全文获取类型
收费全文 | 7528篇 |
免费 | 1433篇 |
国内免费 | 1644篇 |
专业分类
测绘学 | 522篇 |
大气科学 | 815篇 |
地球物理 | 2883篇 |
地质学 | 3596篇 |
海洋学 | 1065篇 |
天文学 | 174篇 |
综合类 | 529篇 |
自然地理 | 1021篇 |
出版年
2024年 | 25篇 |
2023年 | 85篇 |
2022年 | 228篇 |
2021年 | 337篇 |
2020年 | 388篇 |
2019年 | 418篇 |
2018年 | 337篇 |
2017年 | 319篇 |
2016年 | 312篇 |
2015年 | 376篇 |
2014年 | 451篇 |
2013年 | 517篇 |
2012年 | 461篇 |
2011年 | 534篇 |
2010年 | 407篇 |
2009年 | 457篇 |
2008年 | 454篇 |
2007年 | 488篇 |
2006年 | 508篇 |
2005年 | 414篇 |
2004年 | 390篇 |
2003年 | 339篇 |
2002年 | 301篇 |
2001年 | 250篇 |
2000年 | 254篇 |
1999年 | 234篇 |
1998年 | 189篇 |
1997年 | 181篇 |
1996年 | 191篇 |
1995年 | 159篇 |
1994年 | 148篇 |
1993年 | 113篇 |
1992年 | 79篇 |
1991年 | 62篇 |
1990年 | 38篇 |
1989年 | 35篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1972年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
52.
The characteristics of the ratios between cadmium (Cd) and phosphorus (P) in settling particles collected from the Okinawa
Trough in the East China Sea were examined using a sediment trap, moored at a depth of 811 m for one year. The Cd/P ratios
varied within a narrow range throughout the year, in spite of the large seasonal change in the total dry mass, Cd, and P fluxes.
The average Cd/P ratio of settling particles was 0.062 (nmol/μmol), which was obviously lower than that of surface seawater around the study site (0.16). This lower ratio in the Okinawa
Trough particles collected using the 811 m-moored trap certainly reflected the mixture of biologically produced organic matter
around the study site and other components that were mainly transported as lateral flux from the shelf edge and slope area
of the East China Sea. 相似文献
53.
中国近海的天然气勘探 总被引:1,自引:0,他引:1
据最新勘探资料,在综合分析中国近海海域天然气勘探现状、资源潜力及其区域分布规律的基础上,分析了我国近海海域天然气勘探的有利区带及目前比较现实的勘探目标,展示了我国近海海域天然气勘探的良好前景。 相似文献
54.
本文在对位于黄海南部陆架上的朝连岛站30年水温资料进行分析时发现,该站的表层水温有周期大于20个月的低频振动,其中以准两年周期和6年周期最显著。陆架水温的这种低频振动是对东亚季风异常的响应。这种低频振动在冬季与渤海冰情的变化同步;在夏季与黄海底层冷水团的强弱相关。同时,这种低频振动在对马暖流上也有一定的反映。 相似文献
55.
56.
Serena M. Moseman Lisa A. Levin Carolyn Currin Charlotte Forder 《Estuarine, Coastal and Shelf Science》2004,60(4):755-770
Modes of colonization, the successional trajectory, and trophic recovery of a macrofaunal community were analyzed over 19 months in the Friendship marsh, a 20-acre restored wetland in Tijuana Estuary, California. Traditional techniques for quantifying macrofaunal communities were combined with emerging stable isotopic approaches for evaluation of trophic recovery, making comparisons with a nearby natural Spartina foliosa habitat. Life history-based predictions successfully identified major colonization modes, although most taxa employed a variety of tactics for colonizing the restored marsh. The presence of S. foliosa did not seem to affect macrofaunal colonization or succession at the scale of this study. However, soil organic matter content in the restored marsh was positively correlated with insect densities, and high initial salinities may have limited the success of early colonists. Total macrofaunal densities recovered to natural marsh levels after 14 months and diversity, measured as species richness and the Shannon index (H′), was comparable to the natural marsh by 19 months. Some compositional disparities between the natural and created communities persisted after 19 months, including lower percentages of surface-feeding polychaetes (Polydora spp.) and higher percentages of dipteran insects and turbellarians in the Friendship marsh. As surficial structural similarity of infaunal communities between the Friendship and natural habitat was achieved, isotopic analyses revealed a simultaneous trajectory towards recovery of trophic structure. Enriched δ13C signatures of benthic microalgae and infauna, observed in the restored marsh shortly after establishment compared to natural Spartina habitat, recovered after 19 months. However, the depletion in δ15N signatures of macrofauna in the Friendship marsh indicated consumption of microalgae, particularly nitrogen-fixing cyanobacteria, while macroalgae and Spartina made a larger contribution to macrofaunal diets in the natural habitat. Future successional studies must continue to develop and employ novel combinations of techniques for evaluating structural and functional recovery of disturbed and created habitats. 相似文献
57.
58.
59.
60.
Fluctuations of peak energy and peak frequency o local wavelet energy spectrum for wind wavesTXFluctuationsofpeakenergyandpeak... 相似文献