全文获取类型
收费全文 | 855篇 |
免费 | 35篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 72篇 |
地球物理 | 160篇 |
地质学 | 264篇 |
海洋学 | 68篇 |
天文学 | 222篇 |
综合类 | 2篇 |
自然地理 | 92篇 |
出版年
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 20篇 |
2014年 | 18篇 |
2013年 | 40篇 |
2012年 | 24篇 |
2011年 | 22篇 |
2010年 | 31篇 |
2009年 | 52篇 |
2008年 | 31篇 |
2007年 | 30篇 |
2006年 | 40篇 |
2005年 | 29篇 |
2004年 | 38篇 |
2003年 | 35篇 |
2002年 | 33篇 |
2001年 | 15篇 |
2000年 | 28篇 |
1999年 | 17篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有899条查询结果,搜索用时 15 毫秒
191.
Superficial sediments (top Im) of the Eastern Mediterranean Basin, Sea of Marmara, Turkey accumulated rapidly (0.087 ± 0.012 g/cm2 · y) by hemipelagic sedimentation with only limited amounts of gravity flow or bottom current action under low oxygenated but not anoxic conditions. They have restricted faunas, relatively higher organic carbon (1–1.8%) and lower calcium carbonate (14–20%) contents than other Eastern Mediterranean Basin sediments. Sedimentation shows little change over the last millenium except for an increase in Cu, Zn, Pb, Cr, and P over the last few centuries. The increase was most likely caused by increased metallurgical activities since the eighteenth century but are not at sufficient levels for the area to be regarded as polluted. 相似文献
192.
193.
The Norwegian wave-power buoy1 consists of a half-immersed floating sphere which is open to the sea at the bottom end. It is a two degree-of-freedom device involving the independent motion of the outer rigid sphere and the pressure across the internal free surface. A simpler model of the device is to represent the oscillatory flow through the bottom opening as another rigid body motion being that of the curved surface which would complete the sphere.The wave-induced forces on this surface and also the outer spherical surface due to independent oscillations of either are determined semi-analytically using a simple extension of the method of Havelock,2 recently simplified and generalised by Hulme,3 for the complete half-immersed sphere. In particular the 2 × 2 added mass and damping matrices are determined as a function of frequency and relative size of bottom opening to sphere radius. These quantities are essential in any theoretical analysis of a multi-degree of freedom wave-energy device. 相似文献
194.
An ion exchange technique has been used to determine the copper complexing capacity (CuCC) of strong organic complexing agents at 21 stations across the continental shelf of the southeastern United States and in the western Sargasso Sea. The concentration of dissolved organic carbon (DOC) and total particulate materal (TPM), two pools of potential complexing agents, was also measured at each station. The CuCC ranged from 0.014 to 1.681 μM Cu dm−3 on the inner shelf, from 0.043 to 0.095 μM Cu dm−3 in mid and outer shelf waters, and from < 0.010 to 0.036 μM Cu dm−3 at the Sargasso Sea stations. The correlation between CuCC and both DOC and TPM is highly significant (α < 0.01). Two synoptic surveys of the distribution of DOC and TPM across the shelf showed that DOC ranges from > 3 mg C dm−3 nearshore to <1 mg C dm−3 offshore and that TPM ranges from > 50 mg dm−3 nearshore to <1 mg dm−3 offshore. Both TPM and DOC are most variable on the inner shelf. These data are consistent with CuCC data which indicate that the CuCC of inner shelf waters was relatively high and very heterogeneous. In contrast, DOC, TPM and copper complexing capacity are low and nearly invariant at the Sargasso Sea stations. We present a model of the distribution of complexing agents in different marine environments and hypothesize that the mechanisms underlying differences between environments relate to differences in the source(s) and nature of complexing agents in each system. 相似文献
195.
196.
Shallow-seismic surveys around the Storegga Slide off western Norway have allowed greater understanding of the development of this part of the European margin. The northern flank of the scarp is formed of seismically well-layered, hemipelagic and distal-glaciomarine deposits in which a variety of luid-escape structures, probably due to gas, are locally abundant. There is evidence of slides that substantially pre-date the earliest slide previously recognized. Surveying on the North Sea Fan to the southwest of the Storegga Slide shows the markedly different nature of the autochthonous sediments on the southern flank of the Storegga Slide; there is a predominance of glacigenic debris flows in the upper part of the sequence, lesser maximum slopes, and an apparent absence of interstitial gas and/or hydrates. This contrast has had considerable effect on slope stability and has influenced the position of the southwestern Storegga Slide boundary. The North Sea Fan succession includes at least three major buried slides, termed the Vigra, Møre and Tampen slides, all of which substantially pre-date the Storegga event and probably pre-date predominantly glacigenic margin sedimentation. Post-late Weichselian slope failure is locally significant. The region has a long, but as yet chronologically poorly defined history of instability in which seismic triggering is considered to have been important. 相似文献
197.
Previous laboratory studies1 have shown that physiological and cellular processes of Mytilus edulis are affected by exposure to low and environmentally realistic concentrations of oil. However, there is little information concerning the rate of recovery from oil exposure and the extent to which physiological recovery may be related to the depuration of hydrocarbons from the tissues. The present study has shown a marked reduction in the feeding rate and scope for growth of mussels exposed to two concentrations of diesel oil (30 and 130 μg/litre) for 8 months. During recovery from oil exposure the depuration of hydrocarbons from the tissues was concomitant with the recovery of physiological performance. Mussels exposed to high oil concentrations (‘high-oil’ mussels) were found to recover more rapidly than those exposed to low oil concentrations (‘low-oil’ mussels), both in terms of depuration and scope for growth, and there was evidence of ‘catch-up’ growth. Recovery of both low- and high-oil mussels was complete after approximately 55 days. 相似文献
198.
Coastal zones are among the most productive and vulnerable areas on the planet. An example of impact on these fragile environments was shown in the case of the "Sea Empress" oil tanker, which ran aground in the Bristol Channel in 1996, spilling 72,000 tons of "Forties" crude oil. The objective was to investigate the sub-lethal cellular pathology and tissue hydrocarbon contamination in marine mussel populations, 4 months after the initial spill, using the neutral red retention (NRR) assay for lysosomal stability in blood cells. NRR was reduced in mussels, and indicative of cell injury, from the two sites closest to the spill in comparison with more distant and reference sites. Lysosomal stability was inversely correlated with polycyclic aromatic hydrocarbon concentrations in mussel tissues. Reduced lysosomal stability has previously been shown to contribute to impaired immunocompetence and to autophagic loss of body tissues. The use of this type of technique is discussed in the context of cost-effective, ecotoxicological tools for Integrated Coastal Zone Management. 相似文献
199.
Maximum wave-power absorption under motion constraints 总被引:1,自引:0,他引:1
D.V. Evans 《Applied Ocean Research》1981,3(4):200-203
An expression is derived for the maximum mean power that can be absorbed by a system of oscillating bodies in waves under a global constraint on their motions. The particular case of a single half-immersed sphere is used to show how the ‘point absorber’ result predicting capture widths in excess of unity must be modified. The theory is also applied to the submerged cylinder wave-energy device and curves are presented which show how the maximum efficiency is affected by restricting the motion of the device. 相似文献
200.