全文获取类型
收费全文 | 1256篇 |
免费 | 79篇 |
国内免费 | 279篇 |
专业分类
测绘学 | 67篇 |
大气科学 | 127篇 |
地球物理 | 474篇 |
地质学 | 568篇 |
海洋学 | 172篇 |
天文学 | 76篇 |
综合类 | 30篇 |
自然地理 | 100篇 |
出版年
2023年 | 13篇 |
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2016年 | 23篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 21篇 |
2012年 | 50篇 |
2011年 | 64篇 |
2010年 | 25篇 |
2009年 | 35篇 |
2008年 | 56篇 |
2007年 | 76篇 |
2006年 | 65篇 |
2005年 | 70篇 |
2004年 | 62篇 |
2003年 | 54篇 |
2002年 | 47篇 |
2001年 | 45篇 |
2000年 | 98篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 38篇 |
1996年 | 28篇 |
1995年 | 49篇 |
1994年 | 30篇 |
1993年 | 59篇 |
1992年 | 40篇 |
1991年 | 50篇 |
1990年 | 39篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 40篇 |
1986年 | 27篇 |
1985年 | 31篇 |
1984年 | 45篇 |
1983年 | 23篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1959年 | 5篇 |
1958年 | 7篇 |
1957年 | 4篇 |
1936年 | 4篇 |
1930年 | 3篇 |
1926年 | 4篇 |
1924年 | 4篇 |
排序方式: 共有1614条查询结果,搜索用时 15 毫秒
11.
海——微生物栖息的特殊环境。特殊的盐类成分,低温,高压,低浓度的有机物质,植物及动物区系的稀少等组成了微生物生命活动的广阔海洋区域一些主要生态特征。 海洋中最初的微生物学研究,早在上一世纪就已进行了,但足它们局限于较狭小的任务—— 相似文献
12.
Responses of a Mediterranean soft bottom community to short-term (1993-1996) hydrological changes in the Rhone river 总被引:1,自引:0,他引:1
The polychaete fauna of muddy bottoms off the Rhone delta (NW Mediterranean) was seasonally sampled at two sites at 70 m depth, from 1993 to 1996. During this period, five severe flood events occurred. A clustering analysis (distance coefficient of Whittaker) and three way fixed factor ANOVAs (site x season x year) showed strong year-to-year changes in species density and community structure, changes that masked seasonal variations. Total density increased by a factor of 3 and density of most species significantly increased following the first flooding event. Changes in the community structure were due to the successive dominance of a few species. The opportunistic species, such as Cossura sp., Mediomastus sp. and Polycirrus sp., exhibited peaks in density 1-3 months after the flood. These peaks were followed by a drastic decline. For species with a long life span, such as Sternaspis scutata, a slower but continuous increase in density was observed which was maintained for several months. The density fluctuations of these species exhibited a good correlation with river flow with time lags of 1-2 years. The successional dynamics observed are explained according to the geographical origin of the floods and the biology and feeding ecology of species. 相似文献
13.
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
14.
海洋中绝大多数硅藻细胞都有叶绿体,且能利用各种无机盐进行光合作用,称为光合硅藻。但也有不少硅藻尚能利用各种有机物质进行异养生活,据报道约50种左右。其中少数几种完全缺少光合色素,不能进行光合作用,只能利用有机碳或有机氮进行专性异养生活。它们主要生活于沿岸潮间带,特别附生于各种多细胞海藻体上。这类单细胞硅藻,种类不多,但为世界广分布的种类。到目前为止,对无色硅藻的研究报道还很少。本文第一作者在分离培养一种无色硅藻Nitzschia alba Lewin and Lewin作 相似文献
15.
17.
18.
激光烧蚀微探针等离子体质谱的地质应用。自1989年以来,我们实验室就积极开展了激光烧蚀微探针(LAM)试样引入系统的研究工作,这种技术适合于ICP—MS分析地质样品中小体积矿物(激光烧蚀孔穴直径低于10—100μm).对某些样品.采用Nd:YAG激光的基本IR波长(1064nm),作为多数用途,4倍频率(uv)的波长(266nm)能产生较小的直径,并较好地形成孔穴. 相似文献
19.
杭州湾南岸潮滩的~(210)Pb分布及其沉积学意义 总被引:1,自引:0,他引:1
杭州湾南岸潮滩的~(210)Pb垂向分布具有随深度波动的特征。湖滩颗粒物在吸附模拟系统中的~(210)Pb分配系数,主要受颗粒物含量的影响。本文从潮滩沉积~(210)Pb初始比度在低于平衡点一侧波动的机理,以及被沉积间断所分隔的有效封闭段的存在出发,提出选择常态沉积层的高~(210)Pb比度窗口,建立以CIC模式估计潮滩沉积速率的方法。 相似文献
20.
Das K Beans C Holsbeek L Mauger G Berrow SD Rogan E Bouquegneau JM 《Marine environmental research》2003,56(3):349-365
The relationship between trophic position through delta13C and delta15N and trace metal concentrations (Zn, Cd, Cu and Hg) was investigated in the tissues of six marine mammal species from the Northeast Atlantic: striped dolphin Stenella coeruleoalba, common dolphin, Delphinus delphis, Atlantic white-sided dolphin Lagenorhynchus acutus, harbour porpoise Phocoena phocoena, white beaked-dolphin Lagenorhynchus albirostris, grey seal Halichoerus grypus stranded on French Channel and Irish coasts. White-beaked dolphins, harbour porpoises, white-sided dolphins, common and striped dolphins display the same relative and decreasing trophic position, as measured by delta15N values, along both the Irish and French channel coasts, reflecting conservative trophic habits between these two places. Hepatic and renal Cd concentrations were significantly correlated to muscle delta13C and delta15N values while Hg, Zn and Cu did not. These results suggest that Cd accumulation is partly linked to the diet while other factors such as age or body condition might explain Hg, Zn or Cu variability in marine mammals. Combined stable isotope and trace metal analyses appear to be useful tools for the study of marine mammal ecology. 相似文献