a large fraction of the magma out of the chamber during an explosive eruption.
Received: 2 January 1997 / Accepted: 22 April 1998 相似文献
988.
989.
西秦岭北缘活断层带断层气的基本特征 总被引:2,自引:1,他引:1
通过对西秦岭北缘活断层带断层气活动基本特征的研究认为:本活断层带是本区地球排气的主要通道;在走滑断层拉分区,地球排放气体活动的强度与地震活动有密切的关系;本带东段断层排气活动比较强,西段断层排气活动比较北,并讨论了两形成差异的原因。 相似文献
990.
河北矾山盆地北缘断层八营段的古地震重复模型 总被引:13,自引:1,他引:12
通过实测断错地貌面,开挖在探槽以及系统的地层年代采样,推断和揭露出矾出盆地北缘断层八营段9万年来总移量量为34m。经7.5万年来共发生过9次古位移事件。其中大探槽揭露的4次事件分别发生在距今:A,2.8万年;B.1.4万年;C,0.75万年和D,656年(?)左右。该段落古地震地重复模型分为两个阶段:9 ̄1.4万年间符合“时间可推测模型”;1.4万年来以来则为“位称衰减模型”。 相似文献