全文获取类型
收费全文 | 151篇 |
免费 | 22篇 |
国内免费 | 45篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 27篇 |
地球物理 | 17篇 |
地质学 | 62篇 |
海洋学 | 59篇 |
天文学 | 2篇 |
综合类 | 16篇 |
自然地理 | 15篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有218条查询结果,搜索用时 843 毫秒
101.
102.
吴堡矿区首采地段水文地质特征及矿床充水条件分析 总被引:1,自引:0,他引:1
从鄂尔多斯盆地东部地下水类型、含水岩组等区域水文地质条件入手,对陕北石炭二叠纪煤田吴堡矿区首期开采地段水文地质条件进行了分析。分析表明,区内第四系松散层含水层在首采区虽然分别较广,但水量相对较小,正常情况下与其下含水层贯通的可能性较小,对于煤矿开采影响较小;基岩风化裂隙潜水、太原组灰岩溶隙裂隙及砂岩裂隙承压水及奥陶系灰岩岩溶承压水是煤矿开采中最为主要的突水类型。从矿坑充水水源、充水通道和充水强度角度对首期开采地段进行了矿床充水因素的研究。研究认为,矿井充水水源为煤层顶底板砂岩裂隙水、灰岩裂隙溶隙承压水及奥陶系岩溶承压水;充水通道主要是煤层开采后顶板形成的冒落带和导水裂隙带以及底板受其承压水的影响而产生的破坏带。建议在矿井设计前对首采地段进行三维地震勘探,进一步查明区内断层性质、规模和易发生矿井涌水的部位,为建井设计、矿坑底板的突水和防治提供依据。 相似文献
103.
104.
105.
106.
Presently, research is lacking regarding the diagnosis and evaluation of habitat degradation in enclosed bay systems. We established a diagnostic model for enclosed bay habitat degradation (EBHD model) using a multi-approach integrated diagnostic method in consideration of driving force-pressure- state-influence-response. The model optimizes the indicator standardization with annual average change rate of habitat degradation as the basic element, to reflect accurately the impact of the change and speed of degradation on the diagnostic results, to quantify reasonably the contribution of individual diagnostic indicator to habitat degradation, and to solve the issue regarding the influence of subjective factors on the evaluation results during indicator scoring. We then applied the EBHD model for the Sansha Bay in Fujian Province, China, evaluated comprehensively the situation of habitat degradation in the bay, and screened out the major controlling factors in the study area. Results show that the diagnostic results are consistent in overall with the real situation of the study area. Therefore, the EBHD model is advantageous in terms of objectivity and accuracy, making a breakthrough in diagnosis and evaluation for habitat degradation in enclosed bay systems. 相似文献
107.
The process of habitat degradation varies in habitat type and driving force which shows certain spatial and temporal heterogeneity on regional scales. In the present study, a new diagnostic model for enclosed bay habitat degradation was established, with which the spatial and temporal variation patterns of habitat degradation during 1991–2012 in Sansha Bay, Fujian, China was investigated. The results show that anthropogenic disturbance is the major controlling factor for the habitat degradation in large temporal heterogeneity in the bay. On the other hand, the habitat degradation experienced signifi cant spatial variations among six sub-bays. Under the joint action of temporal and spatial heterogeneity, the degradation trend in growing scale shows a more signifi cant correlation with the distribution of local leading industries along shorelines. Therefore, we quantifi ed the main characters of habitat degradation in Sansha Bay, and have understood the relationship between the status of habitats spatio-temporal variation value and the main controlling factor leading to the changes. However, a defi ciency of this research is the lack of or inaccessible to the detailed data, which shall be better solved in the future study for accessing more data from more sources. 相似文献
108.
109.
城市化、新型工业化及全球化进程的进一步融合,公共安全问题发生频度将大大增加.由于防范意识的淡薄,以及预警不力等因素导致对突发事件类别和级别较难合理的判识,对应急管理机构和平台资源较难高效的应用.给人民生命财产安全带来极大的隐患.通过以数据为核心、标识为主线,提出G/S模式,在此基础上实现应急预案建模,结合四川省应急指挥系统进行验证,建立一套原型系统,为应急管理的高可用性、高安全性服务;为国家的产业化推广提供理论基础与技术支持. 相似文献
110.
Transient response of a beam on viscoelastic foundation under an impact load during nondestructive testing 总被引:1,自引:1,他引:0
Beam responses under an impact NDT load are studied using the Fourier and Laplace transforms. Numerical computation is performed for a parametric study of beam and load parameters. It is shown that under an impact load, the time duration for displacement to vanish is ten times longer than that for velocity and acceleration. The maximum response is achieved first in acceleration, followed by velocity, and finally displacement, all of which occur before the impact load is removed. At the moment that the impact load is removed from the beam, there is a discontinuity in the velocity and acceleration responses, but not in displacement response. The effect of K and ph on beam response is much less significant than that of El and C, which have similar effect on beam response. As El increases, peak values of displacement, velocity and acceleration response decrease. The effect of K on beam response only becomes appreciable after the impact load is removed. While the peak of displacement remain almost unchanged as K increases, the displacement response decays to zero faster for large K values than for small K values. 相似文献