全文获取类型
收费全文 | 21456篇 |
免费 | 4336篇 |
国内免费 | 6040篇 |
专业分类
测绘学 | 2143篇 |
大气科学 | 4074篇 |
地球物理 | 5130篇 |
地质学 | 11672篇 |
海洋学 | 3023篇 |
天文学 | 790篇 |
综合类 | 2199篇 |
自然地理 | 2801篇 |
出版年
2024年 | 149篇 |
2023年 | 464篇 |
2022年 | 1319篇 |
2021年 | 1504篇 |
2020年 | 1202篇 |
2019年 | 1466篇 |
2018年 | 1507篇 |
2017年 | 1329篇 |
2016年 | 1424篇 |
2015年 | 1314篇 |
2014年 | 1521篇 |
2013年 | 1520篇 |
2012年 | 1578篇 |
2011年 | 1539篇 |
2010年 | 1506篇 |
2009年 | 1339篇 |
2008年 | 1199篇 |
2007年 | 1069篇 |
2006年 | 871篇 |
2005年 | 766篇 |
2004年 | 574篇 |
2003年 | 485篇 |
2002年 | 437篇 |
2001年 | 502篇 |
2000年 | 523篇 |
1999年 | 695篇 |
1998年 | 573篇 |
1997年 | 517篇 |
1996年 | 502篇 |
1995年 | 413篇 |
1994年 | 391篇 |
1993年 | 335篇 |
1992年 | 313篇 |
1991年 | 205篇 |
1990年 | 166篇 |
1989年 | 136篇 |
1988年 | 111篇 |
1987年 | 78篇 |
1986年 | 59篇 |
1985年 | 49篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1958年 | 14篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
991.
CHENG Yang XIAO Qinghui LI Tingdong LI Yan FAN Yuxu XU Liquan GUO Lingju PANG Jinli 《《地质学报》英文版》2021,95(4):1086-1098
This study focuses on the geology, geochemistry, zircon U-Pb geochronology and tectonic settings of the three types of seamount basalts from the Xingshuwa subduction accretionary complex in the Xar Moron area, eastern margin of the Central Asian Orogenic Belt(CAOB). The seamount remnants are composed of carbonate 'cap' sediments, large volumes of pillow and massive basalts, carbonate breccia slope facies and radiolarian cherts. Group 1 basalts are characterized by high contents of P2 O5 and TiO2 with alkaline affinity and LREE enrichment, indicating that they are derived from intraplate magma. Group 2 basalts display N-MORB LREE depletion patterns, indicating that they were formed at a mid-ocean ridge. Group 3 basalts have shown distinct Nb depletion and high Th/Yb ratios, indicating that they were generated in an island arc tectonic setting. The zircon U-Pb age of Group 1 basalt sample XWT18-131 is 576.4 ± 9.4 Ma, suggesting that the oceanic island seamount was the product of intraplate magmatism related to a mantle plume or 'hot spot' in the late Neoproterozoic. The zircon U-Pb age of Group 2 basalt sample XWT18-132 is 483 ± 22 Ma, indicating that the Paleo-Asian Ocean(PAO) was continuously expanding in the Early Ordovician. The zircon U-Pb age of Group 3 basalt sample XWT18-101 is 240.5 ± 8.2 Ma, suggesting that this area underwent the evolutionary path of ocean-continent transition, developing towards continentalization during the Middle Triassic. Thus, we believe that there was both mantle plume-related intraplate magmatism and intraoceanic subduction during the evolution of the PAO, the CAOB possibly being an evolutionary model of an intraoceanic subduction and mantle plume magmatism complex. 相似文献
992.
ZHANG Chenglong QIN Y YANG Yicheng FENG Zuohai LIU Xijun LI Saisai WAN Lei WANG Chunzeng 《《地质学报》英文版》2021,95(3):740-749
It is unclear whether the South China blocks have an affinity with continental Gondwana due to a lack of direct Pan-African magmatic and metamorphic features. In this study, we conducted U-Pb geochronological and Lu-Hf isotopic analyses for detrital zircons from a sandstone of the Chang’an Formation of the Nanhua Group in the Longsheng region of northern Guangxi, with the aim of constraining the timing of sedimentation and information as to its source, as well as seeking evidence for Pan-African events in the South China blocks. The results show that the ages of detrital zircons peaked at 654.7 ± 6.2 Ma, 773.2 ± 4.1 Ma and 821.9 ± 6.5 Ma, with some at 920–870 Ma; the youngest age indicates the existence of the Pan-African thermal event. The εHf(t) and TDM2 values demonstrate that the study area has experienced three stages of crustal growth at 3.0–2.4 Ga, 2.1–1.5 Ga and 1.3–0.9 Ga. With intensively distributed Neoproterozoic mafic-ultramafic and granitic plutons emplaced at 830–810 Ma along the southwestern section of the Jiangnan Orogenic Belt and positive εHf(t) values from a large group of zircon grains, it is proposed that the sediments of the Chang’an Formation (of Nanhua Group) were largely sourced from the southeastern margin of the Yangtze block. Comparison with the zircon age spectra of the Cathaysian block shows that about 79% of the Pan-African aged detrital zircon grains that have TDM2 = 1352–1031 Ma and εHf(t) = 3.68–8.79, were sourced from the recycled Grenvillian crust of the Cathaysian block, suggesting that the Cathaysian block had a close connection with Gondwana. 相似文献
993.
LIU Tianlun CHEN Siyu ZHANG Bo CAI Ked HAN Baofu QU Junfeng GUO Lei WANG Meng 《《地质学报》英文版》2021,95(5):1431-1455
The western segment of the Main Tianshan shear zone (MTSZ) branches into three major dextral strike-slip shear zones in the Borohoro Ranges, northwestern China. Mylonitic rocks within these zones exhibit vertical foliations, subhorizontal lineations, and dextral kinematics. The microstructures and CPO patterns of calcite and quartz in the tectonites suggest shearing at temperatures of 200°C to 500°C or above. The amount of dextral displacement along the zones is less than 100 km. LA-ICP-MS U-Pb dating of zircons from some pre-kinematic granites gave ages of 364–325 Ma and 316 Ma, and zircons from a syn-kinematic leucogranite gave an age of 291 Ma. We propose that dextral shearing along the MTSZ started in the earliest Permian. Our data indicate that collision between the Yili and Junggar plates might have finished before 325 Ma or 316 Ma, with a tectonic transformation from 325 Ma to 300 Ma, resulting in intracontinental transpression from 300 Ma or 291 Ma. We suggest that the formation of the Kazakhstan orocline (KO) took place in two stages, with the early stage of bending driven by convergence related to oblique subduction, and the late stage possibly associated with lateral disarticulation as a result of the dextral strike-slip shear zones. 相似文献
994.
表生环境中的地球化学反应速率具有显著的尺度效应.许多地球化学反应的野外观测速率比实验室观测速率要低2~5个数量级,给不同尺度的研究成果的对比和外推造成了极大困难.本文总结了地球化学反应速率随时间和空间尺度变化的影响因素,着重分析了地球化学反应速率的主控过程随尺度变化的现象,以及亚尺度的非均质性造成的尺度效应.最后介绍了几种尺度转换的研究方法.由于地球化学反应速率的尺度效应普遍存在,在对地球化学反应速率进行外推时需要了解它的局限性以及选取适当的外推方法. 相似文献
995.
物探方法是寻找地下水的重要勘查手段之一.在查明区域水文地质条件的基础上,本文采用音频大地电磁测深和高密度电阻率法对海南省琼中县榕木村花岗岩区深部赋水断裂破碎带的位置、深度、规模和产状特征进行了探测,结果表明:赋水断裂破碎带主要表现为"凹槽"状或"条带"状低阻异常;可以采用激电半衰时(Th)、偏离度(r)以及视电阻率(ρs)等参数进行断裂破碎带含水层位置判别.通过水文地质钻探揭露,含水层位置与物探解译结果基本一致,证明激电半衰时和偏离度以及视电阻率等参数可以较可靠地确定赋水构造的位置和深度.综合物探勘查方法为水文地质钻井孔位设计提供了有效技术支撑,可对在类似地区进行地下水探测提供参考. 相似文献
996.
四川省大地构造演化研究已有百余年的历史,不同时期、不同学派在不同的尺度上提出了不同的大地构造单元划分方案,其中仍存在诸多争议。本文结合近30年来四川省特别是造山带地区开展的蛇绿岩和洋板块地层等调查和研究成果,以李廷栋所提出的洋板块地质学理念为指导思想,以区域主构造事件形成的优势大地构造相的时空结构组合和存在状态为基本原则,划分出秦-祁-昆造山系、勉县-略阳对接带、北羌塘-三江造山系以及扬子克拉通4个一级构造单元,包括11个二级构造单元和24个三级构造单元。 相似文献
997.
998.
Dissolution characteristics of deep?buried dolostone in the Member 5 of Ordovician Majiagou Formation in southern Ordos Basin 下载免费PDF全文
The different types of deep-buried dissolution process in the Member 5 of Ordovician Majiagou Formation in the southern Ordos Basin and its influence on the reservoir properties are studied in this paper. It shows that three types of mechanisms include organic acid fluid, hydrothermal fluid and TSR are identified through studies of core observation, thin section analysis, inclusion temperature, trace elements and rare earth elements. It is found that the dissolution of organic acid fluid causes the stratified dissolution pores, film-like asphaltene and ring-like asphaltene, while hydrothermal fluid causes the non-selective dissolution pores without petrofabric, veins of pyrites, massive pyrites and the association of hypothermal minerals. Four occurrence models of dissolution include, (1) the deep-buried dissolution of low-temperature hydrothermal fluid occurs in Zhiluo Period of Middle Jurassic; (2) the deep-buried dissolution of organic acid fluid started from the late Middle Jurassic followed by the first hydrocarbon injection; (3) the deep-buried dissolution of middle-high temperature hydrothermal fluid occurred in the Dongsheng Period of Early Cretaceous; (4) TSR occurred at the end of Early Cretaceous with the second larger hydrocarbon injection. Both organic acid fluid and hydrothermal fluid can improve the porosity and permeability of reservoir, but the hydrothermal fluid is more effective than that of organic acid fluid. 相似文献
999.
Zhang Yabing Liu Xinrui Guo Pengshuang Jia Peng Yang Tianhong Ren Fengyu 《Landslides》2021,18(7):2465-2481
Landslides - In this paper, the slope rock mass is numerically characterized by considering hydraulic and mechanical properties using two distinct element models. The flow rate and permeability are... 相似文献
1000.
Wu Youyin Zhang Ming Yang Long Liu Tao Zhang Taili Sun Qiang Wang Bo Xie Xinpeng 《Landslides》2021,18(7):2565-2574
Landslides - At about 04:00 on 10 August 2019, the heavy rainfall carried by Typhoon Lekima induced a catastrophic rockslide in Shanzao Village, Yongjia County, China. The heavy rainfall triggered... 相似文献