全文获取类型
收费全文 | 19496篇 |
免费 | 2611篇 |
国内免费 | 3335篇 |
专业分类
测绘学 | 942篇 |
大气科学 | 700篇 |
地球物理 | 1993篇 |
地质学 | 9986篇 |
海洋学 | 1892篇 |
天文学 | 5111篇 |
综合类 | 1267篇 |
自然地理 | 3551篇 |
出版年
2024年 | 88篇 |
2023年 | 217篇 |
2022年 | 547篇 |
2021年 | 635篇 |
2020年 | 601篇 |
2019年 | 728篇 |
2018年 | 544篇 |
2017年 | 557篇 |
2016年 | 603篇 |
2015年 | 655篇 |
2014年 | 1070篇 |
2013年 | 1079篇 |
2012年 | 1080篇 |
2011年 | 1263篇 |
2010年 | 1306篇 |
2009年 | 1601篇 |
2008年 | 1505篇 |
2007年 | 1402篇 |
2006年 | 1399篇 |
2005年 | 1194篇 |
2004年 | 1069篇 |
2003年 | 954篇 |
2002年 | 824篇 |
2001年 | 788篇 |
2000年 | 723篇 |
1999年 | 599篇 |
1998年 | 475篇 |
1997年 | 319篇 |
1996年 | 268篇 |
1995年 | 230篇 |
1994年 | 205篇 |
1993年 | 209篇 |
1992年 | 142篇 |
1991年 | 101篇 |
1990年 | 79篇 |
1989年 | 60篇 |
1988年 | 55篇 |
1987年 | 26篇 |
1986年 | 34篇 |
1985年 | 46篇 |
1984年 | 32篇 |
1983年 | 30篇 |
1982年 | 26篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1971年 | 2篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
221.
Shigenao Maruyama Koutaro Tsubaki Keisuke Taira Seigo Sakai 《Journal of Oceanography》2004,60(3):563-568
Deep seawater in the ocean contains a great deal of nutrients. Stommel et al. have proposed the notion of a “perpetual salt fountain” (Stommel et al., 1956). They noted the possibility of a permanent upwelling of deep seawater with no additional external energy source. If
we can cause deep seawater to upwell extensively, we can achieve an ocean farm. We have succeeded in measuring the upwelling
velocity by an experiment in the Mariana Trench area using a special measurement system. A 0.3 m diameter, 280 m long soft
pipe made of PVC sheet was used in the experiment. The measured data, a verification experiment, and numerical simulation
results, gave an estimate of upwelling velocity of 212 m/day.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
222.
223.
应用勘探层分析及石油资源专家系统对XH凹陷下第三系勘探目的层的三个勘探层烃资源量作出了综合预测,结果表明,凹陷内各勘探层,尤其是渐新统勘探层,烃资源量相当可观。提出在渐新统内的地层圈闭中可进一步作详细的勘探工作。 相似文献
224.
225.
226.
227.
Catch-quota balancing in multispecies individual fishing quotas 总被引:2,自引:1,他引:2
Individual fishery quotas (IFQs) are an increasingly prevalent form of fishery management around the world, with more than 170 species currently managed with IFQs. Yet, because of the difficulties in matching quota holdings with catches, many argue that IFQs are not appropriate for multispecies fisheries. Using on-the-ground-experience with multispecies IFQ fisheries in Iceland, New Zealand, Australia, and Canada, we assess the design and use of catch-quota balancing mechanisms. Our methodology includes a mix of interviews with fishery managers, industry representatives, and brokers, literature review, and data analysis. We find that a combination of incentives and limits on use rates for the mechanisms provide sufficient flexibility to the quota owner without the fishery manager incurring excessive levels of overexploitation risk. Contrary to some opinions, these programs are evidence that it is possible to implement IFQ programs for multispecies fisheries and that they can be profitable and sustainable. 相似文献
228.
报道一种新的有效催化剂-碘-钒盐和在一定条件下合成四溴邻苯二甲酸酐的方法。探讨催化剂的组成配比、用量、温度及废酸循环使用等因素对合成方法的影响。该催化剂的催化效果和常用的碘、碘-铁催化剂相同,适用于四溴邻苯二甲酸酐的合成。 相似文献
229.
Abstract. A component analysis of the sugar and lipid fraction in foam layers around kelp beds on the South African west coast showed the following trends: In the residue of foam drainage of both 12 h and 120 h old foam the sugar fraction is represented by mannose (33–41 %), galactose (4–30%), fucose (3–29%) and glucose (19–26%). With the exception of fucose, the same components could be found in foam filtration. In the lipid fraction the main fatty acids are palmitic (23.3–27.3%), oleic (14.0–5.5%) and timnodonic acid (11.2–9.1%). Selacholeinic acid was only found in 12 h old foam while lignoceric acid could not be located in foam filtration. Against expectation mannitol was not identified in quantifiable amounts in foam samples although it is the dominant component of kelp mucilage, whose presence is of major importance for foam formation. Hypotheses explaining the lack of mannitol are forwarded. Component sugar and lipid content for 11 of foam was calculated and estimation of sugar and lipid content in an average foam patch (volume of 30001) is given. The importance of foam formation as a mechanism for binding and transfer of energy in the marine environment is emphasized. 相似文献
230.