全文获取类型
收费全文 | 3453篇 |
免费 | 828篇 |
国内免费 | 684篇 |
专业分类
测绘学 | 125篇 |
大气科学 | 92篇 |
地球物理 | 160篇 |
地质学 | 998篇 |
海洋学 | 3111篇 |
天文学 | 5篇 |
综合类 | 247篇 |
自然地理 | 227篇 |
出版年
2024年 | 54篇 |
2023年 | 131篇 |
2022年 | 193篇 |
2021年 | 210篇 |
2020年 | 231篇 |
2019年 | 223篇 |
2018年 | 170篇 |
2017年 | 174篇 |
2016年 | 193篇 |
2015年 | 161篇 |
2014年 | 232篇 |
2013年 | 255篇 |
2012年 | 230篇 |
2011年 | 240篇 |
2010年 | 194篇 |
2009年 | 224篇 |
2008年 | 154篇 |
2007年 | 183篇 |
2006年 | 195篇 |
2005年 | 192篇 |
2004年 | 163篇 |
2003年 | 165篇 |
2002年 | 139篇 |
2001年 | 94篇 |
2000年 | 111篇 |
1999年 | 88篇 |
1998年 | 49篇 |
1997年 | 48篇 |
1996年 | 47篇 |
1995年 | 33篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 30篇 |
1991年 | 23篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4965条查询结果,搜索用时 15 毫秒
991.
992.
A fungal epizootic in mussels at a deep-sea hydrothermal vent 总被引:1,自引:0,他引:1
Cindy Lee Van Dover Megan E. Ward Joseph L. Scott Jamie Underdown Brooke Anderson Christina Gustafson Matthew Whalen & Ryan B. Carnegie 《Marine Ecology》2007,28(1):54-62
Mass mortalities due to disease are important determinants of population and community structure in marine ecosystems, but the speed at which an epizootic may sweep through a population, combined with rapid selection for disease‐resistant stocks, can mask the ecological impact of disease in all but the most closely monitored populations. We document an emergent epizootic event in the deep sea that is occurring in mussels (Bathymodiolus brevior) at the Mussel Hill hydrothermal vent in Fiji Basin and we identify the causal agent as a black yeast (order Chaetothyriales) that elicits a pronounced host immune response and is associated with tissue deterioration. The yeast was not observed in other invertebrate taxa (the gastropods Ifremeria nautilei, Alviniconcha aff. hessleri; the limpets Lepetodrilus schrolli, Symmetromphalus aff. hageni; the polychaetes Branchipolynoe pettiboneae, Amphisamytha cf. galapagensis) associated with the mussel bed, nor in mussels (Bathymodiolus brevior) collected from adjacent Lau Basin mussel beds. Massive mussel mortality resulting from the fungal infection is anticipated at the Mussel Hill site in Fiji Basin; we expect that epizootic outbreaks in dense invertebrate communities have the potential to be major determinants of community structure in deep‐sea chemosynthetic ecosystems. The possibility that submersible assets may serve as vectors for transport of the fungus warrants further attention. 相似文献
993.
沿海生态城市的海洋指标体系研究——以厦门市为例 总被引:1,自引:0,他引:1
生态城市是21世纪城市发展的模式.海洋指标体系可以指导沿海生态城市的建设,促进沿海城市的海洋资源与环境管理.本文剖析了生态城市的内涵,提出了生态城市的内涵包括健康、安全和发展.其中健康包括活力和结构;安全包括暴露水平、敏感性和恢复力;发展包括发展的潜力和协调能力.论述了生态城市指标体系构建的原则和结构;在此基础上,以厦门市为例,构建了沿海生态城市的海洋指标体系,讨论了指标体系构建的一些关键问题. 相似文献
994.
Over the next several decades, arctic marine mammals will face threats from six areas of human influence: climate change, environmental contaminants, offshore oil and gas activities, shipping, hunting, and commercial fisheries. This paper reviews these factors, the nature and magnitude of the threats they pose, current scientific understanding and management of those threats, and the potential for effective conservation action. Climate change, offshore oil and gas activities, and commercial fisheries likely pose the greatest threats. Addressing the combined effects of all six factors, however, will be particularly difficult but essential to prevent declines beyond those that have already occurred. 相似文献
995.
Transitioning ocean governance into an ecosystem-based approach requires improved knowledge of ecosystems and existing management systems. While there has been increased effort to compile and synthesize ecological data, relatively little scholarship has been focused on improving and understanding ocean management systems. This paper presents a unique dataset that makes objective analyses of ocean management possible across multiple jurisdictions and sectors in the California Current. Following an explanation of the criteria used to compile relevant statutes and regulations, the paper suggests applications for the dataset including education and policy uses and ecosystem-based management tool development to identify and measure problems of fragmented management. 相似文献
996.
Javier Caraveo‐Patiño Yiqun Wang Luis A. Soto Kebreab Ghebremeskel Catherine Lehane Michael A. Crawford 《Marine Ecology》2009,30(4):437-447
The radiation of the mammalian land species that became the baleen whales happened about 27–34 Mya. Mammals require omega 6 fatty acids for reproduction. With this long exposure to the omega 3‐rich marine food chain, the Gray whale (Eschrichtius robustus) might be expected to have lost its requirement for omega 6 fatty acids. We report an unexpectedly high content of omega 6 arachidonic acid (ArA) in the Gray whale liver and muscle lipids. This whale migrates 10,000 km from the cold polar, omega 3 oil‐rich food chain to that of the breeding lagoons of the tropical waters. The food web of tropical waters is a source of omega 6 fatty acids, which are hardly present in the cold polar food web. We suggest the reason for this longest of migrations from cold to warm waters is to meet the requirement for omega 6 fatty acids for mammalian reproduction and brain growth. This extreme conservation of omega 6 fatty acids in Gray whale biology has critical implications for mammalian biology and especially for whale conservation. 相似文献
997.
998.
我们已从文蛤肉中提取得到1种具有抗癌活性的多肽,命名为Mer2.本文报道Mer2对体外培养的肺癌A549细胞的生物学效应.采用溴化二苯偶氮盐(MTT)法检测Mer2对肺癌A549细胞的抑制效果,并应用细胞形态观察法、Hoechst荧光染色和流式细胞术等方法,探讨了Mer2对细胞形态、细胞周期的影响.结果表明,Mer2对体外培养的肺癌A549细胞的生长有较强的抑制作用,对作用含量和时间均具有一定的依赖性.Met2使细胞形态发生明显变化,明显地出现凋亡峰,但并没有出现明显细胞周期阻滞现象.这表明文蛤多肽可能通过诱导细胞凋亡从而抑制癌细胞的生长. 相似文献
999.
产碱性纤维素酶海洋细菌的筛选、鉴定及酶学性质研究 总被引:3,自引:1,他引:3
用CMC平板筛选方法,从青岛近海海域海水中分离出一株产碱性纤维素酶的海洋菌株QM11,经16S rDNA鉴定,该菌株为Cytophaga fucicola.对该菌的生物学特性研究表明,其最适生长温度为27℃,生长温度范围为4~48℃,为耐冷菌;在pH7.0~8.0、含3.0%NaC1的培养基条件下,最适宜菌株生长和产酶;QM11所产碱性纤维素酶最适反应温度为40℃,最适反应pH为9.0,在碱性条件下具有较高的酶活性和较好的稳定性.Mn2+、Fe3+对酶反应具有促进作用,Cu2+、Pb2+对酶反应具有抑制作用. 相似文献
1000.
离子色谱-电感耦合等离子体质谱联用测定海水中的IO3^-和I^- 总被引:1,自引:0,他引:1
研究了离子色谱-电感耦合等离子体质谱(IC-ICPMS)联用技术直接进样测定海水中IO3^-和I^-的方法.采用IonPacAG23离子色谱保护柱分离IO3^-和I^-,以浓度4.0mmol/dm3的KOH为流动相,流量为1.0cm3/min,每个样品的分析时间为2.5min.采用2.5×10^-3cm^3的进样量,IO3^-和I^-的检出限分别达到0.6和0.4nmol/dm2,可满足海水中碘形态的定量分析.该方法的IO3^-和I^-浓度范围在2.0nmol/dm3~2.0μmol/dm3. 相似文献