全文获取类型
收费全文 | 5051篇 |
免费 | 818篇 |
国内免费 | 942篇 |
专业分类
测绘学 | 978篇 |
大气科学 | 1118篇 |
地球物理 | 1434篇 |
地质学 | 1965篇 |
海洋学 | 596篇 |
天文学 | 25篇 |
综合类 | 266篇 |
自然地理 | 429篇 |
出版年
2024年 | 21篇 |
2023年 | 40篇 |
2022年 | 145篇 |
2021年 | 172篇 |
2020年 | 190篇 |
2019年 | 242篇 |
2018年 | 160篇 |
2017年 | 237篇 |
2016年 | 211篇 |
2015年 | 236篇 |
2014年 | 254篇 |
2013年 | 294篇 |
2012年 | 277篇 |
2011年 | 262篇 |
2010年 | 247篇 |
2009年 | 327篇 |
2008年 | 315篇 |
2007年 | 347篇 |
2006年 | 301篇 |
2005年 | 319篇 |
2004年 | 278篇 |
2003年 | 235篇 |
2002年 | 218篇 |
2001年 | 193篇 |
2000年 | 212篇 |
1999年 | 171篇 |
1998年 | 135篇 |
1997年 | 143篇 |
1996年 | 130篇 |
1995年 | 92篇 |
1994年 | 111篇 |
1993年 | 74篇 |
1992年 | 62篇 |
1991年 | 48篇 |
1990年 | 24篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有6811条查询结果,搜索用时 762 毫秒
991.
汶川8.0级特大地震汉源县震害特点与烈度异常成因探讨 总被引:1,自引:0,他引:1
本文在汉源县地震灾害调查的基础上,通过收集前人在该区已取得的成果资料,采用综合分析、类比等方法,对汉源县地震烈度异常区震害及造成异常的原因进行了分析探讨。汉源县建筑物破坏形式以水平地震作用造成的“X”型剪切破坏为主,竖向地震造成的破坏较少。地震波传播路径、场地土层条件和地形地貌条件三者的耦合是造成汉源县烈度异常的主要原因,其中场地土层中占优势厚度的砾石层是造成场地地震波放大的主要内因。本文取得的初步结论为更加深入地科学研究本区地震烈度异常的原因提供了新思路。 相似文献
992.
993.
This paper summarizes the relevant results of the design, construction, testing, and implementation of a nominal 120 kN magnetorheological damper developed to control a free‐plan tall building in Santiago, Chile, equipped with two 160‐ton tuned masses. Cyclic as well as hybrid simulation tests were performed on the prototype damper. Global building responses using measured MR properties showed good correlation with analytical estimations. Also, a proposed physical controller for the MR damper was validated through hybrid and building pull‐back tests. Its performance is essentially equivalent to that of an LQR controller, but the information needed in its implementation is considerably less. Pull‐back tests of 10 cm amplitude were performed on one mass along the flexible edge of the building and its response controlled using the passive and controlled modes of the MR damper. The MR damper was capable of controlling the TM displacements very effectively, as well as the simulated building response for different ground motions and harmonic excitation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
994.
The 2009 L’Aquila, Italy earthquake highlighted the seismic vulnerability of historic masonry building structures due to improper "strengthening" retrofit work that has been done in the last 50 years. Italian seismic standards recommend the use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete (RC) or steel elements, inserting RC tie-beams in the masonry and new RC floors, and using RC jacketing on the shear walls. The L’Aquila earthquake revealed the numerous limitations of these interventions, because they led to increased seismic forces (due to greater additional weight) and to deformation incompatibilities of the incorporated elements with the existing masonry walls. This paper provides a discussion of technical issues pertaining to the seismic retrofit of the Santa Maria di Collemaggio Basilica and in particular, the limitations of the last (2000) retrofit intervention. Considerable damage was caused to the church because of questionable actions and incorrect and improper technical choices. 相似文献
995.
为了解边界层厚度的大尺度分布及其气候循环特征,基于逐日ERA 40 再分析边界层厚度资料,采用统计学方法计算边界层厚度分4个时次的季节循环、年较差等气候特征场,对全球边界层厚度分布及其季节演变特征进行了研究。结果表明:全球较厚的边界层分布与大地形、沙漠等下垫面的分布有直接联系;陆地强边界层分布存在“08时”现象,即陆地较厚边界层中心分布在当地时间08时经线附近;在大洋上南北纬30°~40°两条纬度带内边界层厚度的月尺度内变率较大,与大气强斜压性的天气系统活跃区一致;月平均日较差的年循环特征存在着季节性南北进退的现象。研究结果对于全面认识和科学利用ERA 40逐日边界层再分析资料有一定帮助。 相似文献
996.
997.
998.
999.
1000.
A Kinematic Thermal Model for Descending Slabs with Velocity Boundary Layers: A Case Study for the Tonga Subducting Slab 总被引:3,自引:0,他引:3
For the purpose of investigating the influence of metastable olivine (MO) phase transformations on both deep seismicity and stagnation of slabs, we constructed a 2-dimensional finite element thermal model for a 120 Ma-old 50o dipping oceanic lithosphere descending at 10 cm/yr with velocity boundary layers, which would mitigate the interference of constant velocity field for the slab. The resulting temperatures show that most of intermediate and deep earthquakes occurring within the Tonga slab are occurring inside the 800oC and 1200oC isotherm, respectively. The elevation of olivine transformation near ~410 km and respective persistence of metastable olivine and spinel within the transition zone and beneath 660 km would thus result in bimodal positive, zonal, negative density anomalies, respectively. These results together with the resulting pressure anomalies may reflect the stress pattern of the Tonga slab: (i) slab pull force exerts above a depth of ~230 km; (ii) MO existence changes the buoyancy force within the transition zone and facilitates slab stagnation at a depth of 660 km; (iii) as the subducting materials accumulated over 660 km, deepest earthquakes occur due to MO transformation; (iv) a flattened ‘slab’ may penetrate into the lower mantle due to the density increment of Sp transformation. 相似文献