全文获取类型
收费全文 | 7575篇 |
免费 | 319篇 |
国内免费 | 87篇 |
专业分类
测绘学 | 248篇 |
大气科学 | 620篇 |
地球物理 | 1752篇 |
地质学 | 2538篇 |
海洋学 | 611篇 |
天文学 | 1429篇 |
综合类 | 29篇 |
自然地理 | 754篇 |
出版年
2022年 | 32篇 |
2021年 | 82篇 |
2020年 | 96篇 |
2019年 | 134篇 |
2018年 | 196篇 |
2017年 | 192篇 |
2016年 | 251篇 |
2015年 | 189篇 |
2014年 | 216篇 |
2013年 | 460篇 |
2012年 | 274篇 |
2011年 | 366篇 |
2010年 | 312篇 |
2009年 | 431篇 |
2008年 | 377篇 |
2007年 | 325篇 |
2006年 | 308篇 |
2005年 | 294篇 |
2004年 | 306篇 |
2003年 | 245篇 |
2002年 | 262篇 |
2001年 | 152篇 |
2000年 | 174篇 |
1999年 | 118篇 |
1998年 | 142篇 |
1997年 | 97篇 |
1996年 | 101篇 |
1995年 | 103篇 |
1994年 | 110篇 |
1993年 | 90篇 |
1992年 | 100篇 |
1991年 | 79篇 |
1990年 | 71篇 |
1989年 | 64篇 |
1988年 | 71篇 |
1987年 | 70篇 |
1986年 | 79篇 |
1985年 | 89篇 |
1984年 | 79篇 |
1983年 | 104篇 |
1982年 | 82篇 |
1981年 | 89篇 |
1980年 | 81篇 |
1979年 | 82篇 |
1978年 | 62篇 |
1977年 | 46篇 |
1976年 | 45篇 |
1975年 | 39篇 |
1974年 | 38篇 |
1973年 | 40篇 |
排序方式: 共有7981条查询结果,搜索用时 15 毫秒
51.
Michael MccGwire 《Marine Policy》1980,4(4):317-322
The purpose of this article is to draw attention to a change in the trend of Soviet naval developments. This change stems from a combination of: (1) a sharp increase in the allocation of resources to naval shipbuilding; (2) a marked rise in the navy's political influence; and (3) a new approach to the role of seapower in Soviet policy. Professor MccGwire, Senior Fellow at the Brookings Institution, USA, believes that both the nature and the significance of the change are being obscured by the fact that for the past decade naval leaders in the West have been talking of ‘a Soviet naval build-up’, and continue to use the same language to describe the very different present situation. There is no general awareness, even within naval circles, that we are now facing a significant change in established trends. This article draws on a longer and more general article.1 相似文献
52.
53.
54.
Studies in marine microbiology relevant to the cultivation of lobster in Fatty Basin were made.
Biomass of bacteria and allied microorganisms in whole seawater column of the basin was very small (2×104 gC), but a large biomass was found in the sediments (3×105 gC).
The decomposition of chitin occurred chiefly in the sediments. The rate of decomposition (500 g/day) was approximately half
of the rate of production. However, the remaining production was considered not to be involved in the chitin cycle of the
basin. This hypothesis was supported by the results of the analysis of the budget of organic matter in the area.
Shell disease of lobster caused by chitinoclastic bacteria was detected, although it was not serious. A destructive yeast
parasite of crustaceans,Metschnikowia, was collected only from a crab in the basin.
This report is dedicated to Professor KenSugawara for his 70 years old anniversary. 相似文献
55.
56.
This paper is concerned with the models appropriate for the dynamic assessment of jack-ups, concentrating particularly on the long-term response due to random ocean waves and on work-hardening plasticity models used for spud-can response. A methodology for scaling of short-term statistics, calculated using a Constrained NewWave technique, is shown in a numerical experiment for an example jack-up and central North Sea location. The difference in long-term extreme response statistics due to various footing assumptions is emphasised. Results for two environmental load conditions are described (one excluding and one including wind and current effects) and the role of sea-state severity in the variation of short-term extreme response statistics is also highlighted. 相似文献
57.
Hayes RA Regondi S Winter MJ Butler PJ Agradi E Taylor EW Kevin Chipman J 《Marine environmental research》2004,58(2-5):665-669
Metallothionein has been assayed in a range of aquatic animal tissues as an indicator of metal exposure. We sequenced chub (Leuciscus cephalus) metallothionein cDNA which showed over 90% homology to common carp, goldfish and stone loach and 77% homology to rainbow trout sequences for metallothionein. We then used the extended primer method to develop an accurate quantitative competitive RT-PCR assay for metallothionein mRNA. RT-PCR was used to measure metallothionein mRNA in feral chub from a range of field sites, with different levels of heavy metal pollution, in the West Midlands, UK. Measurements were complemented by analysis of liver and gill metallothionein protein by capillary electrophoresis. There was no significant difference in the metallothionein protein levels between fish of different rivers and there was no evidence of elevation of mRNA at the sites of highest metal exposure. The level of metal exposure (e.g. zinc, nickel and cadmium each ranging between 15 and 28 microg/l ) at the pH (7.5-8.5) of these rivers appears insufficient to elevate hepatic or gill metallothionein in chub. A lack of elevation of hepatic metallothionein mRNA in chub exposed to zinc, copper and manganese for 24 h and 10 days in the laboratory also suggests a non-responsiveness of this species. 相似文献
58.
The seismic expression of a salt-filled channel which cuts across the Mid North Sea High in Quadrant 37 is described, with features interpreted as being produced by salt-edge dissolution forming both eastern and western margins of the channel. The apparent half-graben nature of the channel is shown to be only superficial, and due to complex faulting associated with, but not defining, its western margin. The shallower faulting here is a Mesozoic to early Tertiary growth fault related to local dissolution of Zechstein salt. The dissolution effect appears in turn to have been localized by the presence of a deeper fault that was already downthrown to the east in Zechstein times, when it seems to have limited the eastward progradation of Zechstein shelf carbonates and anhydrites, and had probably ceased to move significantly before the onset of the Late Cimmerian erosional phase. The origin of this arcuate fault is tentatively ascribed to subsidence around a granite batholith. Zechstein salt originally spread some distance to the east and west of the channel; it was dissolved from the edges inwards, mainly before the Late Cretaceous, giving rise to a thicker Mesozoic sequence on parts of the flanks of the channel than in the middle. Besides providing an interesting structural case history, the features described have implications regarding Zechstein sedimentation, reservoir potential, the tectonic history of the North Sea, and the nature of the Mid North Sea High itself. 相似文献
59.
A survey of diffraction/radiation analyses has been performed on behalf of the International Ship and Offshore Structures Congress, Committee I.2. This paper presents the results from the survey, including data from 17 organisations plotted in a common format. The variability of the computed hydrodynamic loads and responses is discussed, and it is concluded that there is a degree of uncertainty in results predicted on the basis of commonly used idealisations. Even in long period waves the variability between the computed results is considerable. To obtain reliable results at the shorter periods associated with heave, pitch and roll resonances of a deep water TLP, much finer meshes than those used by most of the participating organisations would be required. 相似文献
60.