全文获取类型
收费全文 | 31篇 |
免费 | 11篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 4篇 |
地球物理 | 9篇 |
地质学 | 17篇 |
海洋学 | 5篇 |
天文学 | 1篇 |
综合类 | 7篇 |
自然地理 | 6篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2009年 | 5篇 |
2007年 | 1篇 |
2003年 | 1篇 |
2002年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有50条查询结果,搜索用时 312 毫秒
21.
22.
Xiaohong Liu Xuemei Shao Eryuan Liang Tuo Chen Dahe Qin Wenling An Guobao Xu Weizhen Sun Yu Wang 《Chemical Geology》2009,268(1-2):147-154
It is important to understand the history and dynamics of climate in a transitional region between areas with different atmospheric circulation patterns, where the vegetation and ecosystems are vulnerable to environmental change. We investigated variations in the long-term oxygen isotope composition (δ18O) in tree rings of Qinghai spruce (Picea crassifolia) and their relationships to climatic parameters in the arid Qilian Mountains of northwestern China from 1870 to 2006. We found that the mean temperature from the previous November to the current February was significantly and positively correlated with the tree-ring δ18O values. The temperature effect, (the positive relationship between the temperature and the precipitation δ18O value) can explain the connection between temperature and the tree-ring δ18O values. Due to pooling of the earlywood and latewood into yearly tree-ring samples, it appears that the cellulose δ18O may be influenced by isotopically nonhomogeneous water sources and climatic conditions during the previous and current growing seasons. Subtle shifts and amplitude deviations in cellulose δ18O, which abruptly became more positive around 1977–1978, may be attributed to the shifting climatic regime in China and to temperature variations, respectively. Our results illustrated the potential for investigating climatic or atmospheric circulation patterns based on oxygen isotope records in tree rings in regions near the interface between different large-scale synoptic circulations. 相似文献
23.
马头山铜金矿床位于康定一锦屏山矿集区,处于锦屏山断裂与康定一水城断裂的交汇部位,是川西南地区新发现的中型铜金矿床。矿体呈现为硫化物石英脉状,赋存于泥盆系泥质粉砂质板岩、碳酸盐化泥晶灰岩和二叠系变质玄武岩中,受断裂构造控制,矿石中硫化物矿物多见黄铁矿、斑铜矿、黄铜矿、方铅矿等。矿石中石英原生流体包裹体观测和激光拉曼光谱分析显示,马头山铜金成矿流体为H_2O-CO_2-NaCl体系,均一温度108.1~439.1℃,盐度3.55%~22.78%NaCleq,密度0.51~1.12 g/cm~3,主成矿阶段流体包裹体具有中低温、中低盐度、低密度、富含CO_2的特征。矿石中硫化物矿物δ~(34)SV-CDT=-4.6‰~8.4‰,具有岩浆来源硫的特征,石英脉中原生流体包裹体的δD=-78.8‰~-48.7‰,δ~(18)O_(H_2O)=-2.1‰~9.3‰,白云石的δ~(13)C_(V-PDB)=-5.3‰~1.7‰,δ~(18)O_(V-SMOW)=19.4‰~25.9‰,表明成矿流体主要为岩浆水,并有地层流体和大气水加入。综合矿床地质特征、流体包裹体特征和S、C、O、H同位素证据,认为马头山铜金矿床为中低温-岩浆热液型铜金矿床。 相似文献
24.
庙顶铜金矿床位于特提斯成矿域与滨太平洋成矿域交界部位,处于多个成矿远景区的交汇地带,成矿条件优越。矿体赋存于泥盆系碳酸盐化凝灰岩、泥质粉砂质板岩、碳酸盐化泥晶灰岩与二叠系变质玄武岩地层中。岩相学表明:矿床的矿石类型有铜金矿化碳酸盐石英脉型、铜金矿化变质岩型和铜矿化钠长石岩型。矿相学研究表明:铜矿物以硫化型为主,其次为氧化型,主要为黄铜矿,其次是斑铜矿及铜蓝;金赋存以含银自然金为主,其次为银金矿,游离金为主要的回收对象。金属矿物的生成顺序为:磁铁矿→黄铁矿→自然金、银金矿、黄铜矿、斑铜矿、辉铜矿、黝铜矿、磁黄铁矿→方铅矿、铜蓝、蓝辉铜矿→褐铁矿、孔雀石、蓝铜矿、氯铜矿。矿床形成经历了变质期、热液期和表生期,其中热液期又分为3个阶段:钠长石-云母-黄铁矿阶段(Ⅰ)、金-石英-多金属硫化物阶段(Ⅱ)和碳酸盐-石英-重晶石阶段(Ⅲ)。电子探针结果表明,矿床的形成过程经历了由高温到低温的变化,成因类型应属岩浆热液矿床。 相似文献
25.
桂北三防地区发现韧性剪切带和韧性断层。其组成岩石是糜棱岩化花岗岩、花岗质初糜棱岩、花岗质糜棱岩、千糜岩。花岗质糜棱岩构造标志指示运动学方向为由西向东向上逆冲推覆性质。剪切带主要变形时代可能是加里东期。 相似文献
26.
海鳗肝脏、胆囊及胰腺的显微结构 总被引:6,自引:0,他引:6
采用光镜技术研究海鳗肝脏、胆囊和胰腺的显微结构。结果表明:海鳗肝小叶不明显,肝门管区不典型。肝细胞较大,呈多边形,糖原和脂滴丰富。核呈圆形或卵圆形,1~2个。胆囊与胆管结构类似其他鱼类。胰腺长条形,紧贴肠左壁,独立存在,少量分布在胆管周围及胆囊壁上。外分泌部由腺泡和各级排泄管组成,内分泌部即胰岛,分散存在于外分泌部之间,胰岛细胞由A,B,D三种细胞组成。A细胞数量较少,位于胰岛周边,夹于B细胞之间,胞质颗粒染成红色;B细胞数量最多,位于胰岛周边,胞质颗粒染成橘黄色;D细胞一般位于胰岛中部染色浅淡的区域,胞质染淡蓝色。 相似文献
27.
Alpine timberline population dynamics under climate change: a comparison between Qilian juniper and Qinghai spruce tree species in the middle Qilian Mountains of northeast Tibetan Plateau 总被引:1,自引:0,他引:1 下载免费PDF全文
Bo Wang Tuo Chen Guobao Xu Xiaohong Liu Wenzhi Wang Guoju Wu Youfu Zhang 《Boreas: An International Journal of Quaternary Research》2016,45(3):411-422
Alpine forest population dynamics are sensitive to climate change. Response patterns are complex, and it is still unclear as to whether or not population dynamics are species‐dependent. In this study, population dynamic patterns for alpine timberline Qilian juniper and Qinghai spruce tree species in the mid Qilian Mountains were determined from approximately 1500 C.E. by applying dendrochronological methods. The results showed that these tree species have different forest population dynamics. The Qinghai spruce recruitment rate was clearly higher than that of Qilian juniper. Furthermore, the temporal population dynamic patterns of Qinghai spruce samples taken at different sites were consistent whereas those of the Qilian juniper samples were not. Qinghai spruce population dynamics were primarily affected by temperature, with positive correlations between temperature and recruitment. By contrast, with the exception of a positive to negative shift in the relationship between temperature and Qilian juniper population dynamics, Qilian juniper recruitment significantly decreased when its density reached a relatively high level. Moreover, a shift in the temperature‐recruitment relationship and a decrease in recruitment occurred simultaneously, indicating that Qilian juniper population dynamics were affected by both temperature and density. Species to species differences were also observed when compared with previous studies within the mid Qilian Mountains, confirming the existence of species‐dependent population dynamic patterns. Forest recruitment dynamic patterns and tree recruitment‐climate relationships may help to provide clues for future studies on forest management, conservation and utilization. 相似文献
28.
Xiaomin Zeng Xiaohong Liu Guobao Xu Wenzhi Wang Wenling An 《Environmental Earth Sciences》2014,72(6):2173-2182
Pollution from urban centers and fossil fuel combustion can decrease forest growth and interfere with physiological processes. To evaluate whether tree growth and the carbon isotope ratio (δ13C) and nitrogen isotope ratio (δ15N) in tree rings can serve as proxies for air pollution, this study compared these indices for poplar (Populus cathayana) growing at urban and suburban locations in Lanzhou, in northwestern China. Basal area increment values were much lower at the urban site than in the suburbs from 1985 to 2009, were negatively correlated with NO2 (r = ?0.56, p < 0.01) and SO2 (r = ?0.52, p < 0.05) emissions from 1990 to 2009, and increased abruptly after the Lanzhou urban steel factory closed. Urban tree-ring δ13C values were not significantly correlated with NO2 and SO2 concentrations, and did not differ significantly between the two sites, indicating that other environmental effects (such as precipitation) masked the pollution effects. Tree-ring δ15N values in the urban samples were much higher than the suburban values. Such differences may be attributable to uptake of 15N-enriched compounds caused by a higher urban N deposition rate. Tree growth is a promising tool for detecting ecophysiological responses of trees to both diffuse and point-source air pollution, but δ13C and δ15N in poplar were not sensitive to point-source air pollution in a heavily polluted environment. 相似文献
29.
Xuanwen Zhang Xiaohong Liu Wenzhi Wang Tingjun Zhang Xiaomin Zeng Guobao Xu Guoju Wu Huhu Kang 《水文研究》2018,32(10):1449-1460
The thermal and moisture balance of permafrost regions has been altered by global warming, profoundly influencing vegetation dynamics and forest carbon cycling. To understand the spatial and temporal characteristics and driving forces responsible for changes in moisture conditions in the permafrost region of the Greater and Lesser Hinggan Mountains, northeastern China, we assessed long‐term trends for temperature, precipitation, and the standardized precipitation‐evapotranspiration index. From 1951 to 2014, annual mean temperature had a significant increase trend and the annual precipitation was not with significant trend. Since 1951, the annual standardized precipitation‐evapotranspiration index has decreased significantly at the boundary between regions with seasonal soil freezing and permafrost, suggesting that conspicuous permafrost degradation and moisture loss has occurred. The study area can be divided into 4 parts with a different balance between thermal and moisture conditions: the northern Songnen Plains, the Hulun Buir Sand Land, the middle reaches of the Heilongjiang River, and the Mohe region. However, only the middle reaches of the Heilongjiang River showed an obvious long‐term drying trend. The 4 areas showed quasi‐periodic oscillation and sea surface temperature during the winter half‐year affected drought intensity in the northern of Songnen Plains. When El Niño strengthened, moisture conditions increased in the northern of Songnen Plains, whereas stronger La Niña events decreased water availability. The result of this study will be beneficial for regional water resource management and prepare for potential drought hazards in the northeastern China. 相似文献
30.
We measured the target strength (TS) of three commercial fish species: whitespotted spinefoot (Siganus canaliculatus), black porgy (Acanthopagrus schlegelii), and creek red bream (Lutjanus argentimaculatus), in the South China Sea. The TS of caged or tethered fish (n=76 total) was measured using a Simrad EY60 portable scientific echosounder at 120 kHz. We evaluated the relationship between TS and total length (TL, cm) for the three species. This is the first attempt to use split-beam acoustics to measure single-fish TS in the South China Sea by Chinese researchers. Our results will improve the accuracy and precision of acoustic abundance estimates of commercially important species and further the development of underwater acoustic survey techniques in fisheries in the South China Sea. 相似文献