全文获取类型
收费全文 | 16159篇 |
免费 | 3705篇 |
国内免费 | 5086篇 |
专业分类
测绘学 | 2114篇 |
大气科学 | 2741篇 |
地球物理 | 3497篇 |
地质学 | 9939篇 |
海洋学 | 2252篇 |
天文学 | 396篇 |
综合类 | 1735篇 |
自然地理 | 2276篇 |
出版年
2024年 | 127篇 |
2023年 | 369篇 |
2022年 | 990篇 |
2021年 | 1155篇 |
2020年 | 948篇 |
2019年 | 1123篇 |
2018年 | 1191篇 |
2017年 | 1000篇 |
2016年 | 1077篇 |
2015年 | 1186篇 |
2014年 | 1225篇 |
2013年 | 1335篇 |
2012年 | 1447篇 |
2011年 | 1416篇 |
2010年 | 1384篇 |
2009年 | 1230篇 |
2008年 | 1108篇 |
2007年 | 984篇 |
2006年 | 866篇 |
2005年 | 722篇 |
2004年 | 534篇 |
2003年 | 440篇 |
2002年 | 463篇 |
2001年 | 407篇 |
2000年 | 371篇 |
1999年 | 341篇 |
1998年 | 221篇 |
1997年 | 217篇 |
1996年 | 188篇 |
1995年 | 143篇 |
1994年 | 171篇 |
1993年 | 115篇 |
1992年 | 95篇 |
1991年 | 68篇 |
1990年 | 54篇 |
1989年 | 41篇 |
1988年 | 45篇 |
1987年 | 33篇 |
1986年 | 15篇 |
1985年 | 22篇 |
1984年 | 4篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 14篇 |
1976年 | 4篇 |
1958年 | 10篇 |
1957年 | 8篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
341.
342.
一种组合优化的多边形化简方法 总被引:2,自引:0,他引:2
以多边形轮廓为目标 ,依据曲线特征点将其分解为一系列的弯曲特征 ,并对此弯曲特征集实施组合优化 ,将入围弯曲首尾相连 ,即可得到最终的化简结果 相似文献
343.
Glacier inventory compilation during the past 20 years and modifications of that for the Eastern Pamir and Banggong Lake indicate that there are 46,342 modern glaciers with a total area and volume of 59415 km2 and 5601 km3 respectively in China. These glaciers can be classified into maritime and continental (including sub-continental and extremely continental) types. Researches show that glaciers in China have been retreating since the Little Ice Age and the mass wastage was accelerated during the past 30 to 40 years. Being an important part of glaciological studies in China, ice core climatic and environmental studies on Tibetan Plateau and in the Antarctica have provided abundant, high resolution information about past climatic and environmental evolution over the Tibetan Plateau and Antarctica. Except for different parameters recorded in ice cores relating to climate and environment changes on Tibetan Plateau, records from ice cores extracted from different glaciers show that the discrepancies in climatic and environmental changes on the north and south parts of the plateau may be the consequence of different influencing effects from terrestrial and solar sources. Glaciological and meteorological phenomena imply that Lambert Glacier valley is an important boundary of climate in the east Antarctica, which is thought to be connected with cyclonic activities and Circum-polar Waves over the Antarctica. 相似文献
344.
Red tides are one of the main coastal catastrophic events in Guangdong Province of southern China. The comparison between the number of red tide events and the development indexes of cities along the coasts of the province shows that the regional differences in red tide outbreaks has close relations with the coastal urban developments. The cause for an initiation of red tide blooms may be natural factors, while wastewater caused by the fast development of population, industry and aquiculture of the coastal cities enhanced the blooms. It may explain why the two periods of frequent outbreaks of the red tides over the last two decades matched the urban developments in the coastal areas of Guangdong not only spatially but also temporally. The red tides in the first period were restricted only to the coasts of middle Guangdong, where urbanization process was at a higher speed than the other coastal areas of the province. In the second period, fast development of the coastal cities in eastern Guangdong led to an increase in the occurrence of red tides in local sea areas of the same coasts. 相似文献
345.
On August 5, 2001, Shanghai was struck by a torrential rainfall due to the passage of a tropical depression (TD). The rainfall intensity has been the strongest in recent 50 years. In this paper, a set of mesoscale re-analyses data and the planetary boundary layer observation from a wind profiler are used to understand the possible mechanism of such a heavy rain. Results show that the outburst of a southerly jet in the lower atmosphere triggered the explosive development of cyclonically vertical vorticity in the region with steep potential temperature surfaces in front of the TD; while the cyclonic vorticity increased notably at higher levels due to the small atmospheric vertical stability of westerly currents in the vicinity of Shanghai. The simultaneous sharp development of cyclonic vorticity at different levels should be the main cause for the torrential rainfall. 相似文献
346.
山西大同-阳高地震活动背景 总被引:2,自引:1,他引:2
通过对大同盆地历史地震活动及大同盆地历史地震活动与华北地震区、山西地震带强震活动的关系的研究,得出山西大同-阳高1989年6.1级地震活动是这一地区历史地震的延续,是华北北部中强地震活动的重要组成部分,具有广义前震的重要意义,其后对应发生的河北张北6.2级地震。标志着华北地震区的地震活动期已进入尾声。 相似文献
347.
Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region. 相似文献
348.
349.
Introduction The Great North China, located at longitude 106E to 124E and latitude 31N to 42N, in-cludes three secondary active tectonic blocks, Ordos, Yanshan and North China plain (Figure 1). The geological tectonics of these three secondary blocks is much different from each other. As a stable block with high rigidity, the Ordos block is mostly surrounded by down-faulted basins with an inactive interior since Cenozoic, although the fault zones along its boundary are strongly active wi… 相似文献
350.
Introduction The Xiuyan earthquake(MS=5.4)on Nov.29,1999,occurred between Hushan town and Pi-anling town at the southeast end of the aftershocks of Haicheng earthquake(MS=7.3).These two earthquakes′sequences are highly similar in the way that the foreshocks are very frequent,focal mechanisms of the main shocks are about the same and fault strikes are approximately in the same direction.It is important to study these earthquakes for further research on seismogenesis to fore-cast earthquake… 相似文献