全文获取类型
收费全文 | 15807篇 |
免费 | 3058篇 |
国内免费 | 4086篇 |
专业分类
测绘学 | 1238篇 |
大气科学 | 3131篇 |
地球物理 | 3991篇 |
地质学 | 8235篇 |
海洋学 | 2067篇 |
天文学 | 603篇 |
综合类 | 1627篇 |
自然地理 | 2059篇 |
出版年
2024年 | 78篇 |
2023年 | 311篇 |
2022年 | 874篇 |
2021年 | 982篇 |
2020年 | 854篇 |
2019年 | 936篇 |
2018年 | 1055篇 |
2017年 | 904篇 |
2016年 | 977篇 |
2015年 | 839篇 |
2014年 | 1042篇 |
2013年 | 1039篇 |
2012年 | 996篇 |
2011年 | 1009篇 |
2010年 | 1003篇 |
2009年 | 917篇 |
2008年 | 828篇 |
2007年 | 721篇 |
2006年 | 609篇 |
2005年 | 565篇 |
2004年 | 447篇 |
2003年 | 401篇 |
2002年 | 375篇 |
2001年 | 421篇 |
2000年 | 451篇 |
1999年 | 626篇 |
1998年 | 525篇 |
1997年 | 473篇 |
1996年 | 471篇 |
1995年 | 368篇 |
1994年 | 360篇 |
1993年 | 307篇 |
1992年 | 284篇 |
1991年 | 186篇 |
1990年 | 156篇 |
1989年 | 126篇 |
1988年 | 101篇 |
1987年 | 71篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 25篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1958年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
本文揭示了天津海岸带影响经济开发的四个方面的地质环境特点;着重探讨三个方面的环境工程地质问题;并防止其形成和减轻地灾害的对策进行了研究。 相似文献
84.
85.
Numericalsimulationofthree-dimensionaltidalcurrentintheBobalSea¥DenZhenxing;YangLianwu;andJoseOzer(ReceivedMay1,1993;accepted... 相似文献
86.
The 25-h measurements of current speed, flow direction, water depth, suspended sediment concentration and salinity were carried out at six anchored stations in the study area during spring and neap tides in winter of 1987 and summer of 1989. Caculations and analyses of the data obtained show that large amounts of suspended sediments are moved back and forth under the action of tidal current, and the net transport of sediment is small, with its predominance upstream in winter and downstream in summer. These calculations and analyses also suggest that the advective transport of sediment is dominant, while the vertical gravitational circulation of the suspended sediment comes next. Meantime, it is indicated that tidal currents play a major role in the suspended sediment transport, and residual flows have effect on the net transport of the suspended sediment, which is more remarkable during neap tide than during spring tide. 相似文献
87.
88.
本文报道了文昌鱼哈氏窝匀浆刺激蟾蜍足细胞释放精子过程所发生的超微结构变化,进一步证实这种匀浆含有类似脊椎动物促黄体生成素活性物质。 相似文献
89.
The present paper deals with the ultrastructural changes of oocyte in the process of maturing in pen shell Atrinapectinata Linne. When it develops from the antecedent growth period to the accelerating growth period the annulate lamellae emerge, the RER better develop, the yolk granules with single and double layer membrane and are visible. In the well-developed mitochondria there is yolk stored. The Golgi vacuoles are brewing yolk granules. At the mature period the annulate lamellae and the Golgi bodies disappear, and there are only a few RER and mitochondria with poor cristae in the cytoplasm. All these might be well used for judging the maturity of the ootids in the process of the artificial propagation. 相似文献
90.
Study of zooplankton ecology in Zhejiang coastal upwelling system-Zooplankton biomass and abundance of major groups 总被引:1,自引:0,他引:1
He Dehu Yang Guanming Fang Shaojin Shen Weilin Liu Hongbin Gao Aigen Huang Shuxin 《海洋学报(英文版)》1988,7(4):607-620
The studied area is a shallow water area that belongs to the East China Sea continent shelf. The distribution of zooplankton biomass is higher inshore than offshore. The maximum abundance is in the inshore edge of the centre of upwelling, which is the superposed area of the salinity front and temperature front, due to the fact that the mixture of three different waters has brought about a concentration of nutrients. The herbivorous Euphausia, Copepoda and Tunicata are the major groups of the abundant area. Tunicata possess the possibility to compete against other kinds of herbivorous zooplankton. This means that there is negative correlation between the distribution of Tunicata and that of Copepoda and Euphausia. The positions of maximum areas of zooplankton biomass, phytoplankton individual and the concentration of phosphates and chlorophyll-a overlap one another. In the centre of upwelling, zooplankton can not adapt itself to the environment of lower temperature and less oxygen even with rich nutrient 相似文献