全文获取类型
| 收费全文 | 5462篇 |
| 免费 | 1068篇 |
| 国内免费 | 1289篇 |
专业分类
| 测绘学 | 417篇 |
| 大气科学 | 1128篇 |
| 地球物理 | 1523篇 |
| 地质学 | 2732篇 |
| 海洋学 | 624篇 |
| 天文学 | 154篇 |
| 综合类 | 610篇 |
| 自然地理 | 631篇 |
出版年
| 2024年 | 12篇 |
| 2023年 | 80篇 |
| 2022年 | 238篇 |
| 2021年 | 265篇 |
| 2020年 | 211篇 |
| 2019年 | 270篇 |
| 2018年 | 316篇 |
| 2017年 | 286篇 |
| 2016年 | 319篇 |
| 2015年 | 262篇 |
| 2014年 | 285篇 |
| 2013年 | 323篇 |
| 2012年 | 264篇 |
| 2011年 | 262篇 |
| 2010年 | 288篇 |
| 2009年 | 285篇 |
| 2008年 | 257篇 |
| 2007年 | 263篇 |
| 2006年 | 206篇 |
| 2005年 | 207篇 |
| 2004年 | 182篇 |
| 2003年 | 183篇 |
| 2002年 | 252篇 |
| 2001年 | 273篇 |
| 2000年 | 244篇 |
| 1999年 | 261篇 |
| 1998年 | 227篇 |
| 1997年 | 196篇 |
| 1996年 | 168篇 |
| 1995年 | 159篇 |
| 1994年 | 149篇 |
| 1993年 | 123篇 |
| 1992年 | 108篇 |
| 1991年 | 79篇 |
| 1990年 | 64篇 |
| 1989年 | 54篇 |
| 1988年 | 45篇 |
| 1987年 | 32篇 |
| 1986年 | 18篇 |
| 1985年 | 22篇 |
| 1984年 | 15篇 |
| 1983年 | 17篇 |
| 1982年 | 9篇 |
| 1981年 | 10篇 |
| 1980年 | 5篇 |
| 1979年 | 5篇 |
| 1978年 | 5篇 |
| 1977年 | 3篇 |
| 1958年 | 8篇 |
| 1954年 | 1篇 |
排序方式： 共有7819条查询结果，搜索用时 375 毫秒
991.
In the aggressive marine environment over a long-term service period,coastal bridges inevitably sustain corrosion-induced damage due to high sea salt and humidity.This paper investigates the strength reduction of coastal bridges,especially focusing on the effects of non-uniform corrosion along the height of bridge piers.First,the corrosion initiation time and the degradation of reinforcement and concrete are analyzed for bridge piers in marine environments.To investigate the various damage modes of the concrete cover,a discretization method with fiber cells is used for calculating time-dependent interaction diagrams of cross-sections of the bridge piers at the atmospheric zone and the splash and tidal zone under a combination of axial force and bending moment.Second,the shear strength of these aging structures is analyzed.Numerical simulation indicates that the strength of a concrete pier experiences dramatic reduction from corrosion initiation to the spalling of the concrete cover.Strength loss in the splash and tidal zone is more significant than in the atmospheric zone when structures’service time is assumed to be the same. 相似文献
992.
Rupture model of the 2013 M_W 6.6 Lushan (China) earthquake constrained by a new GPS data set and its effects on potential seismic hazard 
下载免费PDF全文
下载免费PDF全文 Vertical records are critically important when determining the rupture model of an earthquake, especially a thrust earthquake. Due to the relatively low fitness level of near-field vertical displacements, the precision of previous rupture models is relatively low, and the seismic hazard evaluated thereafter should be further updated. In this study, we applied three-component displacement records from GPS stations in and around the source region of the 2013 MW6.6 Lushan earthquake to re-investigate the rupture model.To improve the resolution of the rupture model, records from both continuous and campaign GPS stations were gathered, and secular deformations of the GPS movements were removed from the records of the campaign stations to ensure their reliability. The rupture model was derived by the steepest descent method(SDM), which is based on a layered velocity structure. The peak slip value was about 0.75 m, with a seismic moment release of 9.89 × 10~(18) N·m, which was equivalent to an M_W6.6 event. The inferred fault geometry coincided well with the aftershock distribution of the Lushan earthquake. Unlike previous rupture models, a secondary slip asperity existed at a shallow depth and even touched the ground surface. Based on the distribution of the co-seismic ruptures of the Lushan and Wenchuan earthquakes, post-seismic relaxation of the Wenchuan earthquake, and tectonic loading process, we proposed that the seismic hazard is quite high and still needs special attention in the seismic gap between the two earthquakes. 相似文献
993.
相山火山盆地主体岩石为一套由熔结凝灰岩、流纹英安岩、流纹英安斑岩、碎斑熔岩、粗斑花岗斑岩及似斑状花岗岩组成的酸性火山-侵入杂岩体, 构成了两个完整的喷发-溢流(侵出)-侵入的岩浆活动亚旋回。本文在野外地质调查的基础上, 采用SIMS、LA-ICP-MS技术对主要岩类进行了高精度的锆石U-Pb年代学研究, 并建立了火山-侵入杂岩体的演化序列。结果表明, 打鼓顶组熔结凝灰岩代表了相山火山-侵入活动的最早期产物, 其锆石U-Pb年龄为140.7±2.7 Ma、140.1±1.8 Ma和138.2±1.6 Ma, 第一亚旋回主体流纹英安岩的锆石U-Pb年龄135.0±1.8 Ma。鹅湖岭组熔结凝灰岩代表了火山-侵入活动的第二亚旋回的开始, 其U-Pb年龄为135.6±1.2 Ma, 第二亚旋回主体碎斑熔岩的锆石U-Pb年龄133.6±1.3 Ma, 沙洲单元的粗斑花岗斑岩和似斑状花岗岩属于该亚旋回最晚期的侵入岩, 其锆石U-Pb年龄代表了相山火山-侵入活动的结束时间(分别为133.4±1.2 Ma和133.9±1.1 Ma)。相山早白垩世火山-侵入活动延续时间较短, 整体上呈现一个连续的过程, 初始时间在141 Ma附近, 结束时间在132 Ma左右。概言之, 第一亚旋回(141~135 Ma)以形成熔结凝灰岩、流纹英安岩和流纹英安斑岩为主, 第二亚旋回(135~132 Ma)以熔结凝灰岩、碎斑熔岩、粗斑花岗斑岩和似斑状花岗岩为主。岩石地球化学和野外地质特征也与两个亚旋回火山-侵入岩浆活动相吻合。 相似文献
994.
1INTRODUCTIONEcosystem services can be divided into two major cat-egories, one is system function, and the other is sys-tem services and goods provision, which provide not only materials such as food and medicine, but also support and maintenance of whole system. Ecological services contribute to the whole economic system, both directly and indirectly, and consequently repre-sent parts of the total value of our economy system (COSTANZA etal., 1997; GUO etal., 2001). Sustainable d… 相似文献
995.
为了提高Gass-Seidel(GS)算法的收敛速度,提出了改进的GS算法(MGS),用于解算高精度曲面模型(HASM)(HASM-MGS)。以高斯合成曲面为研究对象,将HASM-MGS与HASM-GS和Matlab提供的函数进行对比,结果表明,达到相同的模拟中误差,HASM-MGS计算时间远小于HASM-GS和Matlab提供的函数;HASM-MGS计算时间与模拟区域的网格数呈非常好的线性关系,时间复杂度比传统的方法降低两个数量级。 相似文献
996.
997.
Natural Hazards - Coastal inundation due to storm tides is computed using ADvanced CIRCulation (ADCIRC) model along the east coast of India. Inland inundation due to storm tides is calculated every... 相似文献
998.
Acta Geotechnica - The spatial variation of the physical–mechanical properties of rock or rock-like materials is an intrinsic characteristic of the materials induced by multiscale material... 相似文献
999.
1000.