全文获取类型
收费全文 | 44355篇 |
免费 | 4367篇 |
国内免费 | 6389篇 |
专业分类
测绘学 | 3452篇 |
大气科学 | 5966篇 |
地球物理 | 9359篇 |
地质学 | 22082篇 |
海洋学 | 3954篇 |
天文学 | 2364篇 |
综合类 | 4089篇 |
自然地理 | 3845篇 |
出版年
2024年 | 131篇 |
2023年 | 393篇 |
2022年 | 1124篇 |
2021年 | 1306篇 |
2020年 | 1115篇 |
2019年 | 1280篇 |
2018年 | 5849篇 |
2017年 | 4985篇 |
2016年 | 3688篇 |
2015年 | 1459篇 |
2014年 | 1477篇 |
2013年 | 1504篇 |
2012年 | 2417篇 |
2011年 | 4080篇 |
2010年 | 3372篇 |
2009年 | 3594篇 |
2008年 | 3058篇 |
2007年 | 3416篇 |
2006年 | 1028篇 |
2005年 | 1034篇 |
2004年 | 1011篇 |
2003年 | 950篇 |
2002年 | 792篇 |
2001年 | 643篇 |
2000年 | 642篇 |
1999年 | 734篇 |
1998年 | 590篇 |
1997年 | 528篇 |
1996年 | 509篇 |
1995年 | 403篇 |
1994年 | 390篇 |
1993年 | 331篇 |
1992年 | 302篇 |
1991年 | 193篇 |
1990年 | 157篇 |
1989年 | 131篇 |
1988年 | 102篇 |
1987年 | 73篇 |
1986年 | 59篇 |
1985年 | 44篇 |
1984年 | 33篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1958年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
961.
962.
963.
964.
A two‐dimensional coupled hydromechanical discontinuum model for simulating rock hydraulic fracturing 下载免费PDF全文
Yu‐Yong Jiao Huan‐Qiang Zhang Xiu‐Li Zhang Hai‐Bo Li Qing‐Hui Jiang 《国际地质力学数值与分析法杂志》2015,39(5):457-481
Within the framework of our discontinuous deformation analysis for rock failure algorithm, this paper presents a two‐dimensional coupled hydromechanical discontinuum model for simulating the rock hydraulic fracturing process. In the proposed approach, based on the generated joint network, the calculation of fluid mechanics is performed first to obtain the seepage pressure near the tips of existing cracks, and then the fluid pressure is treated as linearly distributed loads on corresponding block boundaries. The contribution of the hydraulic pressure to the initiation/propagation of the cracks is considered by adding the components of these blocks into the force matrix of the global equilibrium equation. Finally, failure criteria are applied at the crack tips to determine the occurrence of cracking events. Several verification examples are simulated, and the results show that this newly proposed numerical model can simulate the hydraulic fracturing process correctly and effectively. Although the numerical and experimental verifications focus on one unique preexisting crack, because of the capability of discontinuous deformation analysis in simulating block‐like structures, the proposed approach is capable of modeling rock hydraulic fracturing processes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
965.
966.
ABSTRACTThe size and spatial distribution of loess slides are important for estimating the yield of eroded materials and determining the landslide risk. While previous studies have investigated landslide size distributions, the spatial distribution pattern of landslides at different spatial scales is poorly understood. The results indicate that the loess slide distribution exhibits a power-law scaling across a range of the size distribution. The mean landslide size and size distribution in the different geomorphic types are different. The double Pareto and inverse gamma functions can coincide well with the empirical probability distribution of the loess slide areas and can quantitatively reveal the rollover location, maximum probability, and scaling exponents. The frequency of loess slides increases with mean monthly precipitation. Moreover, point distance analysis showed that > 80% of landslides are located < 3 km from other loess slides. We found that the loess slides at the two study sites (Zhidan and Luochuan County) in northern Shaanxi Province, China show a significant clustered distribution. Furthermore, analysis results of the correlated fractal dimension show that the landslides exhibit a dispersed distribution at smaller spatial scales and a clustered distribution at larger spatial scales. 相似文献
967.
968.
Ranganath Navalgund 《Journal of the Indian Society of Remote Sensing》2018,46(3):483-489
969.
970.