全文获取类型
收费全文 | 2273篇 |
免费 | 198篇 |
国内免费 | 407篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 305篇 |
地球物理 | 248篇 |
地质学 | 565篇 |
海洋学 | 133篇 |
天文学 | 1311篇 |
综合类 | 67篇 |
自然地理 | 160篇 |
出版年
2024年 | 6篇 |
2023年 | 52篇 |
2022年 | 44篇 |
2021年 | 50篇 |
2020年 | 47篇 |
2019年 | 49篇 |
2018年 | 55篇 |
2017年 | 46篇 |
2016年 | 57篇 |
2015年 | 71篇 |
2014年 | 92篇 |
2013年 | 99篇 |
2012年 | 102篇 |
2011年 | 164篇 |
2010年 | 124篇 |
2009年 | 200篇 |
2008年 | 209篇 |
2007年 | 212篇 |
2006年 | 177篇 |
2005年 | 172篇 |
2004年 | 148篇 |
2003年 | 152篇 |
2002年 | 93篇 |
2001年 | 102篇 |
2000年 | 82篇 |
1999年 | 61篇 |
1998年 | 70篇 |
1997年 | 29篇 |
1996年 | 17篇 |
1995年 | 25篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 10篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2878条查询结果,搜索用时 15 毫秒
951.
The interest in the national levels of the terrestrial carbon sink and its spatial and temporal
variability with the climate and CO2 concentrations has been increasing. How the climate and the increasing
atmospheric CO2 concentrations in the last century affect the carbon storage in continental China was
investigated in this study by using the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM).
The estimates of the M-SDGVM indicated that during the past 100 years a combination of increasing CO2
with historical temperature and precipitation variability in continental China have caused the total
vegetation carbon storage to increase by 2.04 Pg C, with 2.07 Pg C gained in the vegetation biomass
but 0.03 Pg C lost from the organic soil carbon matter. The increasing CO2 concentration in the 20th
century is primarily responsible for the increase of the total potential vegetation carbon. These
factorial experiments show that temperature variability alone decreases the total carbon storage by
1.36 Pg C and precipitation variability alone causes a loss of 1.99 Pg C. The effect of the increasing
CO2 concentration alone increased the total carbon storage in the potential vegetation of China by
3.22 Pg C over the past 100 years. With the changing of the climate, the CO2 fertilization on China's
ecosystems is the result of the enhanced net biome production (NBP), which is caused by a greater
stimulation of the gross primary production (GPP) than the total soil-vegetation respiration. Our study
also shows notable interannual and decadal variations in the net carbon exchange between the atmosphere
and terrestrial ecosystems in China due to the historical climate variability. 相似文献
952.
应用电感耦合等离子体质谱法(ICP-MS)测定地球化学调查样品中的碘,主要采用封闭溶样、混合酸溶、碱熔和半熔法进行样品处理,但由于碘在土壤和沉积物中的存在形态较为复杂,有高碘酸根、碘酸根、碘离子,且碘为卤族元素,第一电离能较高,在样品处理及上机测定环节中存在溶出不彻底、记忆效应强、稳定性较差等问题。本文采用碳酸钠-氧化锌半熔法处理样品,乙醇-沸水提取后用732型阳离子交换树脂将溶液中大量阳离子分离,采用内标法ICP-MS测定样品溶液中的碘。通过优化溶样程序提升了样品溶出效果,优化测定介质及内标元素消除记忆效应,提升了结果稳定性,建立了一套完善的ICP-MS测定碘的方法。使用土壤和沉积物国家一级标准物质进行方法验证,方法检出限为0.045μg/g,方法检测下限为0.15μg/g,方法精密度(RSD,
953.
马攸木金矿床是产于西藏雅鲁藏布江缝合带西段重要的独立岩金矿床。本文通过显微测温分析首次发现该矿床的富CO2流体包裹体具有临界均一的特征,成矿流体属于超临界流体。研究结果表明:成矿流体主要为低盐度的CO2-H2O超临界流体。超临界流体可能是从岩浆出溶的,这种流体萃取了围岩中的金等成矿元素。流体经历了相分离-不均一捕获-跨越临界点-大气降水加入的过程,正是由于成矿流体在跨越临界点时析出部分成矿物质,形成早期矿化体;成矿后期流体与大气降水混合最终导致矿质大量沉淀。 相似文献
954.
955.
无机与有机混合成因的天然气藏 总被引:13,自引:2,他引:11
东营凹陷西南部花沟地区发现的二氧化碳气藏,多数专家认为是幔源气,本文通过该区高青断裂下降盘的一个二氧化碳藏与其上倾方向上的一生物甲烷气藏的对比研究,认为它们都是无机与有机混合成因的气藏,二氧化碳质量分数较高的气藏幔源气为主,混有少量有机成因气;生物甲烷气藏以有机成因气为主,混有少量无机气,根据碳同位素组成和稀有气体同位素组成分析,认为研究区不存在纯的幔源气,文中还对这些气藏的形成进行了分析。 相似文献
956.
Ian Smail R. J. Ivison J.-P. Kneib L. L. Cowie A. W. Blain A. J. Barger F. N. Owen G. Morrison 《Monthly notices of the Royal Astronomical Society》1999,308(4):1061-1068
We have used deep ground-based imaging in the near-infrared (near-IR) to search for counterparts to the luminous submillimetre (submm) sources in the catalogue of Smail et al. For the majority of the submm sources the near-IR imaging supports the counterparts originally selected from deep optical images. However, in two cases (10 per cent of the sample) we find a relatively bright near-IR source close to the submm position, sources that were unidentified in the deep Hubble Space Telescope ( HST ) and ground-based R -band images used by Smail et al. We place limits on colours of these sources from deep high-resolution Keck II imaging and find they have 2 σ limits of ( I − K )≳6.8 and ( I − K )≳6.0, respectively. Both sources thus class as extremely red objects (EROs). Using the spectral properties of the submm source in the radio and submm we argue that these EROs are probably the source of the submm emission, rather than the bright spiral galaxies previously identified by Smail et al. This connection provides important insights into the nature of the enigmatic ERO population and faint submm galaxies in general. From the estimated surface density of these submm-bright EROs we suggest that this class accounts for the majority of the reddest members of the ERO population, in good agreement with the preliminary conclusions of pointed submm observations of individual EROs. We conclude that the most extreme EROs represent a population of dusty, ultraluminous galaxies at high redshifts; further study of these will provide useful insights into the nature of star formation in obscured galaxies in the early Universe. The identification of similar counterparts in blank-field submm surveys will be extremely difficult owing to their faintness ( K ∼20.5, I ≳26.5). Finally, we discuss the radio and submm properties of the two submm-bright EROs discovered here and suggest that both galaxies lie at z ≳2. 相似文献
957.
958.
959.
960.
How vertical fish distribution may affect survey results 总被引:8,自引:7,他引:1
Aglen A.; Engas A.; Huse I.; Michalsen K.; Stensholt B. K. 《ICES Journal of Marine Science》1999,56(3):345-360