全文获取类型
收费全文 | 1800篇 |
免费 | 283篇 |
国内免费 | 188篇 |
专业分类
测绘学 | 450篇 |
大气科学 | 104篇 |
地球物理 | 257篇 |
地质学 | 705篇 |
海洋学 | 546篇 |
天文学 | 3篇 |
综合类 | 142篇 |
自然地理 | 64篇 |
出版年
2024年 | 5篇 |
2023年 | 24篇 |
2022年 | 65篇 |
2021年 | 65篇 |
2020年 | 77篇 |
2019年 | 72篇 |
2018年 | 53篇 |
2017年 | 125篇 |
2016年 | 98篇 |
2015年 | 108篇 |
2014年 | 122篇 |
2013年 | 103篇 |
2012年 | 152篇 |
2011年 | 133篇 |
2010年 | 79篇 |
2009年 | 83篇 |
2008年 | 105篇 |
2007年 | 90篇 |
2006年 | 90篇 |
2005年 | 69篇 |
2004年 | 70篇 |
2003年 | 63篇 |
2002年 | 57篇 |
2001年 | 56篇 |
2000年 | 44篇 |
1999年 | 41篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 43篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
排序方式: 共有2271条查询结果,搜索用时 15 毫秒
81.
82.
Social models of population vulnerability to disasters increasingly include the notion that vulnerability has a strong temporal component. While this temporality is typically conceptualized as objective (making vulnerability “dynamic,” “multiscalar,” and/or “historical”), it consistently fails to acknowledge that among stakeholders managing hazardscapes temporality is also a social process in which subjective experience of time may play a role in creating situations of population vulnerability. This paper proposes that the temporal situatedness of a population relative to past hazard events and the quality with which stakeholders engage hazard memory-chains combine to significantly influences its vulnerability to natural hazards. It is proposed that this temporal vulnerability is characterized by shared, population level potential for surprise and can be evaluated by exploration of time-series depth and temporal reference points in historical ecological narratives and documents. Based on ethnohistoric research conducted from 2002 to 2006 in flood-prone eastern North Carolina (USA), it is illustrated how temporal vulnerability was relatively higher in the Neuse River watershed located at the City of Kinston than surrounding watersheds. Due to the combination of factors including the damming of the Neuse River in the 1980s, outdated official floodplain maps, relatively unmonitored floodplain development, the stochastic timing of flood events (placing the last major flood more than a generation away), technological optimism, and turnover of floodplain officials and residents, local stakeholders were seriously misinformed about the space-time risks involved both before and after the disaster of Hurricane Floyd (1999) happened. To deal with this inconsistency, the temporal rarity of Hurricane Floyd as a “500-year event” has been motivated and embraced by many in an effort to continue life-as-is. The paper proposes that the concept of temporal vulnerability is further explored and used as key dimension in the vulnerability sciences. 相似文献
83.
Shore platforms frequently exhibit steps or risers facing seaward, landwards or obliquely across‐shore. A combination of soft copy photogrammetry, ortho‐rectification, geo referencing and field measurement of step height are linked in a GIS environment to measure step retreat on chalk shore platforms at sample sites in the south of England over two periods, 1973–2001, 2001–2007. The methods used allow for the identification, delineation and measurement of historic change at high spatial resolution. The results suggest that while erosion of chalk shore platforms by step backwearing is highly variable, it appears to be of similar magnitude to surface downwearing of the same platforms measured by micro‐erosion meters (MEMs) and laser scanning, in a range equivalent to 0·0006 – 0·0050 m y?1 of surface downwearing. This equates to annual chalk volume loss from the platforms, by the two erosion processes combined, of between 0·0012 m3 m?2 and 0·0100 m3 m?2. Results from the more recent years' data suggests that step retreat has variability in both space and time which does not relate solely to climatic variability. The results must be viewed with caution until much larger numbers of measurements have been made of both downwearing and step erosion at higher spatial and temporal resolution. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
84.
基于云平台的遥感信息公共服务研究 总被引:2,自引:0,他引:2
云平台作为云计算服务的基础架构,在计算机网络的基础上提供各种计算资源的统一管理和动态分配。文章提出的基于云平台的遥感信息公共服务,就是借助云平台先进的基础架构和管理方式,构建快速有效的遥感信息公共服务,推进遥感信息的应用和遥感信息事业的进步。文章在引进云平台技术的基础上,分析遥感信息公共服务平台的架构和关键技术,并对服务平台的应用前景和进一步研究进行展望。 相似文献
85.
Geographic information system (GIS) based methodologies are widely used to various problems. However, its potential for application to strategic maritime search and rescue (SAR) planning remains largely unexplored. To investigate the applicability of GIS-based tools to this problem, this paper presents an approach to evaluate accessibility and response times in a sea area. Such information aids to objectify the response effectiveness of a SAR system, which is important for rational resource allocation. The presented methodology accounts for the main characteristics of maritime response, namely spatial accessibility, capabilities of search and rescue units (SRUs) and prevailing wave conditions, which affect the attainable SRU speeds. An application to the Finnish areas of the Gulf of Finland is shown. Despite the existence of some difficulties with currently available tools (e.g. accurate and user-friendly spatial wave models and challenges with using raster-based methods in topologically complex areas) and limitations in knowledge (e.g. the SRU capabilities in actual operations), the results indicate that the methodology provides good opportunities for enhancing maritime decision making. 相似文献
86.
基于RS与GIS技术,采用分形理论对渭北台塬县级城市空间扩张特征进行分析。结果表明:1990—2010年台塬区县级城市加速扩张,总面积扩大了2.86倍,年均增长率达8.7%。1990,2000,2010年县级城市空间形态分维值均值分别为1.08,1.09,1.21,变异系数分别为3.06,3.09,3.93,城市空间形态总体简单但渐趋复杂且不断分化。异速生长模型标度因子b值均小于1,人均城市空间较为合理但远未达到最优状态。1990—2000年城市以填充型扩张为主,2000—2010年以外延型扩张为主,用地集约性呈下降趋势。空间上,铜川塬、宝鸡塬扩张较快,人地关系较差;咸阳塬扩张最快,人地关系一般;渭南塬扩张相对较慢,人地关系较优。总体上,亟待加强城市规划以构建节约型城市空间增长模式。 相似文献
87.
华北地块北缘金矿预测 总被引:4,自引:1,他引:3
对华北地块北缘的金矿进行了成因分类,共分为3大类7亚类.利用地质体单元法对3大金矿类型进行了单元划分,共划分出214个单元.在综合信息成矿理论的指导下,对本区的岩浆重熔热液型金矿、岩浆同熔热液型金矿床以及火山-次火山热液型金矿床分别采用特征分析,对矿产资源的产出位置进行了估计,采用成矿概率估计对各单元的成矿可能性进行分级,共预测出24个最有远景的工作区. 相似文献
88.
将可信赖平台模块(TPM)芯片引入车载自组织网VANET,提出了一种有效保护地理位置信息路由协议GPSR(贪婪周边无状态路由协议)的可信安全机制,从而能够防止恶意篡改路由协议和邻居位置信息表的行为。在NS2.30下对网络真实场景进行了模拟,证实此可信安全路由协议模型是正确的、有效的和合理的。 相似文献
89.
90.
操作系统信任基的设计研究 总被引:2,自引:0,他引:2
石文昌 《武汉大学学报(信息科学版)》2010,(5)
把操作系统中为计算平台的可信性提供支持的元素的集合定义为操作系统信任基(TBOS),建立了TBOS的设计思想,提出了TBOS的体系结构,重点诠释了TBOS体系结构中的基本信任基、可信基准库、控制机制、度量机制、判定机制和支撑机制等关键成分的核心思想、TBOS的隔离与交互能力以及动态扩展特性,同时讨论了TBOS实现中涉及到的关键问题。 相似文献