全文获取类型
收费全文 | 277篇 |
免费 | 37篇 |
国内免费 | 104篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 45篇 |
地球物理 | 55篇 |
地质学 | 55篇 |
海洋学 | 189篇 |
天文学 | 1篇 |
综合类 | 36篇 |
自然地理 | 34篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 19篇 |
2013年 | 17篇 |
2012年 | 22篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 12篇 |
2005年 | 16篇 |
2004年 | 11篇 |
2003年 | 26篇 |
2002年 | 23篇 |
2001年 | 17篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有418条查询结果,搜索用时 625 毫秒
151.
不同盐度养殖Ⅰ龄花鲈(Lateolabrax japonicus)的生长特性差异分析 总被引:1,自引:0,他引:1
利用室外水泥池,采用全人工配合饵料投喂的方法对花鲈(Lateolabrax japonicus)进行为期274d的养殖实验,分别测定其在不同养殖盐度条件下的生长状况、成活率、特定生长率和饲料系数。结果表明,在盐度12—18时花鲈生长速度、成活率和特定生长率较高。通过回归分析得出,其生长速度的最适盐度为16—17;盐度12和18组饲料系数较低,分别为1.57和1.62,盐度30组最高;各组间在成活率方面差异不显著。因此,Ⅰ龄花鲈养殖的最适宜生长盐度理论值为16—17,在此条件下可实现较高的生长速度、特定生长率和饲料转换率。 相似文献
152.
饲料中锌含量对斜带石斑鱼(Epinephelus coioides)生长、饲料效率、矿物质含量和体组成的影响 总被引:2,自引:0,他引:2
以ZnSO4·7H2O为锌源,用锌添加量为0、20、40、60、80和100mg/kg的实验饲料投喂斜带石斑鱼12周,研究其对斜带石斑鱼生长、饲料效率、矿物质含量和体组成的影响.结果表明,各实验组的增重率,饲料效率,存活率和全鱼、脊椎骨、鳞片的锌含量无显著差异.全鱼、脊椎骨和鳞片的锰含量均随着饲料中锌的添加而降低,锰和锌存在明显的拮抗关系.全鱼的铁含量随着饲料中锌的添加而降低.全鱼、脊椎骨和鳞片的钙、磷、镁含量均不受饲料中锌含量的影响.饲料中添加锌对全鱼水分、灰分,肌肉水分、脂肪,形态学指标,红细胞比容和血红蛋白含量没有显著影响.饲料中不添加锌时,全鱼的蛋白、脂肪和肌肉的蛋白、灰分含量较低.实验结果表明基础饲料中33mg/kg的锌已经满足斜带石斑鱼生长的需求,能使鱼体锌达到饱和. 相似文献
153.
Chiee-Young Chen Chien-Cheng Lai Kuo-Shu Chen Chien-Chung Hsu Chin-Chang Hung Meng-Hsien Chen 《Marine pollution bulletin》2014
Muscles of 115 North Pacific albacore (ALB, Thunnus alalunga) and 75 Pacific bigeye tuna (BET, Thunnus obesus), collected from 2001 to 2006, were analyzed. No ALB, but 13 large BET had organic mercury (OHg) concentrations exceeding 1 μg g−1 wet weight. For both ALB and BET, total mercury (THg) and OHg concentrations were significantly and positively correlated with fork length (FL) and body weight. The muscle Hg bioaccumulation rates of BET were higher than those of ALB, particularly in the adult fish. Moreover, the lines had crossover points among the two species that imply the young BET (FL < 110 cm) contains lower muscle Hg concentrations than ALB of the same size. The suggested weekly dietary intake of ALB and small-BET meats is 340 g, and of BET meat it is 150 g for a 60-kg person based on the provisional tolerable weekly intake (PTWI) of methylmercury set by the WHO. 相似文献
154.
晚石炭世莫斯科期刺毛类(Chaetetids)是重要的造礁生物,在全球范围内广泛分布并建造礁体。中国已报道的刺毛类礁主要分布在辽东太子河流域,产在上石炭统本溪组海相灰岩中。刺毛类生长形态多样,有层状、板状、丘状、分枝状和柱状,主要以板状覆盖沉积物的方式造礁。研究区刺毛类礁中刺毛类生长形态及其所主导的生物群落在垂向上变化明显,由此将礁体的建造划分为三个阶段:(1)定殖阶段:刺毛类较少,生长方式单一,多以层状形态生长在棘屑滩上。层状刺毛类体积小,抗浪能力较弱,很难在其周围创造水流平缓的可供其他底栖生物生存的环境。因而该阶段群落生物种类单一,数量稀少;(2)繁盛阶段:刺毛类丰富,生长形态多样,以板状、分枝状和丘状为主。板状刺毛类单独形成的礁骨架,或与分枝状和丘状刺毛类组合起来的礁骨架,都能在其周围一定范围营造适宜底栖生物生存的环境,因此该阶段群落的生物多样性高;(3)衰退阶段:刺毛类很少,多为薄层状,断续生长在棘屑组成的基底上。薄层状刺毛类很脆弱,基本失去改善周围环境的能力,因此该阶段群落生物多样性很低。以上分析说明刺毛类生长形态的变化可以影响生物群落的组成和演化。生物群落的演化过程就是礁体建造的过程。从刺毛类生长形态的角度研究礁体建造过程,为分析由具有多种生长形态的造礁生物建造的生物礁的成礁机制提供新思路。 相似文献
155.
《Marine Policy》2017
A generic framework (FW) for the monitoring and evaluation of spatially managed areas (here defined as marine areas subject to a planning and management regime) was developed and tested in nine marine areas of 13 European countries under the EU funded project MESMA (Monitoring and Evaluation of Spatially Managed Areas). This paper describes the lessons learned in the use of the FW and draws conclusions for its future use and development. The selected case studies represented diverse spatial scales, management status and complexity, ranging from sub-national areas to entire national coastlines, and large offshore regions. The application of the FW consisted of seven steps: starting with (i) context setting and (ii) gathering of relevant ecosystem information, human activities and management goals; it continues with (iii) indicator selection and (iv) risk assessment; and the final steps considers the (v) analysis of findings and (vi) the evaluation of management effectiveness, to end up with (vii) the revision and proposal of adaptation to current management. The lessons learnt through the application of the FW in the case studies have proved the value of the FW. However, difficulties rose due to the diversity of the nature and the different stages of development in planning and management in the case study areas; as well as, limited knowledge on ecosystem functioning needed for its implementation. As a conclusion the FW allowed for a flexible and creative application and provided important gap analyses. 相似文献
156.
《Marine Policy》2017
The global aquaculture sector has grown continuously over the past 40 years, though unevenly among countries. Differences in factors such as inputs, climate, management, technology, markets, social environment, and institutions might be reasons for the disparities in growth. This study focuses on institutions, by analyzing the relationship between annual growth in the production of the major aquaculture countries and the quality of their institutions over three decades (1984–2013). Based on an ex-ante set of criteria, seventy-four aquaculture countries from five different regions - Africa, the Americas, Asia, Europe and Oceania - were selected. Annual percentage change in total aquaculture production, in terms of quantity and value, was used as a proxy for sector development. Three indices - governance, corruption, and competitiveness - were used as institutional quality proxies. Empirical results suggest that the aquaculture growth did not significantly correlate with the quality of institutions. By region, Africa had the fastest growth in the aquaculture sector, though from a low base, with 7.35% and 9.28% higher annual percentage change in aquaculture quantity and value respectively, than the Asian region. While, the European region experienced significantly lower annual percentage change in aquaculture quantity, a difference of 3.78% compared to the Asian region. Furthermore, the study found that total aquaculture production was not positively correlated with eco-label certification. The study is concluded by discussing the “aquaculture paradox.” 相似文献
157.
158.
Seasonal temperature patterns may have changed through time in response to current global warming. However, the temporal resolution of available proxy records is not sufficient to quantify paleotemperature seasonality prior to anthropogenic forcing of the climate. In the present study, we reconstructed seasonal and inter-annual temperature patterns of the North Sea during the last 140 years, the Allerød Interglacial and the Late Medieval Climate Optimum using sclerochronological and δ18Oaragonite data from bivalve shells, Arctica islandica. On average, the climate during 1278–1353 AD was ca. 1.1°C colder and seasonality was ca. 60% less than today. During the Allerød, long-term temperatures remained about 3.2°C below present values, and absolute summer and winter anomalies were ca. ?4 and ?2.7°C, respectively. However, seasonality was statistically indistinguishable from today. Long-term average temperatures compare well with existing data for the Late Medieval and Allerød, but detailed information on seasonality during the studied time intervals has never been presented before. Our data also demonstrated that annual instrumental and δ18Oaragonite-derived temperatures did not always match. This difference is explained by (1) NAO-driven salinity changes, which influence the temperature estimation from δ18Oaragonite and (2) food-driven changes in growth rates; portions of the shell that formed more rapidly are overrepresented in carbonate samples. Our study indicated that individual bivalve shells can open discrete, near-century long, ultra-high-resolution windows into the climate past. Such information can be vital for testing and verifying numerical climate models. 相似文献
159.
利用三维强风暴动力-电耦合模式,数值模拟了风暴演变过程 中电活动对冰雹增长及地面降雹的影响. 结果指出,带电冰雹与云内强电场作用使地面降雹 量增加约50[HTK]髎[HTSS],雹块直径增大0.7mm,降雹时间滞后约3min. 文中还讨论了强电 场通过对水成物降落速度的调制来影响冰雹微观增长过程,即主要是影响碰并过程和冰雹融 化过程. 电活动使冰雹源、汇总量都减少,但汇总量减少更多,总体效果使冰雹总量增加, 数目减少,冰雹长得更大,更易降落到地面. 相似文献
160.
春季生殖真鲷仔、稚、幼鱼的摄食与生长 总被引:7,自引:0,他引:7
1996年5 ̄6月份在本院海水育苗试验场对人工培养的春季生殖真鲷仔、稚、幼鱼的摄食和生长特性进行分析,旨在为该种群早期发育阶段的生物学积累资料,并为开展大批量苗种生产提供依据。结果表明,在水温在23℃时,仔鱼约经55 ̄60h左右开口摄食,开口饵料为小型臂尾轮虫。以后随着鱼体的生长(〉10mm),摄食桡足类的比例迅速增加。对285尾仔、稚、幼鱼观察,在实验条件下,其摄食率达100%。摄食量约占体重的 相似文献