全文获取类型
收费全文 | 317篇 |
免费 | 41篇 |
国内免费 | 67篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 7篇 |
地球物理 | 71篇 |
地质学 | 116篇 |
海洋学 | 166篇 |
天文学 | 15篇 |
综合类 | 32篇 |
自然地理 | 11篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 4篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 26篇 |
2014年 | 18篇 |
2013年 | 18篇 |
2012年 | 16篇 |
2011年 | 18篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 24篇 |
2007年 | 19篇 |
2006年 | 19篇 |
2005年 | 18篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有425条查询结果,搜索用时 15 毫秒
71.
72.
73.
<正>A theoretical model of a friction pendulum system(FPS) is introduced to examine its application for the seismic isolation of spatial lattice shell structures.An equation of motion of the lattice shell with FPS bearings is developed.Then, seismic isolation studies are performed for both double-layer and single-layer lattice shell structures under different seismic input and design parameters of the FPS.The influence of frictional coefficients and radius of the FPS on seismic performance are discussed.Based on the study,some suggestions for seismic isolation design of lattice shells with FPS bearings are given and conclusions are made which could be helpful in the application of FPS. 相似文献
74.
新疆伊吾阿勒吞昆多蛇绿混杂岩特征 总被引:1,自引:0,他引:1
前人将唐巴勒-卡拉麦里缝合线置于伊吾县以南哈尔里克山塔水河一线。1993年巴瑞士等在伊吾西北大黑山发现超镁铁岩-镁铁岩洋壳残片,认为卡拉麦里蛇绿岩从伊吾西北大黑山一带向东延伸。2009年笔者参与伊吾县阿尔通盖一带1∶5万区域地质矿产调查工作,于伊吾县以北阿勒吞昆多一带发现阿勒吞昆多蛇绿混杂岩,该蛇绿岩中斜长花岗岩形成于早石炭世((351±6)Ma),大地构造为哈萨克斯坦-准噶尔板块及准噶尔微板块、唐巴勒-卡拉麦里古生代沟弧体系。在研究前人资料基础上,提出阿勒吞昆多蛇绿混杂岩为卡拉麦里蛇绿岩(属唐巴勒-卡拉麦里缝合线)向东延伸部分,唐巴勒-卡拉麦里缝合线(沟弧体系)西起唐巴勒,向东经达拉布特-卡拉麦里-塔克扎勒-大黑山至伊吾县阿勒吞昆多一带,可能延伸至蒙古境内。 相似文献
75.
The OGC standard for 3D city modeling is widely used in an increasing number of applications.It defines five consecutive Levels of Detail(LoD0 to LoD4 with increasing accuracy and structural complexity),in which LoD3 includes all exterior appearances and geometrical details and subsequently requires much storage space.A new LoD is introduced as shell model with the exterior shell of the LoD3 model and the opening objects like windows,doors as well as smaller faade objects are projected onto walls.In this paper,a user survey is presented.The results of this survey show that the shell model can give users almost the same visual impression as the LoD3 model.Furthermroe,algorithms are developed to extract the shell model from LoD3 model.Experiments show that this shell model can reduce up to 90% storage of the original LoD3 model.Therefore,on one hand it can be used as a substitute for a LoD3 model for the visualization on small displays.On the other hand,it can be treated as a sub-level of detail(SLoD3) in CityGML,since it retains almost the same amount of information but requires much less storage space. 相似文献
76.
通过试验,研究自主研发的压电主动杆件在单层网壳结构中的主动智能控制问题.利用集传感器、作动器和承受荷载等功能于一体的压电主动杆件,对网壳结构的地震响应振动实施主动智能控制.结果表明,这种压电主动构件作为网壳结构的内在控制源,可以有效地控制网壳结构的地震响应,起到抑制网壳振动的作用. 相似文献
77.
78.
The mollusc Watsonella crosbyi was studied on the basis of material from the lower Cambrian Dahai Member of the Zhujiaqing Formation in eastern Yunnan, China and the Pestrotsvet Formation of the Aldan River region in the Siberian Platform. This fossil had been excessively described under different names in the literature, such as Heraultia varensalensis Cobbold, 1935, H. sibirica Missarzhevsky, 1974, Heraultipegma yunnanensis He and Yang, 1982, H. yannanese He and Yang, 1982, Watsonella yunnanensis, W. crosbyi Grabau, 1900, etc. Taxonomic revision shows that other species are junior synonyms of W. crosbyi. Analysis of functional morphology implies that W. crosbyi may be rather a helcionelloid than a rostroconch since its univalved conch is untorted endogastric and lacks a rostrum and a true internal pegma. Replicas of the original microstructures preserved on the surfaces of phosphatic internal moulds confirm that the shell consists of two layers. The inner layer is lamello-fibrillar, and the outer layer is spherulitic prismatic. The widespread geographical occurrences in both siliciclastic and carbonate rocks of the late Terreneuvian indicate that W. crosbyi is an important index fossil for global correlations and subdivision of the Cambrian Series 1 (Terreneuvian). The first appearance datum (FAD) of W. crosbyi is suggested to be a potential GSSP (Global Boundary Stratotype Section and Point) candidate marker for defining the base of the Cambrian Stage 2. 相似文献
79.
80.
A postbuckling analysis is presented for a shear deformable anisotropic laminated cylindrical shell with stiffener of finite length subjected to axial compression. The material of each layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on a higher order shear deformation shell theory with von Kármán-Donnell-type of kinematic nonlinearity and including the extension/twist, extension/flexural and flexural/twist couplings. The ‘smeared stiffener’ approach is adopted for the beam stiffeners. This arrangement allows the beam stiffeners to be assembled directly into the global stiffness matrix. The nonlinear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, grid, axial, ring stiffened, and unstiffened shells. The results confirm that there exists a compressive stress along with an associate shear stress and twisting when the anisotropic shell is subjected to axial compression. The postbuckling equilibrium path is unstable for the moderately thick cylindrical shell under axial compression and the stiffened shell structure is imperfection-sensitive. 相似文献