全文获取类型
| 收费全文 | 2409篇 |
| 免费 | 541篇 |
| 国内免费 | 696篇 |
专业分类
| 测绘学 | 259篇 |
| 大气科学 | 113篇 |
| 地球物理 | 620篇 |
| 地质学 | 1994篇 |
| 海洋学 | 158篇 |
| 天文学 | 8篇 |
| 综合类 | 242篇 |
| 自然地理 | 252篇 |
出版年
| 2024年 | 18篇 |
| 2023年 | 50篇 |
| 2022年 | 106篇 |
| 2021年 | 106篇 |
| 2020年 | 98篇 |
| 2019年 | 132篇 |
| 2018年 | 104篇 |
| 2017年 | 124篇 |
| 2016年 | 132篇 |
| 2015年 | 144篇 |
| 2014年 | 168篇 |
| 2013年 | 162篇 |
| 2012年 | 201篇 |
| 2011年 | 174篇 |
| 2010年 | 166篇 |
| 2009年 | 153篇 |
| 2008年 | 118篇 |
| 2007年 | 151篇 |
| 2006年 | 152篇 |
| 2005年 | 135篇 |
| 2004年 | 129篇 |
| 2003年 | 125篇 |
| 2002年 | 102篇 |
| 2001年 | 98篇 |
| 2000年 | 127篇 |
| 1999年 | 63篇 |
| 1998年 | 65篇 |
| 1997年 | 55篇 |
| 1996年 | 51篇 |
| 1995年 | 51篇 |
| 1994年 | 43篇 |
| 1993年 | 30篇 |
| 1992年 | 31篇 |
| 1991年 | 13篇 |
| 1990年 | 19篇 |
| 1989年 | 14篇 |
| 1988年 | 13篇 |
| 1987年 | 7篇 |
| 1986年 | 4篇 |
| 1985年 | 3篇 |
| 1984年 | 1篇 |
| 1983年 | 1篇 |
| 1981年 | 1篇 |
| 1979年 | 6篇 |
排序方式： 共有3646条查询结果，搜索用时 15 毫秒
431.
Hyunhee Park 《The Cartographic journal》2013,50(1):92-93
Abstract
432.
机载LiDAR数据逐航带平差与航带区域网平差对比 总被引：1，自引：0，他引：1
机载LiDAR系统获取的点云数据在经过预处理解算后仍会残余部分系统误差,因此,在利用点云数据生成DEM等相关数字产品之前,必须检查并改正这部分系统误差。以此为主要目标,本文对机载LiDAR数据的逐航带平差与航带区域网平差展开研究,并以Microsoft Visual Studio 2008 C++为开发平台、基于实测数据对比了两者在完成多航带构成的测区平差时的精度,结果表明:机载LiDAR数据的航带区域网平差方法相较于LZD算法可有效降低逐航带平差导致的误差累积,精度更高。 相似文献
433.
434.
受气候控制的洪水事件沉积因其短暂性、广布性和周期性等特征,具有相对的等时效应,可以作为地层划分和对比的标志层。通过分析不同规模周期下的事件沉积和正常沉积特征,并结合基准面旋回理论,识别出济阳坳陷惠民凹陷临盘地区始新统孔店组一段—沙河街组四段下亚段红层短期、中期和长期三个级次的基准面旋回特征,短期旋回以洪水期和间洪水期内发育的不同类型沉积微相组合为特征,中期旋回以发育一套完整的洪水期—间洪水期沉积为标志,长期旋回则以多个中期旋回组成的地层叠加为特征;以此为依据将惠民凹陷临盘地区孔店组一段—沙河街组四段下亚段划分为5个长期旋回、16个中期旋回及若干个短期旋回层序,并对第一个长期旋回进行了精细层序地层对比,在此基础上建立了干旱气候控制下的红层层序的划分和对比模式。 相似文献
435.
基于气候变化特征的红层划分对比——以东营凹陷南坡为例 总被引：1，自引：0，他引：1
首次利用气候变化特征,对由于缺少特征古生物化石资料而长期难以进行地层划分的东营凹陷南坡始新统沙河街组四段下亚段——孔店组一段的红层进行了有效划分。采用基于孢粉化石Ephedripites相对含量约束下的测井数据法恢复相对古气候变化,首先根据Ephedripites相对含量的变化确定气候变化拐点(最干旱点)的位置段,再根据能谱测井数据或常规测井数据计算出的连续粘土矿物组成确定气候拐点的具体点,即为层位界线。根据标准井测井数据建立的数学模型,可以对该井附近新钻探井的红层进行划分对比,其科学性、合理性已被之后的勘探成果所证实。该方法为缺少古生物化石数据的"哑地层"划分提供了一种新思路。 相似文献
436.
《International Geology Review》2012,54(3):311-321
Orogenic gold (Au) deposits are the most important type, accounting for more than half of the world's proven Au reserves. They are mainly controlled by three key factors: (1) abundant andesitic rocks (SiO2 of 55–60 wt.%) at depth, which have systematically higher Au contents than other rock types; (2) a pervasive transition from greenschist facies to amphibolite facies metamorphism within a short period, which releases S2?-rich fluids that may scavenge Au from host rocks; and (3) deformation and fracturing under a compressive/transpressive tectonic regime. Orogenic belts at convergent margins are the best places for such mineralization because convergent margins are rich in andesites; the transition from greenschist to amphibolite facies recrystallization commonly occurs as a result of collision, compression, and thickening at convergent margins, forming large amounts of Au-rich fluids within a short period of time; and strong deformation and fracturing during orogenic processes provide channels for fluid transportation. Moreover, the overlying plate is injected and enriched by auriferous fluids released during amphibolite facies metamorphism of the subducting plate. The Pacific plate changed course by ～80° (from SW to NW) at approximately 125–122 Ma, reflecting an altered thermal structure and the elevation of the South Pacific plate attending the appearance of the plume head that formed the Ontong Java large igneous province. Consequently, the tectonic regime changed from extension to compressive/transpressive in eastern China, causing deformation, thickening, and metamorphism of the overriding plate, especially along weak crustal belts (e.g. overlying plates of palaeosutures), which resulted in world-class mineralization of orogenic Au deposits. During this process, pyrite changed to pyrrhotite during the transition from greenschist to amphibolite facies, releasing sulphur. Sulphur mobilized and scavenged Au and other chalcophile elements into metamorphic ore-forming fluids. A series of NE-trending compressive faults were formed at ?120 Ma as a result of continuous compression of the subducting Pacific plate, releasing these ore-forming fluids. Auriferous carbonate-rich quartz veins and/or metasomatized Au-bearing wall rocks were formed due to the decompression of the ascending ore-forming fluids. Orogenic belts along the margins of the North China craton and the Jiangnan block were the most favourable regions for mineralization. Compared with the former, the latter has much smaller proven Au reserves. However, more exploration is needed along the margins of the Jiangnan block. Promising targets include accessory faults and kink points of large, NE-trending Cretaceous faults that transect greenschist facies metamorphic rocks of the Niuwu and Jingtan Groups, etc. 相似文献
437.
《International Geology Review》2012,54(4):430-441
The Trans-Mexican Volcanic Belt (TMVB) is an igneous arc built above the Middle America subduction zone. Its western section is being extended orthogonally to its axis by several arrays of active normal faults with a combined length of 450 km and including up to 1.5 km of throw. Until now, intra-arc extension in the TMVB has been considered the result of either rifting or retreat of the Rivera and Cocos plates. Observations worldwide and numerical models, however, appear to contradict these ideas. Continental extension in convergent margins takes place where the upper plate moves away from the trench, and the subduction zone is only weakly coupled with the overlying plate. In western Mexico, neither of these relationships applies. A new numerical model presented here is able to explain satisfactorily the state of brittle failure of the TMVB. The model embodies the first-order physics of the northern Middle America subduction zone, and its boundary conditions are consistent with the convergence history of the Rivera and North America plates. Modelling results show that periods of accelerated subduction between the Rivera and North America plates give rise to an increase in suction force under the fore arc. The over-riding plate then bends downwards, building up tensional stress inside the volcanic arc. Failure of the arc follows within 1 million years of pulse initiation. Analysis of the results shows that the steep subduction angle of the Rivera slab, the relief of the volcanic plateau, and the thermal weakening of the lower crust facilitated the failure of the arc. The model demonstrates that a highly coupled subduction zone can cause extension, albeit limited, in the over-riding plate. 相似文献
438.
《International Geology Review》2012,54(6):672-694
The Great Xing’an Range in Northeast China is located in the eastern part of the Central Asian Orogenic Belt. From north to south, the Great Xing’an Range is divided into the Erguna, Xing’an, and Songliao blocks. Previous U–Pb zircon geochronology results have revealed that some ‘Precambrian metamorphic rocks’ in the Xing’an block have Phanerozoic protolith ages, questioning whether Precambrian basement exists in the Xing’an block. We present laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results for zircons from suspected Precambrian metamorphic rocks in the Xing’an block. Meta-rhyolites of the Xinkailing Group in Nenjiang yield magmatic ages of 355.8 Ma. Detrital zircons from phyllites of the Xinkailing Group in Duobaoshan yield populations of ca. 1505, ca. 810, and ca. 485 Ma, with the youngest peak constraining its depositional age to be <485 Ma. Zircons from amphibolitic gneisses of the Xinkailing Group in Nenjiang have magmatic ages of 308.6 Ma. Mylonitic granites of the Xinkailing Group in Nenjiang have zircon magmatic ages of 164 Ma. Detrital zircons from two-mica quartz schists of the Luomahu Group in the Galashan Forest yield ca. 2419, ca. 1789, ca. 801, ca. 536, ca. 480, and ca. 420 Ma, with the youngest peak indicating its depositional age as <420 Ma. Detrital zircons from mylonitized sericite–chlorite schist of the Ergunhe Formation in Taerqi yield populations of 982–948, ca. 519, and ca. 410 Ma, with the youngest peak demonstrating that its depositional age is <410 Ma. These zircon ages for a range of lithologies show that the Great Xing’an Range metamorphic rocks formed during the Phanerozoic (164–485 Ma) and that this crust is mostly Palaeozoic. Based on these results and published data, we conclude that there is no evidence of Precambrian metamorphic basement in the Xing’an block. In summary, the age data indicate that Precambrian metamorphic basement may not exist in the Xing’an region. 相似文献
439.
《International Geology Review》2012,54(4):473-480
On 12 May 2008 and 20 April 2013, respectively, the devastating magnitude 7.9 (Wenchuan) and magnitude 7.0 (Ya’an) earthquakes struck the southwestern Longmen Shan fault zone (LMSFZ), the eastern margin of the Tibetan Plateau. These events were notable because they occurred in a heavily populated area and resulted in severe damage and loss of life. Here we present an integrated analysis of potential field anomalies and a crustal-scale seismic reflection image to investigate the crustal structure and some tectonic relationships associated with these devastating events. Our results show that the western margin of the Yangtze crustal block possesses an irregular margin that extends westward beyond the LMSFZ to the northeast and merges gradually with the LMSFZ to the southwest. We interpret this variation in deep structure to create a lateral heterogeneity in the local stress regime that explains the observed variations in fault geometry and slip distribution, as well as seismicity, of the LMSFZ. This structural complexity results in a differential build-up of stress as the Tibetan Plateau is being extruded eastward. Thus, the results of this research can help identify potential natural hazard zones and focus efforts on hazard mitigation. 相似文献
440.
