全文获取类型
收费全文 | 540篇 |
免费 | 147篇 |
国内免费 | 96篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 5篇 |
地球物理 | 88篇 |
地质学 | 562篇 |
海洋学 | 46篇 |
天文学 | 3篇 |
综合类 | 27篇 |
自然地理 | 47篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 23篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 26篇 |
2016年 | 29篇 |
2015年 | 30篇 |
2014年 | 34篇 |
2013年 | 36篇 |
2012年 | 43篇 |
2011年 | 41篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 36篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 33篇 |
2004年 | 21篇 |
2003年 | 27篇 |
2002年 | 13篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 17篇 |
1993年 | 6篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有783条查询结果,搜索用时 15 毫秒
141.
142.
鄂尔多斯盆地三叠系延长组主要发育东北和西南两大沉积体系,东北的河流三角洲体系已为大量的勘探研究资料所证实,而西南体系因受勘探程度限制,目前研究不够。本文通过最新钻探成果,结合盆地西南部露头资料,确立盆地西南地区三叠系延长组为冲积扇-扇三角洲沉积体系,发育冲积扇、扇三角洲、湖泊(浊积)相。冲积扇以西南缘平凉崆峒山和汭水河剖面为代表,扇三角洲及湖泊(浊积)相为区内钻井剖面所证实。长6-长8为区内主力油层组,地层保存完整,钻探程度相对较高。扇三角洲前缘砂体类型以水下分流河道为主,局部发育河口坝,浊积体以厚层块状为主。长8亚期为扇三角洲前缘亚相最发育期,横向形成自西南向东北延伸的三支前缘砂体带,是石油聚集的重要区带;长7亚期随着湖盆沉降,周边抬升强烈,湖岸较陡,大量发育浊积体系;长6亚期湖退导致扇三角洲再次发育,但规模较长8亚期弱。扇三角洲前缘砂体单层厚度大,砂岩粒度较粗,颗粒分选及物性好,是石油富集的最有利相带。 相似文献
143.
塔里木盆地塔东凸起西部中上奥陶统地震层序与海底扇沉积 总被引:7,自引:0,他引:7
根据区域地震资料研究塔里木盆地塔东凸起西部中上奥陶统层序地层格架及沉积演化, 在中上奥陶统识别出了2个地震层序, 发现了叠置的丘状前积反射地震单元, 综合岩心观察、岩屑录井和薄片资料, 确认为海底扇沉积体.海底扇沉积主要由块状砂、砾岩, 递变层理砂岩, 平行层理砂岩, 砂纹层理粉砂岩, 变形或包卷层理粉砂岩, 水平层理泥质粉砂岩或粉砂质泥岩, 块状或递变的粉砂质泥岩和泥岩等岩相组成, 形成于中扇和外扇环境, 物源来自研究区南部的岛弧带.海底扇的发现对于塔东凸起乃至整个塔里木盆地中上奥陶统油气勘探具有重要意义. 相似文献
144.
145.
徐州——宿州弧形双冲——叠瓦扇逆冲断层系统 总被引:51,自引:1,他引:51
郯庐断裂西徐州--宿州地区存在丰一个向西突出的弧形构造,其东侧后缘为倾向腹地的双冲构造,前缘为背驭式的叠瓦扇。东西向的不老河断层和宿北断层将其分为具有不同发育特征的三段。这是华北板块与扬子板块斜冲对接过程中,由于双沟推覆体向NW的反向推力,由东向西间歇式跳跃发展而形成的。该构造后期还被前缘的反向断层,前渊的重力滑动构造和腹地的指状断陷盆地所复杂经。这是不同于Boyer和Elliott简单模式的一种 相似文献
146.
广西横县六景火车站南侧,角度不整合覆盖下泥盆统莫丁组和那叫组下段,被新近系大面积覆盖而呈两部分远距离割裂状态的一套“二元结构”特征显著的红色泥砂基底碳酸盐岩粗巨砾岩及其横向相变部分,长期以来未被将其作为一个冲积扇的有机统一体进行研究。经笔者两次实地踏勘,系统采样和分析,以现代山麓冲积扇鉴别特征为主,辅以古冲积扇特征,综合分析认为该套沉积系列相关分割露头分别为一古近系冲积扇所残存扇根、扇中和扇缘。该冲积扇为一典型的古近纪早期干旱气候条件下,母岩区为陡峻碳酸盐岩山体的古山麓冲积扇。 相似文献
147.
锦屏电站辅助洞为A、B线的上下行单线隧道,线间距35 m,单线长175 km,由于隧道埋深大且无任何条件修建斜竖井做到长隧短打,只能从近东西向相向掘进,同时又由于工程的西端场地极其狭窄,不能满足有轨运输施工条件。通过技术论证,大胆创新,引入公路运营通风的理念,将射流通风运用于本工程的施工通风,从理论研究结合现场通风测试验证,成功地解决了巷道式射流风机选型、布置及通风管理等关键技术。通过双孔独头掘进9600 m的施工通风效果检测表明,洞内空气质量的各项指标均达到国家环卫标准,实现内燃作业、无轨运输,取得了 相似文献
148.
Facies, depositional model and stratigraphic architecture of Pleistocene giant Gilbert-type fan deltas are presented, based on outcrop data from the Derveni–Akrata region along the southern coast of the Gulf of Corinth, Greece. The common tripartite consisting of topset, foreset and bottomset [Gilbert, G.K., 1885. The topographic features of lake shores: Washington, D.C., United States Geol. Survey, 5th Annual Report, 69–123.] has been identified, as well as the most distal environment consisting of turbidites, and is organised in a repetitive pattern of four main systems tracts showing a clear facies and volumetric partitioning.The first systems tract (ST1) is characterised by the lack of topset beds and the development of a by-pass surface instead, thick foresets and bottomset beds, and thick well-developed turbiditic systems. This systems tract (ST1) is organised in an overall progradational pattern. The second systems tract (ST2) is characterised by a thin topset and almost no foreset equivalent. This systems tract is not always well-preserved and is organised in an overall retrograding trend with a landward shift in the position of the offlap break. The offshore is characterised by massive sandy turbidites. The third systems tract (ST3) is characterised by small-scale deltas prograding above the staked topsets of the giant Gilbert-type fan delta. Those small Gilbert-type fan deltas are generally organised in a pure progradation evolving to an aggradational–progradational pattern. In the distal setting of those small Gilbert-type fan deltas, almost no deposits are preserved on the remaining topography of the previous Gilbert-type fan delta. The fourth systems tract (ST4) is characterised by continuous vertically aggrading topsets that laterally pass into aggrading and prograding foresets. Bottomsets and distal turbiditic systems are starved. This fourth systems tract (ST4) is organised in an overall aggrading trend.These giant Gilbert-type fan deltas correspond to the Middle Group of the Corinth Rift infill and their stratigraphic development was strongly influenced by evolving rift structure. They record the migration of the depocenter from the rift shoulder to the rift axis in four main sequences from ca. 1.5 to 0.7 Ma, related to the migration of fault activity. It is worth noting that the maximum paleobathymetry was recorded during the final stage of the progradation of the Middle Group, suggesting that the rift climax was diachronous at the scale of the entire basin. The rapid (< 1 Ma) structural and sedimentological evolution, the migration of fault activity as well as the youth of the Corinth Rift, are probably exceptional factors allowing the characterisation of such diachronism. 相似文献
149.
Quaternary sedimentology of the Rose Creek fan delta, Walker Lake, Nevada, USA, and implications to fan-delta facies models 总被引:1,自引:0,他引:1
The 3·2 km long Rose Creek fan delta of west‐central Nevada is prograding from an active rift margin into the 32 m deep Walker Lake. A case study of the forms, processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub‐aerial origin, and the distal zone is of lacustrine origin. Pebbly to bouldery rock‐avalanche mounds >100 m thick (Facies A) and muddy to bouldery debris flow levées 0·5 to 2·0 m thick (Facies B) dominate the proximal zone, whereas mostly matrix‐supported cobbly pebbly debris flow lobes 0·1 to 1·0 m thick (Facies C) typify the medial zone. Surficial pebble lags and gully fills (Facies D) are widespread in both zones but, in exposures, comprise only partings or lenticles between debris flow units. The distal fan delta mainly consists of lakeshore to lake‐bottom tracts formed by extensive wave reworking of debris flow facies. Nearshore deposits include erosional cobbly boulder lag beaches (Facies E), pebbly constructional beaches attached at headcuts or on barrier spits (Facies F), pebbly upper shoreface (Facies G) and sandy lower shoreface (Facies H) tracts positioned lakeward of the beach, and pebbly landward‐dipping foresets (Facies I) and backshore‐pond sand and mud (Facies J) present landward of the spits. Erosional lag beaches fringe the windward north side of the fan‐delta front, attached constructional beaches characterize the central zone, and southward‐elongating barrier spits typify the leeward south side, extending from the zone of greatest projection of the fan delta into the lake. Shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south, combined with the arcuate shape of the fan‐delta front. The spits overlie a platform deposited below common wave base consisting of south‐east‐trending cones of pebbly Gilbert foresets (Facies K) and sandy toesets (Facies L). Typically slumped silt and mud (Facies M) fringe both this platform and lower shoreface sand in deeper water. This case demonstrates facies types and patterns that are inconsistent with the widely promoted fan‐delta facies model having a front consisting of an apron of radially directed Gilbert foresets deposited where sub‐aerial flows enter the lake. The Rose Creek fan‐delta front instead features a sharp contact between sub‐aerial and lakeshore facies formed where waves erode, sort and redistribute heterogeneous debris flow sediment into the various shallow‐to‐deep lake facies. Gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front. This facies scenario results from the infrequency of fan‐building events versus nearly constant wind‐induced waves, a scenario that, in contrast to the popular Gilbert model, probably is the norm for fan deltas. The level of Walker Lake, and thus the position of wave reworking on the Rose Creek fan delta, fluctuated over a range of ~157 m during the last 18 kyr, producing complex interfingering between sub‐aerial and lakeshore facies across a 1700 m wide radial belt, typifying a wave‐modified, freestand lacustrine fan delta. 相似文献
150.
Cao Shuyang Akira Nishi Kimitaka Hirano Shigehira Ozono Hiromori Miyagi Hiromori Kikugawa Yuji Matsuda Yasuo Wakasugi 《Boundary-Layer Meteorology》2001,101(1):61-76
An actively controlled wind tunnel equipped with multiple fansand airfoils has been developed, mainly for the purpose of reproducing the atmospheric boundary layer (ABL) for wind engineering applications. Various fluctuating flows can be achieved in this wind tunnel by altering the input data of the fans and airfoils through computer control. In this study, the ABL is physically simulated in this wind tunnel, and particular attention ispaid to the simulation of the profile of Reynolds stress. The method of generating the fluctuating flow and the experimental results of reproducing the ABL are presented. As the results show, the spatial distribution of Reynolds stress is satisfactorily simulated, and the profiles of other statisticalturbulent parameters, such as mean velocity, turbulent intensity, integral scale and power spectrum are successfully reproduced simultaneously. 相似文献