全文获取类型
收费全文 | 21559篇 |
免费 | 4213篇 |
国内免费 | 5830篇 |
专业分类
测绘学 | 2101篇 |
大气科学 | 3817篇 |
地球物理 | 5032篇 |
地质学 | 11837篇 |
海洋学 | 3203篇 |
天文学 | 766篇 |
综合类 | 2127篇 |
自然地理 | 2719篇 |
出版年
2024年 | 126篇 |
2023年 | 409篇 |
2022年 | 1136篇 |
2021年 | 1374篇 |
2020年 | 1172篇 |
2019年 | 1295篇 |
2018年 | 1403篇 |
2017年 | 1217篇 |
2016年 | 1286篇 |
2015年 | 1208篇 |
2014年 | 1391篇 |
2013年 | 1467篇 |
2012年 | 1472篇 |
2011年 | 1500篇 |
2010年 | 1473篇 |
2009年 | 1309篇 |
2008年 | 1278篇 |
2007年 | 1051篇 |
2006年 | 951篇 |
2005年 | 852篇 |
2004年 | 695篇 |
2003年 | 681篇 |
2002年 | 721篇 |
2001年 | 711篇 |
2000年 | 637篇 |
1999年 | 758篇 |
1998年 | 601篇 |
1997年 | 523篇 |
1996年 | 504篇 |
1995年 | 407篇 |
1994年 | 392篇 |
1993年 | 336篇 |
1992年 | 293篇 |
1991年 | 196篇 |
1990年 | 161篇 |
1989年 | 137篇 |
1988年 | 112篇 |
1987年 | 78篇 |
1986年 | 62篇 |
1985年 | 53篇 |
1984年 | 35篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1958年 | 12篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
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
94.
95.
Numericalsimulationofthree-dimensionaltidalcurrentintheBobalSea¥DenZhenxing;YangLianwu;andJoseOzer(ReceivedMay1,1993;accepted... 相似文献
96.
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
97.
98.
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
99.
A nutrient dynamic model coupled with a 3D physical model has been developed to study the annual cycle of phytoplankton production in the Yellow Sea. The biological model involves interactions between inorganic nitrogen (nitrate and ammonium), phosphate and phytoplankton biomass. The model successfully reproduces the main features of phytoplankton-nutrient variation and dynamics of production. 1. The well-mixed coastal water is characterized by high primary production, as well as high new production. 2. In summer, the convergence of tidal front is an important hydrodynamic process, which contributes to high biomass at frontal areas. 3. The evolution of phytoplankton blooms and thermocline in the central region demonstrate that mixing is a dominant factor to the production in the Yellow Sea. In this simulation, nitrate- and ammonium-based productions are estimated regionally and temporally. The northern Yellow Sea is one of the highly ranked regions in the Yellow Sea for the capability of fixing carbon and nitrogen. The annual averaged f-ratio of 0.37 indicates that regenerated production prevails over the Yellow Sea. The result also shows that phosphate is the major nutrient, limiting phytoplankton growth throughout the year and it can be an indicator to predict the bloom magnitude. Finally, the relative roles of external nutrient sources have been evaluated, and benthic fluxes might play a significant role in compensating 54.6% of new nitrogen for new production consumption. 相似文献
100.
The probability of fractal determination of coastal types based on GIS is preliminarily discussed with China as an example. Finally, some significant conclusions are drawn: (1) The fractal dimension of coastline of the bedrock coast is larger than that of the plain coast on the same scale map; (2) As far as the bedrock coast is concerned, the larger fractal dimension of coastline of the bedrock coast on the same scale map indicates that the bedrock coast is probably not typical; (3) As far as the plain coast is concerned, the smaller fractal dimension of coastline of the plain coast on the same scale map indicates that it is probably the silt plain coast; (4) The different substantial compositions affect the fractal dimensions of coastlines of different coastal types. In general, the coast which lies in the north of the Hangzhou Bay consists of sand mainly, its surface is flat, and it is connected with the coastal plain, its landform is broad shoal, its total change is comparatively homogenous in the tidal dynamic process, and thus, the relatively smaller fractal dimension of coastline results from this. For the bedrock coast, there is more bedrock, the coastline is comparatively smooth and straight, being affected by the faults and ocean dynamic process, which result in the larger fractal dimension. 相似文献