全文获取类型
收费全文 | 580篇 |
免费 | 121篇 |
国内免费 | 339篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 58篇 |
地球物理 | 51篇 |
地质学 | 544篇 |
海洋学 | 109篇 |
天文学 | 1篇 |
综合类 | 55篇 |
自然地理 | 140篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 42篇 |
2020年 | 36篇 |
2019年 | 41篇 |
2018年 | 23篇 |
2017年 | 35篇 |
2016年 | 30篇 |
2015年 | 44篇 |
2014年 | 38篇 |
2013年 | 67篇 |
2012年 | 59篇 |
2011年 | 51篇 |
2010年 | 58篇 |
2009年 | 49篇 |
2008年 | 71篇 |
2007年 | 56篇 |
2006年 | 78篇 |
2005年 | 52篇 |
2004年 | 42篇 |
2003年 | 30篇 |
2002年 | 26篇 |
2001年 | 22篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有1040条查询结果,搜索用时 140 毫秒
191.
ZHONG Yi CHEN Zhong GONZALEZ Francisco Javier ZHENG Xufeng LI Gang LUO Yun MO Aibin XU Antao WANG Shuhong 《海洋学报(英文版)》2018,37(7):41-54
Ferromanganese nodules and crusts contain relatively high concentration of rare earth elements(REE) and yttrium(REY),with a growing interest in exploitation as an alternative to land-based REY resources.On the basis of comprehensive geochemical approach,the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed.The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity.Total REY contents range from 69.1×10~(–6) to 2 919.4×10~(–6),with an average value of 1 459.5×10~(–6).Especially,the enrichment rate of Ce content is high,accounting for almost 60% of the total REY.This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts.Moreover,the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin.Finally,Light REE(LREE) and heavy REE(HREE) oxides of the ferromanganese deposits in the study area can be classified into four grades: non-enriched type,weakly enriched type,enriched type,and extremely enriched type.According to the classification criteria of rare earth resources,the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals. 相似文献
192.
193.
根据广西近岸海域2015年3、5、8、11月4个航次的海水中营养盐监测数据,分析了广西近岸海域海水中营养盐的时空分布特征,应用潜在性富营养化评价模式对整个海域水质富营养化程度进行了评价。结果表明:广西近岸海域富营养化状态总体良好,时空分布受陆源污染的影响,营养盐质量浓度呈湾内-湾口-湾外递减趋势。多数站位点氮磷比常年大于Redfield比值,处于磷限制状态。钦州湾内和大风江口是富营养化最为严重的水域,其次是防城港湾内、廉州湾内和铁山港湾,呈磷限制状态,容易在磷污染增高时,爆发富营养化,应特别加以监测与控制。 相似文献
194.
冷水珊瑚也称为深水珊瑚, 在生物多样性、生态资源和科研价值等方面具有重要意义。文章对采自南海北部冷泉区的冷水珊瑚骨骼碎屑进行测定, 鉴定出冷水珊瑚2个种(Crispatotrochus sp.1和Crispatotrochus sp.2), 以及4个属[Balanophyllia (Balanophyllia)、Balanophyllia (Eupsammia)、Lochmaeotrochus和Enallopsammia]。测定的冷水珊瑚的δ13C为-7.36‰~-1.15‰, δ18O为-1.38‰~3.67‰, 与全球冷水珊瑚碳氧同位素组成相似, 但明显不同于南海暖水珊瑚、冷泉碳酸盐岩及低温热液成因碳酸盐岩的碳氧同位素组成。 相似文献
195.
东昆仑造山带花岗岩类Pb-Sr-Nd-O同位素特征 总被引:29,自引:1,他引:29
本文报道了东昆仑造山带三叠纪辉长岩、花岗岩类及其包裹体的Pb、Sr、Nd和O同位素组成。东昆仑造山带花岗质岩石全岩和长石Pb同位素组成相差不大,具明显的造山带Pb同位素特征;Sr同位素初始值(ISr)变化于0.70144~0.70972之间,暗示幔源成因;εNd值变化于-4.49939~-9.19258之间,具壳源成因特点;Nd同位素模式年龄(tDM)在1.38~1.761Ga之间,与中元古代变质岩相当;O同位素组成变化范围7.8~9.5,表明花岗岩类成岩物质主要来自地壳。综合岩石的同位素组成,结合矿物学、岩石地球化学的研究,表明花岗岩浆主要起源于地壳,但与来自地幔的基性岩浆曾发生过混合作用,从而导致同位素组成趋于一致。 相似文献
196.
Microsatellite markers have become one kind of the most important molecular tools used in various researches. A large number of microsatellite markers are required for the whole genome survey in the fields of molecular ecology, quantitative genetics and genomics. Therefore, it is extremely necessary to select several versatile, low-cost, efficient and time- and labor-saving methods to develop a large panel of microsatellite markers. In this study, we used Zhikong scallop (Chlamys farreri) as the target species to compare the efficiency of the five methods derived from three strategies for microsatellite marker development. The results showed that the strategy of constructing small insert genomic DNA library resulted in poor efficiency, while the microsatellite-enriched strategy highly improved the isolation efficiency. Although the mining public database strategy is time- and cost-saving, it is difficult to obtain a large number of microsatellite markers, mainly due to the limited sequence data of non-model species deposited in public databases. Based on the results in this study, we recommend two methods, microsatellite-enriched library construction method and FIASCO-colony hybridization method, for large-scale microsatellite marker development. Both methods were derived from the mi-crosatellite-enriched strategy. The experimental results obtained from Zhikong scallop also provide the reference for microsatellite marker development in other species with large genomes. 相似文献
197.
介绍少数民族文字(维吾尔文)在地图编制中的应用。从编制方法及少数民族文字(维吾尔文)处理技巧等方面,阐述该技术在地图编制中的实现。 相似文献
198.
Molecular identification of scallop planktonic larvae using species-specific microsatellites 总被引:3,自引:0,他引:3
ZHAN Aibin HU Xiaoli BAO Lisui LU Wei PENG Wei WANG Mingling HU Jingjie 《海洋学报(英文版)》2008,27(5):134-146
The identification of scallop larvae is essential to understand the population structure and community dynamics and to assess the potential environmental impacts caused by scallop larvae released or escaped. However, the larvae identification by morphological characteristics is notoriously difficult, mainly due to the small size (usually being less than 150 μm) and vague morphological characteristics among different scallop species. A simple and accurate molecular method was developed to identify four economically farmed scallop species, the Zhikong scallop Chlamys farreri, the noble scallop C. nobilis, the bay scallop Argopecten irradians and the Yesso scallop Mizuhopecten yessoensis. The tests used the high degree of species-specific microsatellite markers, which was specified by transferability analyses, assessed by reference individuals and evaluated by BLAST searches. The sensitivity test indicated that the species-specific microsatellites were sensitive enough for the detection of 1% -2% larvae in mixed plankton samples. Larvae collected from scallop hatcheries and their effluents and from the artificially controlled crosses were well identified to the species/hybrid level. The results demonstrated that the one-step PCR-based assay was technically simple, inexpensive and robust in identification analyses, and also less sensitive to initial quality of template DNA extracted from the ethanol-preserved samples for several years. 相似文献
199.
在3维地形环境仿真中,经常需要输出大量文本信息.通常的做法是用位图方式进行渲染,但在某些情况下(如嵌入式操作系统)无法实现这一功能.针对某些3维地形环境仿真中位图方式渲染文本的局限性,研究如何用点阵方式渲染文本.研究内客包括点阵字库的创建和点阵文本的渲染,并根据实时渲染中不同类型文本的特点,将点阵文本的渲染分为缓存和非缓存两种方式.最后在基于VxWorks嵌入式系统的3维地形环境中实现了点阵文本的渲染. 相似文献
200.
A class of coupled system of the E1 Ni(n)o/La Ni(n)a-Southern Oscillation (ENSO) mechanism is studied. Using the perturbed theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behavior of solution for corresponding problem is considered. 相似文献