全文获取类型
收费全文 | 2376篇 |
免费 | 462篇 |
国内免费 | 830篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 249篇 |
地球物理 | 327篇 |
地质学 | 2051篇 |
海洋学 | 563篇 |
天文学 | 2篇 |
综合类 | 117篇 |
自然地理 | 346篇 |
出版年
2024年 | 24篇 |
2023年 | 38篇 |
2022年 | 100篇 |
2021年 | 100篇 |
2020年 | 81篇 |
2019年 | 132篇 |
2018年 | 73篇 |
2017年 | 90篇 |
2016年 | 117篇 |
2015年 | 107篇 |
2014年 | 144篇 |
2013年 | 163篇 |
2012年 | 175篇 |
2011年 | 165篇 |
2010年 | 130篇 |
2009年 | 151篇 |
2008年 | 164篇 |
2007年 | 159篇 |
2006年 | 147篇 |
2005年 | 120篇 |
2004年 | 109篇 |
2003年 | 116篇 |
2002年 | 118篇 |
2001年 | 135篇 |
2000年 | 102篇 |
1999年 | 125篇 |
1998年 | 78篇 |
1997年 | 85篇 |
1996年 | 62篇 |
1995年 | 62篇 |
1994年 | 55篇 |
1993年 | 78篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 39篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1979年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有3668条查询结果,搜索用时 31 毫秒
831.
本文根据厦门港湾12个柱样沉积物的抱粉分析结果,划分出三个饱粉带,探讨了其沉积环境与古气候演化史。Ⅲ榛属-藜科-水龙骨科带,以榛和草本为主,表明为稀树草原植被和温凉干燥气候,陆相沉积,形成于晚更新世晚期至早全新世;Ⅱ栎属、栲属、栗属一水龙骨科带,表明为繁盛的常绿阔叶林和茂密的灌木草本植被,气候最湿润暖热,为冰后期海面最高时期,海相沉积,形成于中全新世;I松属-禾本科-蕨属、水龙骨科带,由成类、草本和针叶树组成,表明主要为针叶树和栽培植被,气候转为暖干,现代沉积,即晚全新世。 相似文献
832.
833.
南海东部海盆海山磁性对比 总被引:1,自引:0,他引:1
根据 1 980年~ 1 987年在南海海盆进行地球物理调查获取的海山地形和地磁异常资料 ,运用虚源法 ,对南海东部海盆区域的 9座海山作了磁性计算及对比。结果表明 :(1 )每座海山非均匀磁性反演的磁异常形态比均匀磁性反演的磁异常形态更接近观测异常 ,海山为非均匀磁化。 (2 )每座海山的非均匀磁化计算的拟合度参数值 (GFR值 )大于均匀磁化计算的拟合度参数值 (GFR0 值 ) ,平均每座海山增加 3 .7。 (3 )海山形成后均向北运移 ,位于东部海盆北侧的5座海山沿纬向位移的平均距离为 9.2 1°,南侧 4座海山沿纬向位移的平均距离为 3 .6 7°;海山均呈逆时针旋转 ,但旋转的角度存在区域性差异 ;东部海盆的运移方式与东邻的吕宋岛、西菲律宾海盆和台湾岛相一致。 (4)海山的磁化强度呈明显的分区性 ,北侧 5座海山的磁化强度大于南侧 4座海山的磁化强度 ,推测东部海盆形成过程中整体向北运动 相似文献
834.
福建海洋资源开发利用及其对策 总被引:3,自引:1,他引:3
本文分析了福建省开发海洋资源的优势、现状和存在问题,结合可持续发展观点为,提出了福建海洋资源永续利用的对策。 相似文献
835.
本文分析了闽东北外海渔场资源特点,并就不同类型的拖网、围网渔具的适渔性对比试验进行了研究,认为以主机功率330.75kw及以上的拖网渔船,使用四片式疏目拖网和以主机功率183.75kw及以上的围网渔船,使用250m×150m的无囊灯光围网,于春、夏汛时在该渔场100m等深线附近海域能较有效地捕捞鲐鲹等中上层鱼类。 相似文献
836.
本文根据1980年厦门港湾底质调查的70个样品,应用R型因子分析方法,对沉积物粒级组成的成因进行分析。结果表明,该海域陆续修建的临海工程对其沉积物组成影响明显,使其由粗粒组成向细粒组成变化。尤其是高集海堤的兴建,泥沙大量淤积;海堤建成后,沉积环境日益稳定,接受沉积物以粉砂、粘土占主导地位。 相似文献
837.
Determination of source parameters of small earthquakes from amplitude ratios of
and
is studied in this paper when the distribution of the regional seismic network is skew to the earthquakes. The distribution
of stations of the seismic network was to one side of the 17 earthquakes chosen from among 39 earthquakes in the east part
of Guangdong and south part of Fujiang Province. The distribution of stations was classified into three types according to
their relative positions with respect to the chosen earthquakes and the experiments of artificial data were done. Excellent
results were also presented in various unfavourable conditions by using the method.
As to the 39 small earthquakes recorded by the network in east Guangdong and south Fujian Province from 1982 to 1986, the
results can be summarized as follows: Most of the fault planes of the earthquakes apear to be steep. Most of the principal
compression stressesP and tensile stressesT are nearly horizontal, concentrating in the WNW-ESE direction.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinia,13, 420–429, 1991. 相似文献
838.
839.
Alexandre Cunha Costa Saskia Foerster José Carlos de Araújo Axel Bronstert 《水文研究》2013,27(7):1046-1060
Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi‐temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi‐arid north‐eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre‐events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
840.
To constrain the evolution of the eastern segment of the Paleo-Asian Ocean (PAO), petrography, geochemistry and zircon U-Pb dating analyses were conducted over the gabbro and rhyolite in the Kaiyuan area, North Liaoning, in the eastern segment of the northern margin of the North China Craton (NCC). Zircon dating results indicate that the gabbros and rhyolite were formed in the Trassic (246 +/- 2Ma, 241 +/- 2Ma, 226 +/- 3Ma and 241 +/- 2Ma). The three gabbros of Triassic have similar geochemical characteristics, originated from the mantle, and were contaminated by crust materials in the process of ascending and emplacement. The Early Triassic gabbro (246Ma) originated from the enriched mantle source metasomatized by fluid. It was formed by 1% partial melting of garnet spinel lherzolite in the extensional environment caused by breaking off slab. The Middle Triassic gabbro (241Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 1% to 2% partial melting of garnet spinel peridotite. The Late Triassic gabbro (226Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 3% similar to 4% partial melting of garnet spinel lherzolite in the post-orogenic extensional environment. The Middle Triassic rhyolite (241Ma) has the characteristic of post collisional I-type granite, that enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements, and negative Nb, Ti, P and Sr anomaly. The low content of Sr and Yb suggested a 30 similar to 40km depth source. The Middle Trassic "bimodal" igneous rocks implied an extensional environment caused by the remainder oceanic crust breaked away at the bottom of the crust. Based on the lithologic association, regional strata information and the chronological data in this paper and published by predecessors, the Triassic magmatism in the eastern segment of the northern margin of the NCC can be divided into five stages: 252 similar to 246Ma, 246 similar to 242Ma, 242 similar to 240Ma, 240 similar to 230Ma and 230 similar to 215Ma. These five magmatic events were the results of the southward subduction and extinction of the PAO: (1) The transformation from active continental margin to syn-collisional setting resulted in the final closure of the PAO (252 similar to 246 Ma); (2) Continuous pushing resulted in orogenic uplift (246 similar to 242Ma); (3) Extension caused by the detachment of the remainder subduction oceanic crust at the bottom of the crust (242 similar to 240Ma); (4) Rapid uplift and crustal thickening (240 similar to 230Ma); (5) Extension of post-orogenic(230 similar to 215Ma). 相似文献