全文获取类型
收费全文 | 356篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 29篇 |
地球物理 | 81篇 |
地质学 | 150篇 |
海洋学 | 21篇 |
天文学 | 53篇 |
综合类 | 1篇 |
自然地理 | 21篇 |
出版年
2019年 | 3篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 17篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1968年 | 5篇 |
1965年 | 3篇 |
1962年 | 3篇 |
1948年 | 3篇 |
排序方式: 共有367条查询结果,搜索用时 15 毫秒
361.
Pumping Tests in Patchy Aquifers 总被引:2,自引:1,他引:2
362.
363.
Impact melt samples from drill hole B1-59 at the 3.8 km diameter Brent crater (Ontario) have been analysed for siderophile trace elements indicative of meteoritic contamination. Samples from the basal melt zone at 823–857 m depth are enriched in Ir, Os, Pd, Ni, Co, Cr and Se over basement, with the abundance pattern suggesting a chondritic projectile for Brent. From a Ni-Cr correlation of 10 melt samples an L or LL chondrite is inferred. The contribution of an ultramafic country rock (alnoite) in the melt is too small to significantly influence its ratio. Glass-rich breccias from the allochthonous breccias filling the crater also contain a meteoritic component. Interelement ratios (e.g. ) are, however, fractionated relative to the melt zone samples. This, as well as the low Au content of all Brent samples, is probably a product of alteration.Additional data on impact melts from the 65 km diameter crater Manicouagan still did not reveal a meteoritic component, as also for the Mistastin crater (28 km diameter) where Cr analyses set an upper limit of 1% of an achondritic projectile component in the melt. Irghizites (tektite like glasses) from the Zhamanshin impact structure have been found to contain high Ni and Co concentrations, and our data show that Ir is also enriched. It is however not possible to define the projectile-type. Enrichment of an Ivory Coast tektite in Ir is confirmed. There are large differences in siderophile element concentrations among tektites, with otherwise similar chemical composition.There are now four known craters formed by chondrites (Clearwater East, Lapparjärvi, Wanapitei, and Brent), with Brent being the smallest of these. For smaller craters the projectiles appear to be limited to iron or stony-iron meteorites, because of atmospheric destruction of relatively small stony meteorites. It appears, however, that all major classes of meteorites are represented among the projectiles at terrestrial impact craters. 相似文献
364.
Julia Bosiö Christian Stiegler Margareta Johansson Herbert N. Mbufong Torben R. Christensen 《Climatic change》2014,127(2):321-334
This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots. 相似文献
365.
366.
Depositional Age of a Fossil Whale Bone from São Paulo Ridge,South Atlantic Ocean,Based on Os Isotope Stratigraphy of a Ferromanganese Crust 下载免费PDF全文
Tatsuo Nozaki Yutaro Takaya Takashi Toyofuku Ayaka Tokumaru Kosuke T. Goto Qing Chang Jun‐ichi Kimura Yasuhiro Kato Katsuhiko Suzuki Adolpho Herbert Augustin Hiroshi Kitazato 《Resource Geology》2017,67(4):442-450
Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13–04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe–Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (187Os/188Os ratio) of the Fe–Mn crust. Major‐ and trace‐element compositions of the crust are similar to those of Fe–Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post‐Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe–Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. 187Os/188Os ratios of three Fe–Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0–3 mm depth in the crust) was identical to that of present‐day seawater within error (~1.06). The value of 0.904 from the basal slice (6–9 mm) equaled seawater values from ca. 4–5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe–Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale‐fall biotic community. 相似文献
367.