全文获取类型
收费全文 | 432篇 |
免费 | 90篇 |
国内免费 | 142篇 |
专业分类
测绘学 | 49篇 |
大气科学 | 78篇 |
地球物理 | 73篇 |
地质学 | 250篇 |
海洋学 | 52篇 |
天文学 | 4篇 |
综合类 | 63篇 |
自然地理 | 95篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 28篇 |
2020年 | 27篇 |
2019年 | 35篇 |
2018年 | 28篇 |
2017年 | 20篇 |
2016年 | 34篇 |
2015年 | 25篇 |
2014年 | 31篇 |
2013年 | 35篇 |
2012年 | 25篇 |
2011年 | 22篇 |
2010年 | 35篇 |
2009年 | 41篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 18篇 |
2005年 | 19篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有664条查询结果,搜索用时 31 毫秒
451.
INTRODUCTIONThequantitativereconstructionofpaleoclimatefactorsisthefocusofstudyonenvironmentinthepast ,andanef fectivetoolforthequantitativeresearchintothepaleocli mateisthetransformationofspore pollendata .ThemainperiodthusinvolvedwastheQuaternaryinste… 相似文献
452.
湘西北奥陶纪层序地层研究 总被引:7,自引:2,他引:7
有关奥陶纪层序地层研究,在湘西北地区尚属首次,通过对11个剖面详细的野外露头层序界面的辨认,追索以及对亚层序的划分和堆形式的识别,将奥陶第初步划分为两个中层序或二级层序,11个正层序或三级层序,根据层序所确定的海平面升降曲线,可与北美、澳大利亚、华北等进行对比。 相似文献
453.
Sequential analysis of China's hazards in geoscience 总被引:1,自引:0,他引:1
Chen Zhiming 《GeoJournal》1996,38(3):259-263
At the request of the IGU Study Group on Rapid Geomorphologic Hazards, the author has dealt with a lot of information on China's hazards in the course of compiling geomorphic hazard inventories. While analyzing those hazards throughout history, especially in the past two decades, the author found that quite many hazards used to be either interrelated or associated with each other. On the basis of a large number of eventful catastrophic cases both in China and its adjacent areas, this paper analyzes and sums up the following seven major sequences with respect to the occurrences and transformations in geo-hazards: 1) Dry-cold wind-drift sand (dust) storm type, 2) Warm-wet water-soil hazards type, 3) Wet-hot typhoon hazards type, 4) Alpine freezing-gravity hazards type, 5) Earthquake-rainstorm and mud-rock flow type, 6) Earthquake-forest fire hazards type and 7) Earthquake-tsunami hazards type. 相似文献
454.
我国西北地区4.5沙尘暴天气研究 总被引:18,自引:8,他引:18
对1994年4月5日发生在中国西北地区的一次强沙尘暴天气,从天气事实、天气学成因以及动力诊断等方面进行了探讨分析,揭示了形成东大风沙尘暴天气的物理机制。采用NCAR客观分析方案进行的动力诊断表明,(1)地面热低压与正涡度中心相互对应,涡度随高度迅速减小(ξZ<0),有利于中低压的发展加强,沙尘暴产生在正涡度区域内;(2)沙尘暴垂直环流特征是南疆至河西中、东部发展一庞大的垂直环流圈,环流中心在150~200hPa层,它起到组织低空中尺度系统的重要作用;(3)在南北经向剖面上,蒙古高压是一个非常深厚的大型天气系统,它一直伸展到对流层上部,形成了自南向北的正环流圈,在高压南部的上升气流中激发大风和沙尘暴;(4)4·5沙尘暴后期低层大气层结稳定,不利于浮尘消散,故浮尘持续时间长 相似文献
455.
New total organic carbon (TOC) data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wnfeng (五峰) Formation and the Longmaxi (龙马溪) Formation in Central Guizhou (贵州) and West Hubei (湖北), respectively, as well as previously reported TOC data from the same intervals in other places on the Yangtze platform of South China, have been used to produce an initial estimate of the primary paleoproductivity via a conventional inverse method (i.e., Rpp-inverse). The values of the Rpp-inverse are estimated to be 32 (43-21) gC/(m2·a) (Wufeng Formation) and 21 (27-16) gC/(m2·a) (Longmaxi Formation). Also, simultaneously, the habitat types (i.e., HT; cf., BA: benthic assemblage) and their temporal and spatial changes have been documented from the same succession, and an initial estimate of the primary paleoproductivity has been produced using a forward method (i.e., Rpp.forward). Being bounded mainly by the peritidai to inner-shelf environment shelly-facies or mixed-facies successions with BAI to BA3 faunas both at the top and the base, which indicates the habitat types from HT Ⅱ1 to HT Ⅲ2, the biohabitat type of the two graptolite-bearing black shale intervals can be limited to HT Ⅲ to HT Ⅳ, corresponding to the inner shelf to the outer shelf, with depths from roughly 60 m to 200-300 m. Based on the current data from the South China Sea and the southern part of the East China Sea, values of Rpp-forward should be about 100 to 400 gC/(m2·a). The difference in the results via the two methods suggests that paleoproductivity estimates from the geological strata need to be made cautiously, with particular attention paid to the paleogeographic setting, oxic-anoxic conditions, as also the preservation factor of organic carbon. 相似文献
456.
457.
Highland barley is an important staple food in the Tibet, and the Tibetan Plateau is experiencing obvious climatic warming. However, few studies have examined the warming effects on highland barley growth and biomass allocation under conditions of controlled experimental warming. This limits our ability to predict how highland barley will change as the climate changes in the future. An experiment of field warming at two magnitudes was performed in a highland barley system of the Tibet beginning in late May, 2014. Infrared heaters were used to increase soil temperature. At the end of the warming experiment (September 14, 2014), plant growth parameters (plant height, basal diameter, shoot length and leaf number), biomass accumulation parameters (total biomass, root biomass, stem biomass, leaf biomass and spike biomass), and carbon and nitrogen concentration parameters (carbon concentration, nitrogen concentration, the ratio of carbon to nitrogen concentration in root, stem, leaf and spike) were sampled. The low- and high-level experimental warming significantly increased soil temperature by 1.52 and 1.98 °C, respectively. Average soil moisture was significantly decreased by 0.03 m3 m-3 under the high-level experimental warming, while soil moisture under the low-level experimental warming did not significantly change. The low- and high-level experimental warming did not significantly affect plant growth parameters, biomass accumulation parameters, and carbon and nitrogen concentration parameters. There were also no significant differences of plant growth parameters, biomass accumulation parameters, and carbon and nitrogen concentration parameters between the low- and high-level experimental warming. Our findings suggest that the response of highland barley growth, total and component biomass accumulation, and carbon and nitrogen concentration to warming did not linearly change with warming magnitude in the Tibet. 相似文献
458.
基于EOF分解的中期平均气温距平客观预报方法 总被引:1,自引:0,他引:1
本文通过将500 hPa高度、850 hPa温度、海平面气压的预报与历史要素场进行EOF分解,并假定EOF分解空间函数(即特征向量)是基本稳定的,建立以EOF分解主分量系列的时间系数、预报站点附近基本要素值的时间序列与预报站点平均气温距平的多元线性逐步回归预报方程,结合ECMWF集合预报数值产品,生成全国范围未来10 d平均气温距平客观预报产品投入业务应用,并采用同号率方法检验。结果表明,客观预报产品在检验时段内,同号率平均值为0.77,明显高于ECMWF集合预报模式2 m温度直接计算得出的同类产品同号率0.63;该客观预报产品不仅在分布范围上,同时在距平幅度上预报效果均较好。此外,相关分析也证明同号率方法在检验中期时效气温距平预报中有其合理性。 相似文献
459.
The opinions vary on the secondary remagnetization mechanisms of carbonate rocks. The prevalent interpretations of magnetic remanences are either chemical in origin that invoked the large-scale migration of orogenic fluids. or thermoviscous magnetization involved burial diagenetic processes. The paleomagnetic study carried out in northwestern part of Henan Province (north of the Qinling orogenic belt) reveals that 90% of carbonate rocks have suffered from the secondary remagnetization. On the basis of rock magnetic experiments, the assemblage of the magnetic minerals, remanent carriers and its formation process, and the possible mechanisms of remagnetization in these carbonate rocks are discussed. 相似文献
460.
区域贫困的地理学分析 总被引:27,自引:3,他引:24
贫困的多维属性和空间属性意味着具备综合性和区域性优势且以“人地关系”为研究核心的地理学在贫困研究和扶贫实践指导方面应大有作为。本文在回顾国内外地理学关注的贫困主题及其研究进展基础上,尝试从地理学视角阐释区域贫困的本质、构成要素、格局、形成过程及应对方案。主要结论为:① 区域贫困的本质是特定时空情境下“人”(贫困主体)、“业”(生计活动)、“地”(自然和社会环境)维度上的剥夺或三者之间耦合失调的过程与状态。② 区域贫困的构成要素包括主体性要素“人”、中介性要素“业”和客体性要素“地”,各要素层面的剥夺以及三要素“人业地”耦合失调形成区域贫困格局类型。③ 区域贫困格局的形成既是主体性要素“人”、中介性要素“业”和客体性要素“地”之间非线性“负向循环累积”过程,也是人类文明进程中主体性要素“人”和客体性要素“地”未与中介性要素“业”的变化相协调在特定地域的表现。④ 区域贫困的系统化干预既需要各要素层面的“靶向干预”,还需要各措施之间的协同,而仿效医院的会诊制度是一种可行的制度安排。 相似文献