全文获取类型
收费全文 | 1599篇 |
免费 | 272篇 |
国内免费 | 407篇 |
专业分类
测绘学 | 90篇 |
大气科学 | 326篇 |
地球物理 | 378篇 |
地质学 | 830篇 |
海洋学 | 260篇 |
天文学 | 75篇 |
综合类 | 172篇 |
自然地理 | 147篇 |
出版年
2024年 | 13篇 |
2023年 | 27篇 |
2022年 | 62篇 |
2021年 | 89篇 |
2020年 | 81篇 |
2019年 | 65篇 |
2018年 | 60篇 |
2017年 | 72篇 |
2016年 | 88篇 |
2015年 | 66篇 |
2014年 | 93篇 |
2013年 | 79篇 |
2012年 | 70篇 |
2011年 | 90篇 |
2010年 | 80篇 |
2009年 | 88篇 |
2008年 | 77篇 |
2007年 | 64篇 |
2006年 | 58篇 |
2005年 | 53篇 |
2004年 | 54篇 |
2003年 | 51篇 |
2002年 | 58篇 |
2001年 | 59篇 |
2000年 | 56篇 |
1999年 | 86篇 |
1998年 | 66篇 |
1997年 | 70篇 |
1996年 | 65篇 |
1995年 | 49篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 59篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2278条查询结果,搜索用时 15 毫秒
81.
82.
Sedimentary evolution of the Holocene subaqueous clinoform off the southern Shandong Peninsula in the Western South Yellow Sea 总被引:1,自引:0,他引:1
Jiandong Qiu Jian Liu Yoshiki Saito Zigeng Yang Baojing Yue Hong Wang Xianghuai Kong 《中国海洋大学学报(英文版)》2014,13(5):747-760
Based on the stratigraphic sequence formed since the last glaciation and revealed by 3000 km long high-resolution shallow seismic profiles and the core QDZ03 acquired recently off the southern Shandong Peninsula, we addressed the sedimentary characteristics of a Holocene subaqueous clinoform in this paper. Integrated analyses were made on the core QDZ03, including sedimentary facies, sediment grain sizes, clay minerals, geochemistry, micro paleontology, and AMS 14 C dating. The result indicates that there exists a Holocene subaqueous clinoform, whose bottom boundary generally lies at 15–40 m below the present sea level with its depth contours roughly parallel to the coast and getting deeper seawards. The maximum thickness of the clinoform is up to 22.5 m on the coast side, and the thickness contours generally spread in a banded way along the coastline and becomes thinner towards the sea. At the mouths of some bays along the coast, the clinoform stretches in the shape of a fan and its thickness is evidently larger than that of the surrounding sediments. This clinoform came into being in the early Holocene(about 11.2 cal kyr BP) and can be divided into the lower and upper depositional units(DU 2 and DU 1, respectively). The unit DU 2, being usually less than 3 m in thickness and formed under a low sedimentation rate, is located between the bottom boundary and the Holocene maximum flooding surface(MFS), and represents the sediment of a post-glacial transgressive systems tract; whereas the unit DU 1, the main body of the clinoform, sits on the MFS, belonging to the sediment of a highstand systems tract from middle Holocene(about 7–6 cal kyr BP) to the present. The provenance of the clinoform differs from that of the typical sediments of the Yellow River and can be considered as the results of the joint contribution from both the Yellow River and the proximal coastal sediments of the Shandong Peninsula, as evidenced by the sediment geochemistry of the core. As is controlled mainly by coactions of multiple factors such as the Holocene sea-level changes, sediment supplies and coastal dynamic conditions, the development of the clinoform is genetically related with the synchronous clinoform or subaqueous deltas around the northeastern Shandong Peninsula and in the northern South Yellow Sea in the spatial distribution and sediment provenance, as previously reported, with all of them being formed from the initial stage of the Holocene up to the present. 相似文献
83.
南海曾母盆地南部陆架边缘三角洲沉积特征 总被引:2,自引:0,他引:2
曾母盆地作为发育于古巽他陆架上的盆地,南部的古巽他河所携带的巨量沉积物和曾母盆地的陆架特征使得陆架边缘三角洲在曾母盆地南部发育成为必然。通过对曾母盆地中中新世以来陆架边缘三角洲的地震、钻井及进积特征分析,认为曾母盆地内陆架边缘三角洲的沉积形态呈分别向陆和向海减薄的楔形体,古巽他河携带多期次的沉积物向陆坡沉积过程中形成多套沉积复合体,这些沉积体由于具有良好的生储条件,因而具有重要的油气勘探价值。 相似文献
84.
85.
山东中生代橄榄安粗岩系火山岩的地质、地球化学特征及岩石成因 总被引:44,自引:0,他引:44
山东中生代橄榄安粗岩系火山岩主要分布在沂沭断裂带及其两侧的断陷型陆相火山盆地中,为早白垩世火山活动的产物.Rb-Sr全岩等时年龄变化于111.4~119.6Ma.岩石组合主要为粗面玄武岩-橄榄安粗岩-安粗岩-粗面岩.这套岩石在化学上具有富碱富钾、富铝贫钛、高氧化系数及富轻稀土和大离子亲石元素的特点,并具有较高的ISr值和明显偏低εNd值.根据对岩石地质、地球化学特征和产出构造环境的详细分析,表明这套岩石的成因应主要是富集型地幔的部分熔融 相似文献
86.
87.
88.
The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging. 相似文献
89.
湘鄂赣二叠纪岩相古地理研究 总被引:4,自引:0,他引:4
湘鄂赣二叠纪沉积盆地是在华南陆块基础上发育而成,具有扬子克拉通北缘被动大陆边缘盆地、扬子克拉通盆地、湘赣板内拉张盆地和华夏克拉通边缘盆地等四类。根据古暴露等标志,建立了各类盆地的沉积层序,并进行了区域对比。在此基础上,本文着重运用层序地层编图法编制了湘鄂赣二叠纪岩相古地理图,深化了该区岩相古地理研究,详细建立了沉积体系域模式和岩相古地理演化特点和控制因素。 相似文献
90.