全文获取类型
收费全文 | 9628篇 |
免费 | 431篇 |
国内免费 | 123篇 |
专业分类
测绘学 | 315篇 |
大气科学 | 778篇 |
地球物理 | 2190篇 |
地质学 | 3401篇 |
海洋学 | 756篇 |
天文学 | 1753篇 |
综合类 | 40篇 |
自然地理 | 949篇 |
出版年
2022年 | 41篇 |
2021年 | 111篇 |
2020年 | 144篇 |
2019年 | 199篇 |
2018年 | 259篇 |
2017年 | 257篇 |
2016年 | 339篇 |
2015年 | 271篇 |
2014年 | 305篇 |
2013年 | 572篇 |
2012年 | 365篇 |
2011年 | 505篇 |
2010年 | 437篇 |
2009年 | 571篇 |
2008年 | 496篇 |
2007年 | 447篇 |
2006年 | 418篇 |
2005年 | 386篇 |
2004年 | 388篇 |
2003年 | 296篇 |
2002年 | 301篇 |
2001年 | 178篇 |
2000年 | 203篇 |
1999年 | 159篇 |
1998年 | 164篇 |
1997年 | 135篇 |
1996年 | 139篇 |
1995年 | 123篇 |
1994年 | 117篇 |
1993年 | 102篇 |
1992年 | 114篇 |
1991年 | 107篇 |
1990年 | 76篇 |
1989年 | 75篇 |
1988年 | 87篇 |
1987年 | 89篇 |
1986年 | 75篇 |
1985年 | 96篇 |
1984年 | 89篇 |
1983年 | 94篇 |
1982年 | 84篇 |
1981年 | 95篇 |
1980年 | 82篇 |
1979年 | 82篇 |
1978年 | 66篇 |
1977年 | 53篇 |
1976年 | 45篇 |
1975年 | 38篇 |
1974年 | 52篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
The Central Trough of the North Sea is not a simple rift graben. It is an elongated area of regional subsidence which was initiated in mid Cretaceous times and continued to subside through to the late Tertiary. Its form is not representative of pre-mid Cretaceous tectonics.In Late Permian times the North Sea was divided into a northern and southern Zechstein basin by the E-W trending Mid North Sea-Ringkøbing-Fyn High. The latter was dissected by a narrow graben trending NNW through the Tail End Graben and the Søgne Basin. The Feda Graben was a minor basin on the northern flank of the Mid North Sea High at this time. This structural configuration persisted until end Middle Jurassic times when a new WNW trend separated the Tail End Graben from the Søgne Basin. Right lateral wrench movement on this new trend caused excessive subsudence in the Tail End and Feda Grabens while the Søgne Basin became inactive.Upper Jurassic subsidence trends continued during the Early Cretaceous causing the deposition of large thicknesses of sediments in local areas along the trend. From mid Cretaceous times the regional subsidence of the Central Trough was dominant but significant structural inversions occurred in those areas of maximum Early Cretaceous and Late Jurassic subsidence. 相似文献
102.
103.
104.
105.
106.
Michael G. Simpson 《Marine environmental research》1992,34(1-4)
As part of a joint workshop organised by the International Council for the Exploration of the Sea (ICES) and the Intergovernmental Oceanographic Commission (IOC) on biological effects monitoring techniques. dad (Limanda limanda) were examined from six spaced stations along a 200 km transect extending from near the mouth of the Elbe River out to the Dogger Bank in the North Sea. Based on historical data, differences in contaminant concentrations in sediments exist along the transect (lipophilic organic xenobiotics at the inshore sites and heavy metals offshore over the Dogger Bank). The most contaminated site sampled was the most inshore, the least contaminated was approximately midway along the transect, with contamination building up again over the farthest point along the transect, over the Dogger Bank. Multiple organs and tissues were examined for full pathology from each fish sampled. Only liver data are presented here (11–20 livers per station). The most significant lesions were considered to be well-developed foci of cellular alteration, high mitotic activity and high neutral lipid accumulation in livers from dab sampled from the most inshore site examined. Livers from the least-contaminated station showed minimal evidence of such changes. Foci of cellular alteration and neutral lipid accumulation were also seen in dab liver sampled from fish from the Dogger Bank site. Thus far, the hepatic changes seen correlate well with the most contaminated sites along the transect. The value of comprehensively examining the histopathology of an organ of toxicological significance, such as the liver in a European species of flatfish, is demonstrated. 相似文献
107.
Martin Hassellv 《Marine Chemistry》2005,94(1-4):111
A new method for the characterization of chromophoric colloidal organic matter in seawater has been applied to samples from the Baltic Sea, Kattegatt and Skagerrak seas. Size fractionation of the sample by Flow Field-Flow Fractionation and measurement of the fluorescent and UV absorbing properties of the individual size fractions result in a relative molar mass distribution (RMM) of the optical properties. The RMM distributions have been used to estimate number and weight average relative molar masses, and polydispersity indices. At least two sources of coloured organic matter were identified from the ratio of fluorescence to UV: the Baltic surface water and the Skagerrak deep water. The dominating processes were mixing and dilution, but processes such as photo bleaching of fluorescence are also believed to be important. The RMM distribution derived from UV detection (1150–1300 Dalton) increased with increasing salinity while that derived for fluorescence (1500–1250 Dalton) decreased with increasing salinity. The specific UV absorbance taken as a proxy of the aromaticity of the chromophoric organic material showed decreasing trend with both increasing salinity and increasing UV derived weight average relative molar mass. Increasing polydispersity of the colloidal material was also observed as a function of salinity. 相似文献
108.
109.
通过对东北太平洋海域中国多金属结核开辟区沉积物间隙水中铜、锰、镍等微量元素的详细研究表明,锰主要受沉积环境的影响,其含量的变化范围在0.16~8.61μg/dm3之间;铜和镍则主要与表层海水的初级生产力有关,研究区内间隙水中铜和镍含量的变化范围分别为0.16~20.8和0.80~3.12μg/dm3,且这些元素在沉积物—水界面处均存在最大浓度梯度.利用“Fick扩散定律”计算表明,锰在研究区主要是从上覆海水向沉积物扩散,是沉积物中锰的主要来源之一;而铜和镍则是从沉积物向上覆海水扩散,是底层海水中铜和镍的主要来源。与表层海水中铜和镍向底层海水的输送通量计算结果相比,底层海水中铜和镍的含量主要受沉积物的控制. 相似文献
110.
cDNA clones for glutathione S-transferases A (GST-A) and A1 (GST-A1) from plaice (Pleuronectes platessa) were expressed as N-terminally 6XHis tagged proteins in Escherichia coli and purified to homogeneity from Ni-NTA silica. GST-A was an efficient catalyst for conjugation of unsaturated alkenals derived from peroxidation of polyunsaturated fatty acids with the highest activity observed with trans-non-2-enal (8 micromol min(-1) mg(-1)). GST-A1 was a very efficient Se-independent glutathione peroxidase with an activity towards cumene hydroperoxide of 25 micromol min(-1) mg(-1). Although the enzymes exhibited moderately high activities towards the model substrate 1-chloro-2,4-dinitrobenzene (CDNB) they exhibited little or no activity towards other common prototypical xenobiotic substrates. Together with data for ontogeny, tissue distribution and inducibility of these enzymes, we contend that a primary function of these enzymes is protection from the harmful effects of lipid peroxidation products generated naturally or exacerbated by xenobiotic exposure. 相似文献