全文获取类型
| 收费全文 | 103篇 |
| 免费 | 25篇 |
| 国内免费 | 53篇 |
专业分类
| 地球物理 | 12篇 |
| 地质学 | 64篇 |
| 海洋学 | 92篇 |
| 综合类 | 11篇 |
| 自然地理 | 2篇 |
出版年
| 2024年 | 1篇 |
| 2023年 | 4篇 |
| 2022年 | 12篇 |
| 2021年 | 12篇 |
| 2020年 | 39篇 |
| 2019年 | 12篇 |
| 2018年 | 20篇 |
| 2017年 | 16篇 |
| 2016年 | 7篇 |
| 2015年 | 8篇 |
| 2014年 | 9篇 |
| 2013年 | 13篇 |
| 2012年 | 2篇 |
| 2011年 | 2篇 |
| 2010年 | 2篇 |
| 2009年 | 1篇 |
| 2008年 | 5篇 |
| 2007年 | 2篇 |
| 2005年 | 1篇 |
| 2004年 | 2篇 |
| 2003年 | 3篇 |
| 2002年 | 1篇 |
| 2001年 | 1篇 |
| 2000年 | 2篇 |
| 1999年 | 2篇 |
| 1997年 | 1篇 |
| 1954年 | 1篇 |
排序方式： 共有181条查询结果，搜索用时 250 毫秒
11.
以水族馆内圈养的北海狮为研究对象,利用长达29 h的连续被动声学观测数据,对北海狮水下声信号类型进行了研究。共检测出22 689个水下声信号,对时长、最小频率、最大频率和峰值频率这4个声学参数采用聚类分析方法将信号分为10种类型:单脉冲(SP)、哨声(WS)、咕咕声(GG)、咚咚声(DS)、狗吠声(BK)、吼叫声(WY)、嗡嗡声(BZ)、撞击声(BG)、单频声(SF)以及咩咩声(BT)。该分类方式涵盖了北海狮92.6%的水下发声。北海狮水下声信号时长的均值为5~1 244 ms,峰值频率一般小于10 kHz。10种类型信号的占比各有不同,BK,BT和BG信号的比例较高;SP,WS和BZ信号的比例次之;DS,WY,SF和GG信号的比例较低。对北海狮水下声信号类型的分析能帮助了解北海狮的声行为特征,对野外北海狮的声学观测具有重要的指导价值。 相似文献
12.
The Western Foothills of Taiwan was known to be composed of Late Oligocene to Pleistocene shallow marine strata continuously deposited on the stable passive Chinese continental margin without significant stratigraphic break. Here we present multiple micropaleontological evidences, including occurrence of larger foraminifera Discocyclina dispansa ex. interc. sella-dispansa and calcareous nannoplanktons, to show that there are Middle Eocene marine strata (first named as the Chungliao Formation) exposed in the Tsukeng anticline of the Western Foothills, central Taiwan. Occurrences of intact tests with thin delicate outer rims and well-preserved embryonic chambers suggest that the Discocyclina dispansa ex. interc. sella-dispansa (Lutetian to Bartonian in the Tethys region) are buried indigenously on shallow inner shelf during an episodic transgression in the Early Middle Eocene. The conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons (Zones NP14–15) in the shale/sandstone alternations overlying the Discocyclina-bearing bed of the Chungliao Formation and calcareous nannofossils of Zone NP16 integrated with an age dating of 38.8 ± 1 Ma (Late Middle Eocene) on zircon grains of the overlying Pinglin Tuff. The Middle Eocene syn-rift sequences (Chungliao Formation and Pinglin Tuff) exposed along the Tsukeng anticline are unconformably covered by the latest Oligocene–Miocene post-rift sequence, a scenario similar to what have been drilled in the East China Sea-Taiwan Strait-South China Sea. This rift basin (named as the Nantou Basin) is sitting on the Peikang Basement High margin which further extends southwestward to the Central Uplift of the Pearl River Mouth Basin in the northern slope of the South China Sea. The present work documents a hitherto unknown occurrence of the exposed early Tertiary marine rift basin sequence in the Western Foothills of Taiwan. The study extends our knowledge of the Western Foothills geohistory from the Late Oligocene downward to the Early Middle Eocene. The occurrence of the Paleogene Nantou rift basin in the Western Foothills may also suggest that there could have similar Paleogene rift sequences exposed in other parts of the Taiwan mountain belt like the Hsüehshan Range and the Central Range east of the Western Foothills. 相似文献
13.
MultiBeam echosounder data were collected during a surface-ship survey of the 22/4b well site in the North Sea in September 2011 using a Teledyne-Reson 7125. Modern multibeam echosounders are instrumental in providing detection and accurate localization of weak to strong bubble plumes. Two survey profiles effectively insonified the bubble plumes rising from the main crater at the well site, providing snapshot data of bubble plume processes. Additionally, three profiles insonified bubble plumes rising from, in, and to the south of a secondary crater, 1.2 km southeast of the main crater. Data processing included a simple algorithm that muted mislocated echoes from incomplete sidelobe suppression. The data processing produced a Cartesian volume of echo intensity from the water column and seabed.Plume geometry was analyzed to investigate a number of important large-scale plume processes, including plume bubble detrainment due to currents and stratification, downwelling flows, sea surface interaction, plume heterogeneity, and other fluid transport processes. The data showed strong upwelling flows, with bubble vertical motions generally much faster than currents. One important finding was that megaplumes create intrusions above the general thermocline, in part because their extensive upwelling flow lifts the thermocline locally. As a result, the intrusion layer deposits dissolved gases in the upper wave-mixed layer of the water column where it is not isolated from the atmosphere, unlike dissolved gases in the lower water column.The analysis shows that high fidelity multibeam echosounder data can provide a wealth of remote sensing information on bubble plume characteristics and processes, with important applications, including blowout monitoring and response, better understanding of megaplumes such as used in lake destratification, and improved characterization of natural seep emission processes. 相似文献
14.
15.
Fresh rocks sampled from the 14.0°S hydrothermal field of the South Atlantic Ridge can be divided into two categories： olivine-gabbro and basalt. The olivine-gabbro is composed mainly of three types of minerals： olivine, clinopyroxene and plagioclase, while a multitude of melt inclusions occur in the plagioclase phenocrysts of the basalts. We analyzed the whole-rock, major and trace elements contents of the basaks, the mineral chemistry of phenocrysts and melt inclusions in the basalts, and the mineral chemistry of olivine-clinopyroxene-plagioclase in the olivine-gabbro, then simulated magma evolution within the crust using the COMAGMAT program. The whole-rock geochemistry shows that all the basalts exhibit typical N-MORB characteristics. In addition, the mineral chemistry characteristics of the olivine-gabbro （low-Fo olivine, low-Mg# clinopyroxene, high-TiO2 clinopyroxene, low-An plagioclase）, show that strong magma differentiation occurred within the crust. Nevertheless, significant discrepancies between those minerals and phenocrysts in the basalts （high-Fo olivine, high-An plagioclase） reflect the heterogeneity of magma differentiation. High Mg# （-~0.72） melt inclusions isobaric partial crystallization simulations suggest that the magma differentiation occurred at the depth shallower than 13.03 km below the seafloor, and both the vertical differentiation column shows distinct discrepancies from that of a steady-state magma chamber. Instead, a series of independent magma intrusions probably occurred within the crust, and their corresponding crystallized bodies, as the primary high-temperature thermal anomalies within the off-axis crust, probably act as the heat source for the development of the 14.0°S hydrothermal system. 相似文献
16.
《Deep Sea Research Part II: Topical Studies in Oceanography》2010,57(15):1303-1312
We present a 3-year multidisciplinary biogeochemical data set taken in situ at the Porcupine Abyssal Plain (PAP) time-series observatory in the Northeast Atlantic (49°N, 16.5°W; water depth ∼4850 m) for the period 2003 to 2005. The high-resolution year-round autonomous measurements include temperature, salinity, chlorophyll-a (derived from in situ chlorophyll-fluorescence) and inorganic nitrate, all at a nominal depth of 30 m on an Eulerian observatory mooring. This study compares these in situ time-series data with satellite chlorophyll-a data, regional data from a ship of opportunity, mixed-layer depth measurements from profiling Argo floats and lateral advection estimates from altimetry. This combined and substantial data set is used to analyse seasonal and inter-annual variability in hydrography and nitrate concentrations in relation to convective mixing and lateral advection. The PAP observatory site is in the inter-gyre region of the North Atlantic where convective mixing ranges from 25 m in the summer to over 400 m in winter when nutrients are supplied to the surface. Small inter-annual changes in the winter mixed layer can result in large changes in nitrate supply and productivity. However the decrease in maximum winter nitrate over the three-year period, from 10 to 7 mmol m−3, cannot be fully explained by convective mixing. Trajectories leading to the PAP site, computed from altimetry-derived geostrophic velocities, confirm that lateral advection cannot be ignored at this site and may be an important process along with convective mixing. Over the three years, there is an associated decrease in new production calculated from nitrate assimilation from 85.4 to 40.3±4.3 gCm−2 a−1. This confirms year-to-year variability in primary production seen in model estimates for the region. The continuous in situ dataset also shows inter-annual variation in the timing of the spring bloom due to variations in heat flux; the 2005 bloom occurred earlier than in 2004. 相似文献
17.
“蛟龙”号是我国首台载人潜水器，也是全球下潜深度最大的作业型载人潜水器。为使“蛟龙”号具有更大的作业空间，其布放回收系统须满足三级海况下布放和四级海况下回收的作业需求。文章介绍“蛟龙”号布放回收系统的系统组成和关键技术，并对其实际应用情况进行分析和总结。研究结果表明：“蛟龙”号的布放回收系统主要包括A形架、拖曳绞车和升降轨道车；拖曳绞车和A形架主吊缆的恒张力控制系统实现布放回收系统的升沉补偿功能，可满足“蛟龙”号三级海况下布放和四级海况下回收的需求；升降轨道车同时可作为“蛟龙”号日常存放、保养和维修的载体。 相似文献
18.
平端深海偏顶蛤(Gigantidasplatifrons)是南海台西南冷泉区的典型优势物种,鳃丝上皮细胞内共生大量甲烷氧化菌,通过甲烷有氧氧化合成有机物为共生体系提供物质能量,是平端深海偏顶蛤赖以生存的重要能量来源器官,溶酶体在共生体系的营养互作和稳态维持中可能发挥重要作用,本研究使用电镜技术观测了常压培养过程中(0d,30d,90d)平端深海偏顶蛤共生体系中共生菌和溶酶体的动态变化,通过鳃上皮含菌细胞超显微结构的变化研究常压培养对深海共生体系的影响,并探讨溶酶体在宿主—共生菌营养传递和共生菌群稳态维持中的关键作用。研究发现,在原位状态样品中(0d)共生菌和溶酶体呈极化分布,细胞结构完整清晰;蓄养30d后,含菌细胞出现明显破碎,共生菌数量大幅降低,溶酶体数量、范围和消化程度大幅增加,对细胞顶端的甲烷氧化菌进行分解;而90d后,共生菌在溶酶体的作用下消失殆尽,鳃部有明显细胞脱落后留下的坑洞,细胞呈现空泡状,无法明确区分各种细胞组分。上述结果展示了长期常压蓄养过程中鳃上皮含菌细胞中溶酶体与甲烷氧化菌的动态变化,推测当共生菌丢失后溶酶体也同步降低活跃度,平端深海偏顶蛤在共生互作中通过溶酶体主导消化和调控共生菌。 相似文献
19.
Deep-sea mussels of the subfamily Bathymodiolinae are common and numerically dominant species widely distributed in cold seeps and hydrothermal vents.During long-time evolution,deep-sea mussels have evolved to be well adapted to the local environment of cold seeps and hydrothermal vents by various ways,especially by establishing endosymbiosis with chemotrophic bacteria.However,biological processes underlying the establishment and maintenance of symbiosis between host mussels and symbionts are largely unclear.In the present study,Gigantidasplatifrons genes possibly involved in the symbio sis with methane oxidation symbionts were identified and characterized by Lipopoly saccharide(LPS) pull-down and in situ hybridization.Five immune related proteins including Toll-like receptor 2(TLR2),integrin,vacuolar sorting protein(VSP),matrix metalloproteinase 1(MMP1),and leucine-rich repeat(LRR-1) were identified by LPS pull-down assay.These five proteins were all conserved in either molecular sequences or functional domains and known to be key molecules in host immune recognition,phagocyto sis,and ly so some-mediated digestion.Furthermore,in situ hybridization of LRR-1,TLR2 and VSP genes was conducted to investigate their expression patterns in gill tissues of G.platifrons.Consequently,LRR-1,TLR2,and VSP genes were found expressed exclusively in the bacteriocytes of G.platifrons.Therefore,it was suggested that TLR2,integrin,VSP,MMP1,and LRR-1 might be crucial molecules in the symbiosis between G.platifrons and methane oxidation bacteria by participating in symbio sis-related immune processes. 相似文献
20.
The Indo-Pacific convergence region is the best target to solve the teo remaining challenge s of the plate tectonics theory,i.e.,subduction initiation and the driving force of plate tectonics.Recent studies proposed that the Izu-Bonin subduction initiation belongs to spontaneous initiation,which implies that it started from extension,followed by low angle subduction.Numerical geodynamic modeling suggests that the initiation of plate subduction likely occurred along a transform fault,which put the young spreading ridge in direct contact with old oceanic crust.This,however,does not explain the simultaneous subduction initiation in the west Pacific region in the Cenozoic.Namely,the subduction initiations in the Izu-BoninMariana,the Aleutian,and the Tonga-Kermadec trenches are associated with oceanic crusts of different ages,yet they occurred at roughly the same time,suggesting that they were all triggered by a maj or change in the Pacific plate.Moreover,low angle subduction induces compression rather than extension,which requires external compression forces.Given that the famous Hawaiian-Emperor bending occurred roughly at the same time with the onset of westward subductions in the west Pacific,we propose that these Cenozoic subductions were initiated by the steering of the Pacific plate,which are classified as induced initiation.Induced subduction initiation usually occurs in young ocean basins,forming single-track subduction.The closure s of Neo-Tethys Oceans were likely triggered by plume s in the south,forming northward subductions.Interestingly,the Indian plate kept on moving northward more than 50 Ma after the collision between the Indian and Eurasian continents and the break-off of the subducted oceanic slab attached to it.This strongly suggests that slab pull is not the main driving force of plate tectonics,whereas slab sliding is. 相似文献