首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   157篇
  免费   12篇
  国内免费   5篇
丛书文集   3篇
教育与普及   1篇
综合类   157篇
自然研究   13篇
  2024年   2篇
  2021年   3篇
  2020年   5篇
  2019年   1篇
  2018年   6篇
  2017年   5篇
  2015年   5篇
  2014年   9篇
  2013年   7篇
  2012年   16篇
  2011年   12篇
  2010年   5篇
  2009年   4篇
  2008年   3篇
  2007年   6篇
  2006年   6篇
  2005年   4篇
  2004年   3篇
  2003年   2篇
  2002年   2篇
  2001年   8篇
  2000年   1篇
  1999年   6篇
  1998年   5篇
  1997年   7篇
  1996年   5篇
  1995年   7篇
  1994年   8篇
  1992年   3篇
  1991年   3篇
  1990年   5篇
  1989年   2篇
  1988年   3篇
  1987年   3篇
  1986年   2篇
排序方式: 共有174条查询结果,搜索用时 187 毫秒
51.
The zooplankton species Oithona davisae is indigenous to coastal areas of Japan and the China Seas. It has, however, successfully invaded many other coastal marine regions such as San Francisco Bay, the Mediterranean Sea, the North Sea and the Black Sea. It is transported most probably in ballast water tanks. This is the first report of O. davisae in the coastal regions of the southern Black Sea (Anatolian coast). Based on monthly plankton sampling at two stations (Sürmene Bay), the seasonal dynamics of O. davisae were investigated. The highest abundance occurred at the coastal station (49,761 ind. m?3) in December and in October at the offshore station (8896 ind. m?3). The egg-carrying copepod O. davisae is more abundant in September (4571 ind. m?3) at the coastal station and in August (952 ind. m?3) at the offshore station. Expansion of this invasive copepod along the Black Sea coasts is reported by another country also. According to our results this invasive species may replace its native congener, Oithona nana. It can be hypothesized that O. davisae is one of the key species for energy transfer to the upper level of the food web from the microbial loop, which has recently become important in the Black Sea.  相似文献   
52.
淤泥质海岸在地貌形态、沉积物构成、水动力特征及冲淤演变规律方面,都与砂质海岸有明显不同。弄清在宽阔淤泥浅滩上破波作用历时及波浪动力的分布对理解淤泥质海岸的沉积和地貌分带性是重要的。为了了解淤泥质海岸冲淤演变规律,需要对淤泥在海水环境中的絮凝、沉降、冲刷特性及密实过程进行一系列专门的室内试验,并根据淤泥沉积物在运动海水中冲淤的物理过程,建立适当的计算模式,本文对此作了探讨。海岸演变通常是一个长期过程,但在人工吹泥条件下,可以发生短期内的明显变化,连云港吹泥站的建立,客观上提供了研究这种短期变化的条件。  相似文献   
53.
本文在多年研究的基础上,改进了青蟹养殖坛的结构及设置方法,探讨出了一套新的坛式养殖实用技术,可供沿海地区利用滩涂养殖青蟹作参考  相似文献   
54.
Intertidal flat systems represent an important coastal geomorphological unit, providing habitat for wild life, land resource for reclamation and protection for the coast against extreme storm events. In addition, the tidal flats covered with flourishing h…  相似文献   
55.
广东省沙质海岸营造防风固沙试验示范林模式研究   总被引:1,自引:0,他引:1  
进行了适生固沙灌,草的选草,草的选育,栽培以及及减轻沿海热带气旋危害并延缓沙土向内陆移动速度等的研究,营造乔,灌,草综合治试验试验模式示范林,并筛选出防风固沙效果好的4个大麻黄优良无性系,3个灌木和5个适于林带前沿至高潮线沙带种植的草木植物,从林带前沿到农田旱地设置 3道防风屏联,采取这些技术措施后,试验示范林内和林后风速降低了43.5-68.7%,4-5m/s风速已不再起飞沙,林内的自然植被增加,喜湿润的植物生长良好,防风固沙效果显著。  相似文献   
56.
亚热带基岩海岸防护林土壤的酶活性   总被引:10,自引:2,他引:8  
研究了我国亚热带基岩海岩主要防护林类型土壤酶活性持征,指出在3种磷酸酶中,酸性磷酸酶活性大于碱性,中性磷酸酶活性。3种磷酸酶与总磷酸酶活性密切相关,但以碱性磷酸酶相关性最高,中性磷酸酶次之,酸性磷酸酸最小。4类土壤酶活性自上而下均逐渐减少。不同森林类型土壤酶活性差异显,林龄越大活性越高,经济林受人为干扰,土壤酶活性居中低水,应采用合理的经营管理措施。  相似文献   
57.
Based on the equations of mo mentum and continuity, a general three-dimensional transport model for suspended sediment by waves and currents is developed by respectively decomposing the instantaneous velocities and concentrations into three different time-scale components. The model is composed of two submode ls. One is a three-dimensional flow field submodel including the influence of waves, and the other is a three-dimensional diffusion submodel for suspended sediment due to waves and currents. The purpose of this study is to provide a theoretical model for further investigating sediment transport by waves and currents in estuarial and coastal areas.  相似文献   
58.
岩质海岩防护林树木根系对土壤抗冲性的强化效应   总被引:11,自引:0,他引:11  
对岩质海岩防护林主要造林树种根系强化土壤抗冲性进行研究,发现根径在0.5mm以下和0.5-1mm的细根对土壤抗冲性的强化效应显著,原因在于数量庞大的细根系直接网络土体、活跃细根系的死亡分解及根系分泌物对土壤结构的间接改良作用。当根径不小于1mm径经的细根在原有基础上每1000cm^3土增加100g根量,树木根系对土壤抗冲强强化值将分别增加21.45(湿地松),12.20(马尾松)、28.99(日本扁柏)和11.34(毛竹)。  相似文献   
59.
《Journal of Natural History》2012,46(13):1621-1632
The diets of all South-East Asian water snakes of the subfamily Homalopsinae are reviewed. New diet observations for 10 species of homalopsine snakes are presented. The data on four of these, Cantoria violacea, Enhydris doriea, E. longicauda and Gerarda prevostina represent the first published diet records for these species. The observations for Fordonia leucobalia, Myron richardsonii andEnhydris enhydris represent the first taxonomically detailed diet records for these three species. The records provided for Cerberus rynchops, Enhydris plumbea and Homalopsis buccata add new taxonomic categories to previous records. The records provided for Cerberus rynchops, E. plumbea and Homalopsis buccata add new taxonomic categories to previous records. Four generalities emerge from our findings: (1) freshwater homalopsines feed primarily on fish and the adults and larvae of amphibians; (2) at least four of the eight estuarial species specialize on crustaceans while two primarily prey on fish; (3) feeding on crustaceans appears to have evolved independently at least twice; (4) prey are usually less than 10% of the predator's mass. The known predators of homalopsines are summarized and include both invertebrates and vertebrates. The microhabitats of the estuarial species are discussed and related to prey and habitat preferences.  相似文献   
60.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号