全文获取类型
收费全文 | 3686篇 |
免费 | 171篇 |
国内免费 | 44篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 291篇 |
地球物理 | 805篇 |
地质学 | 1408篇 |
海洋学 | 272篇 |
天文学 | 652篇 |
综合类 | 12篇 |
自然地理 | 372篇 |
出版年
2021年 | 40篇 |
2020年 | 65篇 |
2019年 | 84篇 |
2018年 | 94篇 |
2017年 | 106篇 |
2016年 | 126篇 |
2015年 | 109篇 |
2014年 | 128篇 |
2013年 | 195篇 |
2012年 | 121篇 |
2011年 | 186篇 |
2010年 | 161篇 |
2009年 | 213篇 |
2008年 | 180篇 |
2007年 | 182篇 |
2006年 | 166篇 |
2005年 | 147篇 |
2004年 | 144篇 |
2003年 | 109篇 |
2002年 | 105篇 |
2001年 | 79篇 |
2000年 | 73篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 58篇 |
1996年 | 59篇 |
1995年 | 45篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 30篇 |
1991年 | 42篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 28篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 32篇 |
1981年 | 42篇 |
1980年 | 31篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1975年 | 16篇 |
1974年 | 29篇 |
1973年 | 28篇 |
1971年 | 16篇 |
排序方式: 共有3901条查询结果,搜索用时 234 毫秒
51.
52.
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
53.
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
54.
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
55.
56.
57.
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
58.
59.
Feeding of benthic foraminifera on diatoms and sewage-derived organic matter: an experimental application of lipid biomarker techniques 总被引:1,自引:0,他引:1
Foraminiferal ecology at sewage outfalls has been investigated in numerous field studies over the last 30 years. Foraminifera have been frequently used as biomonitors of sewage pollution since they are both abundant and ubiquitous. Sewage outfalls have been demonstrated to have both positive and negative effects on adjacent foraminiferal populations, but it has never been shown conclusively why sewage affects foraminifera in these ways. Such information on the impact mechanisms of sewage pollution is essential if foraminifera are to be used as sewage pollution biomonitors, and also to understand the ecology of these important protists. One possible cause of a positive effect is the direct consumption of sewage-derived particulate organic matter (POM) by the foraminifera themselves. However this hypothesis has never been tested experimentally. Here, lipid (fatty acid and sterol) biomarker techniques were applied to study the ingestion of two potential food items by the foraminiferan Haynesina germanica in the laboratory. An experiment was conducted to confirm that the laboratory conditions were conducive to the survival and feeding of the foraminifera. In this experiment, foraminifera were provided with the pennate diatom Phaeodactylum tricornutum, which was considered to be a suitable food source. After 2 weeks, a four-fold increase in the levels of the diatom fatty acid biomarker, 20:5(n-3), in the foraminifera suggested that they had fed actively on the diatoms and survived under the experimental conditions. These experimental conditions were used in the main experiment, where foraminifera were fed the POM from sewage. Lipid biomarker analysis indicated that H. germanica did not consume secondary treated sewage-derived POM. Neither fatty acid profiles in the sewage nor coprostanol, the diagnostic human faecal sterol, were detected in foraminifera after exposure to the potential sewage food source. However, foraminifera may have consumed bacteria associated with the sewage in the experiment. The findings are discussed in terms of current EU legislation on sewage treatment that has affected the composition of sewage discharges, and therefore possibly reduced the nutritive value of sewage to the marine benthos. 相似文献
60.
Total dissolved selenium and selenium species have been measured in the Rhône river delta and the Gulf of Lions within the framework of the EROS-2000 project. The Rhône river concentration of total selenium averages 2.30 nM with important variations related to river discharge. During estuar-ine mixing, the concentrations of total dissolved selenium, selenite and selenate (calculated as the difference between total dissolved and selenite) decrease linearly with increasing salinity, without significant interconversion between selenium species. In the open Mediterranean waters of the Gulf of Lions the total dissolved selenium increases from 0.5 nM in the surface waters to 0.9 nM in the deep waters. Organic selenium has been observed in Mediterranean deep water, an observation which is different from those from the Atlantic and the Pacific Oceans. The distributions of total inorganic selenium (Σ5e), selenite and selenate are strongly related to phosphate and silicate concentrations as observed previously for the major oceans. 相似文献