全文获取类型
收费全文 | 111篇 |
免费 | 21篇 |
国内免费 | 34篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 36篇 |
地球物理 | 7篇 |
地质学 | 40篇 |
海洋学 | 21篇 |
综合类 | 21篇 |
自然地理 | 10篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2002年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1996年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
排序方式: 共有166条查询结果,搜索用时 15 毫秒
141.
Measurements were made of the degree of trace metal pyritization (DTMP) and ancillary characteristics of four undisturbed sediment cores collected from the subtidal zone of the Nanpaishui Estuary on the Western Bank of the Bohai Sea, a seriously polluted inland sea in northeastern China. The remarkably low concentrations of organic carbon (<0.72%) in these sediments likely constrained sulfate reduction rates, and the low concentrations of acid volatile sulfide (AVS) (<12.5 μmol g−1) limited the sequestration of metals through association with pyrite. The most consistent cause of inter-station differences and depth variations in the degree of pyritization was differences in pyrite metal concentrations rather than reactive metal concentrations. Reactive metal concentrations were in several cases negatively correlated with pore water concentrations, consistent with a dissolution/precipitation mechanism. The relationship between pore water metal concentrations and DTMPs was evidenced by a qualitative similarity of the inter-station variability of these same parameters. 相似文献
142.
In our trials, from 2007 to 2008, of mass production of seedlings of Hizikia fusiformis using synchronization techniques, problems of a "dark thalli" phenomenon and epiphytes contamination severely threatened the health of juvenile seedlings. In this investigation, we optimized conditions for improving the growth of juvenile seedlings. Seven string collectors were seeded with zygotes and a series of experiments were conducted including direct exposure to solar irradiance, co-culture with Ulva spp. and treatment with sodium hypochlorite. It was found that direct exposure to solar irradiance (maximum: 1 740 μmol photons/(m2?s)) for 2 h per day could efficiently enhance the growth of young seedlings and simultaneously inhibit the growth of epiphytic algae. In this treatment, 50-day old seedlings could reach an average of 0.44 cm in length and possess up to nine leaflets. However, a single treatment with 18-mmol/L sodium hypochlorite for 10 min severely harmed 15-day old seedlings. In comparison, weekly treatment with 2.2-mmol/L sodium hypochlorite for 10 min brought no apparent harm to seedlings and eliminated epiphytic algae efficiently. However, this treatment significantly increased the detachment rate of seedlings. Inoculating Ulva spp. onto the collector caused a dramatic decrease in the number of seedlings. However, the growth of the remaining seedlings appeared unhampered. All collectors except the control were daily sprayed with a high pressure water jet from the 8th day post fertilization. From the first day to 50th day, no "dark thallus" was observed on any of the seven collectors. We believe that well-timed daily exposure to solar irradiance would favor H. fusiformis in its early growing stages. 相似文献
143.
Displacement back analysis is a common method to identify mechanical geo‐material parameters using the monitored displacement. How to obtain a global optimum solution in large space search of highly non‐linear multimodal is a key point of optimum back analysis. The paper presents a new back analysis that is an integration of evolutionary support vector machines (SVMs), numerical analysis and genetic algorithm. The non‐linear relationship between the mechanical geo‐material parameters to be identified and the corresponding displacement values of key points is learned and represented by evolutionary SVMs in global optimum. Numerical analysis is used to create training and testing samples for recognition of SVMs. Then, performing a global optimum search on the obtained SVMs using genetic algorithm can identify the mechanical geo‐material parameters. The proposed algorithm is tested by back analysis of an elastic plate and an elastic–plastic plate and used to recognize mechanical parameters of subclay, strongly weathered tuff and weakly weathered tuff of Bachimen slope, Funing expressway, Fujian, China. The results indicate that applicability of the proposed algorithm with enough accuracy. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
144.
针对GIS数据的多维、海量、动态性等特点,本文设计了基于四叉树和双缓存机制的GIS动态数据可视化模型,并详细地介绍并阐述该模型的数据存储规格和数据可视化方法及其特点。基于四叉树索引结构和多线程双缓存机制,构建GIS动态数据可视化模型,探讨多线程分层绘制动态对象方法和GIS空间数据库实时更新方法,实现GIS海量数据的动态化、序列化、实时可视化表达。并测试对比了常见可视化算法与本算法之间的显示效率,发现本研究算法针对多种GIS图形类型、大数据量GIS数据显示,均有较高的效率提升,实验证明该方法稳定可行,可为其他GIS动态数据的可视化提供参考。 相似文献
145.
146.
147.
Integrity monitoring algorithms for airport surface movement 总被引:2,自引:2,他引:0
Navigation algorithms are proposed for carrier phase ambiguity integrity monitoring to support aircraft surface movement.
The enhanced integrity monitoring algorithm addresses the very stringent integrity requirements for surface movement by the
use of multiple test statistics and a group separation concept for single and multiple failure detection and exclusion. The
algorithms are subject to a detailed performance characterization for precision approaches and airport surface movement, using
simulations as well as static and dynamic field trials, taking into account operational specificities, such as multipath and
potential decorrelations between the reference station and aircraft due to ionospheric anomalies. Results show that the proposed
algorithms have the potential to satisfy airport surface movement requirements if the ionospheric anomalies are monitored
using a special ground-based network. 相似文献
148.
基于C4.5算法的道路网网格模式识别 总被引:1,自引:1,他引:0
道路网模式的识别对于地图综合、数据匹配和空间分析具有重要意义。网格模式是道路网中的典型模式之一。本文提出一种基于C4.5算法的网格模式识别方法。该方法以道路网中的网眼多边形为基本单元,根据上下文关系将其标识为属于网格模式和不属于网格模式两类。首先采用形状参量和关系参量描述网眼多边形,然后,基于决策树C4.5算法分别对5维参量和3维参量构造分类器,运用10折交叉验证获得具有说服力的结果,其Kappa值分别为0.63和0.66,正确率分别为81.7%和82.9%,置信度90%的置信区间分别为[0.785, 0.846]和[0.797, 0.857]。在新数据上进行了识别效果的验证,结果表明该分类器可用于网格模式的识别。研究试图将传统模式识别和数据挖掘的理论方法应用于空间问题的解答中。 相似文献
149.
150.
2009年6月3日商丘市强飑线过程分析 总被引:3,自引:1,他引:2
利用商丘新一代天气雷达(CINRAD/SB)观测资料,以及MICAPS资料和自动气象站观测资料,对2009年6月3日发生在商丘的一次以大风为主,并伴有降水、雷电发生的强飑线天气过程进行了分析。分析表明:地面辐合线是这次强对流和飑线天气过程的触发机制。高空冷涡后部冷空气南下,近地层为暖中心,形成了上冷下暖的位势不稳定层结;风力突增、气压涌升、气温骤降、湿度猛升等气象要素变化符合飑线特征。飑线最大回波强度达69dBz,最大负径向速度值达-37m/s,强回波区呈“厂”字形,位于回波区前沿,移动速度快,并具有径向风速辐合等特征。径向速度场上表现为高层负径向速度中心值的迅速减小和低层负径向速度中心值的快速增大。 相似文献