全文获取类型
收费全文 | 76245篇 |
免费 | 1244篇 |
国内免费 | 830篇 |
专业分类
测绘学 | 2259篇 |
大气科学 | 5540篇 |
地球物理 | 14529篇 |
地质学 | 27269篇 |
海洋学 | 6669篇 |
天文学 | 18107篇 |
综合类 | 292篇 |
自然地理 | 3654篇 |
出版年
2022年 | 472篇 |
2021年 | 807篇 |
2020年 | 839篇 |
2019年 | 936篇 |
2018年 | 2106篇 |
2017年 | 2019篇 |
2016年 | 2520篇 |
2015年 | 1407篇 |
2014年 | 2419篇 |
2013年 | 4063篇 |
2012年 | 2505篇 |
2011年 | 3250篇 |
2010年 | 2791篇 |
2009年 | 3616篇 |
2008年 | 3116篇 |
2007年 | 3138篇 |
2006年 | 3001篇 |
2005年 | 2265篇 |
2004年 | 2229篇 |
2003年 | 2161篇 |
2002年 | 2067篇 |
2001年 | 1825篇 |
2000年 | 1734篇 |
1999年 | 1462篇 |
1998年 | 1479篇 |
1997年 | 1387篇 |
1996年 | 1232篇 |
1995年 | 1195篇 |
1994年 | 1069篇 |
1993年 | 919篇 |
1992年 | 873篇 |
1991年 | 886篇 |
1990年 | 931篇 |
1989年 | 787篇 |
1988年 | 773篇 |
1987年 | 888篇 |
1986年 | 761篇 |
1985年 | 953篇 |
1984年 | 1043篇 |
1983年 | 957篇 |
1982年 | 915篇 |
1981年 | 789篇 |
1980年 | 759篇 |
1979年 | 712篇 |
1978年 | 704篇 |
1977年 | 618篇 |
1976年 | 556篇 |
1975年 | 552篇 |
1974年 | 548篇 |
1973年 | 600篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
A comparison of methods for the calculation of the hydrodynamic characteristics of arrays of wave power devices is presented. In particular, the plane-wave approximation and an exact multiple scattering formulation have been used to compute exciting wave forces, hydrodynamic coefficients and q factors for arrays of interacting wave power devices. The results obtained are compared with each other, and accuracy aspects of the computations are stressed and critically assessed. 相似文献
972.
S. B. Dharmadhikari E. Garcia S. Espinoza J. Dominguez J. M. Goris 《Ocean Engineering》1978,5(3):165-180
This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock. 相似文献
973.
Considerable metal enrichments have been found in hydrothermal fluids and metalliferous sediments off the central Lesser Antilles Volcanic Arc. The elements variably enriched in the fluids as a result of the hydrothermal activity are Fe, Mn, As, Si, B, Li and in the sediments, Fe, P, Mo, As, Sb, Hg, Cu and Pb. Variations in the concentrations of these elements in both fluids and sediments along the arc result from a number of factors, the most important of which is the stage that each island's volcano has reached in its eruptive cycle. Although hydrothermal mineralization on the sea floor off the islands is only low grade, phase separation in the hydrothermal fluids at depth could be leading to higher grade stockwork mineralization below the vent fields or the discharge of metal rich brines on the lower flanks of the volcanic islands. 相似文献
974.
975.
976.
Integrated coastal management (ICM) is an emerging approach in East Africa for the solution of various coastal issues. This paper is intended to provide an update on the current practical aspects concerning the ICM process and related policies and strategies in Madagascar. Efforts are being made in Madagascar for the mutual integration of numerous coastal projects and activities within the Environment Program of the National Environmental Action Plan. The foundations for an ICM program, built during an ICM workshop, which took place at the end of 1996 upon existing activities, are being expanded presently. These developments concern, above all, the institutional aspects related to the formulation of an ICM program. Therefore, the actual situation sees an overgrowing collaboration of the national and international agencies involved in the implementation of coastal projects, in an expandingly integrating way, within an institutional framework that grows progressively stronger. The case of Madagascar suggests reflections on how ICM can mitigate potential sectoral conflicts as well as on, how the sometimes complex nature of the social and cultural issues may influence the development of an ICM program. The need for monitoring ICM is stressed and the role of outside partners clarified. 相似文献
977.
We report the results of petrological, geochemical and rock magnetic studies of basalt dredged from the eastern end of the west Sheba Ridge during cruise 11/1979 of R. R. S. Shackleton to the Western Gulf of Aden. The ridge is part of the Red Sea-Gulf of Aden spreading axis and the basalts are olivine tholeiites. The abundances of some elements are characteristic of normal MORB (mid-ocean ridge basalt) but other elemental abundances suggest affinites with transitional-type MORB.The observed magnetic properties are interpreted in terms of the composition, concentration and microstructure of the magnetic mineral fraction by recourse to the available data on synthetic analogues. The analysis has been carried out in greater detail than has been attempted in previous magneto-petrological studies. It appears that submarine weathering of the magnetic minerals (maghemitization) brings about not only the expected change in composition but also a fall in concentration of the magnetic fraction. This could result from the removal-of-iron oxidation mechanism operating in the submarine environment. It is also found that the fall in remanence with increasing degree of maghemitization is not explicable in terms of the change in composition and concentration of the magnetic minerals. A further influence—probably microstructural change—significantly reduces the remanence intensity. 相似文献
978.
979.
980.
Water surface profiles and horizontal and vertical water particle velocity components have been measured to investigate the properties of intermediate depth waves generated in the laboratory. The data has been compared with linear wave theory. It was found that linear theory predicted the attenuation of velocity field with depth successfully and that it overestimates both components of velocity slightly. 相似文献