全文获取类型
收费全文 | 2100篇 |
免费 | 380篇 |
国内免费 | 687篇 |
专业分类
测绘学 | 304篇 |
大气科学 | 291篇 |
地球物理 | 391篇 |
地质学 | 1424篇 |
海洋学 | 200篇 |
天文学 | 119篇 |
综合类 | 161篇 |
自然地理 | 277篇 |
出版年
2024年 | 13篇 |
2023年 | 40篇 |
2022年 | 128篇 |
2021年 | 131篇 |
2020年 | 120篇 |
2019年 | 117篇 |
2018年 | 103篇 |
2017年 | 95篇 |
2016年 | 112篇 |
2015年 | 125篇 |
2014年 | 127篇 |
2013年 | 164篇 |
2012年 | 122篇 |
2011年 | 149篇 |
2010年 | 138篇 |
2009年 | 148篇 |
2008年 | 150篇 |
2007年 | 154篇 |
2006年 | 155篇 |
2005年 | 125篇 |
2004年 | 84篇 |
2003年 | 74篇 |
2002年 | 70篇 |
2001年 | 68篇 |
2000年 | 56篇 |
1999年 | 66篇 |
1998年 | 54篇 |
1997年 | 41篇 |
1996年 | 31篇 |
1995年 | 35篇 |
1994年 | 44篇 |
1993年 | 36篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1958年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有3167条查询结果,搜索用时 218 毫秒
981.
武汉市江夏区大桥新区红旗村文化大道附近发生岩溶塌陷,其上覆盖层为黏土。文章针对该类型岩溶塌陷,结合岩溶发育特征、土体物理力学性质、水文地质条件和人类工程活动等影响因素,对致塌模式进行了综合分析,得出在溶沟底部分布有软塑至流塑状的力学性质较差的红黏土,溶沟底部发育的溶蚀裂隙与下部的溶洞或通道相联通;流塑状红黏土流失至下部岩溶通道中,形成土洞;钻探施工、楼房载荷、振动作用加速黏土体的软化、崩解和溶蚀作用,进而加速土洞向上发展。此外,地基开挖减少上覆黏土厚度,降低了土体抗剪强度,最终在上覆土体自身重力和附加荷载作用下发生塌陷。根据土体受力情况,得出塌陷力学模型,并利用数据进行验证,其验证结果与实际相符合,并结合致塌模式和力学分析提出应增强土体抗塌性能、增加建筑物地基稳定性和减缓岩溶系统水动力因素变化的防治措施。 相似文献
982.
983.
984.
Finding the critical slip surface and estimating the landslide volume are of primary importance for slope seismic design. However, this may be difficult due to the uncertainty of ground motions. To address this problem, a new method for calculating uncertainties is recommended in this paper, especially for the critical slip surface and landslide volume under random earthquake ground motions. Firstly, a series of intensity–frequency nonstationary random earthquake ground motions were generated based on an improved orthogonal expansion method. A given number of potential slip surfaces were set in a soil slope. Subsequently, the factor of safety (FOS) of each slip surface for all ground motions was calculated and the minimum FOS curves were obtained. It was found that the critical slip surfaces and failure times are uncertain under different earthquakes. The Monte Carlo method was used to verify the accuracy of probability density evolution method (PDEM), and the results of the PDEM and the Monte Carlo method are consistent, meaning that the PEDM has higher computational efficiency. Moreover, the distributions of earthquake-triggered landslide volume and landslide depth were analyzed by considering equivalent extreme events. Both landslide volume and depth exhibit a normal distribution for a homogeneous soil slope. The framework of this study is meaningful for slope seismic design in engineering, for example, the location of critical slip surface can be used for slope reinforcement, and the distribution of sliding volume can be used for disaster assessment. 相似文献
985.
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
986.
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
987.
Phenological metrics-based crop classification using HJ-1 CCD images and Landsat 8 imagery 总被引:1,自引:0,他引:1
Xiaochun Zhang Qinxue Xiong Liping Di Junmei Tang Jin Yang Huayi Wu 《International Journal of Digital Earth》2018,11(12):1219-1240
Crop type data are an important piece of information for many applications in agriculture. Extracting crop type using remote sensing is not easy because multiple crops are usually planted into small parcels with limited availability of satellite images due to weather conditions. In this research, we aim at producing crop maps for areas with abundant rainfall and small-sized parcels by making full use of Landsat 8 and HJ-1 charge-coupled device (CCD) data. We masked out non-vegetation areas by using Landsat 8 images and then extracted a crop map from a long-term time-series of HJ-1 CCD satellite images acquired at 30-m spatial resolution and two-day temporal resolution. To increase accuracy, four key phenological metrics of crops were extracted from time-series Normalized Difference Vegetation Index curves plotted from the HJ-1 CCD images. These phenological metrics were used to further identify each of the crop types with less, but easier to access, ancillary field survey data. We used crop area data from the Jingzhou statistical yearbook and 5.8-m spatial resolution ZY-3 satellite images to perform an accuracy assessment. The results show that our classification accuracy was 92% when compared with the highly accurate but limited ZY-3 images and matched up to 80% to the statistical crop areas. 相似文献
988.
丝绸之路经济带国际集装箱陆路运输的经济适应范围 总被引:6,自引:1,他引:5
丝绸之路经济带国际集装箱陆路运输规模与日俱增,其中铁路在陆路运输中占据重要地位。研究分析了丝绸之路经济带内中国国际集装箱运输现状,建立了多式联运竞争的分析模型,并利用调研收集的数据对以重庆和西安为起点的国际集装箱陆路运输经济适应区域进行了定量分析。结果表明,受海运价格的影响,中亚地区、蒙古国及俄罗斯的西伯利亚区、乌拉尔区、伏尔加河沿岸区和中央联邦区是丝绸之路经济带铁路运输的比较优势区域,乌克兰、白俄罗斯、波兰及俄罗斯的西北联邦区、南方联邦区等是优势扩展区,而欧洲和亚洲其他大部分区域的海运(海陆联运)优势远大于铁路联运。 相似文献
989.
990.
大陆岩石圈的增厚及对流剥离对青藏高原隆升的影响 总被引:1,自引:0,他引:1
伴随着印度板块对欧亚板块南缘的碰撞、挤压,青藏高原地壳及下伏地幔岩石圈的厚度增加了1倍。增厚岩石圈热结构的变化可导致高原海拨下降约1500m。其对流剥离并被较热的软流圈物质替代可用以解释青藏高原自8百万年或3百万年前开始的快速隆升。大陆岩石圈的增厚及热结构变化和对流剥离可能是青藏高原自9百万年前开始的夷平—快速隆升过程的主导控制因素。 相似文献