全文获取类型
收费全文 | 48882篇 |
免费 | 12207篇 |
国内免费 | 18016篇 |
专业分类
测绘学 | 9687篇 |
大气科学 | 6529篇 |
地球物理 | 8815篇 |
地质学 | 32264篇 |
海洋学 | 9391篇 |
天文学 | 583篇 |
综合类 | 4209篇 |
自然地理 | 7627篇 |
出版年
2024年 | 380篇 |
2023年 | 1150篇 |
2022年 | 3130篇 |
2021年 | 3812篇 |
2020年 | 3007篇 |
2019年 | 3644篇 |
2018年 | 3077篇 |
2017年 | 2940篇 |
2016年 | 2854篇 |
2015年 | 3608篇 |
2014年 | 3384篇 |
2013年 | 4278篇 |
2012年 | 4646篇 |
2011年 | 4627篇 |
2010年 | 4534篇 |
2009年 | 4197篇 |
2008年 | 4243篇 |
2007年 | 4043篇 |
2006年 | 3870篇 |
2005年 | 3230篇 |
2004年 | 2450篇 |
2003年 | 1741篇 |
2002年 | 1750篇 |
2001年 | 1567篇 |
2000年 | 1297篇 |
1999年 | 548篇 |
1998年 | 220篇 |
1997年 | 164篇 |
1996年 | 102篇 |
1995年 | 73篇 |
1994年 | 64篇 |
1993年 | 46篇 |
1992年 | 61篇 |
1991年 | 23篇 |
1990年 | 46篇 |
1989年 | 13篇 |
1988年 | 15篇 |
1987年 | 26篇 |
1986年 | 33篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 26篇 |
1973年 | 4篇 |
1963年 | 4篇 |
1957年 | 18篇 |
1954年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
991.
992.
Early Yanshanian post-orogenic granitoids in the Nanling region
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Early Yanshanian magmatic suites predominate absolutely in the Nanling granite belt. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late orogenic event and the initiation of Pangaea break-up, indicating that a new orogenic Wilson cycle is about to start. Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous. 相似文献
993.
994.
995.
996.
997.
依据高温高压岩石破裂实验结果并结合理论分析,对 附近区域不同深度温压条件下岩石变形破坏性质及破坏失稳的力学行为进行了研究,在一次应力加载循环中,发生破坏的部位随时间具有向深部下迁的趋势。考虑到深度温压条件下岩石的渐进式破坏行为及突发失稳,对主震前震中附近区域小地震活动的增强、平静、活化等现象,以及b值等时间序列参数变化的可能机理进行初步探讨,并简单讨论了两类平静和两类b值变化的可能原因。 相似文献
998.
介绍了利用卫星云图资料估算黄河中游面雨量的基本方法:将GMS卫星1h间隔的可风和红外云图作为判别的两个特性进行分类,确定红外光线资料的所有最小值点作为对流核;多参照Negri-Adler的方法,应用斜率参数消除卷云;应用-维云模式确定红外线图上对流核的降水率,层状云降水通过一个温度阈值给出。另外,通过2001年7月26日至28日黄河流域出现的一次较强降雨过程进行应用分析,得出结论--利用卫星云图估算黄河中游地区平均雨量的方法具有很好的实用价值。 相似文献
999.
PRELIMINARY NUMERICAL STUDY OF TOPOGRAPHIC EFFECTS OF THE TIBETAN PLATEAU ON SURFACE DIRECT RADIATION 总被引:3,自引:0,他引:3
To improve the simulating ability of a model,this paper presents a scheme of calculatingdirect radiation at land surface with topography in the model.A numerical study is conducted forthe topographic effects of the Tibetan Plateau on the direct radiation using NCEP terrain data.Results show that,after taking account into the topographic radiation effect,the regional averageof the radiation over the Plateau obviously increases in the local early morning and late afternoon,but changes less around noon.The effect is stronger in winter than that in summer.Andheterogeneous topography has also affected the distribution of the radiation in this area.A simplenumerical experiment shows that considering the effect will lead ground temperature to increase onthe slope having more sunshine,and vice versa. 相似文献
1000.
According to statistic analysis on sea surface temperature(SST)anomaly features in theNorth Pacific in winters and springs prior to the summer flood/drought in the middle and lowerreaches of the Yangtze River(hereafter referred to as MLRY),a strong signal SST key area thataffects local flood/drought is put forward,that is the equatorial eastern Pacific.The response ofgeneral circulation in the Northern Hemisphere to SST anomaly in the key area is furtherinvestigated. The low frequency wave train structure of correlation between the eastern PacificSST and the height at 500 hPa in the Northern Hemisphere is also studied,which reflects thedynamic features of teleresponse of local flood/drought at extratropics to tropical SST anomaly.Through introducing SST anomaly in the strong signal area in numerical experiments,the flood inYangtze River Valley is successfully simulated and the similar wave train pattern in the flow field isobtained too.Altogether,the physical picture and dynamic mode of the flood in the Yangtze RiverValley are described in this work. 相似文献