全文获取类型
收费全文 | 91篇 |
免费 | 19篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 2篇 |
地球物理 | 7篇 |
地质学 | 64篇 |
海洋学 | 54篇 |
综合类 | 11篇 |
自然地理 | 5篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有148条查询结果,搜索用时 15 毫秒
91.
John V. Mensah 《Singapore journal of tropical geography》2005,26(2):212-226
It has been posited that small‐scale industry – businesses with less than 30 workers – provides a large share of employment and income in Ghana. This paper examines the proposition that while such enterprises in the informal sector are said to act as a sponge to soak up surplus labour in marginal activities, they are unprofitable. Using data from a survey in 1998 of 175 micro and small‐scale enterprises in the Central Region of Ghana, the paper also confirms problematic aspects of employment in this sector including the lack of formal contracts, irregular pay, low remuneration, non‐existent social protection and only marginal employment growth. The implication is that the small‐scale industry sector is not economically sustainable in its present form in Ghana. 相似文献
92.
93.
试样经焙烧、王水分解后,在8%的王水介质中,MIBK负载泡塑吸附[AuCl_4]~-。灰化吸附泡塑或硫脲溶液解脱,用中子活化法测定Au。取10g样品,可测定0.000x~xxμg/g的Au。用于金标样的定值,具有良好的精密度和准确度。 相似文献
94.
Assessment of the effectiveness of natural coral fragmentation as a dispersal mechanism for coral reef‐boring sponges
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Eastern Pacific reefs are mostly made up of interlocking coral branches of Pocillopora, which are easily broken by physical forces associated with heavy swells and winds. In this study we investigated the potential of these coral fragments to enable propagation of boring sponges. For this, we quantified the frequency of occurrence and diversity of boring sponges in fragments of corals recently trapped among the branches of live colonies, and later tested the hypothesis that these sponges colonize new branches of corals. Nearly 80% of the coral colonies investigated had coral fragments among their branches, and 69% of these coral fragments contained boring sponges (11 species), some of these sponges in reproduction (23% of them carried oocytes). To test whether sponges inhabiting coral fragments could colonize new branching corals we transplanted them to healthy branches, and to branches whose living tissue was mechanically eliminated to simulate damage produced by grazing and death after bleaching and other causes of coral tissue mortality. All the transplanted coral fragments cemented to each new colony by means of calcification, and of the three sponge species tested (Cliona vermifera, Cliona tropicalis and Thoosa mismalolli) only C. vermifera was able to colonize both new living branches (26.9%) and cleaned branches (65.5%). The apparent capability of C. vermifera to colonize by direct contact may be another key ability of this species to maintain high frequency of occurrence in Pacific coral reefs. However, although C. tropicalis and T. mismalolli were not able to colonize new coral substrata by direct contact, coral fragments have the potential to contribute to local persistence of these sponges and to their dispersal, both by asexual (fragments) and sexual means (transport of sexual products). The present findings may partly explain the current increase of excavating sponges on deteriorating reefs with a large availability of dead branching corals. 相似文献
95.
采用特殊工艺,以褐藻酸钠为原料,制成多孔性可吸收止血海绵。用正交试验法对止血海绵的配方进行了综合研究,并选出了最佳配方为:褐藻酸钠的浓度3%,粘度18CPS(厘泊)成型剂0.6%,络合剂1%,柔软剂8%。实验研究止血海绵的纤维结构与配方的关系。所得产品质地柔软,密度均匀,有一定弹性,易溶于水。这种止血海绵的含水量是8—10%,pH值为6,5,吸水率为200%。试验指出止血海绵有一定的抑菌作用。 相似文献
96.
97.
98.
Diverse and abundant siliceous sponge spicules were found in the latest Permian beds, Dongpan and Ma'anying sections, South China, including 52 types and 85 forms. Further investigation on these spicules allows us to understand extinction patterns and processes of deep-water sponges. These sponge spicules rapidly decreased below the Permian/Triassic boundary (PTB), and the extinction rates reach up to 88%-90% for types and 88%-92% for forms. Their extinction pattern is a gradual one that consists of two stages: the first is characterized by a gentle and slow extinction speed and low extinction rate, and the second by sharp and fast extinction speed and high extinction rate. The morphological extinction process is involved in the disappearance first of the triaxons and tetraxons, then of the polyaxons and demas, and last of monaxons. In exterior structure extinction, the complex spicules with branches and spines became extinct more easily than did smooth spicules. After the end-Permian mass extinction, only five common and smooth forms survived: Oxeas A, Oxeas B, Strongles B, Oxy-orthpentactines and Oxy-orthohexactines A. 相似文献
99.
对采自我国南海海域的蓖麻海绵Biemnasp .的化学成分进行了研究。从中分离出 4个结晶化合物。经FT -IR ,MS ,1 HNMR ,1 3 CNMR ,DEPT等波谱方法鉴定分别为正二十八酸(Ⅰ) ,正十六酸 (Ⅱ) ,穿贝海绵甾醇 (Ⅲ )和biemnamide (Ⅳ )。报道了 (Ⅰ) ,(Ⅱ) ,(Ⅲ )的化学结构和 (Ⅳ )的生理活性 相似文献
100.
海绵城市作为城市雨洪管理、人居环境改善的重要手段,在水资源、水环境及水灾害问题突出的湿陷性黄土地区开展具有现实意义.为保证湿陷性黄土地区海绵城市建设的有效性与安全性,通过梳理黄土水分入渗规律、湿陷机理及湿陷性黄土地区海绵城市建设的研究趋势和不足,总结了湿陷性黄土地区海绵城市安全有效推进所面临的问题主要有:海绵城市建设需... 相似文献