全文获取类型
收费全文 | 402篇 |
免费 | 57篇 |
国内免费 | 46篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 33篇 |
地球物理 | 78篇 |
地质学 | 180篇 |
海洋学 | 64篇 |
天文学 | 27篇 |
综合类 | 23篇 |
自然地理 | 57篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 19篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 27篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 24篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 21篇 |
2000年 | 11篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 24篇 |
1996年 | 2篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有505条查询结果,搜索用时 15 毫秒
1.
为有效对港区大气污染进行治理、分析船舶尾气,本文详细介绍了一种基于高斯烟羽模型,通过MATLAB模拟仿真模型,其包括实验仿真过程、技术原理及理论模型对船舶尾气扩散进行的研究。该模型是在传统的高斯烟羽模型的基础上,通过对实源像源进行加权选择输入参数;通过矢量合成确定了气体扩散的方向,利用合成后的"风速"进行计算仿真,有效模拟了船舶尾气在港区或者海洋环境中的气体扩散模型。其模型简单且可以有效模拟船舶尾气扩散。并且进一步对后续模型的精确优化进行分析。 相似文献
2.
New sources of data such as ‘big data’ and computational analytics have stimulated innovative pedestrian oriented research. Current studies, however, are still limited and subjective with regard to the use of Google Street View and other online sources for environment audits or pedestrian counts because of the manual information extraction and compilation, especially for large areas. This study aims to provide future research an alternative method to conduct large scale data collection more consistently and objectively on pedestrian counts and possibly for environment audits and stimulate discussion of the use of ‘big data’ and recent computational advances for planning and design. We explore and report information needed to automatically download and assemble Google Street View images, as well as other image parameters for a wide range of analysis and visualization, and explore extracting pedestrian count data based on these images using machine vision and learning technology. The reliability tests results based on pedestrian information collected from over 200 street segments in Buffalo, NY, Washington, D.C., and Boston, MA respectively suggested that the image detection method used in this study are capable of determining the presence of pedestrian with a reasonable level of accuracy. The limitation and potential improvement of the proposed method is also discussed. 相似文献
3.
Blogging, social networking, and other Web 2.0 practices have sparked widespread debate about the status and future of privacy. This paper examines an explicitly geographical aspect of Web 2.0 with respect to these debates: the geospatial web, or ‘geoweb’. As part of fundamental shifts in the kinds of geographic information available, its circulation, and representative forms it assumes, the geoweb implies new objects of privacy concern and subsequent privacy-related negotiations over the aggregate of its component information, technologies, and data praxes. Thus we argue that privacy must not only be revisited, but indeed re-conceptualized. Whereas prior research on privacy vis-à-vis geographic information technologies has tended to question what privacy ‘is’, we focus instead on the constitutive outcomes of societal struggles over privacy. We examine how privacy is being negotiated around two geoweb services - Google Street View and the Twitter GeoAPI - to illustrate that these contestations produce privacy as a social object in particular ways. We show that public discourse around actual or anticipated privacy harms stemming from geoweb services and their uses, as well as the preventatives and remedies proposed or implemented to address such harms, reconstitute the objects and practices of privacy concern, and alter the roles and relationships of state, civil and corporate actors in the construction of privacy. Finally we suggest that the geoweb raises new privacy concerns because some of its representational forms - namely geo-tagged images and self-authored texts - facilitate identification and disclosure with more immediacy and less abstraction. 相似文献
4.
高温熔融研制钾长石玻璃标准物质初探 总被引:1,自引:1,他引:0
激光剥蚀多接收等离子体质谱(LA-MC-ICPMS)是进行原位微区分析微量元素和同位素的重要技术之一,标准样品与样品之间的基体匹配是解决影响该技术准确分析的基体效应和分馏效应的首选方案。长石(特别是长石微区)的Pb同位素组成是示踪岩石形成和演化历史的重要途径,而LA-MC-ICPMS技术则是进行长石Pb同位素原位微区分析的关键技术,然而目前国内外尚没有合适的长石Pb同位素分析标准。文章研究探讨了利用高温炉进行原位微区分析钾长石中Pb同位素组成所用外部标准物质合成条件,结果表明,常规的74μm(200目)碎样无法得到均一的钾长石玻璃,需要将初始钾长石粉末研磨至1300目以下;高温炉合成温度为1680℃;熔融时间为2 h;采用液氮方式淬火。制成的钾长石玻璃除表面具有轻微的不均一性外,内部的Pb同位素比值为1.90779±0.00009(208Pb/206Pb,2s),0.75899±0.00004(207Pb/206Pb,2s),20.909±0.002(206Pb/204Pb,2s),15.871±0.002(207 Pb/204 Pb,2s)和39.888±0.005(208 Pb/204 Pb,2s),相应的相对标准偏差(RSD)分别为0.007%、0.008%、0.016%、0.016%和0.021%。表明利用本研究方法合成的钾长石玻璃可作为潜在的钾长石中Pb同位素组成原位微区分析外部校准物质。 相似文献
5.
6.
7.
The photocatalytic activity of combustion synthesized nanocrystalline CeAlO3 was determined for the degradation of four anionic and four cationic dyes. The perovskite oxide showed high‐photocatalytic activity and a complete degradation of all the dyes was possible within 2 h. The photocatalytic activity of the compound was comparable with the activity of the commercial Degussa P‐25 TiO2 catalyst. The degradation of dyes was found to follow first order kinetics and the first order degradation rate constants were determined. 相似文献
8.
In this work, the possible exploitation of fiber-reinforced composites in the context of maritime transportation of compressed natural gas (CNG) is investigated. In addition to a more conventional steel configuration, two different fiber materials, carbon and glass, are considered as construction materials for pressure vessels (PVs) to be stored on board ships, with thickness optimized by FEM analysis.The considered scenario is represented by the transportation of CNG from an offshore well to a terminal on shore. Fleets of ships carrying CNG in pressure vessels manufactured with the investigated materials are generated by means of a ship synthesis model (SSM) software and compared on the basis of technical and economical indicators.The choice of the construction material influences considerably the weight of the PVs, which represent a major item of total ship weight and reflects directly on the general transport performances in terms of resistance, seakeeping and reliability in the service. On the other hand, capital as well as operating expenditures are considerably affected by the choice. When exploring the design space, the ship synthesis model is able, at a preliminary stage of the design, to account for the various technical and economical aspects, their implications and relationships. Results are presented of computations carried out in a specific case, identified by the annual gas production and other characteristics of the well terminal and a cruising route for the ships. The comparison is carried out on the basis of the cost per transported unit of gas and of the percentage of success in the transportation process. The computations show that the choice of the PV material has a key influence on the results in terms of optimal number, dimensions and speed of the ships. 相似文献
9.
10.
不同预处理方法对南海东沙海域沉积物粒度的影响 总被引:1,自引:0,他引:1
通过采用不同方法对东沙沉积物样品进行了预处理,并采用综合法进行了粒度分析,以探讨东沙沉积物中碳酸盐和有机质对其粒度的影响。结果表明,去除有机质后沉积物的平均粒径和63~4μm粒径范围内的组分明显减小,有机质含量变化与平均粒径变化呈明显负相关,说明东沙沉积物中有机质的沉积是伴随细粒悬浮物质和胶体物质沉积下来的,且对细颗粒有明显的絮凝作用;去除碳酸盐后沉积物的平均粒径呈减小趋势,但粒径范围内组分含量的变化不明显,且碳酸盐含量的变化与沉积物粒径变化的关系也不甚密切。 相似文献