全文获取类型
收费全文 | 365篇 |
免费 | 35篇 |
国内免费 | 69篇 |
专业分类
测绘学 | 99篇 |
大气科学 | 19篇 |
地球物理 | 66篇 |
地质学 | 158篇 |
海洋学 | 47篇 |
天文学 | 2篇 |
综合类 | 22篇 |
自然地理 | 56篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 23篇 |
2013年 | 43篇 |
2012年 | 22篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 17篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 23篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有469条查询结果,搜索用时 15 毫秒
271.
Dan Bowman 《自然地理学》2013,34(1):34-46
Seven subaerial, low energy beaches in the SE Mediterranean were surveyed biweekly for 13 months. Beach level data were computer-processed and plotted as time-series profile diagrams that differentiated the subaerial beach into three basic subenvironments: backshore, berm, and swash-zone. Heterogeneous seasonal trends in beach sand budget, erosion/accretion patterns, occurrence of ridges and berm-crests, and in pollution by seaborne tar were observed. The profile stations also showed very different degrees of seasonality, although located along similar beaches. Local beachrock protection, when evident, effectively masked seasonality by significantly lowering beach dynamics. Biweekly, seasonal, and annual fluctuations of the beach sand-budget were computed. Average annual net sand flux at the seven beaches was 66 m3/m of beach front, though wide variations occurred. Annual changes in the sand budget along the study area exceeded volumetric changes within the profile, indicating longshore sand transfer. Synchronism of beach behavior prevailed only at the seasonal level. However, intra-seasonal fluctuations for the different profile stations were out of phase, indicating poor synchronism of beach response due to longshore movement of rhythmic topography. Profile changes were thus often unrelated to concomitant wave-climate changes. The overall heterogeneous beach response was in sharp contrast to the identical wave climate, similar bathymetry, and sedimentology of the studied beaches. 相似文献
272.
Daoqin Tong Richard L. Church 《International journal of geographical information science》2013,27(5):795-816
Uncertainties and errors associated with aggregation have long been recognized in the study of spatial problems. In facility location modeling, while much has been done to examine the aggregation of large datasets of discrete points, errors and uncertainties involved in aggregating continuous spatial units are not well understood. This study focuses on the effects of aggregating continuous spatial units into discrete points within the context of the location set covering problem. We propose new measures to understand and quantify errors associated with a continuous aggregation scheme. In a real-world application, the proposed methods can be used to suggest an appropriate aggregation scheme before the application of the location model. We demonstrate the concepts developed here with an empirical study of siting emergency warning sirens in the city of Dublin, OH. 相似文献
273.
Many researchers have examined the impact of detailed soil spatial information on hydrological modelling due to the fact that such information serves as important input to hydrological modelling, yet is difficult and expensive to obtain. Most research has focused on the effects at single scales; however, the effects in the context of spatial aggregation across different scales are largely missing. This paper examines such effects by comparing the simulated runoffs across scales from watershed models based on two different levels of soil spatial information: the 10‐m‐resolution soil data derived from the Soil‐Land Inference Model (SoLIM) and the 1:24000 scale Soil Survey Geographic (SSURGO) database in the United States. The study was conducted at three different spatial scales: two at different watershed size levels (referred to as full watershed and sub‐basin, respectively) and one at the model minimum simulation unit level. A fully distributed hydrologic model (WetSpa) and a semi‐distributed model (SWAT) were used to assess the effects. The results show that at the minimum simulation unit level the differences in simulated runoff are large, but the differences gradually decrease as the spatial scale of the simulation units increases. For sub‐basins larger than 10 km2 in the study area, stream flows simulated by spatially detailed SoLIM soil data do not significantly vary from those by SSURGO. The effects of spatial scale are shown to correlate with aggregation effect of the watershed routing process. The unique findings of this paper provide an important and unified perspective on the different views reported in the literature concerning how spatial detail of soil data affects watershed modelling. Different views result from different scales at which those studies were conducted. In addition, the findings offer a potentially useful basis for selecting details of soil spatial information appropriate for watershed modelling at a given scale. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
274.
Quantifying aggregation and change in runoff source in accordance with catchment area increase in a forested headwater catchment 下载免费PDF全文
There has been a great deal of research interest regarding changes in flow path/runoff source with increases in catchment area. However, there have been very few quantitative studies taking subscale variability and convergence of flow path/runoff source into account, especially in relation to headwater catchments. This study was performed to elucidate how the contributions and discharge rates of subsurface water (water in the soil layer) and groundwater (water in fractured bedrock) aggregate and change with catchment area increase, and to elucidate whether the spatial variability of the discharge rate of groundwater determines the spatial variability of stream discharge or groundwater contribution. The study area was a 5‐km2 forested headwater catchment in Japan. We measured stream discharge at 113 points and water chemistry at 159 points under base flow conditions. End‐member mixing analysis was used to separate stream water into subsurface water and groundwater. The contributions of both subsurface water and groundwater had large variability below 1 km2. The contribution of subsurface water decreased markedly, while that of groundwater increased markedly, with increases in catchment area. The specific discharge of subsurface water showed a large degree of variability and decreased with catchment area below 0.1 km2, becoming almost constant above 0.1 km2. The specific discharge of groundwater showed large variability below 1 km2 and increased with catchment area. These results indicated that the variabilities of stream discharge and groundwater contribution corresponded well with the variability of the discharge rate of groundwater. However, below 0.1 km2, it was necessary to consider variations in the discharge rates of both subsurface water and groundwater. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
275.
从空间数据场的角度出发,提出了一种基于场论的层次空间聚类算法(简称HSCBFT)。该算法是通过模拟空间实体间的凝聚力来描述空间实体间的相互作用,进而采取层次凝聚的策略进行聚类。通过实验分析可以发现,层次空间聚类算法具有如下优势:①空间聚类簇中各空间实体很好地满足了空间邻近且专题属性相似的要求;②能发现任意形状的空间簇,且具有良好的抗噪性;③输入参数较少。 相似文献
276.
277.
文章从全区气象网络的可靠性现状出发,简要介绍了虚拟路由冗余协议V R R P的原理,分析了改造建设的需求,阐述了改造建设的整体规划,提出应用V R R P协议提升全区气象网络的可靠的解决方案,从保护投资和提高网络可靠性的角度提出一种实用的解决方案。 相似文献
278.
针对信息化海洋测绘这一重要问题进行了探讨,就目前存在的一些模糊认识进行了分析澄清。对相关文献涉及的数据信息准确性、语言表述严谨性和学术观点合理性问题,进行了核实和讨论,提出了我们的观点:一是认为对一些重要数据的引用有误,容易误导读者,影响到引用数据的权威性;二是认为海洋测绘一直就归属于测绘学科,而不是游离其外,更不宜将其纳入海洋学;三是认为不能简单用海图集合这个概念来代替海洋测绘的成果或数据集合,海图集合论不是海洋测绘的核心理论;四是认为海洋测绘一直就是按照纵向分离、横向融合的理念和模式发展的,不依信息化进程而改变,改变的只是它的发展深度和广度。 相似文献
279.
280.
黑曲霉对含钾矿物的解钾作用与机理分析 总被引:4,自引:0,他引:4
通过测定黑曲霉(Aspergillus niger)对含钾矿粉的解钾量、黑曲霉作用含钾矿粉后的代谢产物(多糖、蛋白质、小分子分泌物)以及微环境中的pH值等,比较静置培养和震荡培养条件下黑曲霉对含钾矿粉的作用效果,并分析震荡培养下黑曲霉对含钾矿粉的风化作用机理。结果显示,震荡培养下黑曲霉对含钾矿粉的转化作用显著大于静置培养,震荡培养下黑曲霉作用含钾矿粉与否导致培养液中的代谢产物以及真菌-矿物聚集体微环境中pH值有显著改变。分析表明,黑曲霉生长形成的真菌-矿物聚集体、黑曲霉菌丝生长及其代谢产物、酸性微环境在含钾矿粉转化过程中发挥重要作用;黑曲霉对含钾矿粉的解钾作用应该是多种因素协同作用导致的综合效果。研究结果对完善真菌风化含钾矿物的作用机理,有效利用微生物转化低品位矿物钾技术提供了参考。 相似文献