全文获取类型
收费全文 | 3127篇 |
免费 | 126篇 |
国内免费 | 77篇 |
专业分类
测绘学 | 88篇 |
大气科学 | 274篇 |
地球物理 | 696篇 |
地质学 | 1058篇 |
海洋学 | 271篇 |
天文学 | 715篇 |
综合类 | 27篇 |
自然地理 | 201篇 |
出版年
2022年 | 18篇 |
2021年 | 44篇 |
2020年 | 56篇 |
2019年 | 54篇 |
2018年 | 82篇 |
2017年 | 89篇 |
2016年 | 110篇 |
2015年 | 85篇 |
2014年 | 82篇 |
2013年 | 168篇 |
2012年 | 102篇 |
2011年 | 142篇 |
2010年 | 153篇 |
2009年 | 148篇 |
2008年 | 145篇 |
2007年 | 126篇 |
2006年 | 113篇 |
2005年 | 110篇 |
2004年 | 129篇 |
2003年 | 120篇 |
2002年 | 160篇 |
2001年 | 147篇 |
2000年 | 99篇 |
1999年 | 67篇 |
1998年 | 52篇 |
1997年 | 47篇 |
1996年 | 41篇 |
1995年 | 48篇 |
1994年 | 45篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 30篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 35篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1978年 | 21篇 |
1976年 | 19篇 |
1975年 | 19篇 |
1974年 | 28篇 |
1972年 | 21篇 |
1971年 | 16篇 |
1970年 | 13篇 |
排序方式: 共有3330条查询结果,搜索用时 15 毫秒
81.
This article presents a physical model for frictional pendulum isolators (FPS) that is ready to be implemented in most commercial software. The model is capable of accounting for effects such as large deformations, sticking, and uplift and impact by sensing the normal loads in the isolators through a gap element. Sticking has been incorporated into the model by extending the Park–Wen hysteretic model to the case of large deformations. The proposed model has been tested against a theoretically ‘exact’ formulation leading to essentially identical results. To facilitate its use, the physical FPS model has been cast into a typical non‐linear structural element format, i.e. with deformation as input and restoring force as output. Examples of a building and a bridge have been chosen to show the potential of the element and to provide further insight into the earthquake response of structures with FPS isolators; in particular, in aspects such as the orientation in placement of the isolator, sticking, P? Δ, and other large deformation effects. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
82.
喜马拉雅造山带中段定结地区拆离断层 总被引:1,自引:1,他引:1
定结地区位于喜马拉雅造山带中段,发育大量的低角度伸展拆离断层,这些拆离断层中部分构成了藏南拆离系的主体。它们基本上垂直于造山带走向伸展,各拆离断层特征显著,普遍发育糜棱岩,糜棱岩类型复杂,主要有硅质糜棱岩、长英质糜棱岩、花岗质糜棱岩。在研究区的北部,拆离断层呈环状产出,构成变质核杂岩三层结构中的中间层,规模一般较大;同时拆离断层使变质核杂岩体盖层中的部分地层拆离减薄;在研究区南部拆离断层呈线状延伸很远,总体上平行造山带延伸,构成了藏南拆离系重要组成部分。部分拆离断层同韧性剪切带平行产出,形成拆离剪切的脆韧性体系。 相似文献
83.
吐哈盆地中央构造带正反转演化特征 总被引:5,自引:3,他引:5
吐哈盆地中央构造带由火焰山构造和七克台构造组成。中央构造带形成于三叠纪晚期至侏罗纪早期,表现为伸展构造特征,生长断层上盘地层厚度明显大于下盘,并于断层上盘所在的台北凹陷形成沉降中心。晚侏罗世,由于拉萨陆块与欧亚大陆的碰撞作用导致吐哈盆地由伸展盆地转变为挤压盆地,中央构造带也于此时发生构造反转,由早期的伸展正断层转变为挤压逆断层。发生于55Ma的喜山构造事件对天山地区产生了深刻的影响,但影响时间略有滞后,大致发生在晚渐新世至早中新世,中央构造带即在此次构造事件中强烈变形,逆冲出露于地表。 相似文献
84.
Reena De S. G. Gaonkar B. V. Srirama Sagina Ram J. R. Kayal 《Journal of Earth System Science》2003,112(3):413-419
A 12-station temporary microearthquake network was established by the Geological Survey of India for aftershock monitoring
of the January 26th, 2001 Bhuj earthquake (M
w 7.6) in the Kutch district of Gujarat state, western India. The epicentres of the aftershocks show two major trends: one
in the NE direction and the other in the NW direction. Fault-plane solutions of the best-located and selected cluster of events
that occurred along the NE trend, at a depth of 15–38 km, show reverse faulting with a large left-lateral strike-slip motion,
which are comparable with the main-shock solution. The NW trending upper crustal aftershocks at depth <10 km, on the other
hand, show reverse faulting with right-lateral strike-slip motion, and the mid crustal and lower crustal aftershocks, at a
depth of 15–38 km, show pure reverse faulting as well as reverse faulting with right-lateral and left-lateral strike-slip
motions; these solutions are not comparable with the main-shock solution. It is inferred that the intersection of two faults
has been the source area for stress concentration to generate the main shock and the aftershocks. 相似文献
85.
U–Pb sensitive high resolution ion microprobe (SHRIMP) dating of zircons from charnockitic and garnet–biotite gneisses from the central portion of the Mozambique belt, central Tanzania indicate that the protolith granitoids were emplaced in a late Archaean, ca. 2.7 Ga, magmatic event. These ages are similar to other U–Pb and Pb–Pb ages obtained for other gneisses in this part of the belt. Zircon xenocrysts dated between 2.8 and 3.0 Ga indicate the presence of an older basement. Major and trace element geochemistry of these high-grade gneisses suggests that the granitoid protoliths may have formed in an active continental margin environment. Metamorphic zircon rims and multifaceted metamorphic zircons are dated at ca. 2.6 Ga indicating that these rocks were metamorphosed some 50–100 my after their emplacement. Pressure and temperature estimates on the charnockitic and garnet–biotite gneisses were obscured by post-peak metamorphic compositional homogenisation; however, these estimates combined with mineral textures suggest that these rocks underwent isobaric cooling to 800–850 °C at 12–14 kbar. It is considered likely that the granulite facies mineral assemblage developed during the ca. 2.6 Ga event, but it must be considered that it might instead represent a pervasive Neoproterozoic, Pan African, granulite facies overprint, similar to the ubiquitous eastern granulites further to the east. 相似文献
86.
We present new data and interpretations on the Neogene tectonics of the Shan scarp area (central Myanmar) and its relationship with the India–Indochina oblique convergence. We describe ductile and brittle fabrics associated with the major features in this area, the Mogok Metamorphic Belt (MMB), the Shan scarp and the Sagaing fault. From these data we identify a succession of two tectonic regimes. First, a dominant NNW–SSE-trending extension, marked by ductile stretching that characterizes the MMB, and associated N70E brittle normal faults. Later, from Middle or Upper Miocene to the Present, these structures were cross-cut by brittle right-lateral faults, among which the most important are the N20W transpressive Shan scarp fault zone and the N–S Sagaing fault. To explain this transition from a dominant transtensive to a transpressive stress regime, that occurred during Miocene, we place our data within a larger geodynamic context. We suggest that, like the intraplate deformation in the Indian Ocean, the end of spreading in the South China sea, the opening of the Andaman basin or the end of subduction within the Indo-Burma range, the change in the tectonic regime in central Myanmar could be in response to a major Miocene regional plate kinematic reorganization. 相似文献
87.
Validation of Landslide Susceptibility Maps; Examples and Applications from a Case Study in Northern Spain 总被引:9,自引:3,他引:9
Remondo Juan González Alberto De Terán José Ramón Díaz Cendrero Antonio Fabbri Andrea Chung Chang-Jo F. 《Natural Hazards》2003,30(3):437-449
A procedure for validating landslide susceptibility maps wasapplied in a study area in northern Spain and the results obtained compared. Validationwas used to carry out sensitivity analysis for individual variables and combinationsof variables. The validity of different map-making methods was tested, as well as theutility of different types of Favourability Functions. The results obtained show thatvalidation is essential to determine the predictive value of susceptibility maps. Italso helps to better select the most suitable function and significant variables, thus improving the efficiency of the mapping process. Validation based on a temporal strategy makes it possible to derive hazard maps from susceptibility maps. 相似文献
88.
89.
Sarbari Ghosh Utpal Kumar De Atmospheric Science Research Department of Physics Jadavpur University Calcutta India Received April revised July 《大气科学进展》1997,(1)
AComparativeStudyoftheAtmosphericLayersbelowFirstLiftingCondensationLevelforInstantaneousPre-MonsoonThunderstormOcurenceatAga... 相似文献
90.
Rapid deforestation is a major problem throughout the tropical world. The conditions and the pace under which societies and economies of the Third World are currently evolving and growing, combined with the specificities of tropical forests, render the latter increasingly vulnerable. Among the major tropical areas of the world, Southeast Asia is perhaps the one where these conditions have had the most impact on the retreat of the forest cover over the last quarter of this century. This is illustrated through the presentation of two maps of the distribution of five basic forest formations in Southeast Asia circa 1970 and circa 1990. The maps are examined and compared, as well as confronted with statistical assessments of deforestation. Finally, the complex causes behind the retreat of the tropical forests as well as the implications of this retreat are briefly discussed. 相似文献