全文获取类型
收费全文 | 6570篇 |
免费 | 1383篇 |
国内免费 | 1782篇 |
专业分类
测绘学 | 944篇 |
大气科学 | 899篇 |
地球物理 | 1265篇 |
地质学 | 3934篇 |
海洋学 | 1041篇 |
天文学 | 129篇 |
综合类 | 466篇 |
自然地理 | 1057篇 |
出版年
2024年 | 23篇 |
2023年 | 91篇 |
2022年 | 278篇 |
2021年 | 366篇 |
2020年 | 299篇 |
2019年 | 383篇 |
2018年 | 327篇 |
2017年 | 336篇 |
2016年 | 347篇 |
2015年 | 351篇 |
2014年 | 392篇 |
2013年 | 487篇 |
2012年 | 544篇 |
2011年 | 540篇 |
2010年 | 543篇 |
2009年 | 552篇 |
2008年 | 528篇 |
2007年 | 518篇 |
2006年 | 482篇 |
2005年 | 444篇 |
2004年 | 330篇 |
2003年 | 265篇 |
2002年 | 285篇 |
2001年 | 260篇 |
2000年 | 204篇 |
1999年 | 117篇 |
1998年 | 65篇 |
1997年 | 64篇 |
1996年 | 58篇 |
1995年 | 33篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 28篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1957年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有9735条查询结果,搜索用时 15 毫秒
1.
2.
本文介绍了1994年7月SL-9彗星撞击木星期间3.6cm和12cm射电连续谱观测的结果.在3.6cm波长上,撞击事件无明显的视效应,在12cm波长上,木星的射电平均视流量增加约20%. 相似文献
3.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
4.
WEIHai-quan JINBo-lu LIUYong-shun 《东北亚地学研究》2004,7(1):28-35
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption. 相似文献
5.
6.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
7.
8.
9.
华北地台东部石炭系—二叠系优质煤储层形成分布控制因素 总被引:5,自引:1,他引:4
优质煤储层在此指厚度大、分布广、储集物性好的煤层。沉积相对优质煤储层的形成和分布有重要控制作用。通过浅海和泻湖淤积填平发育起来的潮坪环境和三角洲环境是最有利的优质煤储层形成环境,煤储层厚度大、分布广。沉积环境对煤储层中的灰分含量和镜质组含量有重要影响,而灰分含量和镜质组含量又直接影响煤储层的储集物性。灰分充填了煤储层中的孔隙,其含量越高,储集物性越差;镜质组有利于割理的形成,其含量越高,储集物性越好。由于在灰分含量、煤岩显微组分等方面的差异,潮坪环境沉积的煤储层的储集物性优于三角洲的煤储层,下三角洲平原沉积的煤储层优于上三角洲平原沉积的煤储层。海平面变化对优质煤储层的形成和分布也有重要控制作用。高位体系煤储层富集,单层厚度大,横向分布相当稳定,尤其是高位体系域晚期,是形成优质煤储层最有利的层位。而水进体系域煤储层稀少,单层厚度小,横向分布不稳定,不利于优质煤储层形成。 相似文献
10.
Development of a 3D GIS and its application to karst areas 总被引:1,自引:0,他引:1
There is a growing interest in modeling and analyzing karst phenomena in three dimensions. This paper integrates geology,
groundwater hydrology, geographic information system (GIS), database management system (DBMS), visualization and data mining
to study karst features in Huaibei, China. The 3D geo-objects retrieved from the karst area are analyzed and mapped into different
abstract levels. The spatial relationships among the objects are constructed by a dual-linker. The shapes of the 3D objects
and the topological models with attributes are stored and maintained in the DBMS. Spatial analysis was then used to integrate
the data in the DBMS and the 3D model to form a virtual reality (VR) to provide analytical functions such as distribution
analysis, correlation query, and probability assessment. The research successfully implements 3D modeling and analyses in
the karst area, and meanwhile provides an efficient tool for government policy-makers to set out restrictions on water resource
development in the area. 相似文献