首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   29篇
  免费   6篇
  国内免费   13篇
测绘学   4篇
大气科学   14篇
地球物理   8篇
地质学   13篇
海洋学   5篇
综合类   1篇
自然地理   3篇
  2024年   2篇
  2023年   4篇
  2022年   5篇
  2021年   3篇
  2020年   4篇
  2019年   3篇
  2018年   1篇
  2017年   2篇
  2016年   4篇
  2015年   2篇
  2013年   1篇
  2012年   1篇
  2011年   4篇
  2010年   1篇
  2009年   1篇
  2008年   1篇
  2006年   1篇
  2002年   1篇
  2001年   1篇
  1999年   2篇
  1998年   2篇
  1993年   1篇
  1992年   1篇
排序方式: 共有48条查询结果,搜索用时 15 毫秒
41.
论文借鉴欧洲控制研究中心以机型为基本单元的延误成本估算模型(简称EC估算模型)及其相关算法,以EC估算模型为基础,补充机型配置比和引入航班执行阶段作为影响参数,估算了24 h中国枢纽机场单位时长延误成本和时间延误总成本,进行了时间延误成本的航线影响分析及中美比较,得到如下结论:① 区域枢纽机场时间延误成本普遍低于复合枢纽机场,但前者中机型单位时长延误成本和登机口成本均高于后者,从中可透视出其分别与中国航线网络中心集聚、航空地理市场(机型配置)需求和航线网络模式应用的密切相关;枢纽机场空中维持成本在时间延误总成本中占比最大,说明中国空中廊道设置存在缺陷。② 枢纽机场间(航线)以及枢纽机场与非枢纽机场之间(航线)时间延误总成本的差异深受航线属性所影响,其根本又在于航空地理市场(机型配置)需求以及空中廊道参与机场位置。③ 中美枢纽机场和枢纽机场间(航线)时间延误成本均有较大差异,主要表现为中国空中维持成本远高于美国,这是由空中廊道特征路径宽度和航迹交叉点数量2个因素造成的。  相似文献   
42.
巢湖西北部水域的有机污染和富营养化   总被引:3,自引:0,他引:3       下载免费PDF全文
于1988年8月和1989年11月在巢湖西部的南淝河下游、河口及湖区采集水样,用GC/MS法分析,检出了酚类、农药、氯代烃类、脂肪烃、苯系物,以及多环芳烃等多种有机污染物,表明巢湖部分水域已受到污染。河水中检出的多环芳烃的浓度要比湖水中的高得多。实验室藻培养液的分析说明,湖水中存在的α-蒎烯、薁、二甲基二硫化物、6-甲基-2-庚酮是来源于生物的;湖水中存在的正十七烷也部分地来源于藻类活动。用富营养化水体作为水源经氯化处理生产自来水,会增加自来水中潜在致突变物质的含量。  相似文献   
43.
Given that the fixed air traffic operation system and functions are difficult to adapt to the great changes of air route structure and airspace demand, the airspace resource allocation is undergoing an evolution from static to flexible and dynamic so as to effectively solve the contradiction between airspace capacity and actual demand. In this process, the dependence on spatiotemporal continuous data is gradually strengthened. This article reviewed the relevant national and international research, and found that from the multi-dimensional expression of basic elements to the feature analysis of specific airspace units, airspace resource allocation deepens and expands in a real-time direction and presents a new mechanism. A series of high density air traffic flow identification methods are developed by introducing time parameters and combined with the flight path model to form a distinct dynamic characteristic. Related applications and practice reflect the structural revolution of airspace resource allocation and promote the solution of practical problems such as airspace congestion and resource allocation. The research and practice of dynamic airspace resource allocation outside China have positive reference significance to our country. However, when simultaneously coping with the hoisting of airside capability and the change of multi-dimensional parameters, we still face the challenges of period-segment matching, micro-macro combination, terminal airspace-air route docking and airspace-land area integration. In the future, geography should further integrate the unique advantages of spatiotemporal interaction and construct a brand-new overall mobile chain of various airspace-land scales to carry out research work deeply.  相似文献   
44.
针对组合导航系统的定位精度与稳定性要求不断提高的现状,该文引入一种观测噪声协方差与抗差自适应相结合的Kalman滤波算法。利用新息向量和移动窗口协方差分析法,动态自适应修正观测噪声协方差阵;通过分析基于状态不符值、方差分量的统计量构造的自适应因子所存在的问题,提出一种由预测残差向量构造的自适应因子。仿真结果表明,该方法能够有效抑制观测异常对组合导航定位精度的影响。  相似文献   
45.
Bai Long  Lu Zi  Du Xinru  Gao Fang 《地球科学进展》2016,31(11):1197-1204
The exploitation of (ultra) low airspace resource has become an important component of optimizing the utilization of airspace and has received worldwide attention. It is the major form for UAV activity, which reveals great socioeconomic prospects. Firstly, the background of exploiting (ultra) low airspace resource and challenge for UAV activities were analyzed in regional areas. Then, legal rights for UAV activities and routes design in overseas and domestic research were reviewed. Second, the forms of regional rules for UAV activities in (ultra) low airspace were summarized, which included height-density rule, coverage area rule and isolation area of rule. Third, based on the air network of UAV(s) and aiming at the demand of aerial lanes for different requirements, the development from the method of 3D city model to the Cost-to-go was prospected. The findings are as follows: UAV activities’ aerial lanes design includes high-density as general rules and coverage area rule, isolation area rule as special rules. On the basis of 3D city model, improved method of Cost-to-go is applied to the choice of the optimal aerial lanes; based on ground buildings and residents’ actual conditions in regional area, the rules and methods are good for the (ultra) low airspace resources development and better solve the problem of UAV activities coordination. Furthermore, the rules and methods play an important role even in the implementation of the national airspace system.  相似文献   
46.
Photochemical smog characterized by high concentrations of ozone (O3) is a serious air pollution issue in the North China Plain (NCP) region, especially in summer and autumn. For this study, measurements of O3, nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO), nitrous acid (HONO), and a number of key physical parameters were taken at a suburban site, Xianghe, in the NCP region during the summer of 2018 in order to better understand the photochemical processes leading to O3 formation and find an optimal way to control O3 pollution. Here, the radical chemistry and O3 photochemical budget based on measurement data from 1-23 July using a chemical box model is investigated. The daytime (0600-1800 LST) average production rate of the primary radicals referred to as ROx (OH + HO2+ RO2) is 3.9 ppbv h-1. HONO photolysis is the largest primary ROx source (41%). Reaction of NO2 + OH is the largest contributor to radical termination (41%), followed by reactions of RO2 + NO2 (26%). The average diurnal maximum O3 production and loss rates are 32.9 ppbv h-1 and 4.3 ppbv h-1, respectively. Sensitivity tests without the HONO constraint lead to decreases in daytime average primary ROx production by 55% and O3 photochemical production by 42%, highlighting the importance of accurate HONO measurements when quantifying the ROx budget and O3 photochemical production. Considering heterogeneous reactions of trace gases and radicals on aerosols, aerosol uptake of HO2 contributes 11% to ROx sink, and the daytime average O3 photochemical production decreases by 14%. The O3-NOx-VOCs sensitivity shows that the O3 production at Xianghe during the investigation period is mainly controlled by VOCs.  相似文献   
47.

利用江苏省1961—2020年70个国家级及1300多个区域自动气象站同时段的日最低气温重构数据,选取最低气温48 h最大降温幅度、累计降温幅度、过程日极端最低气温和寒潮过程持续天数共4个要素作为寒潮灾害气象致灾因子,综合信息熵权法和专家打分法确定各致灾因子权重,构建寒潮过程致灾危险性评估模型,形成致灾危险性指数长时间序列,采用百分位法确定危险等级。基于智能网格气温预报数据,计算寒潮过程预估致灾危险性指数,在此基础上结合承灾体暴露度及脆弱性信息,构建寒潮过程风险预评估模型,对高分辨率人口、国内生产总值(Gross Domestic Product,GDP)和小麦等承灾体进行风险预估,同时考虑前期气温对小麦生长的影响,修正了小麦脆弱性指标。结果表明:(1)江苏省历年寒潮过程发生频次总体呈现20世纪后40年多、21世纪前20年少的态势,北部地区发生频次显著多于南部地区;寒潮过程的气象致灾因子强度大体上具有西部强于东部、北部强于南部的分布特征;(2)通过对2022年11月28日—12月3日江苏全省性寒潮天气过程的个例分析,可以得出与实际灾情基本相符的寒潮天气过程的致灾危险性预评估和风险预估结果。

  相似文献   
48.
顾心如 《物探与化探》1999,23(4):317-318
介绍了用古地磁研究地质构造问题时倾伏褶皱地层产状的校正方法,推导了换算公式,以提醒同行们的关注.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号