全文获取类型
收费全文 | 4247篇 |
免费 | 183篇 |
国内免费 | 58篇 |
专业分类
测绘学 | 102篇 |
大气科学 | 333篇 |
地球物理 | 906篇 |
地质学 | 1525篇 |
海洋学 | 418篇 |
天文学 | 780篇 |
综合类 | 20篇 |
自然地理 | 404篇 |
出版年
2022年 | 18篇 |
2021年 | 48篇 |
2020年 | 75篇 |
2019年 | 99篇 |
2018年 | 113篇 |
2017年 | 118篇 |
2016年 | 137篇 |
2015年 | 119篇 |
2014年 | 144篇 |
2013年 | 226篇 |
2012年 | 146篇 |
2011年 | 201篇 |
2010年 | 188篇 |
2009年 | 236篇 |
2008年 | 215篇 |
2007年 | 211篇 |
2006年 | 189篇 |
2005年 | 159篇 |
2004年 | 156篇 |
2003年 | 118篇 |
2002年 | 119篇 |
2001年 | 82篇 |
2000年 | 93篇 |
1999年 | 82篇 |
1998年 | 66篇 |
1997年 | 69篇 |
1996年 | 62篇 |
1995年 | 58篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 38篇 |
1991年 | 47篇 |
1990年 | 27篇 |
1989年 | 35篇 |
1988年 | 39篇 |
1987年 | 44篇 |
1986年 | 29篇 |
1985年 | 43篇 |
1984年 | 37篇 |
1983年 | 29篇 |
1982年 | 32篇 |
1981年 | 39篇 |
1980年 | 40篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 32篇 |
1976年 | 27篇 |
1975年 | 22篇 |
1974年 | 33篇 |
1973年 | 30篇 |
排序方式: 共有4488条查询结果,搜索用时 15 毫秒
61.
A coding error in the s-Coordinate Primitive Equation Model (SPEM) has led to misleading statements about the behaviour of the Mellor–Yamada level 2 parameterization of vertical mixing. It has been claimed that the scheme removes static instability only very slowly and preserves statically unstable stratifications for an unrealistic long time. This note corrects this statement by demonstrating that the Mellor–Yamada mixing scheme, if implemented correctly, tends to overestimate rather than underestimate vertical mixing in seasonally ice-covered seas. Similar to other mixing schemes with the same behaviour, this leads to spurious open ocean deep convection, an unrealistic homogenization of the water column, and a significant reduction of sea ice volume. 相似文献
62.
To use two small fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae) and the Japanese medaka Oryzias latipes (Belloniformes) as testing models in molecular ecotoxicology, we have cloned the cytochrome P450 1A (CYP1A) gene after screening of both genomic DNA libraries, and sequenced 11,863 and 7,243 bp including all the exons and introns with promoter regions, respectively. The Rivulus and the medaka CYP1A gene consisted of seven exons (including non-coding exons) with high homology to mammals. In the promoter region, Rivulus CYP1A gene has seven xenobiotic response elements (XREs) and two metal response elements (MREs), while the Japanese medaka CYP1A gene has six XREs and four MREs. Interestingly, medaka CYP1A gene has a number of MREs at the promoter, which may affect its response on metal exposure. We describe here the gene structure of both fish CYP1A genes. 相似文献
63.
Despite the severity of tropical cyclone ‘Winifred’, which crossed the Great Barrier Reef on 1 February 1986, there were little long-term effects on lagoon surface sediments from reefs in its path. Short-term effects were apparent only at one particularly exposed area. These were: an increase in proportion of the coarse fraction, the establishment of sand ripples, and the destruction of the mounds produced by callianassid shrimps (normally the dominant topographic feature). Within six weeks this area was indistinguishable from a typical reef lagoon. This is probably the result of sediment reworking by callianassid shrimp, involving selective burial of the coarse fragments and transport to the surface of finer particles. Sediment turnover rates by callianassids are commensurate with change to the sediment within the relatively short period observed. The sediment fauna responded quickly to the changes in sediment type. Immediately after the cyclone the disturbed area supported a fauna typical of the coarse sediments on the shallow reef flat, as the sediment reverted to a more normal type so the fauna changed back to that typical of a reef lagoon. 相似文献
64.
Cheng-Han Tsai Min-Chih Huang Fu-Ji Young Yin-Chern Lin Hsien-Wen Li 《Ocean Engineering》2005,32(10):4936-1259
Except the commonly selected pressure transfer function derived from the linear wave theory, a previous study on the pressure transfer function for recovering surface wave from underwater pressure transducer suggested that the pressure transfer function is a function of frequency parameter only. With careful analysis, this study showed that the pressure transfer function should include a transducer submergence parameter as that given by the linear theory. It was found that the previously suggested empirical formula should be restricted to measurements with the pressure transducer close to the surface; otherwise overestimation of wave height would result. Field measurements were carried out with an acoustic wave gauge and a synchronized pressure transducer located at various depths with submergence parameter close to 1 (near the sea floor). It was shown that the previous one-parameter empirical formula might overestimate the significant wave height by more than 30%. This study found that with deep-water wave bursts excluded, the transfer function based on the linear wave theory provided a fairly good estimation on the significant wave heights, with an average deviation of 3.6%. 相似文献
65.
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
66.
67.
68.
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
69.
70.
We investigated whether trochophore larvae of the polychaete Hesiocaeca methanicola, which lives on exposed ice‐like methane hydrates between 500 and 600 m, could consume near‐bottom picoplankton. In laboratory trials larvae significantly reduced the growth rates of all types of picoplankton, including heterotrophic bacteria, Prochlorococcus sp., Synechococcus‐type cyanobacteria and phototrophic eucaryotes <3 μm. Our findings suggest that these types of plankton may be important food sources for deep‐sea planktotrophic larvae. 相似文献