全文获取类型
收费全文 | 1701篇 |
免费 | 106篇 |
国内免费 | 195篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 59篇 |
地球物理 | 344篇 |
地质学 | 681篇 |
海洋学 | 516篇 |
天文学 | 27篇 |
综合类 | 100篇 |
自然地理 | 217篇 |
出版年
2024年 | 7篇 |
2023年 | 23篇 |
2022年 | 33篇 |
2021年 | 37篇 |
2020年 | 43篇 |
2019年 | 64篇 |
2018年 | 52篇 |
2017年 | 129篇 |
2016年 | 134篇 |
2015年 | 132篇 |
2014年 | 152篇 |
2013年 | 199篇 |
2012年 | 120篇 |
2011年 | 111篇 |
2010年 | 90篇 |
2009年 | 142篇 |
2008年 | 61篇 |
2007年 | 99篇 |
2006年 | 81篇 |
2005年 | 48篇 |
2004年 | 24篇 |
2003年 | 40篇 |
2002年 | 40篇 |
2001年 | 34篇 |
2000年 | 27篇 |
1999年 | 42篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1988年 | 6篇 |
排序方式: 共有2002条查询结果,搜索用时 31 毫秒
1.
Tomoki Oda Tomohiro Egusa Nobuhito Ohte Norifumi Hotta Nobuaki Tanaka Mark B. Green Masakazu Suzuki 《水文研究》2021,35(5):e14177
Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest. 相似文献
2.
Factors influencing biodeposit production by the New Zealand freshwater mussel Echyridella menziesii
Kevin J. Collier Susan J. Clearwater Paula H. M. W. Neijenhuis Susanna A. Wood 《新西兰海洋与淡水研究杂志》2018,52(1):1-15
Laboratory experiments on the New Zealand freshwater mussel Echyridella menziesii were used to investigate the short-term effects (7–8 days) of food type on rates of biodeposition and benthic substrate respiration. Post-feeding biodeposition rates ranged from 0.34 to 1.52?mg?g?1?h?1 (mean?=?0.50?mg g?1?h?1) and were unaffected by the addition of toxin-producing Microcystis. Addition of suspended sediment (30?mg?L?1) visibly altered substrate composition, and increased total and inorganic biodeposit production rates by 24–33% compared to mussels fed commercial phytoplankton stock. Biodeposition rates of mussels in lake bed substrates were 38% higher than those in silica sand for identical feeding regimes, suggesting that a significant proportion of material produced in this experiment could have been derived from feeding on organic matter in the lake bed sediments. Respiration rates were higher in treatments with Microcystis but were unaffected by the presence of mussels. This laboratory study suggests that biodeposition by E. menziesii is resilient to short-term exposure to Microcystis, and highlights the ability of mussels to alter benthic substrate composition by incorporating suspended sediment into substrates. 相似文献
3.
Natural Resources Research - Sand failure and production occurs when the formation stress exceeds the strength of the formation, which is derived majorly from the natural material that cements the... 相似文献
4.
Maarten A. Prins Hongbo Zheng Kay Beets Simon Troelstra Patrick Bacon Ilse Kamerling Wouter Wester Martin Konert Xiangtong Huang Wang Ke Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84
The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
《Chinese Astronomy and Astrophysics》2005,29(2):120-130
Confronted by observations, the difficulties to explain the formation of the iron Kα lines in active galactic nuclei (AGNs) in the context of the current “reflection disk-photoelectric absorption-fluorescence line” model are discussed in detail, and it is further pointed out that a newly recognized line emission mechanism — the Cerenkov line-like radiation could be the dominant mechanism to produce the AGN iron Kα line. The negative effect of the hydrogen plasma on the refractive index is proved to be negligible. The Cerenkov iron Kα line emission is calculated for the optically thin case and compared with the observations. The reasonableness of this new mechanism is verified, thus providing a new scenario for the physical situation around a black hole. 相似文献
6.
Mihoko Hoshino Mitsuyoshi Kimata Norimasa Nishida Masahiro Shimizu 《Physics and Chemistry of Minerals》2008,35(2):59-70
Dissakisites from Trimouns dolomite mine, France, have two kinds of single crystals: chemical-zoned and homogeneous types.
Back-scattered electron microprobe (BSE) images of these dissakisites reveal both Ca–Al rich dark zones and Fe-ΣREE rich bright
zones. Crystal structures of three dark and two bright zones in a chemical-zoned dissakisite and of a homogeneous zone in
unzoned dissakisite were refined to individual R indices (about 3.0–5.0%) based on 1,400 observed [|F
0| > 4σF
0] reflections measured with MoKα X-radiation using the single crystal diffractometer. The differences in brightness between
their BSE images arise from those in coupled substitutions of the elements occupying A2 and M3 sites. The main reason for
these differences is that ten-coordinated A2 polyhedra and M3 octahedra are directly linked through their shared edge, which
creates a great potential for making this coupled substitution. This zoning indicates that formation of the whole zoned crystal,
where each zone could be grown steadily with its crystallographic axes mutually parallel to each other, may be identified
as autoepitaxy. 相似文献
7.
8.
《Marine Policy》2005,29(5):391-405
Integrated oceans management (IOM) is emerging in the international arena as a tool in meeting requirements for sustainable use of ocean space and marine resources. Australia and Canada are at the forefront of these developments and, being without set precedents, each state has adopted quite different strategies to implement IOM—Australia adopting a policy-driven approach delivered through Regional Marine Plans and Canada developing legislation that provided a framework for policy implementation delivered through an Integrated Management Framework. Despite these significant differences, examination of initiatives in both states indicates that there are also significant commonalities and shared experiences, providing important lessons for implementing IOM. 相似文献
9.
Khalid Maskaoui Tianling Zheng Huasheng Hong Zhiming Yu Zhong Hu Yun Tian Lizhe Cai 《海洋学报(英文版)》2003,22(3):443-451
The surface and bottom waters samples were collected from six locations in Xiamen western sea. The quantified estimation of bacterial production (3H-thymidine method) and observation of bacterial heterotrophic activity (14C-glucose method) have been made in order to have a better understanding of the role of marine bacteria and their activities. The results showed that the mean value of bacterial heterotrophic activity was 9×108 cells/(L.h) in the surface waters and 2.6×108 cells/(L.h) in the bottom waters. The mean value of bacterial production was 38×108 cells/(L.h) in the surface waters and 7.1×108 cells/(L.h) in the bottom waters. The relationship between bacterial production, heterotrophic activity, POC and DOC measured during this survey were discussed. The good understanding of the relationship between bacteria activity and total coliform was addressed. 相似文献
10.
以p-硝基苯酚-β-D-氨基葡萄糖苷(pNP-NAG)为底物,研究产物类似物:p-羧基苯酚和苯酚对青蟹N-乙酰-β-D-氨基葡萄糖苷酶(NAGase,Ec3.2.1.52)活力的影响.结果表明:p-羧基苯酚和苯酚对该酶有抑制的作用,IC50分别为20.0和100.0mmol/dm^3.p-羧基苯酚和苯酚对酶的抑制均表现为竞争性类型,其抑制常数K1分别为5.03和25.67mmol/dm^3.结合产物N-乙酰-β-D-氨基葡萄糖(NAG)抑制作用表现为反竞争性类型,判断NAGase水解pNP-NAG反应为有序双双反应(Ordered Bi Bi). 相似文献