全文获取类型
收费全文 | 8465篇 |
免费 | 729篇 |
国内免费 | 505篇 |
专业分类
测绘学 | 2752篇 |
大气科学 | 354篇 |
地球物理 | 1401篇 |
地质学 | 1996篇 |
海洋学 | 1263篇 |
天文学 | 49篇 |
综合类 | 762篇 |
自然地理 | 1122篇 |
出版年
2024年 | 11篇 |
2023年 | 32篇 |
2022年 | 117篇 |
2021年 | 187篇 |
2020年 | 227篇 |
2019年 | 223篇 |
2018年 | 179篇 |
2017年 | 374篇 |
2016年 | 291篇 |
2015年 | 374篇 |
2014年 | 449篇 |
2013年 | 634篇 |
2012年 | 534篇 |
2011年 | 554篇 |
2010年 | 458篇 |
2009年 | 499篇 |
2008年 | 608篇 |
2007年 | 600篇 |
2006年 | 586篇 |
2005年 | 465篇 |
2004年 | 435篇 |
2003年 | 329篇 |
2002年 | 317篇 |
2001年 | 257篇 |
2000年 | 199篇 |
1999年 | 180篇 |
1998年 | 126篇 |
1997年 | 101篇 |
1996年 | 57篇 |
1995年 | 64篇 |
1994年 | 46篇 |
1993年 | 42篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有9699条查询结果,搜索用时 618 毫秒
261.
数字摄影测量与计算机视觉 总被引:8,自引:2,他引:8
张祖勋 《武汉大学学报(信息科学版)》2004,29(12):1035-1039,1105
从摄影测量的角度出发,在回顾摄影测量的发展历程及其最新进展的基础上,系统分析了数字摄影测量与计算机视觉的共同点及其本质差异,指出数字摄影测量的下一步发展必须与计算机视觉的理论和最新发展相结合。 相似文献
262.
论数字城市工程及其技术体系 总被引:16,自引:0,他引:16
分析了数字城市的内涵 ,基于数字工程思想 ,总结了数字城市的工程结构与技术体系 ,进而阐述了数字城市的意义与建设策略。 相似文献
263.
264.
随着Internet技术的飞速发展,以及对数字地球概念的深入探讨,WebGIS已经是GIS发展的必然趋势。本文在WebGIS技术基础上,以中国矿业大学为例,论述了基于MapObjects IMS及VB6.0语言的数字校园网上发布的实现过程。 相似文献
265.
土地利用动态管理系统研发中的若干问题研究 总被引:2,自引:0,他引:2
土地利用管理是土地管理的核心内容之一。土地利用动态变化加剧了土地管理的压力,建设具有辅助决策功能的土地利用动态信息系统是大势所趋。本文在阐述建设此系统的重要意义基础上,讨论了系统研发中几个关键问题,即“动态”管理的实现、空间数据和属性数据集成管理和决策的初步实现等。本文提出的解决方法,对于类似土地信息系统的建设具有普遍的指导意义。 相似文献
266.
熊庆文 《武汉大学学报(信息科学版)》2004,29(2):111-115
讨论了一个面向工作流的项目管理系统中 ,各类计划、实施、监督管理、汇总报表等结构化文档及非结构化文档的存储访问系统的构造方法 ,并设计与实现了一个数字化测绘生产管理系统实例 相似文献
267.
C. J. Hapke 《地球表面变化过程与地形》2005,30(6):679-697
High‐resolution historical (1942) and recent (1994) digital terrain models were derived from aerial photographs along the Big Sur coastline in central California to measure the long‐term volume of material that enters the nearshore environment. During the 52‐year measurement time period, an average of 21 000 ± 3100 m3 km?1 a?1 of material was eroded from nine study sections distributed along the coast, with a low yield of 1000 ± 240 m3 km?1 a?1 and a high of 46 700 ± 7300 m3 km?1 a?1. The results compare well with known volumes from several deep‐seated landslides in the area and suggest that the processes by which material is delivered to the coast are episodic in nature. In addition, a number of parameters are investigated to determine what influences the substantial variation in yield along the coast. It is found that the magnitude of regional coastal landslide sediment yield is primarily related to the physical strength of the slope‐forming material. Coastal Highway 1 runs along the lower portion of the slope along this stretch of coastline, and winter storms frequently damage the highway. The California Department of Transportation is responsible for maintaining this scenic highway while minimizing the impacts to the coastal ecosystems that are part of the Monterey Bay National Marine Sanctuary. This study provides environmental managers with critical background data on the volumes of material that historically enter the nearshore from landslides, as well as demonstrating the application of deriving historical digital terrain data to model landscape evolution. Published in 2005 by John Wiley & Sons, Ltd. 相似文献
268.
On the basis of about 300 earthquake wave forms observed in the Shidian M
S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to
estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3,
the seismic moments are 1010–1016 N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×105–20×105Pa. Through the statistical analyses of variation of corner frequency f
c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously
lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly
higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and
stress drops before and after the main shock have index significance to the precursory information before a strong earthquake.
The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main
shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of
lower stresses.
Foundation item: Scientific and Technological Key Project of Yunnan Province (2001NG46) 相似文献
269.
从信息技术的角度看,工程勘察实际上是一种“信息获取、信息理解和信息应用”的过程。作为一项技术和服务,工程勘察的信息化应由工程勘察业务信息化和工程勘察管理信息化两方面组成。工程勘察信息化的作用包括信息化辅助业务和管理、信息化支撑业务和管理以及信息化提升业务和管理三个层次。当前,有必要对工程勘察企业信息化的模式、工程勘察业务信息化提升的方式和工程勘察信息化的标准化等问题做进一步研究,以推动工程勘察信息化向深度和广度发展。 相似文献
270.
Local geography and gender are two major factors determining which crop varieties are cultivated in a case study of two rural villages in Bangladesh. This paper explores the interrelationships between gender, agrobiodiversity, and the use of, and preferences for, improved and local crop varieties. These are examined in relation to rice, minor field crops, and home garden fruits and vegetables. Reasons for both the displacement and the persistence of local varieties (LVs) are analysed in comparison to improved variety (IV) diffusion. The research evaluates agrobiodiversity through the number, types, and varieties of crops grown in fields and home gardens. The desired agroecological, economic, and cultural characteristics of crops grown document how respondents rank their variety preferences. Variety preferences and the perceived importance of LV preservation are compared with what is actually grown. The study indicates that there was little variation between villages in their approach towards the use of IV and LV rice; IVs were cultivated for their high yields and LV rice for taste and culinary uses. However, there were significant differences in relative agricultural dependence between the two villages which led to unique variety preferences. In both villages, women's preferences for IVs or LVs play a major role in crop choices, particularly as they manifest themselves in gendered domains of authority. 相似文献