全文获取类型
收费全文 | 503篇 |
免费 | 74篇 |
国内免费 | 95篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 4篇 |
地球物理 | 122篇 |
地质学 | 106篇 |
海洋学 | 340篇 |
天文学 | 4篇 |
综合类 | 55篇 |
自然地理 | 37篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 27篇 |
2014年 | 22篇 |
2013年 | 50篇 |
2012年 | 27篇 |
2011年 | 23篇 |
2010年 | 14篇 |
2009年 | 32篇 |
2008年 | 28篇 |
2007年 | 40篇 |
2006年 | 26篇 |
2005年 | 32篇 |
2004年 | 17篇 |
2003年 | 20篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 18篇 |
1999年 | 20篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 15篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 1篇 |
排序方式: 共有672条查询结果,搜索用时 46 毫秒
101.
Carolyn W. Burns 《新西兰海洋与淡水研究杂志》2013,47(3):477-482
Few workers have used enclosures specifically to study interactions between zoo‐plankton and cyanobacteria. Differences among studies in enclosure size, nutrient level, plankton abundance and species composition, presence or absence of fish, and length of experiments make generalisations difficult. Zooplankton had no direct effect on the growth of ungrazed cyanobacteria (Anabaena flos‐aquae, Aphanizomenon flos‐aquae, large Microcystis colonies) in short‐term (<5 days) and long‐term (> 1 month) enclosure studies. When large cyanobacteria were abundant, some Daphnia spp. snowed reduced reproduction and development. When large grazers were abundant they suppressed the growth of edible, colonial cyanobacteria (Aphanizomenon elenkinii, small Microcystis colonies). By altering the ambient light and nutrient environment, large zooplankton may suppress cyanobacteria; evidence for the importance of grazers in promoting cyanobacterial dominance by removing competing phytoplankton species is equivocal. Zooplankton may suppress nitrogen fixation by cyanobacteria through ammonia excretion and may promote a change in dominance from diatoms to cyanobacteria through recycling phosphorus but not silicon. 相似文献
102.
《African Journal of Marine Science》2013,35(4):395-406
Kelp forests along South Africa's southwest coast occur in a region of biogeographical overlap. Commonly referred to as transition-zone kelp forests, these dynamic ecosystems are particularly susceptible to grazing from species such as urchins. This study explores relationships between urchins and macroalgae in transition-zone kelp forests along the western side of False Bay. Six kelp forests in this region were sampled. At each site, the urchin Parechinus angulosus and kelp Ecklonia maxima were counted, percentage cover of understorey algae was recorded, and drift algae were collected. Despite variability in urchin and algal cover across sites, kelps generally increased from north to south, while urchins did the opposite. Urchins were negatively associated with macroalgae, although this relationship was weak. A localised threshold of 50 urchins m–2 was identified, above which kelp density failed to increase above 10 m–2 and percentage cover of understorey algae usually remained below 20%. Surprisingly, no relationship was discovered between drift algae and attached algae. The findings highlight the complexity of these cool-water environments. To better understand the role of urchins in this system, particularly under changing climate trends, experimental research into the feeding behaviour and possible effects of urchins on attached algae in the presence/absence of drift algae is advised. 相似文献
103.
P. K. Misra S. Kishore S. K. Singh A. K. Jauhri 《Journal of the Geological Society of India》2009,73(3):325-334
The present paper records eight Rhodophycean taxa from the Kallakudi limestone of the Uttatur Group (Lower Cretaceous) exposed
in the quarries at Kallakudi and Olaipadi near Govindarajapatnam of the Cauvery Basin, south India. Of these, four species
(Melobesioideae gen. et sp. indet 1, Melobesioideae gen. et sp. indet 2, Lithophyllum alternicellum and Pseudoamphiroa propria) belong to corallinaceae family, one species (Polystrata alba) is assigned to Peyssonneliaceae family, two species (Solenopora urgoniana and Parachaetetes asvapatii) are placed under Solenoporaceae; and one species (Sporolithon sp.) is referable to Sporolithaceae family. Among these, three taxa (Solenopora urgoniana, Lithophyllum alternicellum and Pseudoamphiroa propria) are recorded for the first time from India. The study also includes observations on ultrastructural morphological features
of Parachaetetes asvapatii. The observations reveal absence of cell fusions, which confirms its affinities with Solenoporaceae. Palaeoecological data
indicate that the assemblage from the sequence at the Kallakudi quarry is characteristic of lagoonal to reefal environment,
whereas the Olaipadi quarry sequence near Govindarajapatnam points to 20 m to 30 m deep environment characterized by high-
to moderate energy conditions. 相似文献
104.
A. M. Stanevich E. N. Maksimova T. A. Kornilova D. P. Gladkochub A. M. Mazukabzov T. V. Donskaya 《Stratigraphy and Geological Correlation》2009,17(1):20-35
Studied assemblages of diverse organic-walled microfossils separated from the Arymas and Debengda formations of the Olenek Uplift include several paleobiological groups of microorganisms. Sufficiently large morphotypes of the first group are identified with remains of cyanobacteria. Morphotypes of variable spiral structure, which dwelt in association or in symbiosis with cyanobionts, are attributed to the same bacterial community. The other group includes a series of different acritarch genera whose characters suggest their affinity with green algae of the order Desmidiales. It is very likely that this group coexisted on siliciclastic shoals with large ancestral forms of the present-day brown algae. Several microfossil taxa have been known before from the Neoproterozoic deposits only. With due regard for the relatively gradual accumulation of sedimentary succession lacking large hiatuses and for the regular series of K-Ar dates characterizing three Riphean formations of the Olenek Uplift, it is possible to suggest that there was the Arymas-Debengda-Khaipakh cycle of long-lasted, almost uninterrupted sedimentation within the time span of 1250–900 Ma. It is also admissible that age ranges of some Late Precambrian microfossils are much larger than their distribution intervals postulated formerly. 相似文献
105.
《Limnologica》2015
We studied the changes in the submerged aquatic vegetation (SAV) and phytoplankton community in a hard water lake during different meteorological conditions. We hypothesized that variations in climatic conditions (precipitation and temperature) can influence the physicochemical parameters of water and, in turn, affect SAV and phytoplankton development. The investigations were performed in Lake Rogóźno (the West Polesie region, Eastern Poland) over 10 years from 2003 to 2013. The physicochemical parameters, the structure of macrophytes and the phytoplankton community in the dry (2003–2006, DP) and wet periods (2007–2013, WP) were analyzed. Between the dry and wet periods, the water color and the concentration of dissolved organic carbon (DOC) increased considerably, whereas water conductivity decreased. Other parameters (concentration of nutrients, water reaction and transparency) were comparable during both periods. When the precipitation and water level were low (DP), charophytes dominated the SAV and cyanobacteria dominated the phytoplankton community. After the precipitation and water level increased (WP), the charophyte population declined and the vascular plants and bryophytes dominated. Furthermore, flagellated algae belonging to the dinophytes and cryptophytes were the most numerous in the phytoplankton community. These changes in the SAV and phytoplankton were linked with the variations of physicochemical parameters determined by the total precipitation and mean air temperature in March. 相似文献
106.
107.
108.
Kelp holdfasts are highly reticulated structures which host a large diversity of small fauna. These microhabitats have been reported to play a crucial role in the biodiversity associated to kelp forest ecosystems. This study aimed at identifying trophic links and the main food sources sustaining food webs within communities associated with kelp holdfasts, through a stable isotope (δ13C and δ15N) approach. Sampling of the main invertebrates inhabiting Laminaria digitata holdfasts, and of their potential food sources, took place in February and May 2007. Stable isotope results reveal that most of the primary consumers, including filter-feeders and deposit-feeders, rely on the particulate organic matter sedimented within kelp holdfasts. Only three grazers departed from this general pattern. The correspondence between the stable isotope ratios of predators and sediment consumers indicated that this source is at the base of the main pathway through which energy and matter transit in the food web. δ15N ranges found for consumers revealed that the food web associated with kelp holdfasts is composed of 3.5 levels. In spite of the low diversity of food sources at the base of the food web, these microhabitats can therefore be considered micro-scale ecosystems, from a functional perspective. 相似文献
109.
南黄海及长江口附近海域绿潮暴发前期微观繁殖体的动态变化 总被引:3,自引:2,他引:1
基于2011年3至5月对南黄海及长江口附近海域的水体与沉积物样品采集及实验室萌发培养实验,分析了绿潮暴发前期该海域微观繁殖体的时空分布特征。结果表明,在调查期间,南黄海水体中微观繁殖体空间分布趋势表现为近岸高远岸低,高值区主要集中在紫菜筏架养殖区附近海域,在122°30'E以东区域未发现有微观繁殖体存在。3,4,5月份该区域海水中平均微观繁殖体数分别为144 ,164和140株/dm3,最大值分别为278,426,和537株/dm3;南黄海沉积物中微观繁殖体数量分布范围介于19~127株/层,表层微观繁殖体数高于底层。长江口以北靠近江苏近岸区域有微观繁殖体存在,数量介于1~10株/dm3,31°N以南区域和河口内未发现有繁殖体分布,由此可排除黄海浒苔等绿藻微观繁殖体由长江水携带入海或来源于长江口南部海域。在春季绿潮暴发前开展该海域微观繁殖体的研究,可为查明绿潮发源地及早期发生发展过程提供基础资料,为预测和预警绿潮发生提供科技支撑。 相似文献
110.
Marine algae contain various bromophenols with a variety of biological activities,including antimicrobial,anticancer,and anti-diabetic effects.Here,we briefly review the recent progress in researches on the biomaterials from marine algae,emphasizing the relationship between the structure and the potential anti-diabetic applications.Bromophenols from marine algae display their hyperglycemic effects by inhibiting the activities of protein tyrosine phosphatase 1B,α-glucosidase,as well as other mechanisms. 相似文献