全文获取类型
收费全文 | 1995篇 |
免费 | 344篇 |
国内免费 | 536篇 |
专业分类
测绘学 | 219篇 |
大气科学 | 425篇 |
地球物理 | 459篇 |
地质学 | 909篇 |
海洋学 | 297篇 |
天文学 | 74篇 |
综合类 | 213篇 |
自然地理 | 279篇 |
出版年
2024年 | 18篇 |
2023年 | 47篇 |
2022年 | 121篇 |
2021年 | 151篇 |
2020年 | 144篇 |
2019年 | 140篇 |
2018年 | 127篇 |
2017年 | 113篇 |
2016年 | 125篇 |
2015年 | 132篇 |
2014年 | 159篇 |
2013年 | 143篇 |
2012年 | 145篇 |
2011年 | 100篇 |
2010年 | 88篇 |
2009年 | 107篇 |
2008年 | 91篇 |
2007年 | 96篇 |
2006年 | 67篇 |
2005年 | 79篇 |
2004年 | 36篇 |
2003年 | 60篇 |
2002年 | 49篇 |
2001年 | 41篇 |
2000年 | 49篇 |
1999年 | 61篇 |
1998年 | 49篇 |
1997年 | 45篇 |
1996年 | 51篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有2875条查询结果,搜索用时 31 毫秒
981.
本文介绍的“存储式光纤陀螺测斜探管”主要解决超高温大井深环境下钻孔轨迹测量“测斜探管”问题,它包括钻孔各孔深井段倾角、方位角、工具面向角及温度的测量。目标是攻克光纤陀螺传感器温度漂移、光纤陀螺惯测组合井下环境适应性、仪器外场标定技术和误差分析校正等关键技术,研制的超高温钻孔轨迹测量仪,使用环境温度可达270 ℃,环境压力120 MPa,通过在高温地热能钻探工程、干热岩钻探工程、科学钻探工程、深部矿产资源勘探和深部油气资源勘探等工程中的应用,拓展应用领域,为超高温大深度钻井轨迹测量提供技术支撑。 相似文献
982.
Shan Huang Yuedong Yao Shuang Zhang Jinghao Ji Ruoyu Ma 《Arabian Journal of Geosciences》2018,11(11):285
Multi-fractured horizontal well (MFHW) is an effective technique to develop unconventional reservoirs. Complex fracture network around the well and hydraulic fractures is formed during the fracturing process. Fracture network and hydraulic fractures are the main seepage channel which is sensitivity to the effective stress. However, most of the existing models do not take the effect of stress sensitivity into account. In this study, a new analytical model was established for MFHW in tight oil reservoirs based on the trilinear flow model. Fractal porosity and permeability were employed to describe the heterogeneous distribution of the complex fracture network, and the stress sensitivity of fracture was considered in the model. The Pedrosa substitution and perturbation method were applied to eliminate the nonlinearity of the model. By using the Laplace transformation method, the analytical solutions in Laplace domain were obtained. Then, validations were performed to show that the model is valid. Finally, sensitivity analysis was discussed. The presented model provides a new approach to the estimation of fracturing effect and can be also utilized for recognizing formation properties of tight oil reservoirs. 相似文献
983.
Jiang Xiangang Huang Jiahua Wei Yunwei Niu Zhipan Chen Fenghui Zou Zuyin Zhu Zhanyuan 《Landslides》2018,15(2):243-255
In this study, a series of natural dam overtopping laboratory tests are reported. In these tests, the effect of seven different sediment mixtures on the breaching process was investigated. According to the test results, three stages of the breaching process of natural dams made of different materials were observed. Backward erosion was the primary cause for the incising slopes. The effects of backward erosion became stronger with the larger fines contents of the materials. With an increase in the median diameter (d 50) of particles, the breaching time became longer. However, the peak discharge became smaller. With an increase in the fines contents (p), the median diameter of the particles and the void ratio were changed, which resulted in a decrease in the breaching time and an increase in the peak discharge. The breaching time and peak discharge were more sensitive to the median diameter than to the fines contents. The relation between breach width and depth was found to follow a logistic function \( W\kern0.5em =\kern0.5em \frac{\zeta }{1\kern0.5em +\kern0.5em {e}^{\left(-k\left(D\kern0.5em -\kern0.5em {D}_0\right)\right)}} \). The parameters ζ, k, and D 0 are defined by a linear relationship with the median diameter and fines content. A breach of the side slope occurred as a tensile failure when the fines contents of the materials were large; otherwise, shear failure occurred. Furthermore, when the materials had fewer fines contents, the volume of the collapsed breach side slope became larger. 相似文献
984.
Jinge Wang Aijun Su Qingbing Liu Wei Xiang Hsin-Fu Yeh Chengren Xiong Zongxing Zou Cheng Zhong Junqi Liu Shen Cao 《Landslides》2018,15(7):1425-1435
The Huangtupo landslide is one of the largest and most destructive landslides still deforming in the Three Gorges area of China. In recent years, most studies on this landslide have been based on the data obtained from an investigation conducted in 2001. To further elucidate the geological structure and evolution of the landslide, we began building a field test site in the area of the sliding mass with the fastest deformation velocity in 2009. A group of tunnels with a total length of 1.1 km has been excavated, and nine boreholes with depths between 76.8 and 127.1 m have been drilled into the sliding body. Additionally, relative monitoring devices, such as borehole inclinometers and crack meters, have been installed. Based on the findings of the previous investigation and the latest tunneling, drilling, and monitoring data, a spatial distribution model of the sliding surfaces of the Huangtupo No. 1 riverside sliding mass has been established using the discrete smooth interpolation (DSI) method. Significant differences are revealed between the previous proposed sliding surface and the latest monitoring data. We propose that the Huangtupo No. 1 sliding mass has two sliding surfaces. Thus, the sliding mass can be further divided into two secondary sliding bodies, which are named the No. 1-1 (east) and No. 1-2 (west) sliding masses. The No. 1-1 sliding mass slid first, and the material along the western boundary slid later, producing the No. 1-2 sliding body, which has a smaller volume and shallower depth. The areas, volumes, and thicknesses of each sliding body have been calculated using a digital 3D model. 相似文献
985.
Qinwen Tan Huiming Tang Lei Fan Chengren Xiong Zhiqiang Fan Meng Zhao Chun Li Dingjian Wang Zongxing Zou 《Landslides》2018,15(12):2499-2508
In recent years, numerous landslide catastrophes have occurred, generating considerable financial losses and other tolls. The deformational and mechanical properties of sliding zone soil would be in primary significance to landslide research, as the sliding zone basically controls the initiation and mobility of the landslide. An in situ triaxial test was carried out on a sample from the sliding zone of the Huangtupo 1# landslide, a subdivision of the Huangtupo landslide in the Three Gorges area of China. The test results indicate that (a) the sliding zone exhibits low compressibility due to the high rock content (54.3%) and long-time consolidation by the overlying soil mass; (b) only decaying creep occurs without abrupt failure, and a constitutive equation with both linear and nonlinear viscoplastic terms is deduced to accurately fit the test data; (c) the surface with an orientation of 35° presents anisotropic traits in terms of displacement, possibly due to cracks that formed at similar orientations within the sample cube; and (d) the creep behavior of the landslide may be closely related to the properties of the sliding zone soil. When a similar stress magnitude to that of the in situ stress environment is applied to the sample, the sliding zone soil behavior matches the landslide deformative behavior. The test results indicate that the Huangtupo 1# landslide will continue to creep, as interpreted from the deformation traits and structural properties of the sample. However, unavoidable limitations of the test and extreme external factors, namely unexpected rainfall and water fluctuation, cannot be ignored. 相似文献
986.
点云滤波是机载LiDAR数据处理的重要步骤.现有滤波算法大部分要建立点云之间的索引关系,增加了算法的复杂度;或需要对原始数据进行内插,导致原有精度损失.本文在对LiDAR点云数据的高程进行统计分析的基础上,引入模糊C均值聚类分析算法,针对大区域平坦复杂城区数据,无须建立索引或进行内插,能够快速简单地实现地面点与非地面点的分类.实验结果表明,该方法切实可行,能够较好地满足精度需求. 相似文献
987.
Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district,South China Block 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Liang Qiu Dan‐Ping Yan Shuang‐Li Tang Nicholas T. Arndt Li‐Ting Fan Qing‐Yin Guo Jian‐Yong Cui 《地学学报》2015,27(6):449-457
The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U–Pb and apatite fission‐track thermochronology. The pitchblende U–Pb results indicate that uranium mineralization occurred at ~801–759 Ma. Fractionation of uranium and lead at ~374–295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission‐track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration. 相似文献
988.
第二次全国土地调查作为一项重大的国情国力调查,现已全面展开。对于各作业队伍而言,要在短时间内完成这项较为复杂的系统工程,有着诸多难点,而外业调查又是重中之重,也是后续工作得以顺利开展的基石,为此笔者对外业调查的前、后期工作做了简要阐述。 相似文献
989.
根据库车河剖面三叠-侏罗系干酪根显微组分的分布特点,将干酪根显微组分划分为5种组合和12种亚组合,结合沉积特征等资料推测每一种亚组合所对应的沉积环境。根据孢粉化石母体植物的生态习性推测三叠-侏罗系沉积时期古气候的变化规律是:由半干旱(俄霍布拉克组)→半潮湿(克拉玛依组下段)→潮湿(克拉玛依组上段-克孜勒努尔组下段)→半干旱、半潮湿(克孜勒努尔组上段-恰克马克组)→半干旱(齐古组、喀拉扎组);由热带、亚热带型气候(俄霍布拉克组-塔里奇克组)→亚热带-暖温带型气候(阿合组-克孜勒努尔组)→亚热带型气候(恰克马克组-喀拉扎组)。根据干酪根显微组分、沉积特征等资料推测俄霍布拉克组、克拉玛依组上部标志层段、黄山街组二-四段中、下部、阳霞组上部标志层段和恰克马克组为该区三叠-侏罗纪五个主要的湖泊(滨浅湖、半深湖-深湖)发育期;齐古组为洪泛湖泊发育期;塔里奇克组、阳霞组下段和克孜勒努尔组为三个主要的沼泽(以河沼为主,如岸后沼泽、分流间沼泽等)发育期。 相似文献
990.
随着信息化程度的提高以及物联网、云计算、SOA等技术的迅速发展,人们对基于车辆位置的各种需求日益增高,为了实现这种多样性的需求,超图软件开发出基于车联网(Telematics)应用的位置服务平台。Telemat-ics服务能够有效地将汽车技术信息、车辆位置信息、人员流动信息、物流信息、交通信息等汇聚在车联网上,从而让这些信息产生更深远的应用价值。本文从SuperMap GIS技术应用出发,结合超图自有的POI搜索引擎、导航引擎、云服务等产品,对基于telematics应用的位置服务平台进行详细的介绍。 相似文献