全文获取类型
收费全文 | 9629篇 |
免费 | 1344篇 |
国内免费 | 2493篇 |
专业分类
测绘学 | 385篇 |
大气科学 | 847篇 |
地球物理 | 3287篇 |
地质学 | 6284篇 |
海洋学 | 795篇 |
天文学 | 760篇 |
综合类 | 688篇 |
自然地理 | 420篇 |
出版年
2022年 | 48篇 |
2021年 | 110篇 |
2020年 | 115篇 |
2019年 | 76篇 |
2018年 | 227篇 |
2017年 | 217篇 |
2016年 | 327篇 |
2015年 | 264篇 |
2014年 | 281篇 |
2013年 | 383篇 |
2012年 | 300篇 |
2011年 | 755篇 |
2010年 | 522篇 |
2009年 | 659篇 |
2008年 | 323篇 |
2007年 | 455篇 |
2006年 | 663篇 |
2005年 | 673篇 |
2004年 | 1264篇 |
2003年 | 829篇 |
2002年 | 589篇 |
2001年 | 484篇 |
2000年 | 310篇 |
1999年 | 297篇 |
1998年 | 368篇 |
1997年 | 321篇 |
1996年 | 208篇 |
1995年 | 169篇 |
1994年 | 161篇 |
1993年 | 350篇 |
1992年 | 323篇 |
1991年 | 171篇 |
1990年 | 93篇 |
1989年 | 114篇 |
1988年 | 51篇 |
1987年 | 89篇 |
1986年 | 60篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1983年 | 28篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 27篇 |
1979年 | 36篇 |
1978年 | 34篇 |
1977年 | 42篇 |
1976年 | 36篇 |
1975年 | 27篇 |
1973年 | 30篇 |
1971年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
491.
地层方面,将测区地层划分为冈底斯腾冲地层区和班公错 怒江结合带,班公湖 怒江结合带中又划分出聂荣微地块和觉翁 余拉山 下秋卡混杂带两个小区;按变质岩调查方法解体了聂荣地块;对原大面积分布的拉贡塘组进行了有效的解体;新建立嘎加组;恢复了郭曲群;将木嘎岗日岩群解体出3个岩组。岩石方面,在测区南部新发现了一套晚二叠世—早三叠世蛇绿岩。构造方面,构造单元表现为各组 下秋卡结合带和桑雄那曲 麦地卡板片的构造格局;新发现达仁乡夺列蛇绿岩体。 相似文献
492.
着重调查了以阿坝盆地为代表的青藏高原东缘新生代盆地的形成演化及其环境变化,新建立了若干生物组合;对第四纪冰川堆积物进行了比较细致的研究,初步建立了气候地层单位;首次于壤塘县曼迪乡上三叠统侏倭组的滑塌堆积层中,采获异地埋葬珊瑚群化石,建立三叠纪双壳类两个生物带;调查了侏倭组、新都桥组、如年各组3个岩石地层单元基本层序、剖面韵律结构及沉积构造;获得若末柯火山岩和小石头山花岗岩Rb Sr等时线年龄。 相似文献
493.
认为牛井山蛇绿构造混杂岩与铜厂街蛇绿岩相当;新建石鼓蛇绿构造混杂岩;沿怒江断裂带多处发现硅质岩、浅变质玄武岩及砂板岩复理石建造;澜沧江构造带东侧发现大量火山岩;结晶基底中有大量变形变质古老花岗岩类。 相似文献
494.
湖泊湿地生态地球化学评价的研究重点为湖泊湿地生态系统中的重金属、植物营养元素及一些有机污染物,评价标准体系相应地包括水质基准、营养物基准、水体沉积物质量基准、饮用水卫生标准、土壤环境质量标准、食品卫生标准、湖泊水库富营养化标准等。 相似文献
495.
496.
The phase relations of quaternary systems are generally represented by projections onto ternary compositional planes. Such
projections often obscure relationships that would only be evident in a three-dimensional tetrahedral plot. The tetrahedral
plot requires that compositions of the minerals and melts be transformed into Cartesian coordinates. It is shown here how
this transformation is carried out. The application is demonstrated by tetrahedral plots of experimental melt compositions
of partially molten lherzolite. Furthermore, the plot can be used to evaluate whether or not a particular basaltic composition
represents a primary melt. The methods are applicable to any four-component system. 相似文献
497.
Tracing the origin of calcium in wet atmospheric deposits is important for environmental studies since it is a dominant acid neutralising cation and an essential nutrient. Here we present the first calcium isotope ratio measurements for rain and snow. Samples from northeastern and southern locations (France, Switzerland, Luxembourg, California and Japan) suggest a carbonate origin. Only at a local scale in a forested watershed (Vosges mountains, France) the Ca isotopic compositions of rainwater indicate that the rainwater becomes admixed with throughfall solution, which is a mixing product of Ca from dissolved atmospheric dust particles and leave excretions. If this proves to be widely true, the contribution of Ca from the canopy could be very important for the neutralisation of acid rain and of the corresponding soil system in forested watersheds. In such cases Ca and Sr cycles are decoupled in the lower atmosphere. In contrast to Sr isotopes, Ca isotopes can be applied to tracing processes occurring in the biosphere. 相似文献
498.
Joeri Kaal Yolanda Carrión Marco Eleni Asouti Maria Martín Seijo Antonio Martínez Cortizas Manuela Costa Casáis Felipe Criado Boado 《Quaternary Science Reviews》2011,30(1-2):161-175
The Holocene fire regime is thought to have had a key role in deforestation and shrubland expansion in Galicia (NW Spain) but the contribution of past societies to vegetation burning remains poorly understood. This may be, in part, due to the fact that detailed fire records from areas in close proximity to archaeological sites are scarce. To fill this gap, we performed charcoal analysis in five colluvial soils from an archaeological area (Campo Lameiro) and compared the results to earlier studies from this area and palaeo-ecological literature from NW Spain. This analysis allowed for the reconstruction of the vegetation and fire dynamics in the area during the last ca 11 000 yrs. In the Early Holocene, Fabaceae and Betula sp. were dominant in the charcoal record. Quercus sp. started to replace these species around 10 000 cal BP, forming a deciduous forest that prevailed during the Holocene Thermal Maximum until ~5500 cal BP. Following that, several cycles of potentially fire-induced forest regression with subsequent incomplete recovery eventually led to the formation of an open landscape dominated by shrubs (Erica sp. and Fabaceae). Major episodes of forest regression were (1) ~5500–5000 cal BP, which marks the mid-Holocene cooling after the Holocene Thermal Maximum, but also the period during which agropastoral activities in NW Spain became widespread, and (2) ~2000–1500 cal BP, which corresponds roughly to the end of the Roman Warm Period and the transition from the Roman to the Germanic period. The low degree of chronological precision, which is inherent in fire history reconstructions from colluvial soils, made it impossible to distinguish climatic from human-induced fires. Nonetheless, the abundance of synanthropic pollen indicators (e.g. Plantago lanceolata and Urtica dioica) since at least ~6000 cal BP strongly suggests that humans used fire to generate and maintain pasture. 相似文献
499.
The use of the exponent K(q) function to delimit homogeneous regions in regional frequency analysis of extreme annual daily rainfall
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A. P. García‐Marín J. Estévez C. Sangüesa‐Pool R. Pizarro‐Tapia J. L. Ayuso‐Muñoz F. J. Jimenez‐Hornero 《水文研究》2015,29(1):139-151
The regional frequency analysis of extreme annual rainfall data is a useful methodology in hydrology to obtain certain quantile values when no long data series are available. The most crucial step in the analysis is the grouping of sites into homogeneous regions. This work presents a new grouping criterion based on some multifractal properties of rainfall data. For this purpose, a regional frequency analysis of extreme annual rainfall data from the Maule Region (Chile) has been performed. Daily rainfall data series of 53 available stations have been studied, and their empirical moments scaling exponent functions K(q) have been obtained. Two characteristics parameters of the K(q) functions (γmax and K(0)) have been used to group the stations into three homogeneous regions. Only five sites have not been possible to include into any homogenous regions, being the local frequency analysis of extreme daily rainfall the most appropriate method to be used at these locations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
500.
Low-order stabilized finite element for the full Biot formulation in soil mechanics at finite strain
Lluís Monforte Pedro Navas Josep Maria Carbonell Marcos Arroyo Antonio Gens 《国际地质力学数值与分析法杂志》2019,43(7):1488-1515
This article presents a novel finite element formulation for the Biot equation using low-order elements. Additionally, an extra degree of freedom is introduced to treat the volumetric locking steaming from the effective response of the medium; its balance equation is also stabilized. The accuracy of the proposed formulation is demonstrated by means of numerical analyses. 相似文献