全文获取类型
收费全文 | 73篇 |
免费 | 18篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 13篇 |
地球物理 | 13篇 |
地质学 | 44篇 |
海洋学 | 23篇 |
天文学 | 1篇 |
综合类 | 4篇 |
自然地理 | 13篇 |
出版年
2024年 | 1篇 |
2021年 | 5篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2012年 | 6篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 10篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
排序方式: 共有112条查询结果,搜索用时 15 毫秒
31.
32.
Growth and energy budget of marine amphipod juvenile Eogammarus possjeticus at different temperatures(20°C,24°C, 26°C, 28°C, 30°C, 32°C and 34°C) were investigated in this study. The results showed that the cumulative mortality rate increased significantly with rising temperature(p0.01), and exceeded 50% after 24 h when temperature was above 30°C. With the temperature increasing from 20°C to 26°C, the ingestion rate and absorption rate increased, but decreased significantly above 28°C(p0.01), indicating a decline in feeding ability at high temperatures. The specific growth rate increased with rising temperature, but decreased significantly(p0.01) after reaching the maximum value at 24°C. Similarly, the oxygen consumption and ammonia emission rates also showed a trend of first increase and then decrease. However, the O:N ratio decreased first and then increased with rising temperature, indicating that the energy demand of E. possjeticus juvenile transferred from metabolism of carbohydrate and lipid to protein. In the energy distribution of amphipods, the proportion of each energy is different. With rising temperature, the ratio of the energy deposited for growth accounted for ingested gross energy showing a trend of decrease, while the energy lost to respiration, ammonia excretion, and feces accounted for ingested gross energy being showed a trend of increase. It seemed that rising temperature increased the metabolism and energy consumption of the amphipods and, meanwhile, decreased the energy used for growth, which may be an important reason for the slow growth and small body size of the amphipods during the summer high-temperature period. 相似文献
33.
秋刀鱼舷提网渔具性能模型试验与海上实测结果的比较评估 总被引:1,自引:0,他引:1
舷提网是秋刀鱼(Cololabis saira)作业的主要方式之一,由于渔获率较高得到迅速推广。模型试验和海上实测是研究网具性能最为普遍的两种方式,两者试验结果的对比评估对于更好地测定网具作业性能具有十分重要的意义。根据2014年11-12月进行的秋刀鱼舷提网静水槽模型试验以及2015年7-10月和2016年6-10月在"鲁蓬远渔019"号船上进行的秋刀鱼舷提网网具性能测试试验测定的网具数据,采用多元线性回归方法,对网具的沉降深度和提升速度进行了标准化,并利用Bootstrap法分析了舷提网模型试验和海上实测试验结果。结果表明:(1)通过Bootstrap法得出标准化后的实测网最大沉降深度的均值分布范围为20.37~29.54 m,95%置信区间为21.76~28.13 m;模型网网具最大沉降深度均值的范围为26.42~37.58 m,95%置信区间为27.70~36.20 m。实测网网具中部最大沉降深度均值大约是模型网网具中部最大沉降深度均值的0.731~0.783倍。(2)通过Bootstrap法得出标准化后的实测网提升速度的均值分布范围为0.107~0.193 m/s,95%置信区间为0.111~0.191 m/s;模型网网具提升速度均值的范围为0.204~0.316 m/s,95%置信区间为0.207~0.312 m/s。实测网网具中部提升速度均值大约是模型网网具中部提升速度均值的0.591~0.611倍。(3)当假设海流速度为0时,求得实测网网具的平均沉降深度为29.14~41.21 m,约为模型网网衣中部最大沉降深度均值的0.751~0.807倍。(4)30 m和60 m水深的海流速度均对实物网网具中部的沉降深度有所影响,60 m水深的流速影响更加显著(P<0.05)。 相似文献
34.
The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice. 相似文献
35.
Jellyfish populations in the southeastern Atlantic off the coast of Namibia have increased subsequent to the decline of small pelagic fisheries at the end of the 1960s, although the environment there has also become warmer and the waters off Walvis Bay have become richer in zooplankton in recent years. Laboratory experiments were conducted with the scyphozoan jellyfish Chrysaora fulgida to investigate the effects of food density (0, 30, 70, 100 or 150 Artemia nauplii 200 ml?1), feeding frequency (once daily or once every third day) and water temperature (12, 16 or 20 °C) on the asexual reproduction, growth and development of polyps. The results of a generalised linear mixed-effects model reveal that all variables impacted asexual reproduction, with greater polyp production attained at higher food concentrations, increased feeding frequencies and increased temperatures. The most common mode of asexual reproduction was by lateral budding. These laboratory results suggest that polyps of C. fulgida may have proliferated off Namibia in recent times, which would contribute to increased numbers of jellyfish there. 相似文献
36.
从涨退水看鄱阳湖水位-湖面面积关系 总被引:1,自引:0,他引:1
鄱阳湖是我国最大的淡水湖,鄱阳湖水位-面积关系对研究鄱阳湖生态环境的变化具有重要意义。目前研究所建立的鄱阳湖水位-面积关系各异,存在一定的不确定性,其原因在于忽略了涨退水对鄱阳湖水位与面积的影响。在考虑鄱阳湖涨水与退水过程的基础上,利用鄱阳湖2000~2014年实测水位数据与对应的遥感影像数据,分析了鄱阳湖同一水位出现多个水面面积情况下湖泊不同面积的空间分布及其成因,并对鄱阳湖水面面积与水位关系的不确定性进行了分析。研究结果表明:(1)鄱阳湖水面面积与水位关系存在不确定性,主要受鄱阳湖涨水与退水过程中鄱阳湖水面比降不同的影响;(2)在同一水位条件下,涨水过程中鄱阳湖水面面积往往大于退水过程的水面面积,同时水面面积的增减变化与涨水退水的幅度变化趋势呈一致性;(3)涨水与退水过程对鄱阳湖水位与面积的影响主要表现在中低水位,随着水位增长到高水位时,这种影响会越来越小。 相似文献
37.
中部崛起背景下的郑汴一体化发展研究 总被引:4,自引:2,他引:2
中部地区崛起战略决策,为中原城市群发展提供了良好的发展环境,也提出了重大而迫切的战略任务.在中原城市群各个城市处于向心集聚为主的发展阶段,中原城市群建设应率先推进郑汴核心区一体化发展.郑汴核心区既是郑汴一体化的空间承载区,也是中原城市群一体化发展的先导区和示范区,需要从发展目标协同、基础设施共建、产业互补共进、资源共事、发展空间与功能协调、实施策略同步等多个方面有序促进郑汴一体化发展. 相似文献
38.
由于受全球变暖和人类活动加剧的影响,预计到2050年上海地区海平原相对升高50 ̄70cm,这会给包括堤坝在内的沿海岸线工程带来新的危害:包括地下水位抬升引起浅基础承载力下降、砂土地震液化加剧和建筑物陷加重、堤坝标准、威胁堤坝安全等问题。从定量的角度研究分析上述危害的严重性,提出综合措施。 相似文献
39.
40.
土地级别与基准地价都是城镇土地利用情况的反映,是揭示土地资产价值的科学方法,是政府宏观调控土地市场、科学合理配置土地资产的价格参考。及时更新土地级别和基准地价是地价管理的基础和前提,也是政府和国土资源行政管理部门的职责。 相似文献