全文获取类型
收费全文 | 312篇 |
免费 | 290篇 |
专业分类
地球物理 | 122篇 |
地质学 | 12篇 |
海洋学 | 399篇 |
综合类 | 42篇 |
自然地理 | 27篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 20篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 25篇 |
2015年 | 33篇 |
2014年 | 28篇 |
2013年 | 40篇 |
2012年 | 28篇 |
2011年 | 35篇 |
2010年 | 25篇 |
2009年 | 22篇 |
2008年 | 24篇 |
2007年 | 21篇 |
2006年 | 26篇 |
2005年 | 18篇 |
2004年 | 21篇 |
2003年 | 14篇 |
2002年 | 17篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
排序方式: 共有602条查询结果,搜索用时 23 毫秒
1.
根据闽东海洋环境监测中心2004年-2006年阂东沿岸生态调查的资料,分析和研究了闽东沿岸浮游植物的生态特征.共鉴定出浮游植物的种类3个门39属共134种,其中硅藻门的种类占总种数的80%,为该调查海域主要门类.主要优势种是中肋骨条藻(Skeletonema costatum)、旋链角毛藻(Chaetoceros curvisetus)、尖刺拟菱形藻(Pseudo—nitzschia pungens)和丹麦细柱藻(Leptocylindrus danicus)等.浮游植物的丰度分布,呈现由调查海域东北侧向西南侧、由近岸向远岸减少的空间特征,夏季高、春季低的季节变化特点,并且有逐年减少的年际变化趋势.本调查海域浮游植物多样性指数较高,群落较稳定. 相似文献
2.
北黄海典型水域春夏季浮游植物的昼夜变化 总被引:1,自引:0,他引:1
根据黄海西北部2006年夏季3个连续站和2007年春季1个连续站垂直分层拖网的调查资料,研究了黄海西北部典型海区浮游植物的昼夜垂直变化.夏季共检出浮游植物79种,主要优势种为旋链角毛藻Chaetoceros curvisetus、梭角藻Ceratium fusus、三角角藻Ceratium tripos和具槽帕拉藻Paralia sulcata;春季检出51种,主要优势种为浮动弯角藻Eucampia zodiacus、具槽帕拉藻和尖刺伪菱形藻Pseudo-nitzschia pungens.夏季L01站受潮汐的影响各水层低潮期浮游植物细胞丰度高于高潮期,垂直分布趋势为表层细胞丰度最高,底层最低.而由于底栖硅藻的细胞再悬浮作用夏季L02、L03站和春季L02站底层细胞丰度高于表层,但各水层细胞丰度的昼夜变化相对较平缓. 相似文献
3.
于2011年2~12月,在南黄海辐射沙脊群海域设置6个采样站位,每逢双月份调查1次,研究该海域浮游植物密度及优势种的时空变化.调查共获得浮游植物87种,以硅藻种类最多.浮游植物密度呈周年双峰变化,分别在4月和8月成峰,4月峰值最大,水样浮游植物平均密度为1.59×104cells/dm3,网样浮游植物平均密度为2.71×106cells/m3,8月峰次之,水样浮游植物的平均密度为1.28×104cells/dm3,网样浮游植物平均密度为7.38×105cells/m3;浮游植物密度在2月和4月,北高南低,6月和8月中部高,外围较低,10月和12月南部高北部低.2月和4月,中肋骨条藻(Skeletonema costatum)为第一优势种,6月和12月虹彩圆筛藻(Coscinodiscus oculus-iridis)为第一优势种,8~10月琼氏圆筛藻(Coscinodiscus jonesianus)为第一优势种,枯水期(2月)铁氏束毛藻(Trichodesmium thiebautii)在局部海域形成优势. 相似文献
4.
浮游藻类的后向散射是水体光谱构成的重要组成部分,作为水体辐射传输模型中的重要参数,高精度的藻类后向散射系数对水体叶绿素a浓度的遥感反演精度至关重要。本文以简化的辐射传输模型-生物光学模型为基础,尝试性分离了太湖浮游藻类的后向散射系数。通过藻类后向散射规律分析,建立了浮游藻类吸收、后向散射特征的叶绿素a反演模型,改善了叶绿素a浓度的遥感反演精度。分析表明:藻类颗粒物的后向散射系数与吸收系数之间存在反比关系,且在560 nm、700 nm附近存在明显的散射峰,与叶绿素a浓度之间相关性显著;低密度藻类水体总悬浮颗粒的后向散射以非色素颗粒为主导,适合采用经典的指数模型模拟后向散射系数,而藻类密度较高的富营养化水体,水体总悬浮颗粒的后向散射以藻类颗粒为主导,传统的指数模型已不适用;采用分离藻类后向散射系数的方法,使得叶绿素a浓度的反演值与真实值相关系数从0.66提高到0.98,相对误差从55%降低到38%,均方根误差(RMSE)也由60.95μg/L降低至13.98μg/L。其真实性检验表明,与经典指数模型方法相比,利用藻类颗粒后向散射分离方法反演叶绿素a浓度,能够显著改善反演精度。 相似文献
5.
C. Svensen D. Vili
i P. Wassmann E. Arashkevich T. Ratkova 《Estuarine, Coastal and Shelf Science》2007,71(3-4):381-390
The aim of this study was to investigate phytoplankton abundance, composition and vertical export in the highly stratified Krka estuary, Croatia. The estuary is stratified throughout the year, and an interface between fresh- and brackish water plays an important role in production and degradation of biogenic matter. Vertical export of particulate organic carbon (POC), phytoplankton carbon (PPC) and faecal pellet carbon (FPC) was studied by deploying sediment traps in the middle and lower reach of the estuary and in the adjacent coastal zone. Zooplankton faecal pellet (FP) production experiments were conducted to provide additional information on the potential contribution of FP to the total carbon flux. High suspended concentrations of POC, chlorophyll a and phytoplankton was found in the lower reaches of the Krka estuary, adjacent to a source of anthropogenic eutrophication. The fraction of organic detritus to the total POC flux was 61–69% inside the estuary but only 7% at the marine station. This indicates that the primary producers in the surface layer of the Krka estuary are decomposed in and below the interface and then settle as detritus to the bottom. Low sedimentation rates in the coastal zone outside the estuary revealed that the eutrophication does not spread out of the estuary. Mesozooplankton played a modest role in vertical flux regulation, due to their low abundance and dominance of smaller forms as well as low faecal pellet production rates. It is concluded that processes taking place at the freshwater-seawater interface are of major importance for the vertical carbon flux in the investigated area. 相似文献
6.
Growth and grazing rate dynamics of major phytoplankton groups in an oligotrophic coastal site 总被引:1,自引:0,他引:1
Andrés Gutiérrez-Rodríguez Mikel Latasa Renate Scharek Ramon Massana Gemma Vila Josep M. Gasol 《Estuarine, Coastal and Shelf Science》2011
There has been more attention to phytoplankton dynamics in nutrient-rich waters than in oligotrophic ones thus requiring the need to study the dynamics and responses in oligotrophic waters. Accordingly, phytoplankton community in Blanes Bay was overall dominated by Prymnesiophyceae, remarkably constant throughout the year (31 ± 13% Total chlorophyll a, Tchl a) and Bacillariophyta with a more episodic appearance (20 ± 23% Tchl a). Prasinophyceae and Synechococcus contribution became substantial in winter (Prasinophyceae = 30% Tchl a) and summer (Synechococcus = 35% Tchl a). Phytoplankton growth and grazing mortality rates for major groups were estimated by dilution experiments in combination with high pressure liquid chromatography and flow cytometry carried out monthly over two years. Growth rates of total phytoplankton (range = 0.30–1.91 d−1) were significantly higher in spring and summer (μ > 1.3 d−1) than in autumn and winter (μ ∼ 0.65 d−1) and showed a weak dependence on temperature but a significant positive correlation with day length. Microzooplankton grazing (range = 0.03–1.4 d−1) was closely coupled to phytoplankton growth. Grazing represented the main process for loss of phytoplankton, removing 60 ± 34% (±SD) of daily primary production and 70 ± 48% of Tchl a stock. Chla synthesis was highest during the Bacillarophyceae-dominated spring bloom (Chl asynt = 2.3 ± 1.6 μg Chl a L−1 d−1) and lowest during the following post-bloom conditions dominated by Prymnesiophyceae (Chl asynt = 0.23 ± 0.08 μg Chl a L−1 d−1). This variability was smoothed when expressed in carbon equivalents mainly due to the opposite dynamics of C:chl a (range = 11–135) and chl a concentration (range = 0.07–2.0 μg chl a L−1). Bacillariophyta and Synechococcus contribution to C fluxes was higher than to biomass because of their fast-growth rate. The opposite was true for Prymnesiophyceae. 相似文献
7.
We conducted studies of phytoplankton and hydrological variables in a semi-enclosed bay in northern China to understand the spatial–temporal variability and relationship between these variables. Samples were collected during seven cruises in Jiaozhou Bay from November 2003 to October 2004, and were analyzed for temperature, nutrients and phytoplankton pigments. Pigments from eight possible phytoplankton classes (Diatoms, Dinoflagellates, Chlorophyceae, Prasinophyceae, Chrysophyceae, Haptophyceae, Cryptophyceae and Caynophyceae) were detected in surface water by high performance liquid chromatography (HPLC). Phytoplankton pigment and nutrient concentrations in Jiaozhou Bay were spatially and temporally variable, and most of them were highest in the northern and eastern parts of the sampling regions in spring (May) and summer (August), close to areas of shellfish culturing, river estuaries, dense population and high industrialization, reflecting human activities. Chlorophyll a was recorded in all samples, with an annual mean concentration of 1.892 μg L−1, and fucoxanthin was the most abundant accessory pigment, with a mean concentration of 0.791 μg L−1. The highest concentrations of chlorophyll a (15.299 μg L−1) and fucoxanthin (9.417 μg L−1) were observed in May 2004 at the station close to the Qingdao Xiaogang Ferry, indicating a spring bloom of Diatoms in this area. Although chlorophyll a and other biomarker pigments showed significant correlations, none of them showed strong correlations with temperature and nutrients, suggesting an apparent de-coupling between the pigments and these hydrological variables. The nutrient composition and phytoplankton community composition of Jiaozhou Bay have changed significantly in the past several decades, reflecting the increasing nutrient concentrations and decline of phytoplankton cell abundance. The unchanged total chlorophyll a levels indicated that smaller species have filled the niche vacated by the larger species in Jiaozhou Bay, as revealed by our biomarker pigment analysis. 相似文献
8.
O. Mangoni M. Modigh P. Mozeti
A. Bergamasco P. Rivaro V. Saggiomo 《Estuarine, Coastal and Shelf Science》2008,77(4):633-644
The photosynthetic properties of phytoplankton populations as related to physical–chemical variations on small temporal and spatial scales and to phytoplankton size structure and pigment spectra were investigated in the Northern Adriatic Sea off the Po River delta in late winter 1997. Large diatoms (fucoxanthin) dominated the phytoplankton in the coastal area whereas small phytoflagellates (mainly 19′-hexanoyloxyfucoxanthin, chlorophyll b, 19′-butanoyloxyfucoxanthin) occurred outside the front. The front was defined by the steep gradient in density in the surface layer separating low-salinity coastal waters from the offshore waters.Physical features of the area strongly influenced phytoplankton biomass distributions, composition and size structure. After high volumes of Po River discharge several gyres and meanders occurred in the area off the river delta in February. Decreasing river discharge and the subsequent disappearance of the gyres and the spreading dilution of the river plume was observed in March. The dynamic circulation of February resulted in high photosynthetic capacity of the abundant phytoplankton population (>3.40 mg m−3). In March, the slow circulation and an upper low-salinity water layer, segregated from the deeper layers, resulted in lack of renewal of this water mass. The huge phytoplankton biomass, up to 15.77 mg chl a m−3, became nutrient depleted and showed low photosynthetic capacity. In February, an exceptionally high PmaxB, 20.11 mg C (mg chl a)−1 h−1 was recorded in the Po River plume area and average PmaxB was three-fold in February as compared to the March recordings, 10.50 mg C (mg chl a)−1 h−1 and 3.22 mg C (mg chl a)−1 h−1, respectively.The extreme variability and values of phytoplankton biomass in the innermost plume area was not always reflected in primary production. Modeling of circulation patterns and water mass resilience in the area will help to predict phytoplankton response and biomass distributions. In the frontal area, despite a considerable variability in environmental conditions, our findings have shown that the phytoplankton assemblages will compensate for nutrient depression and hydrographic constraints, by means of size and taxonomic composition and, as a result, the variability in the photosynthetic capacity was much less pronounced than that observed for other parameters. 相似文献
9.
于2008年7月(平水期)、10月(枯水期)和次年5月(丰水期)对新疆阿勒泰地区福海县第一农场水库浮游植物进行了生态学调查.共采集到浮游植物8门75种(属),其中绿藻28种、硅藻21种、蓝藻13种、裸藻6种、黄藻2种、甲藻2种、隐藻2种和金藻1种,绿藻和硅藻在种类组成上占明显优势.各期优势种不尽相同:平水期优势种为类颤藻鱼腥藻、广源小环藻、小球藻和月牙藻;枯水期优势种有卷曲鱼腥藻和小席藻;丰水期的优质种则为小席藻、美丽颤藻和细链丝藻.备期浮游植物种类组成呈现显著差异(P<0.01),浮游植物细胞密度在不同时期差异也显著(P<0.01),其变化趋势为:平水期(6.35±2.07×106 ind/L)>枯水期(3.18±0.43×106 ind/L)>丰水期(2.86±0.49×106 ind/L).库区水温变化是影响水体浮游植物种类组成、密度和多样性指数变化的主要因素. 相似文献
10.
根据2009年8月份对北部湾(18°N~22°N,107°E~110°E)海域12个采水站位的调查,分析夏季调查区浮游植物的群落结构特征。通过Uterm hl方法共鉴定出浮游植物4门60属90种(不包括未定种),群落组成以硅藻为主,其次是甲藻。浮游植物生态类群以广温广布型种为主,调查区的优势种为菱形海线藻(Thalassionema nitzschioides)、柔弱角毛藻(Chaetoceros curvesitus)、尖刺伪菱形藻(Pseudo-nitzschia pungens)和萎软几内亚藻(Guinardia flaccida),此外蓝藻门的铁氏束毛藻(Trichodesmiumthiebaultii)也作为优势种出现。调查区细胞丰度介于0.330~19.765×103/L,平均为4.677×103/L。调查区表层浮游植物丰度由近岸区向湾中部逐渐降低,而且甲藻在调查区的近岸站位出现高值。调查区浮游植物丰度在垂直方向随着水深的增加而递减。Shan-non-Wiener多样性指数和Pielou均匀度指数在调查区的近岸站位出现低值区,群落结构稳定性较差。 相似文献