全文获取类型
收费全文 | 2460篇 |
免费 | 547篇 |
国内免费 | 407篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 49篇 |
地球物理 | 797篇 |
地质学 | 1574篇 |
海洋学 | 332篇 |
天文学 | 21篇 |
综合类 | 82篇 |
自然地理 | 533篇 |
出版年
2024年 | 10篇 |
2023年 | 40篇 |
2022年 | 89篇 |
2021年 | 104篇 |
2020年 | 98篇 |
2019年 | 112篇 |
2018年 | 89篇 |
2017年 | 102篇 |
2016年 | 115篇 |
2015年 | 108篇 |
2014年 | 141篇 |
2013年 | 179篇 |
2012年 | 116篇 |
2011年 | 146篇 |
2010年 | 120篇 |
2009年 | 144篇 |
2008年 | 160篇 |
2007年 | 180篇 |
2006年 | 149篇 |
2005年 | 101篇 |
2004年 | 146篇 |
2003年 | 100篇 |
2002年 | 101篇 |
2001年 | 82篇 |
2000年 | 92篇 |
1999年 | 62篇 |
1998年 | 77篇 |
1997年 | 59篇 |
1996年 | 67篇 |
1995年 | 71篇 |
1994年 | 51篇 |
1993年 | 43篇 |
1992年 | 33篇 |
1991年 | 19篇 |
1990年 | 12篇 |
1989年 | 24篇 |
1988年 | 19篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有3414条查询结果,搜索用时 484 毫秒
121.
122.
123.
Ye Yuyao Wang Changjian Zhang Hong’ou Yang Ji Liu Zhengqian Wu Kangmin Deng Yingbin 《地理学报(英文版)》2020,30(12):1985-2001
Journal of Geographical Sciences - Population migration, especially population inflow from epidemic areas, is a key source of the risk related to the coronavirus disease 2019 (COVID-19) epidemic.... 相似文献
124.
Theoretical aspects of cap-rock and fault seals for single- and two-phase hydrocarbon columns 总被引:6,自引:0,他引:6
Cap-rock seals can be divided genetically into those that fail by capillary leakage (membrane seals) and those whose capillary entry pressures are so high that seal failure preferentially occurs by fracturing and/or wedging open of faults (hydraulic seals). A given membrane seal can trap a larger oil column than gas column at shallow depths, but below a critical depth (interval), gas is more easily sealed than oil. This critical depth increases with lower API gravity, lower oil GOR and overpressured conditions (for the gas phase). These observations arise from a series of modelling studies of membrane sealing and can be conveniently represented using pressure/ depth (P/D) profiles through sealed hydrocarbon columns. P/D diagrams have been applied to the more complex situation of the membrane sealing of a gas cap underlain by an oil rim; at seal capacity, such a two-phase column will be always greater than if only oil or gas occurs below the seal.These conclusions contrast with those for hydraulic seals where the seal capacity to oil always exceeds that for gas. Moreover, a trapped two-phase column, at hydraulic seal capacity will be less than the maximum-allowed oil-only column, but more than the maximum gas-only column. Unlike membrane seals, hydraulic seal capacity should be directly related to cap-rock thickness, in addition to the magnitude of the minimum effective stress in the sealing layer and the degree of overpressure development in the sequence as a whole.Fault-related seals are effectively analogous to membrane cap-rocks which have been tilted to the angle of the fault plane. Consequently, all of the above conclusions derived for membrane cap-rocks apply to both sealing faults sensu stricto (fault plane itself seals) and juxtaposition faults (hydrocarbon trapped laterally against a juxtaposed sealing unit). The maximum-allowed two-phase column trapped by a sealing fault is greater than for equivalent oil-only and gas-only columns, but less than that predicted for a horizontal membrane cap-rock under similar conditions. Where a two-phase column is present on both sides of a sealing fault (which is at two-phase seal capacity), a deeper oil/water contact (OWC) in one fault block is associated with a deeper gas/oil contact (GOC) compared with the adjacent fault block. If the fault seal is discontinuous in the gas leg, however, the deeper OWC is accompanied by a shallower GOC, whereas a break in the fault seal in the oil leg results in a common OWC in both fault blocks, even though separate GOC's exist. Schematic P/D profiles are provided for each of the above situations from which a series of fundamental equations governing single- and two-phase cap-rock and fault seal capacities can be derived. These relationships may have significant implications for exploration prospect appraisal exercises where more meaningful estimates of differential seal capacities can be made.The membrane sealing theory developed herein assumes that all reservoirs and seals are water-wet and no hydrodynamic flow exists. The conclusions on membrane seal capacity place constraints on the migration efficiency of gas along low-permeabiligy paths at depth where fracturing, wedging open of faults and/or diffusion process may be more important. Contrary to previous assertions, it is speculated that leakage of hydrocarbons through membrane seals occurs in distinct pulses such that the seal is at or near the theoretically calculated seal capacity, once this has been initially attained.Finally, the developed seal theory and P/D profile concepts are applied to a series of development geological problems including the effects of differential depletion, and degree of aquifer support, on sealing fault leakage, and the evaluation of barriers to vertical cross-flow using RFT profiles through depleted reservoirs. It is shown that imbibition processes and dynamic effects related to active cross-flow across such barriers often preclude quantitative analysis and solution of these problems for which simulation studies are usually required. 相似文献
125.
运用粒度参数分析、黏土矿物含量分析、Flemming三角图示法和Gao-Collins二维的"粒度趋势分析"等方法,对采自莱州湾海域的表层沉积物样品和黏土矿物样品进行分析,了解了该研究区域的沉积环境及沉积物的运移趋势。研究区由岸向海沉积物类型大致依次为砂-粉砂质砂-砂质粉砂-粉砂-黏土质粉砂,并且研究区表层沉积物在近岸区域呈现较为明显的平行岸线的条带状特征;同时沉积物的平均粒径、分选系数、偏态、峰态等粒度参数也呈现出良好的正相关性或负相关性;研究区黏土矿物为伊利石、蒙脱石、绿泥石、高岭石,除伊利石分布大致为黄河三角洲近岸低,向研究区东北方向逐渐升高外,其余的黏土矿物都表现出了近岸高,远海低的分布特征,且主要物源为黄河物质输入。Flemming三角图研究区所有采样点大部分分布在Ⅱ区,少部分分布在Ⅲ区,说明研究区整体水动力较强;采样点在A—E区均有分布,但在C、D两区分布最多,说明研究区沉积物粒径较集中。研究区表层沉积物整体呈由岸向海输运的趋势,具体来看,黄河沉积物入海后向北、向东、向南运移,研究区内沉积物的来源是黄河输沙以及周围入海的小河流的输沙和沿岸冲刷的物质。 相似文献
126.
渤海湾盆地垦利断裂带构造与油气关系研究 总被引:6,自引:2,他引:6
本文在分析垦利断裂带断裂构造特征的基础上,探讨了该地区断裂构造对油气运聚的控制作用。研究表明,垦利断裂带油气沿断层运聚主要有2种模式:①沿断层垂向运移和聚集;②横穿断层的运移和聚集。油气大规模地横穿断层的运移和聚集主要发生在垦利和垦东6断层的深部和浅部层段。根据在垦利断裂带已发现的油田(藏)总结出4种成藏模式,即同层成藏、潜山成藏、跨断层成藏和沿断层成藏,认为该地区的油气分布受构造因素控制,并对该地区隐蔽圈闭(油气藏)的勘探前景作了分析。 相似文献
127.
不同应力状态下地层渗透系数的变化及其对流体运移影响的数值模拟研究 总被引:13,自引:3,他引:13
本文选择地层渗透系数受应力影响而变化作为研究流体运移的基础。压实固结和构造作用所产生应力对渗透系数影响的有限元数学模拟研究表明,平均有效应力与介质渗透性能呈负相关的变化趋势,应力驱动流体由应力高值区向应力低值区运移。 相似文献
128.
Jian Cao Zhijun Jin Wenxuan Hu Yijie Zhang Suping Yao Xulong Wang Yueqian Zhang Yong Tang 《Marine and Petroleum Geology》2010
Calcite veins and cements occur widely in Carboniferous and Permian reservoirs of the Hongche fault zone, northwestern Junggar Basin in northwest China. The calcites were investigated by fluid inclusion and trace-element analyses, providing an improved understanding of the petroleum migration history. It is indicated that the Hongche fault behaved as a migration pathway before the Early Cretaceous, allowing two oil charges to migrate into the hanging-wall, fault-core and footwall reservoirs across the fault. Since the Late Cretaceous, the Hongche fault has been sealed. As a consequence, meteoric water flowed down only into the hanging-wall and fault-core reservoirs. The meteoric-water incursion is likely an important cause for degradation of reservoir oils. In contrast, the footwall reservoirs received gas charge (the third hydrocarbon event) following the Late Cretaceous. This helps explain the distribution of petroleum across the fault. This study provides an example of how a fault may evolve as pathway and seal over time, and how reservoir diagenetic minerals can provide clues to complex petroleum migration histories. 相似文献
129.
基于位置大数据的国庆假期青藏高原人群分布时空变化模式挖掘 总被引:1,自引:0,他引:1
人类活动是引起青藏高原生态环境发生改变的重要因素。很多学者对青藏高原史前人类活动和近几十年的人口分布格局与人口流动开展了大量研究,但有关人群时空分布的精细尺度研究相对缺乏。海量的位置大数据为认识高原人群短期的动态变化提供了新途径。本文利用手机定位数据、人口迁徙数据等高时空分辨率的位置大数据,通过时间序列分解方法和基于统计检验的异常判别方法,分析了2017年国庆期间青海与西藏的人群分布时空变化特征,并探讨了假期旅游行为及人口迁徙与变化特征之间的关系。研究结果显示:① 在省级和城市整体尺度上,定位请求量的假期变化在时间上呈现先降后升的“潮汐”变化模式;② 在精细网格尺度上,西宁和拉萨城市及周边地区的人群分布变化在空间上呈现中心跌、周边涨的“离心化”变化模式。国庆假期人们向城市周边热门景点移动聚集的旅游行为和城市之间的人口迁徙都是导致西宁和拉萨周边地区定位请求量上涨的重要潜在原因,而两座高原城市中心定位请求的下跌不仅与人口迁徙有关,还与假期人类日常行为及定位请求频次的变化等因素有关。通过位置大数据挖掘节庆假期人群分布的时空变化,不仅加深了对高原人口分布格局与流动变化的认识,也为高原城镇化与生态保护的精细化管理与决策提供支撑。 相似文献
130.
对汶川8.0级地震前后陕西地区地倾斜观测资料的分析发现,汶川地震前陕西地区地倾斜存在沿龙门山断裂带方向由东北向西南震中迁移,震后地倾斜反向迁移,迁移平均速度为3~4 km/天。进一步分析认为,震前陕西地区地倾斜向震源迁移可能对汶川8.0级地震起到了触发作用,而震后地倾斜向远场迁移有可能是诱发陕甘川交界的中强余震的主因。 相似文献