全文获取类型
收费全文 | 9149篇 |
免费 | 1781篇 |
国内免费 | 2444篇 |
专业分类
测绘学 | 827篇 |
大气科学 | 424篇 |
地球物理 | 2950篇 |
地质学 | 6809篇 |
海洋学 | 1230篇 |
天文学 | 83篇 |
综合类 | 419篇 |
自然地理 | 632篇 |
出版年
2024年 | 53篇 |
2023年 | 178篇 |
2022年 | 275篇 |
2021年 | 322篇 |
2020年 | 375篇 |
2019年 | 455篇 |
2018年 | 377篇 |
2017年 | 466篇 |
2016年 | 467篇 |
2015年 | 491篇 |
2014年 | 640篇 |
2013年 | 601篇 |
2012年 | 564篇 |
2011年 | 643篇 |
2010年 | 490篇 |
2009年 | 685篇 |
2008年 | 718篇 |
2007年 | 720篇 |
2006年 | 699篇 |
2005年 | 518篇 |
2004年 | 537篇 |
2003年 | 425篇 |
2002年 | 392篇 |
2001年 | 343篇 |
2000年 | 323篇 |
1999年 | 272篇 |
1998年 | 242篇 |
1997年 | 213篇 |
1996年 | 159篇 |
1995年 | 143篇 |
1994年 | 139篇 |
1993年 | 98篇 |
1992年 | 98篇 |
1991年 | 49篇 |
1990年 | 48篇 |
1989年 | 38篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Ching-Hui Tsai Shu-Kun Hsu Yi-Ching Yeh Chao-Shing Lee Kanyuan Xia 《Marine Geophysical Researches》2004,25(1-2):63-78
Magnetic data suggest that the distribution of the oceanic crust in the northern South China Sea (SCS) may extend to about 21 °N and 118.5 °E. To examine the crustal features of the corresponding continent–ocean transition zone, we have studied the crustal structures of the northern continental margin of the SCS. We have also performed gravity modeling by using a simple four-layer crustal model to understand the geometry of the Moho surface and the crustal thicknesses beneath this transition zone. In general, we can distinguish the crustal structures of the study area into the continental crust, the thinned continental crust, and the oceanic crust. However, some volcanic intrusions or extrusions exist. Our results indicate the existence of oceanic crust in the northernmost SCS as observed by magnetic data. Accordingly, we have moved the continent–ocean boundary (COB) in the northeastern SCS from about 19 °N and 119.5 °E to 21 °N and 118.5 °E. Morphologically, the new COB is located along the base of the continental slope. The southeastward thinning of the continental crust in the study area is prominent. The average value of crustal thinning factor of the thinned continental crust zone is about 1.3–1.5. In the study region, the Moho depths generally vary from ca. 28 km to ca. 12 km and the crustal thicknesses vary from ca. 24 km to ca. 6 km; a regional maximum exists around the Dongsha Island. Our gravity modeling has shown that the oceanic crust in the northern SCS is slightly thicker than normal oceanic crust. This situation could be ascribed to the post-spreading volcanism or underplating in this region. 相似文献
62.
A theoretical and an experimental investigation was carried out, where a carbon fibre corrugated circular cylinder was tested to destuction under external hydrostatic pressure. The theoretical investigation was via the finite element method, where the structure was modelled with several orthotropic axisymmetric thin-walled shell elements. The experimental observations were aided with strategically placed strain gauges. Comparison between theory and experiment showed that the experimentally observed buckling pressure was a little lower than the theoretical prediction. This may have been due to the fact that the model had slight initial geometrical imperfections in the circumferenential direction. 相似文献
63.
韩宗珠 《中国海洋大学学报(自然科学版)》1994,(1)
以微量元素、稀土元素、Sr和Nd同位素变异特征为依据,确定鲁苏榴辉岩为多成因、多来源和多阶段,指出主要是在印支期扬子陆块与华北陆块碰撞造山作用过程中,挤入的上地幔碎片以及不同原岩类型的壳内高压变质岩碎块。燕山晚期的区域构造热事件使得某些榴辉岩的同位素体系再平衡。 相似文献
64.
65.
IwrincrIONOn the evolution of palcoenvironment, salt-water encroachmnt and the distributionof subsurface brine in the LaizhOu Bay area, many researches had been carried out, and muchknowledge abeut the gcolOgical features in this area since Late QUaternary was aCquired' ) (H8nand Wu, l992; Han and Meng, l994; Wen et al. l989). However there was IittIe studyon the sediment geOChemical characteristics since Quaternary. In this Paper, the element strati-graphic characteristics and evolut… 相似文献
66.
A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena. 相似文献
67.
68.
非常规管节点疲劳寿命分析与计算 总被引:6,自引:1,他引:6
对非常规管节点的疲劳寿命进行了分析研究,用SESAM计算疲劳载荷,应用精细有限元分析计算热点应力,用规范的S—N曲线计算管节点的疲劳寿命。通过实例计算表明,这些处理对非常规管节点疲劳寿命分析与计算是很有效的。 相似文献
69.
Geochemistry of trace elements and Sr-Nd isotopes of foraminifera shell from the Okinawa Trough 总被引:1,自引:0,他引:1
INTRODUCTIONProvenanceofmarinesedimentshasalwaysbeenafocusedprobleminmarinesedimentge ology.Recognitionofendmembersandestimationoftheirrelativeproportionsfrommixedsedimentshavebeenakeycontentinthestudyofprovenance .Forthisaim ,itisnecessarytoselectendme… 相似文献
70.
A finite element model is set up and experimental tests are performed to help understand the behavior of a concrete canoe and subsequently optimize its design. First, the performance criteria that must be satisfied to participate at the annual ASCE/Master Builders competition are described. Then, the finite element model and the different loading cases that were studied are presented. Results from these loading cases are discussed and used to optimize the material properties as well as the thickness of the hull and the dimensions of the gunwale and reinforcing ribs. Static and dynamic experimental tests were also conducted to validate the results of the finite element analyses. The results indicate that the main stresses and strains are caused by the static load cases. The additional stresses caused during races are small. 相似文献