全文获取类型
收费全文 | 1742篇 |
免费 | 141篇 |
国内免费 | 323篇 |
专业分类
测绘学 | 42篇 |
大气科学 | 26篇 |
地球物理 | 337篇 |
地质学 | 187篇 |
海洋学 | 859篇 |
综合类 | 103篇 |
自然地理 | 652篇 |
出版年
2024年 | 11篇 |
2023年 | 47篇 |
2022年 | 104篇 |
2021年 | 116篇 |
2020年 | 109篇 |
2019年 | 107篇 |
2018年 | 86篇 |
2017年 | 107篇 |
2016年 | 91篇 |
2015年 | 96篇 |
2014年 | 118篇 |
2013年 | 124篇 |
2012年 | 100篇 |
2011年 | 109篇 |
2010年 | 84篇 |
2009年 | 78篇 |
2008年 | 83篇 |
2007年 | 85篇 |
2006年 | 75篇 |
2005年 | 71篇 |
2004年 | 51篇 |
2003年 | 49篇 |
2002年 | 34篇 |
2001年 | 33篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 1篇 |
排序方式: 共有2206条查询结果,搜索用时 546 毫秒
981.
对青海省祁连山永久冻土区天然气水合物DK一2钻孔的11件样品进行分析,通过微生物群落分析来探寻水合物层样品与非水合物层样品的差别。在11件样品中均发现了细菌16SrDNA,未检测到海洋天然气水合物地区常见的古菌16SrDNA、mc以(I,Ⅱ)、pmoA、mmoX和mxaF。分析得到的细菌16SrDNA分属5个门,包括变形杆菌门、放线菌门、拟杆菌门、厚壁菌门和异常球菌一栖热菌门,随着样品深度的增加,细菌多样性有降低的趋势。对非水合物层样品DK2—19和水合物层样品DK2—25进行细菌系统发育树分析,发现这2个样品群落结构相差较大。水合物层样品与非水合物层样品细菌群落对比后发现,水合物层样品中叫一变形杆菌的比例低于非水合物层样品中1一变形杆菌的比例,而Arthrobacter属多发现于非水合物层的样品中。 相似文献
982.
J. Harlay L. ChouC. De Bodt N. Van OostendeJ. Piontek K. SuykensA. Engel K. SabbeS. Groom B. DelilleA.V. Borges 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(2):111-127
Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO2 fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers. 相似文献
983.
2009 年冬季南海北部网采浮游植物群落结构 总被引:1,自引:0,他引:1
根据2010年1月6~30日对南海北部的调查取样,作者对该海域网采浮游植物的分布和群落结构特征等进行了分析。共鉴定浮游植物4门52属155种(包括变形及变种),主要以温带近岸和广布性种为主,其中硅藻有38属94种,占总种数的60.6%;甲藻有12属58种,占总种数的37.4%;浮游植物平均细胞丰度为36.46×10^4个/m^3,硅藻平均细胞丰度为13.77×10^4个/m^3,甲藻平均细胞丰度为1.39×10^4个/m^3,铁氏束毛藻(Trichodesmium thiebautii)平均细胞丰度为21.30×10^4个/m^3。粤东近岸区域是浮游植物高密集区,珠江口及其西南沿岸其次,而浮游植物稀疏区主要在调查区的中部海域,呈现出沿远岸区域逐渐降低的平面分布格局。除铁氏束毛藻为绝对优势种外,主要优势种有:菱形海线藻(Thalassionema nitzschioides)、短刺角毛藻(Chaetoceros messanensis)、圆筛藻(Coscinodiscus spp.)、粗根管藻(Rhizosolenia robusta)及角毛藻(Chaetoceros spp.)等。浮游植物群落香农.威纳物种多样性指数(H’)平均值为4.50,Peilou均匀度指数(J)平均值为0.81。浮游植物多样性程度较高,与细胞丰度平面分布基本呈相嵌分布,仅在近岸出现低值。 相似文献
984.
Ecology of macrobenthos in the south of Zhejiang coastal waters 总被引:1,自引:0,他引:1
为了解浙江南部近岸海域海洋生态环境质量的现状及其变化趋势,2009年4月对浙江南部近岸海域的12个站位进行了大型底栖生物的分类、组成、丰度、生物量以及多样性的研究.应用Bray—Curtis相似性系数聚类和多维尺度排序,对浙江南部近岸海域的大型底栖生物进行群落划分;采用丰度生物量比较法分析群落的稳定性;并研究了对大型底栖生物产生影响的主要环境因子.本次调查共鉴定大型底栖生物109种,多毛类、软体动物和甲壳动物构成主要类群.平均生物量为23.38g/m^2,平均丰度为335.5ind/m^2,平均生物多样性指数为2.69.数量组成:生物量以软体动物居首(13.29g/m^2),鱼类次之(3.68g/m^2);丰度以多毛类居首(268.0ind/m^2),软体动物次之(51.7ind/m^2).浙江南部近岸海域可划分为3个群落.与环境因子进行相关性分析表明,有机污染含量、深度、溶解氧含量、盐度和悬浮物含量是对浙江南部近岸海域大型底栖生物产生影响的主要环境因子.总体上,除了瓯江口和乐清湾海域受到一定扰动,浙江南部近岸海域大型底栖生物环境质量较好,群落结构较为稳定. 相似文献
985.
986.
987.
Ciliated protozoa play important roles in micro-ecosystems, especially in marine biotopes. However, few studies have been carried out on the periphytic, or aufwuch, forms in mariculture waters so far. In this study, we sampled periphytic ciliate communities in two closed mariculture ponds (ponds CP1 and CP2) and a natural seawater reservoir (pond RP) using a glass slide method to evaluate their colonizing processes and general ecological features, as well as their application as water quality indicators. We analyzed species compositions, structural parameters (species number, richness, diversity, evenness, abundance and dBP) and functional parameters (G, Seq and T90%). Pond RP was characterized by higher levels of structural parameters (except for abundance and dBP) and more equal proportion of the major taxonomic groups. The values of Seq were significantly higher in pond RP and similar in both pond CP1 and CP2. It was also demonstrated that environmental factors, including NO2-H, NO3-H, NH3-H, soluble reactive phosphate, temperature and pH, were the first principal factors affecting the communities. Among them, temperature and chemical factors were all significantly and negatively correlated with species number (P<0.01), richness (P<0.01), diversity (P<0.01), and positive correlated with abundance (P<0.01). Opposite correlations between pH and structural parameters were observed. This study showed that there were significant differences in species composition, structural parameters and functional parameters of the periphytic ciliate communities among the ponds, which were in agreement with the water quality. Results of this study confirmed the periphytic ciliate communities to be useful bioindicators of water quality in intensive mariculture waters. 相似文献
988.
M. Söffker K.A. SlomanJ.M. Hall-Spencer 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(8):818-825
The abundance and behaviour of fish on and around coral reefs at Twin Mounds and Giant Mounds, carbonate mounds located on the continental shelf off Ireland (600-1100 m), were studied using two Remotely Operated Vehicle (ROV) dives. We recorded 30 fish taxa on the dives, together with three species of Scleractinia (Lophelia pertusa, Madrepora oculata and Desmophyllum cristagalli) and a diverse range of other corals (Antipatharia, Alcyonacea, and Stylasteridae). Stands of live coral provided the only habitat in which Guttigadus latifrons was observed whereas Neocyttus helgae was found predominantly on structural habitats provided by dead coral. Significantly more fish were found on structurally complex coral rubble habitats than on flatter areas where coral rubble was clogged with sand. The most common species recorded was Lepidion eques (2136 individuals), which always occurred a few cm above bottom and was significantly more active on the reefs than on sedimentary habitats. Synaphobranchus kaupii (1157 indiv.), N. helgae (198 indiv.) and Micromesistius poutassou (116 indiv.) were also common; S. kaupii did not exhibit habitat-related differences in behaviour, whilst N. helgae was more active over the reefs and other structured habitats whereas M. poutassou was more active with decreasing habitat complexity. Trawl damage and abandoned fishing gear was observed at both sites. We conclude that Irish coral reefs provide complex habitats that are home to a diverse assemblage of fish utilising the range of niches occurring both above and within the reef structure. 相似文献
989.
西藏乌柳群落特征 总被引:2,自引:0,他引:2
以一江两河流域为研究区,通过对西藏乌柳群落的典型地块设置11个标准地进行调查,分别从主要优势树种表现、物种组成、物种多样性、林分生长、地径结构、树高结构和树高-地径曲线等方面,分析了西藏乌柳群落的主要群落学和测树学特征。研究结构表明,1.西藏乌柳群落物种组成较为单一,群落中的物种数一般为1~4种,优势树种在群落中所占的比例较大,均大于85%;2.地径主要分布于5.0 cm以下,树高分布于1.0~5.0 m间,树高-地径服从二次曲线分布;3.由于群落物种组成较为单一,香农物种多样性指数均<1,SW和S、E的变化趋势大致相同,且与ED变化趋势相反。 相似文献
990.