全文获取类型
收费全文 | 33254篇 |
免费 | 18366篇 |
国内免费 | 42983篇 |
专业分类
测绘学 | 3216篇 |
大气科学 | 21185篇 |
地球物理 | 12213篇 |
地质学 | 34478篇 |
海洋学 | 16183篇 |
天文学 | 724篇 |
综合类 | 4228篇 |
自然地理 | 2376篇 |
出版年
2024年 | 157篇 |
2023年 | 313篇 |
2022年 | 574篇 |
2021年 | 902篇 |
2020年 | 1978篇 |
2019年 | 5439篇 |
2018年 | 5570篇 |
2017年 | 5310篇 |
2016年 | 5316篇 |
2015年 | 4785篇 |
2014年 | 4204篇 |
2013年 | 4840篇 |
2012年 | 4616篇 |
2011年 | 4426篇 |
2010年 | 4390篇 |
2009年 | 3707篇 |
2008年 | 3033篇 |
2007年 | 3008篇 |
2006年 | 2640篇 |
2005年 | 2492篇 |
2004年 | 2781篇 |
2003年 | 2508篇 |
2002年 | 2236篇 |
2001年 | 2014篇 |
2000年 | 1618篇 |
1999年 | 1584篇 |
1998年 | 1659篇 |
1997年 | 1724篇 |
1996年 | 1329篇 |
1995年 | 1293篇 |
1994年 | 1159篇 |
1993年 | 1126篇 |
1992年 | 959篇 |
1991年 | 719篇 |
1990年 | 687篇 |
1989年 | 568篇 |
1988年 | 483篇 |
1987年 | 380篇 |
1986年 | 308篇 |
1985年 | 240篇 |
1984年 | 273篇 |
1983年 | 163篇 |
1982年 | 200篇 |
1981年 | 141篇 |
1980年 | 107篇 |
1979年 | 111篇 |
1978年 | 47篇 |
1977年 | 44篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 893 毫秒
301.
Under the artificial condition the 59Fe morphology in sea water, its concentration in sediment and phytoplankton, its distribution and metabolism in tissue organs of marine animals were studied. The results showed that the morphology of 59Fe was in a particulate state in sea water. The adsorption rule of 59Fe by three kinds of sediments was similar. The concentration ability of 59Fe by phytoplankton was very strong. The critical concentration organs of S9Fe by marine animals were viscera. The gross radioactivity of 59Fe was mainly concentrated in protein. The concentration factor of 59Fe by DNA was the highest one. After excretion experiment, 59Fe of all the tissue organs was not detected. Small part of59Fe remained in the organic acid and protein state. There was a redistribution process in sediment for59Fe. 相似文献
302.
The relationship between tidal current field and sediment transport in the Huanghai Sea and the Bohai Sea 总被引:2,自引:0,他引:2
-Based on a two-dimensional numerical M2 tidal model of the Huanghai and Bohai Seas, sediment transport of particles with different sizes in the computational area is given. It is concluded that tidal currents play an important role in sediment transport and deposition in the Huanghai and Bohai Seas. 相似文献
303.
Wen Shengchang 《海洋学报(英文版)》1988,7(3):325-343
The method developed by Wen et al. (1988 a) for deriving theoretical wind wave frequency spectrum in deep water is extended to the case of water of finite depth, in which a parameter η=H/d is introduced, where H and d represent the average wave height and water depth respectively. The derived spectra reduce to those in deep water when η=0. The case of η=1/2 corresponds to waves impending to break because of the effect of the bottom. Simplified forms of spectra are given. The theoretical results agree with the observed spectra well. 相似文献
304.
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
305.
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
306.
Based on the analysis of new data of a total of 60 000 km, the authors propose a new spreading model of the tectonic evolution of the South China Sea Basin and suggest that magnetic anomalies in the Basin are the magnetic anomalies of a new type in marginal basins, that the tectonic development of the Basin can be divided into three seafloor spreading phases and that the southward migration of spreading ridge is related to the asymmetric spreading. 相似文献
307.
Based on the shear effect of internal wave currents in stratified fluid, the necessary condition for the possible existence of an internal wave and the sufficient condition under which there will be no internal wave are deduced starting from the continuity equation of incompressible fluid. The above two conditions are verified by the measured results from vertical current meter arraies at some observation stations in the Bohai Sea and the South Huanghai Sea. In the treatment of measured results, first of all, the tidal period components are separated from the measured currents by Fourier-analysis method, and then the internal wave currents of tidal period from the tidal period components in the light of some considerations. The analytical results of observed currents are well consistent with theoretical analysis. Furthermore, one can also deduce some features of internal waves therefrom. Consequently, it is concluded that the observation from a vertical current meter array is an important means to verif 相似文献
308.
AN ECOSYSTEM MODEL ANALYSIS OF THE EFFECT OF MINE TAILINGS ON THE EUPHOTIC ZONE OF A PELAGIC ECOSYSTEM 总被引:1,自引:0,他引:1
A computer analysis was performed on experimental results obtained when mine tailings were added to seawater. The Mixed Upper-Layer Ecotrophie Simulation (MULES) model was tested by changing the extinction coefficient and the abundance of heterotrophic zooflagellates. Increasing the extinction coefficient resulted in a delay of phytoplankton growth, an increase in zooplankton standing stock and better growth of autotrophic flagellates compared with diatoms. Zooflagellates in the ecosystem influence the growth of zooplankton; secondary production by zooplankton was markedly depressed at low levels of zooflagellates. These results are believed to be of general significance for the diagnosis of suspended sediment effects on planktonic ecosystems. 相似文献
309.
310.
We establish the equations of finite element approximation for three-dimensional ocean current and calculate the Kuroshio current in the eastern sea area off Taiwan Province. The interpolation error of finite element approximation is given as Eq. (3. 14). 相似文献