全文获取类型
| 收费全文 | 1002篇 |
| 免费 | 157篇 |
| 国内免费 | 151篇 |
专业分类
| 测绘学 | 128篇 |
| 大气科学 | 29篇 |
| 地球物理 | 162篇 |
| 地质学 | 675篇 |
| 海洋学 | 85篇 |
| 天文学 | 10篇 |
| 综合类 | 119篇 |
| 自然地理 | 102篇 |
出版年
| 2024年 | 5篇 |
| 2023年 | 2篇 |
| 2022年 | 25篇 |
| 2021年 | 27篇 |
| 2020年 | 36篇 |
| 2019年 | 34篇 |
| 2018年 | 24篇 |
| 2017年 | 40篇 |
| 2016年 | 40篇 |
| 2015年 | 41篇 |
| 2014年 | 47篇 |
| 2013年 | 77篇 |
| 2012年 | 47篇 |
| 2011年 | 56篇 |
| 2010年 | 48篇 |
| 2009年 | 46篇 |
| 2008年 | 52篇 |
| 2007年 | 65篇 |
| 2006年 | 52篇 |
| 2005年 | 54篇 |
| 2004年 | 44篇 |
| 2003年 | 45篇 |
| 2002年 | 48篇 |
| 2001年 | 44篇 |
| 2000年 | 52篇 |
| 1999年 | 40篇 |
| 1998年 | 43篇 |
| 1997年 | 30篇 |
| 1996年 | 27篇 |
| 1995年 | 21篇 |
| 1994年 | 24篇 |
| 1993年 | 21篇 |
| 1992年 | 14篇 |
| 1991年 | 11篇 |
| 1990年 | 5篇 |
| 1989年 | 6篇 |
| 1988年 | 5篇 |
| 1987年 | 4篇 |
| 1986年 | 5篇 |
| 1984年 | 1篇 |
| 1983年 | 1篇 |
| 1978年 | 1篇 |
排序方式： 共有1310条查询结果，搜索用时 15 毫秒
111.
112.
重点研究了吐哈盆地构造单元的类型、构造属性及其与构造反转之间的关系等相关问题.吐哈盆地的构造单元可归为2种不同类型的体系:坳陷/隆起-凹陷/凸起类型的体系和构造带类型的体系.前者为沉积构造单元,具有同沉积构造的属性.可代表盆地形成时期的伸展性结构与构造;后者则为变形构造单元,具有"后生或次生"构造的属性,反映或代表了后期的构造反转.吐哈盆地"东西分块"应是同沉积期构造格局的表象,"南北分带"则主要是后期挤压与构造反转的结果.由此也进一步证明,吐哈原型盆地属伸展性盆地,后期则因挤压改造而发生了构造反转.前述各种特征则可能是此类构造反转盆地所具有的特殊的地质构造现象. 相似文献
113.
软刚臂系泊系统是一种利用压载质量为浮式生产储油装置(FPSO)提供回复力的单点系泊方式。为快速准确地评估多铰接组成的软刚臂系统的受力状态,避免应用高复杂度的有限元软件,进而快速完成优化设计等任务,建立一种静力计算方法十分有必要。因此,针对由刚臂(YOKE)、柔性系泊腿和压载舱组成的刚柔多体系统,以分解组合的方式,提出一种二维静力计算方法,用以研究FPSO软刚臂系泊系统的静力特性。该方法主要依靠软刚臂的几何构型,在有限铰接约束下,形成非线性静力平衡方程,建立了压载舱式水上软刚臂单点系泊系统二维静力平衡计算算法。采用OrcaFlex、SESAM等软件开展了理论和数值对比分析,同时与系泊试验结果开展验证分析。对比结果表明,文中所提方法计算精度较高,可为软刚臂单点系泊系统的研究提供可靠支持。 相似文献
114.
利用8个典型的固定剖面资料,对坡度、水深、沉积物底质、单宽侵蚀量和淤积量进行了分析。研究表明:黄河改道后,CS5—CS8剖面的三角洲前缘和前三角洲的侵蚀较为剧烈,各剖面三角洲前缘侵蚀较为强烈;蚀淤泥沙在纵向上由三角洲前缘向前三角洲搬运,在横向上沿近岸向西北方向运移;近岸颗粒粗化较为显著,尤其是在废弃的流路入海口处。 相似文献
115.
Studies on migration pathways remain qualitative, albeit extensive quantification of migration forcing. In this study, hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the Third Member of Eocene Shahejie Formation in the Dongying Depression, Bohai Bay Basin, eastern China, on the basis of their lithofacies and physical properties, spatial relationships, and data availability; secondary migration conduits are then quantified. A carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals. The carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration. A method of quantifying sandstone carrier units using common physical properties is developed. First, a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes. Second, physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory. Third, the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit. Last, the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters. The results for sandstone carrier units in the Third Member of the Shahejie Formation are used in numerical models addressing Pleistocene secondary migration. The model results explain the discovered accumulation and hydrocarbon shows well; and the model predictions on exploration targets have been confirmed by drilling. 相似文献
117.
The La Peña alkaline complex (LPC) of Miocene age (18–19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400–2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km2 and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW–SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N–S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R′), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW–SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by dikes cross-cutting the clinopyroxenite, (3) a malignite facies that causes a small breccia in the clinopyroxenite, (4) a central syenite facies that develops breccias at the contact with the clinopyroxenite and, finally, (5) porphyry necks and a system of radial dikes intruding all units. At the moment of the emplacement different mechanisms would have acted, they summarized in: 1) opening of discontinuities synchronous to the magma circulation as the principal mechanism for formation of dikes and conduits; 2) stoping processes, that play an important role in the development of the breccia zone and enabling an efficient transference of material during the emplacement of the syenitic magma and 3) shear-related deformation (regional stress), affected the internal fabric of the facies, causing intracrystalline deformation and submagmatic flow, which is very evident in the central syenite intrusive. The kinematic analysis of shear planes allows proposing that emplacement of the LPC took place in a transtensive regime, which would have occurred in the back-arc of the Andes orogen, during a long period spanning from Miocene to the present, of the compressive deformation responsible, westward and at the same latitude, for the development of the Aconcagua fold and thrust belt. 相似文献
118.
基于多源遥感数据提取投入产出数据,采用考虑非期望产出的超效率EBM模型对2000—2015年山东省县域生态效率进行测度,在此基础上采用核密度估计、空间自相关等方法对山东省县域生态效率的时空特征进行分析。研究表明：①山东省县域生态效率呈现波动式发展趋势;高值区与低值区存在显著空间分化,胶东半岛与济南都市圈构成高值集聚区,鲁西北、鲁西南、鲁南地区形成低值连绵带;②山东省县域生态效率无明显的两极分化现象,处于高值区、低值区的县域生态效率值变化较大,生态效率空间非均衡性逐渐扩大;③山东省县域生态效率存在显著空间正相关,且空间集聚性呈现增强态势;县域生态效率存在空间俱乐部趋同特征。 相似文献
119.
在大倾角像片的相机检校中,经典共线方程是采用欧拉角（妒,纠,Ⅳ）描述旋转矩阵的,该方法受限于无法获取位置与姿态的初始值,结果可能导致迭代不收敛。共线方程中的旋转矩阵还可以直接利用方向余弦或单位四元数来描述,相机检校时可以无需依赖位置与姿态的初始值。在相同实验数据、初始值和收敛条件的实验中,直接利用方向余弦描述旋转矩阵的方法明显优于单位四元数方法,主要体现在收敛情况和计算结果接近欧拉角方法两个方面。建议在非量测相机检校时,最好选用直接利用方向余弦描述旋转矩阵的共线方程方法。 相似文献
120.