全文获取类型
收费全文 | 12345篇 |
免费 | 1662篇 |
国内免费 | 1494篇 |
专业分类
测绘学 | 2278篇 |
大气科学 | 1275篇 |
地球物理 | 2943篇 |
地质学 | 2565篇 |
海洋学 | 1059篇 |
天文学 | 281篇 |
综合类 | 1292篇 |
自然地理 | 3808篇 |
出版年
2024年 | 58篇 |
2023年 | 154篇 |
2022年 | 396篇 |
2021年 | 526篇 |
2020年 | 508篇 |
2019年 | 583篇 |
2018年 | 466篇 |
2017年 | 590篇 |
2016年 | 567篇 |
2015年 | 605篇 |
2014年 | 707篇 |
2013年 | 854篇 |
2012年 | 771篇 |
2011年 | 811篇 |
2010年 | 706篇 |
2009年 | 666篇 |
2008年 | 667篇 |
2007年 | 723篇 |
2006年 | 663篇 |
2005年 | 603篇 |
2004年 | 600篇 |
2003年 | 509篇 |
2002年 | 441篇 |
2001年 | 388篇 |
2000年 | 332篇 |
1999年 | 261篇 |
1998年 | 237篇 |
1997年 | 216篇 |
1996年 | 167篇 |
1995年 | 156篇 |
1994年 | 113篇 |
1993年 | 113篇 |
1992年 | 79篇 |
1991年 | 52篇 |
1990年 | 47篇 |
1989年 | 49篇 |
1988年 | 32篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
541.
基于3S技术的土地动态监管系统研究 总被引:1,自引:0,他引:1
研究目的:针对目前县级国土资源土地利用动态监管的现状和要求,探讨了采用信息化手段如移动执法和在线分析等工具辅助土地执法监察管理,建立土地动态监管新模式.研究方法:采用全B/S架构,ArcGIS Server Standard 9.3 GIS平台和ArcPad 7.1嵌入式GIS平台,建立土地动态监管系统.研究结论:利用3S技术建立的土地动态监管系统可以满足土地监管工作信息化需求,操作简单便捷,适合基层土地管理人员使用,同时有助于提高工作效率,降低调查成本,规范土地执法监察行为. 相似文献
542.
����ARģ�͵��Ϻ������������Ԥ����� 总被引:2,自引:1,他引:1
????AR?????????????????????????????????????AIC?????AR????????????????????,AR??4?????????????????????AR(4)???????????δ??10??????????????????? 相似文献
543.
Zongming Wang Yubo Zhang Bai Zhang Kaishan Song Zhixing Guo Dianwei Liu Fang Li 《中国地理科学(英文版)》2008,18(2):137-145
The landscape pattern of Da'an County, Northeast China has undergone significant changes since the 1950s as a result of climatic change and human activities. The aim of this paper is to quantitatively study landscape pattern and its spatial dynamics of Da'an County at the landscape level over the nearly 50-year span. Patch dynamics were examined according to land use and land cover change processes built from a series of images, as well as topographic maps, and temporal patterns built from landscape pattern metrics. The transition matrix of landscape patch types and changes of various landscape metrics were applied. The results showed that, from 1956 to 2000, the landscape within the study area had undertaken a complicated evolution in landscape structure and composition. The outstanding characteristic is that saline-alkali land increased and grassland decreased. As some smaller patches amalgamated, the heterogeneity of patch decreased. All those changes were the synthetic result of both climatic and anthropogenic influences, but the predominant factor was different in different parts. In the southern part of the study area, the landscape pattern changes resulted from the modification of climate obviously, while in the northern part, the landscape pattern changes were mainly caused by human activities, such as the conversion between farmland and saline-alkali land. This phenomenon showed that human activities played more important role in the north than in the south of Da'an County. 相似文献
544.
GU Xiaokun DAI Bing CHEN Baiming 《中国地理科学(英文版)》2008,18(1):41-46
The goal of land consolidation in China is still to develop agricultural production. The study of landscape effects of land consolidation projects (LCPs) faces many difficulties because of the lack of government's interest and data. This paper, taking Tianmen City of Hubei Province in Central China as an example, presents a methodology for analyzing landscape effects of LCPs by GIS and Fragstats3.3. It describes landscape effects with indexes of Patch Density (PD), Largest Patch Index (LPI), Landscape Shape Index (LSI), Interspersion and Juxtaposition Index (IJI), Aggregation Index (AI), and Shannon's Diversity Index (SHDI), showing more regular shape, simpler structure and less habitat diversity after LCPs. It computes ten landscape indexes of four categories of patches including Cultivated Land, Road, Water Channel, and River and Pond. The indexes show that 1) cultivated land becomes more fragmental in patch area, less irregular in patch shape and more concentrated in block; 2) the transport capacity of roads and irrigation and drainage capacity of water channels have been improved; 3) the landscape change of river and pond can be summarized as decreasing scale, more regular shape, reducing connectivity and diversity of the class. LCPs can facilitate agricultural production as well as protect cultivated land and food security. However, it is doubted that the increase of cultivated land from LCPs results from the reducing in landscape diversity of water area. 相似文献
545.
海峡两岸城市绿地遥感监测与对比分析 总被引:2,自引:1,他引:1
以福州和台北的ASTER和TM遥感影像为数据源,提取两市中心城区绿地信息并计算景观生态指标。对比分析结果表明:1988~2004年期间,两市中心城区面积增加,绿地面积及其所占比例减少,但福州城镇扩张速度和绿地面积所占比例下降幅度远大于台北;两市绿地斑块形状趋向简化,连通性变小,聚集程度降低;与2004年福州相比,2003年台北中心城区绿地的形状更规则,连通性更强,聚集程度较高。 相似文献
546.
蒋海良 《地球信息科学学报》2008,10(3):357-362
第二次全国农业普查户表、村表与农业用地表的耕地面积差异,主要是由设计普查指标、普查时点、统计口径、登录技术等因素所致。另外,村与村之间界线不清,普查员对三权(所有权、使用权、承包经营权)理解模糊,对农户承包口粮田、种粮大户、户之间土地流转等混淆,以及土地全部征收、土地部分征收、土地未征收、"预征土地"等导致耕地面积的差异。由于城市不断向四周拓展,占用了大量的耕地,土地整理、易地待保、占补平衡进入实质性操作,人们的生存环境受到影响,对耕地面积的差异评估,产生诸多值得深思的问题。 相似文献
547.
��³������ִ��������о� 总被引:3,自引:3,他引:0
????????1956??1999??????????????????????????顢?????顢?????????????????????????????б??????е??????Щ???????????????4??????У?1956??1978????????????????????????????????ε????Ms7.4?????????????й??1978??1985???1990??1995?????????????????????????鶫??????Ms6.2 ??Ms6.1?????й?? 相似文献
548.
����GPS�������е�������Ŀ������о� 总被引:8,自引:3,他引:5
?????????12??GPS???????????????????????????GPS???????????????????????????????????GPS?????????????б???????????????3mm?????????????????????????仯????????????????????????? 相似文献
549.
�봨8.0������ǰ��ؿǴ�ֱ�α���� 总被引:5,自引:0,他引:5
??????8.0?????????????????????????????????????Ms8.0?????????????α????????:???????????α???????????????????????????????????仯???????????????????????????????????????????????????????????????????????????????α??????? 相似文献
550.
�봨����ǿ��۲� 总被引:1,自引:0,他引:1
????????????????;???????????????????????????????????????????????????????????????????????????? 相似文献