全文获取类型
收费全文 | 621篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 17篇 |
地球物理 | 169篇 |
地质学 | 245篇 |
海洋学 | 48篇 |
天文学 | 77篇 |
综合类 | 1篇 |
自然地理 | 64篇 |
出版年
2019年 | 7篇 |
2017年 | 14篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 21篇 |
2013年 | 28篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 26篇 |
2009年 | 29篇 |
2008年 | 29篇 |
2007年 | 22篇 |
2006年 | 28篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1968年 | 4篇 |
1965年 | 6篇 |
1964年 | 4篇 |
1962年 | 4篇 |
1953年 | 5篇 |
1952年 | 4篇 |
1951年 | 5篇 |
1950年 | 4篇 |
1949年 | 8篇 |
排序方式: 共有635条查询结果,搜索用时 15 毫秒
71.
Sediments of eight groyne fields along the middle course of the River Elbe (river km 287?390) were geochemically studied. The 78 sediment samples were analysed for pH and grain size distribution. The grain size fraction < 2 μm was used for mineralogical and chemical analysis: semiquantitative clay mineral analysis; total element content (Al, Ca, Fe, K, Mn, Cd, Cr, Cu, Ni, Pb, Zn), total inorganic and organic C, and bonding form fractionation with a six‐step sequential chemical extraction. The latter was performed on selected samples (n = 32). The sediments along the Elbe's course are still contaminated with heavy metals far above the local geogenic background level. An enrichment factor of more than 15 was calculated for zinc. Cr and Ni are the elements with the lowest enrichment. The bonding form analysis of selected heavy metals shows a dominance of relatively immobile bonding forms, e. g. the moderately reducible and the residual fraction, which implies a relative low mobility potential. Only Zn poses a higher potential threat to the environment, since it has a higher percentage of the first three extracted phases: adsorbed, carbonate, and easily reducible fraction. 相似文献
72.
73.
朱义年 《中国地球化学学报》2003,22(4):302-312
Gneiss-distilled water interaction at room temperature was investigated with batch-reactors to study water-rock reaction and geochemical evolution of the aqueous phase with time. The ion concentrations in water were controlled not only by the dissolution of primary minerals, but also by the precipitation of secondary minerals. The decreasing fraction sizes of gneiss could favor dissolution and precipitation simultaneously. Ca^2 and K^ were the major cations, and HCO3^- was the major anion in water. All the ions except Ca^2 increased in concentration with time. The Ca^2 release from the rock to the aqueous phase was initially much faster than the release of K^ , Na^2 and Mg^2 . But after about 5 - 24 hours, the Ca^2 concentrations in water decreased very slowly with time and became relatively stable. During the experiment, the water varied from the Ca-( K)-HCO3-type water to the K-Ca-HCO3-type water, and then to the K-(Ca, Na)-HCO3-type water. The water-gneiss interaction was dominated by the dissolution of Kfeldspar in the solution. The remaining secondary minerals were mainly kaolinite, illite and K (Mg) -mica. 相似文献
74.
Hashimoto S Kurihara R Strüssmann CA Yamasaki T Soyano K Hara A Shiraishi H Morita M 《Marine pollution bulletin》2003,46(4):459-465
Endocrine disrupting chemicals such as organochlorines have been detected in a large number of marine fish. Histological observation of the gonads, measurement of serum vitellogenin (VTG) level and of liver polychlorinated biphenyl (PCB) content were performed to evaluate the reproductive health and the contamination with endocrine disruptors in bigeye tuna Thunnus obesus, collected in the northern Pacific Ocean in 1999 and 2000. Abnormalities commonly found in species affected by endocrine disruptors such as the presence of oocytes in the testis or elevated serum VTG levels were not found in any of males examined. Both males and females had only small amounts of liver PCB content. The results suggest that currently there is little if any risk of organochlorine contamination or endocrine disruption of gonadal function in bigeye tuna from the northern Pacific Ocean. However, further studies are necessary to evaluate the health status of the open sea fishery resources. 相似文献
75.
76.
77.
78.
79.
Results of a semi-implicit two-step method for the simulation of markedly nonlinear flow in coastal seas 总被引:1,自引:0,他引:1
Results of a numerical method for the simulation of nonlinear flow in coastal seas are presented. The method is based on a neutral semi-implicit scheme which is modified into a stability-enhancing two-step algorithm. By means of this method the simulation of highly nonlinear flow patterns is possible in a stable and economic way. Three examples of models of different North Sea coastal regions are discussed under certain aspects to demonstrate the reliability of the method. 相似文献
80.