全文获取类型
收费全文 | 8708篇 |
免费 | 2140篇 |
国内免费 | 3013篇 |
专业分类
测绘学 | 1332篇 |
大气科学 | 1350篇 |
地球物理 | 2075篇 |
地质学 | 4892篇 |
海洋学 | 1833篇 |
天文学 | 114篇 |
综合类 | 916篇 |
自然地理 | 1349篇 |
出版年
2024年 | 63篇 |
2023年 | 208篇 |
2022年 | 591篇 |
2021年 | 736篇 |
2020年 | 528篇 |
2019年 | 653篇 |
2018年 | 594篇 |
2017年 | 536篇 |
2016年 | 563篇 |
2015年 | 638篇 |
2014年 | 628篇 |
2013年 | 770篇 |
2012年 | 765篇 |
2011年 | 812篇 |
2010年 | 780篇 |
2009年 | 686篇 |
2008年 | 636篇 |
2007年 | 662篇 |
2006年 | 574篇 |
2005年 | 485篇 |
2004年 | 374篇 |
2003年 | 234篇 |
2002年 | 220篇 |
2001年 | 249篇 |
2000年 | 183篇 |
1999年 | 159篇 |
1998年 | 90篇 |
1997年 | 89篇 |
1996年 | 65篇 |
1995年 | 54篇 |
1994年 | 37篇 |
1993年 | 47篇 |
1992年 | 26篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 16篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1958年 | 3篇 |
1957年 | 4篇 |
1954年 | 6篇 |
1937年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
利用激光粒度仪测试超细煤粉的粒度。对测试超细煤粉试样粒度时的试样浓度、测试温度、分散时间、分散剂的种类及浓度等方面的影响进行了实验研究,给出了激光粒度仪测试超细煤粉粒度的最佳实验条件。 相似文献
162.
163.
164.
165.
The Zhangjiakou–Penglai seismotectonic zone (ZPSZ) lies in the northern part of North China and extends along the Zhangjiakou–Beijing–Tianjin–Bohai Bay–Penglai–Yellow Sea. It is about 900 km long and some 250 km wide in a northwest direction. The great Sanhe-Pinggu (MS=8.0) earthquake occurred on September 1679 and the Tangshan (MS=7.8) earthquake on July 1976 caused serious economic and life losses. According to some differences in crust structure and regional tectonic stress field, the ZPSZ is divided into western and eastern segment by the 117°E line for study on long-term seismic hazard analysis. An analysis of Gutenberg–Richter's empirical relation of earthquake-frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a Poisson process, and these calculations indicate that the earthquake occurrence probability of MS=6.0–6.9 is 0.77–0.83 in the eastern segment and the earthquake occurrence probability of MS=7.0–7.9 is 0.78–0.80 in the western segment of the ZPSZ during a period from 2005 to 2015. 相似文献
166.
呼和浩特市城市边缘区景观格局动态变化研究 总被引:2,自引:0,他引:2
利用GIS技术对1987,2000年两期航空遥感影像进行空间叠加对比分析,从斑块及景观2个尺度对呼和浩特市城市边缘区景观格局变化进行了研究。结果表明:在斑块尺度上,边缘区两期景观结构均以农田景观为基质,研究期内,农田景观、草地景观等缓慢减少,建筑景观明显增多;在景观尺度上,边缘区景观多样性指数趋于增大,优势度指数趋于降低.景观组分趋于复杂化、破碎化和多元化。分析其影响因素可知:经济发展和城市化的加快、政策导向是变化的根本原因,人口的增加、土地利用方式的改变是变化的直接原因。 相似文献
167.
提出了一种基于DCT变换的盲图像水印算法。实验表明 ,该算法对典型攻击具有较好的鲁棒性。 相似文献
168.
Possible Impacts of the Arctic Oscillation on the Interdecadal Variation of Summer Monsoon Rainfall in East Asia 总被引:18,自引:5,他引:18
The influences of the wintertime AO (Arctic Oscillation) on the interdecadal variation of summer monsoon rainfall in East Asia were examined. An interdecadal abrupt change was found by the end of the 1970s in the variation of the AO index and the leading principal component time series of the summer rainfall in East Asia, The rainfall anomaly changed from below normal to above normal in central China, the southern part of northeastern China and the Korean peninsula around 1978. However,the opposite interdecadal variation was found in the rainfall anomaly in North China and South China.The interdecadal variation of summer rainfall is associated with the weakening of the East Asia summer monsoon circulation. It is indicated that the interdecadal variation of the AO exerts an influence on the weakening of the monsoon circulation. The recent trend in the AO toward its high-index polarity during the past two decades plays important roles in the land-sea contrast anomalies and wintertime precipitation anomaly. The mid- and high-latitude regions of the Asian continent are warming, while the low-latitude regions are cooling in winter and spring along with the AO entering its high-index polarity after the late 1970s. In the meantime, the precipitation over the Tibetan Plateau and South China is excessive, implying an increase of soil moisture. The cooling tendency of the land in the southern part of Asia will persist until summer because of the memory of soil moisture. So the warming of the Asian continent is relatively slow in summer. Moreover, the Indian Ocean and Pacific Ocean which are located southward and eastward of the Asian land, are warming from winter to summer. This suggests that the contrast between the land and sea is decreased in summer. The interdecadal decrease of the land-sea heat contrast finally leads to the weakening of the East Asia summer monsoon circulation. 相似文献
169.
In this paper, we discuss the development of electronic atlas in China, with focus on the issues of visualization. We particularly categorise this development into four periods, and then analyse the characters in each period and discuss the visualization issues. The four periods are highlighted: 1) Infant period (<1990) characterized as computer assisted mapping with products of screen maps; 2) Starting period (1991-1995) characterized as object-oriented mapping with products of interactive maps/atlases; 3) Advancing period (1996-2000) characterized as integrated mapping with products of multimedia cartographic maps; 4) New era (> 2001) characterized as web mapping and adaptive map design with products of Internet maps and atlas as well as adaptive maps. It is obvious that the development follows the logical way from static to dynamic, and even real time visualization, from single user to multiple users, from presentation to exploration for effective communication and knowledge construction. Current research and development projects are focused on customisation of atlas information systems for real-time tasks, Internet operability, small displays and mobile environments. The major challenges involved in each of such customisation processes are identified and commented in relation to the further development of visualization. 相似文献
170.