全文获取类型
收费全文 | 508篇 |
免费 | 48篇 |
国内免费 | 40篇 |
专业分类
测绘学 | 114篇 |
大气科学 | 39篇 |
地球物理 | 71篇 |
地质学 | 111篇 |
海洋学 | 31篇 |
天文学 | 8篇 |
综合类 | 58篇 |
自然地理 | 164篇 |
出版年
2023年 | 2篇 |
2022年 | 21篇 |
2021年 | 25篇 |
2020年 | 21篇 |
2019年 | 25篇 |
2018年 | 19篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 31篇 |
2013年 | 34篇 |
2012年 | 28篇 |
2011年 | 35篇 |
2010年 | 24篇 |
2009年 | 26篇 |
2008年 | 26篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 23篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 11篇 |
2001年 | 17篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有596条查询结果,搜索用时 15 毫秒
121.
根据等效原理及理论自洽的要求,把光速不变原理推广到弯曲时空。并在此基础上阐明了坐标、坐标变换,物理量的描述与测量等最基本问题的物理意义。 相似文献
122.
123.
人类活动对公元1194年以来黄河河口延伸速率的影响 总被引:9,自引:0,他引:9
以近 50年来的观测资料和公元 1 1 94年以来苏北废黄河和现代黄河的历史文献资料为基础,在宏观时间尺度上 (1 0 2 ~ 1 0 3年 )研究了人类活动对黄河口延伸速率的影响。结果表明,废黄河口的延伸可以分为两个阶段,1 1 94~ 1 578年为第一阶段,河口延伸速率较慢 ;1 579~ 1 855年为第二阶段,河口延伸速率大大加快。 1 855年以来现代黄河河口延伸速率的变化曲线可以分为 3个阶段,分别用 3条斜率不同的直线来拟合。 3条直线之间的两个转折点可以代表人类活动的方式和强度发生改变的临界点。由此建立了人类活动影响下现代黄河三角洲河口延伸过程的三阶段模式。 相似文献
124.
分析山东 90年代产业结构变动趋向的时空差异 ,探讨产业结构变动的原因及地区产业结构变动能力 ,并对山东产业结构走向及产业结构在地区间的协调发展提出建议。 相似文献
125.
126.
该文介绍了测绘地理信息档案分类法、档案实体分类和档案信息分类理论,并结合测绘地理信息档案的特点,探讨了它们在测绘地理信息档案管理中的应用,提出了包含数字档案在内的测绘地理信息实体分类方法,探讨了基于档案管理系统的测绘地理信息档案分类目录的组织形式。 相似文献
127.
宫林成 《测绘与空间地理信息》2016,(7):118-120
根据当前信息化测绘体系建设工作推进情况和存在的问题,本文提出了"信息化测绘体系建设=装备引进+资源整合+技术改造+系统建设+安全防护"的构想,构建动态、及时和按需的测绘生产和服务模式,进一步加强资源整合,强调了"人"的信息化的重要性和途径,详细阐述了测绘生产单位依托实际项目来持续改进建设工作的意见和建议。 相似文献
128.
Ko Ko Lwin Komei Sugiura Koji Zettsu 《International journal of geographical information science》2016,30(8):1579-1593
We can collect, store, and analyze a huge amount of information about human mobility and social interaction activities due to the emergence of information and communication technologies and location-enabled mobile devices under cyber physical system frameworks. The high spatial resolution of population data on a multi-temporal scale is required by transport planners, human geographers, social scientists, and emergency management teams. In this study, we build a space-time multiple regression model to estimate grid-based (500 m × 500 m) spatial resolution at multi-temporal scale (30-min intervals) population data based on the space-time relationship among geospatially enabled person trip (PT) survey data and incorporate both mobile call (MC) and geotagged Twitter (GT) data. Since using geospatially enabled PT survey data as dependent variables enables us to acquire actual population amounts, which strongly depend on MCs and social interaction activities. Although many grids have a strong correlation between PT and MC/GT, some show fewer correlation results, especially where the grids have factories, schools, and workshops in which fewer MCs are found but a large population is presented. Although GT data are sparser than MCs, people from amusement and tourist areas can be detected by GT data. The space-time multiple regression model can also estimate the different amounts of populations based on human travel behavior that changes over space and time. According to accuracy assessments, the night-time estimated results, especially between 00:00 and 06:30, strongly correlate with national census data except in places where the grids have railway and subway stations. 相似文献
129.
Monsuru Adepeju Gabriel Rosser 《International journal of geographical information science》2016,30(11):2133-2154
Many physical and sociological processes are represented as discrete events in time and space. These spatio-temporal point processes are often sparse, meaning that they cannot be aggregated and treated with conventional regression models. Models based on the point process framework may be employed instead for prediction purposes. Evaluating the predictive performance of these models poses a unique challenge, as the same sparseness prevents the use of popular measures such as the root mean squared error. Statistical likelihood is a valid alternative, but this does not measure absolute performance and is therefore difficult for practitioners and researchers to interpret. Motivated by this limitation, we develop a practical toolkit of evaluation metrics for spatio-temporal point process predictions. The metrics are based around the concept of hotspots, which represent areas of high point density. In addition to measuring predictive accuracy, our evaluation toolkit considers broader aspects of predictive performance, including a characterisation of the spatial and temporal distributions of predicted hotspots and a comparison of the complementarity of different prediction methods. We demonstrate the application of our evaluation metrics using a case study of crime prediction, comparing four varied prediction methods using crime data from two different locations and multiple crime types. The results highlight a previously unseen interplay between predictive accuracy and spatio-temporal dispersion of predicted hotspots. The new evaluation framework may be applied to compare multiple prediction methods in a variety of scenarios, yielding valuable new insight into the predictive performance of point process-based prediction. 相似文献
130.
Assimilating satellite radiances into Numerical Weather Prediction (NWP) models has become an important approach to increase the accuracy of numerical weather forecasting. In this study, the assimilation technique scheme was employed in NOAA’s STMAS (Space-Time Multiscale Analysis System) to assimilate AMSU-A radiances data. Channel selection sensitivity experiments were conducted on assimilated satellite data in the first place. Then, real case analysis of AMSU-A data assimilation was performed. The analysis results showed that, following assimilating of AMSU-A channels 5–11 in STMAS, the objective function quickly converged, and the channel vertical response was consistent with the AMSU-A weighting function distribution, which suggests that the channels can be used in the assimilation of satellite data in STMAS. With the case of the Typhoon Morakot in Taiwan Island in August 2009 as an example, experiments on assimilated and unassimilated AMSU-A radiances data were designed to analyze the impact of the assimilation of satellite data on STMAS. The results demonstrated that assimilation of AMSU-A data provided more accurate prediction of the precipitation region and intensity, and especially, it improved the 0–6h precipitation forecast significantly. 相似文献