全文获取类型
收费全文 | 6269篇 |
免费 | 1333篇 |
国内免费 | 1766篇 |
专业分类
测绘学 | 763篇 |
大气科学 | 893篇 |
地球物理 | 1432篇 |
地质学 | 3557篇 |
海洋学 | 1005篇 |
天文学 | 271篇 |
综合类 | 651篇 |
自然地理 | 796篇 |
出版年
2024年 | 50篇 |
2023年 | 132篇 |
2022年 | 432篇 |
2021年 | 472篇 |
2020年 | 391篇 |
2019年 | 425篇 |
2018年 | 470篇 |
2017年 | 412篇 |
2016年 | 480篇 |
2015年 | 434篇 |
2014年 | 474篇 |
2013年 | 499篇 |
2012年 | 476篇 |
2011年 | 453篇 |
2010年 | 446篇 |
2009年 | 389篇 |
2008年 | 349篇 |
2007年 | 305篇 |
2006年 | 321篇 |
2005年 | 227篇 |
2004年 | 172篇 |
2003年 | 147篇 |
2002年 | 130篇 |
2001年 | 125篇 |
2000年 | 120篇 |
1999年 | 166篇 |
1998年 | 113篇 |
1997年 | 111篇 |
1996年 | 90篇 |
1995年 | 94篇 |
1994年 | 78篇 |
1993年 | 74篇 |
1992年 | 57篇 |
1991年 | 40篇 |
1990年 | 33篇 |
1989年 | 38篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1965年 | 2篇 |
1958年 | 3篇 |
1957年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有9368条查询结果,搜索用时 15 毫秒
111.
112.
Christine Baus HsuWen Hung Frank Sacher Michael Fleig Heinz‐Jürgen Brauch 《洁净——土壤、空气、水》2005,33(2):118-132
In Germany, the gasoline additive methyl tert‐butyl ether (MTBE) is almost constantly detected in measurable concentrations in surface waters and is not significantly removed during riverbank filtration. The removal of MTBE from water has been the focus of many studies that mostly were performed at high concentration levels and centred in understanding the mechanisms of elimination. In order to assess the performance of conventional and advanced water treatment technologies for MTBE removal in the low concentration range further studies were undertaken. Laboratory experiments included aeration, granulated activated carbon (GAC) adsorption, ozonation and advanced oxidation processes (AOP). The results show that the removal of MTBE by conventional technologies is not easily achieved. MTBE is only removed by aeration at high expense. Ozonation at neutral pH values did not prove to be effective in eliminating MTBE at all. The use of ozone/H2O2 (AOP) may lead to a partly elimination of MTBE. However, the ozone/H2O2 concentrations required for a complete removal of MTBE from natural waters is much higher than the ozone levels applied nowadays in waterworks. MTBE is only poorly adsorbed on activated carbon, thus GAC filtration is not efficient in eliminating MTBE. A comparison with real‐life data from German waterworks reveals that if MTBE is detected in the raw water it is most often found in the corresponding drinking water as well due to the poor removal efficiency of conventional treatment steps. 相似文献
113.
介绍了东海大桥钻孔灌注桩基础的施工技术 ,对一些关键技术做了详细说明 ,还讨论了海上钻孔灌注桩施工成孔设备的选择及所用的淡水泥浆的配制 相似文献
114.
Analysis of village accessibility and its impact on land use dynamics in a mountainous province of northern Vietnam 总被引:5,自引:0,他引:5
Jean-Christophe Castella Pham Hung Manh Suan Pheng Kam Lorena Villano Nathalie Rachel Tronche 《Applied geography (Sevenoaks, England)》2005,25(4):308-326
Surveys carried out in mountainous areas of northern Vietnam at research sites selected across a gradient of market integration, revealed strong relationships between the location of the village with respect to the national road network and the nature of its land-use systems, its poverty level and more generally its potential for development. We developed and tested in Bac Kan province a method to give an objective and quantitative definition of accessibility over a large geographic area. Accessibility maps integrated in a provincial GIS showed that despite recent improvements to the road network, some remote areas do not benefit from recent development. 相似文献
115.
116.
Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China 总被引:3,自引:0,他引:3
Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate. 相似文献
117.
在准噶尔盆地西北缘,寻找岩性圈闭油气藏已是至关重要的问题。但人们几乎还是用常规的手段来寻找岩性油气藏,没有实质性进展。本文是以利用宽方位角采集的地震数据为基础,对数据进行高保真资料处理和参考标准层的层拉平解释。利用前人的区域地质研究成果和钻井解释成果对侏罗系的沉积环境进行了精细的描述,确定了拐19井区在下侏罗统三工河组的出油层段附近的沉积环境由湖泊相-三角洲前缘相-河流相-湖泊相的演化过程。利用地震属性解释的结果也能较好地反映目标区的沉积环境变迁,并且与区域地质、测井解释结果相吻合,为寻找油气提供了很好的依据。由此得出利用地震属性可以进行沉积环境变迁分析,为油田寻找岩性圈闭及油气藏做出贡献。 相似文献
118.
119.
浙江磐安蕨类植物资源及其开发利用 总被引:5,自引:0,他引:5
调查统计,磐安共有蕨类植物112种,隶属于60属、34科。地理成分分析表明,种的地理成分以东亚分布,特别是中国一日本分布为主,区系显示出较明显的亚热带一暖温带过渡的特征。同时从水平分布、垂直分布和生态分布三种分布型分析了磐安蕨类植物资源的分布规律,并根据其用途,划分为药用植物资源、食用植物资源、观赏植物资源等。在以上研究的基础上,提出了合理开发利用磐安蕨类植物资源的一些建议。 相似文献
120.
Mixing of event and pre‐event water in a shallow Entisol in sloping farmland based on isotopic and hydrometric measurements,SW China
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Water percolation and flow processes in subsurface geologic media play an important role in determining the water source for plants and the transport of contaminants or nutrients, which is essential for water resource management and the development of measures for pollution mitigation. During June 2013, the dynamics of the rainwater, soil water, subsurface flows and groundwater in a shallow Entisol on sloping farmland were monitored using a hydrometric and isotopic approach. The results showed that effective mixing of rainwater and soil water occurred in hours. The rebound phenomenon of δD profiles in soils showed that most isotope‐depleted rainwater largely bypassed the soil matrix when the water saturation in the soil was high. Preferential‐flow, which was the dominant water movement pattern in the vadose zone, occurred through the whole soil profile, and infrequent piston‐flow was mainly found at 20–40 cm in depth. The interflow in the soil layer, composed of 75.2% rainwater, was only generated when the soil profile had been saturated. Underflow in the fractured mudrock was the dominant flow type in this hillslope, and outflow was dominated by base flow (groundwater flow) with a mean contribution of 76.7%. The generation mechanism of underflow was groundwater ridging, which was superimposed upon preferential‐flow composed mainly of rainwater. The quick mixing process of rainwater and soil water and the rapid movement of the mixture through preferential channels in the study soil, which shows a typical bimodal pore size distribution, can explain the prompt release of pre‐event water in subsurface flow. Water sources of subsurface flows at peak discharge could be affected by the antecedent soil water content, rain characteristics and antecedent groundwater levels. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献