全文获取类型
| 收费全文 | 113篇 |
| 免费 | 17篇 |
| 国内免费 | 19篇 |
专业分类
| 测绘学 | 12篇 |
| 大气科学 | 4篇 |
| 地球物理 | 11篇 |
| 地质学 | 40篇 |
| 海洋学 | 24篇 |
| 综合类 | 11篇 |
| 自然地理 | 47篇 |
出版年
| 2022年 | 6篇 |
| 2021年 | 7篇 |
| 2020年 | 5篇 |
| 2019年 | 9篇 |
| 2018年 | 7篇 |
| 2017年 | 10篇 |
| 2016年 | 4篇 |
| 2015年 | 4篇 |
| 2014年 | 6篇 |
| 2013年 | 8篇 |
| 2012年 | 3篇 |
| 2011年 | 6篇 |
| 2010年 | 4篇 |
| 2009年 | 7篇 |
| 2008年 | 5篇 |
| 2007年 | 2篇 |
| 2006年 | 10篇 |
| 2005年 | 9篇 |
| 2004年 | 4篇 |
| 2003年 | 6篇 |
| 2002年 | 1篇 |
| 2001年 | 6篇 |
| 1999年 | 5篇 |
| 1998年 | 2篇 |
| 1997年 | 4篇 |
| 1996年 | 2篇 |
| 1995年 | 1篇 |
| 1994年 | 2篇 |
| 1992年 | 1篇 |
| 1988年 | 2篇 |
| 1985年 | 1篇 |
排序方式： 共有149条查询结果，搜索用时 31 毫秒
91.
Seasonally variation of water salinity is observed worldwide, the mechanisms of water salinity are not well understood due to natural factors and anthropogenic activities. Quantification water salinity source are challenging since complex influence factors, especially in agricultural regions irrigated with multi-water sources. In the lowland area of North China Plain, transferred water, brackish shallow groundwater and fresh deep groundwater were combinative utilized to relieve prominent contradictions between regional water shortages and grain production. In this study, influence factors of surface water (canal water, pond water) and shallow groundwater salinity were identified and quantified through statistical analysis, deuterium excess, and ionic relationship. Salinity of canal water and pond water increased in dry season and decreased in rainy season, while salinity of shallow groundwater decreased in dry season after water transfer and rainy season, but increased in dry season. Evaporation and mineral dissolution were main factors for surface water salinity in dry season, with mineral dissolution was the more important one. The contribution ratio of evaporation and mineral dissolution for canal salinity were 4.4 and 49.1% in dry season after water transfer, 7.1 and 34.4% in dry season, and that for pond water salinity were 12.4 and 18.3% in dry season, respectively. Precipitation and surface runoff were main factors for surface water salinity in rainy season. The contribution of surface runoff for canal water and pond water salinity were 66.1 and 45.8%, respectively. Salinity of canal water and shallow groundwater was temporary decreased by water transfer. Domestic sewage from rural areas had larger influence than agricultural activities for salinity increase of pond water and shallow groundwater. Mineral dissolution was the main contributor for shallow groundwater salinity, with contribution ratio larger than 60% in different periods. This study demonstrated and quantified salinity source of surface water and shallow groundwater and may deepen our understanding of water management under multi-water resources utilization. 相似文献
92.
维持控制点水位稳定是保证输水渠道安全有效运行的前提.以控制点水位偏差为主要抑制因子,基于线性二次型(LQR)指标,构建了渠道系统水位偏差、偏差变率和流量控制的全状态空间模型,将加入预测模块的线性二次型算法在渠道系统的全状态空间中进行分析和综合,提出了扰动可预知模型的构造方法.通过脉冲响应测试来加深对算法结构的理解,使用南水北调中线电子渠道平台对算法有效性进行验证,验证结果表明,该算法在渠道运行工况改变后,仍能够维持渠道的稳定运行,算法设计极具潜在的应用价值. 相似文献
93.
冀中廊坊市是资源性严重缺水城市,加之近年旱情严重,水资源短缺形势异常严峻,水资源紧缺已成为制约廊坊市可持续发展的瓶颈.北运河是廊坊市的主要有水河道,也是北京市主要的排污河道.其河道径流量具有量多、稳定、水质较好等特点.本文就北运河水资源的规律特点,指出了有利的地形条件、丰富的河道水量、众多的水利工程以及逐步改善的水体水... 相似文献
94.
The Optimal Cross-section Design of the “Trapezoid-V” Shaped Drainage Canal of Viscous Debris Flow 总被引：1，自引：0，他引：1
Debris flow drainage canal is one of the most widely used engineering measures to prevent and manage debris flow hazards.The shape and the sizes of the cross-section are important parameters when design debris flow drainage canal.Therefore,how to design the appropriate shape and sizes of the cross-section so that the drainage canal can have the optimal drainage capacity is very important and few researched at home and abroad.This study was conducted to analyze the hydraulic condition of a Trapezoid-V shaped drainage canal and optimize its cross-section.By assuming characteristic sizes of the cross-section,the paper deduced the configuration parameter of the cross-section of a Trapezoid-V shaped debris flow drainage canal.By theory analysis,it indicates that the optimal configuration parameter is only related to the side slope coefficient and the bottom transverse slope coefficient.For this study,the Heishui Gully,a first-order tributary of the lower Jinsha River,was used as an example to design the optimal cross-section of the drainage canal of debris flow. 相似文献
95.
96.
从北极海运货源角度出发,根据北极贸易、油气开发以及远东-西北欧、远东-北美东部当前海运货量状况,分析得出未来北极航道主要货物类型和规模的最大理论值为：（1）从俄罗斯、北欧北极地区到远东的液化天然气单向贸易流型式,到2030年,为1 000万t;（2）从远东到欧美的集装箱货物双向贸易流型式,北极东北航道、中央航道分担远东到西北欧航线的货运量,北极西北航道分担远东到北美东部的货运量,如果技术上能够低成本保障全季航行,按分担传统运河航线50%计算,到2030年,北极航道集装箱货运规模最大值约为1 743万TEU,是2011年传统运河航线的85%。由此得出结论：近中期东北航道天然气运输占据主要地位,但对北极航道更大运输需求是集装箱运输。此外,本文还比较了北极航道与运河航线的成本。 相似文献
97.
分析1981—2014年7—9月影响皖北东部地区的台风特征,统计不同台风路径和降雨量之间的关系,研究不同路径下皖北东部出现暴雨的环流场特征,结果表明:(1)西北行、陆面转向、海面转向和其他类路径的台风都可以影响皖北东部,并产生降水。其中产生降水个例最多的台风路径为陆面转向类,次多为西北行类。(2)台风影响时无降水、非暴雨和暴雨3类降水个例的500 hPa平均环流场对比分析表明:当有台风影响皖北东部时,配合西风槽或副高阻挡更有利于产生强降水。(3)西北行类台风暴雨的环流场特征是华北到河套存在西南-东北走向高压带阻挡使台风停滞少动;海面转向类台风暴雨环流场特征是河套东部存在低槽与台风相互作用;陆面转向类台风暴雨环流场可以分为3类:贝湖两槽一脊型、贝湖单槽型和副热带高压阻挡型。 相似文献
98.
湖北长阳丹水撇洪渠出口左岸边坡稳定性分析及治理 总被引：1，自引：0，他引：1
根据对该边坡的变形破坏特征及形成条件分析，属滑移-拉裂型边坡。经受了诸如自重应力、构造应力、卸荷变形、降雨等内外因素作用，斜坡岩体沿软弱结构面发生滑移变形。随着剪裂面上的拉应力集中而产生拉裂缝，一旦破坏面贯通，将导致边坡破坏。用计算和经验相结合的方法确定了潜在滑面的位置，并通过参数反演，对滑坡的稳定性进行了定量评价。通过技术经济比较，针对边坡的形成机制、边坡各个部位的变形发展特点及其重要性，采取了分区治理措施。既达到了治理效果又节省了人力物力，可供从事类似22程评价和治理的22程人员参考。 相似文献
99.
Collembola diversity in changing agricultural landscapes of the Thar Desert: A case study in Sriganganagar district of Rajasthan, India 总被引：1，自引：0，他引：1
Seven species of Collembola were recorded from the Thar Desert in India for the first time. Their existence and establishment has been attributed to the change in land use pattern of Sriganganagar district due to the development of canal irrigation. Sampling was done at two distant localities, in which one has been under irrigated agricultural activities since 60–70 years, while at the second locality, such activities began 20 years back. Two species, Xenylla obscura and Isotomodes dagamae, dominated the collembolan communities at all sites. The samples from first locality were rich both in number of individuals as well as species. The sites were hierarchically clustered into a dendrogram to present an analytical picture of community development of collembolan species against the time-scale of succession. Attention was sought to study the insect fauna and their activities in relation to the ongoing greening the desert program. 相似文献
100.