全文获取类型
收费全文 | 1315篇 |
免费 | 81篇 |
国内免费 | 89篇 |
专业分类
林业 | 196篇 |
农学 | 46篇 |
基础科学 | 22篇 |
221篇 | |
综合类 | 418篇 |
农作物 | 92篇 |
水产渔业 | 239篇 |
畜牧兽医 | 170篇 |
园艺 | 41篇 |
植物保护 | 40篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 27篇 |
2021年 | 38篇 |
2020年 | 49篇 |
2019年 | 50篇 |
2018年 | 39篇 |
2017年 | 47篇 |
2016年 | 75篇 |
2015年 | 54篇 |
2014年 | 77篇 |
2013年 | 117篇 |
2012年 | 111篇 |
2011年 | 89篇 |
2010年 | 79篇 |
2009年 | 60篇 |
2008年 | 75篇 |
2007年 | 57篇 |
2006年 | 59篇 |
2005年 | 63篇 |
2004年 | 48篇 |
2003年 | 41篇 |
2002年 | 30篇 |
2001年 | 31篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1485条查询结果,搜索用时 0 毫秒
941.
根据2009年7-9月南太平洋长鳍金枪鱼延绳钓探捕数据,对南太平洋长鳍金枪鱼的钓捕技术、南太平洋的海上环境、渔获组成和长鳍金枪鱼的的生物特征进行了分析,对影响渔获产量的因素、渔获冷藏加工、渔获销售相关情况进行了总结,针对生产实际存在的问题提出了建议,以期为今后在该区域长鳍金枪鱼生产提供参考。 相似文献
942.
943.
Antony J. W. Taylor 《Asia Pacific viewpoint》2003,44(2):177-193
Abstract: The methods adopted in the appraisal of the trauma of three communities after different disasters in the South Pacific are described and discussed. The outcome affirms the need for non‐indigenous clinicians to be ready to adjust their concepts and methods to suit the cultural frameworks they encounter when they are invited abroad, and for local health professionals to be ready to share their knowledge and skills with their collegues from abroad. The outcome, it is argued, should improve the quality of service provided at all stages of disaster recovery, and still enable questions to be raised about matters of fundamental concern – such as the power of religious belief and of social justice in the process of healing. These questions were found to be of particular importance in the context of the South Pacific cultures. 相似文献
944.
A quantitative understanding of both natural and anthropogenic sediment sources is needed to accurately assess and predict the potentially adverse effects of land development on aquatic ecosystems. The main objective of this study was to quantify sediment production and delivery rates in a dry tropical environment on the island of St. John in the eastern Caribbean. One to three years of measurements were used to determine values and empirical functions for estimating sediment production from streambanks, treethrow, undisturbed hillslopes, zero-order sub-catchments, unpaved road surfaces, and road cutslopes. Sediment production also was measured from both undisturbed and roaded first-order sub-catchments. 相似文献
945.
946.
The pygmy bluetongue lizard, Tiliqua adelaidensis, occupies spider burrows as home sites. It is an endangered species, known from only 19 small natural grassland sites in the mid-north of South Australia, all on privately owned land. Habitat requirements of the pygmy bluetongue lizard were investigated at four sites. Both within and between sites, lizards were more likely to be found in areas with a greater number of deep spider burrows. Areas where lizards were not found tended to lack these burrows. Strong site similarities were found for a range of habitat parameters examined. Within these grasslands there was no specific vegetation community associated with areas occupied by pygmy bluetongue lizards. However there was a distinct vegetation community associated with an absence of lizards. Generally there was no difference in the abundance and diversity of ground dwelling invertebrates between areas with and without lizards. As the only protected area of natural grassland within the known distribution, Mokota Conservation Park was assessed as a potential reintroduction site. It was found to be unsuitable due to a low number of deep spider burrows and a vegetation community similar to that found in uninhabited areas of known lizard inhabited sites. Unless other conservation areas can be established, preservation of this lizard will rely on habitat management by private land holders. Community goodwill and informed advice to the land holders will be essential in this process. 相似文献
947.
近年来,随着珍稀野生动物的逐渐减少和灭绝,学界对其的关注与研究越来越多。目前学术界研究较多的有亚洲象、华南虎、犀牛、麝等。但目前的研究显得碎散,尚还存在不少研究的空白点,客观的概括,也还有待于提高。 相似文献
948.
Cities in the Latin America and Caribbean (LAC) region and around the world are setting long-term greening goals that include planting more trees and increasing green cover. Research in LAC cities has mainly focused on biodiversity and vegetation, with little understanding of the mechanisms underlying the decisions through which stakeholders achieve urban greening. Exploring stakeholders’ views about urban forest management and governance can provide us with an opportunity to identify needs and research gaps for urban greening and urban forestry in LAC. To our knowledge, there has never been a region-wide empirical study to capture these stakeholder views. Here we explore how stakeholders working in urban forestry in LAC, including governmental, and non-governmental professionals, define urban forests, and view management and governance issues as well as educational opportunities. We used an online survey based on a combination of open- and closed-ended questions. The survey was delivered to participants at the first two regional conferences on urban forests in LAC organized by the United Nations. We collected 91 responses from stakeholders working in 50 different cities of varying population sizes across 6 LAC bioregions. Most respondents considered parks, planted green corridors, street trees, and remnant forests in urban and peri-urban areas as components of urban forests. Stakeholder views on management and governance were divided in two distinct perspectives, one dominated by public participation issues, and another one related to operational issues. Most respondents considered operational and management tools for urban forests to exist in LAC cities, but they disagreed on the existence of inventories, long-term strategies, and ways for the public to engage in urban forestry. Responses also revealed that some educational opportunities, such as arboricultural certification, are still relatively scarce and in high demand in the region. This study provides a regional baseline and first insights into a more diverse view of urban forestry which could be enriched with more empirical studies in the future. 相似文献
949.
950.
Christopher J. Katalinas John D. Robinson Allan E. Strand Tanya Darden Karl Brenkert Michael R. Denson 《Fisheries Management and Ecology》2019,26(3):224-235
The South Carolina Department of Natural Resources (SCDNR) began stocking red drum, Sciaenops ocellatus (Linnaeus), in 1989 to augment the abundance of juveniles available for recreational harvest in South Carolina estuaries. While stock enhancement can help supplement wild populations under high fishing pressure, releasing hatchery‐raised fish into the wild also presents the risk of decreased genetic diversity. An individual‐based model (IBM) was developed to forecast the genetic influences of stocking on the wild spawning population to inform responsible stocking strategies. Model results indicated the SCDNR red drum stock enhancement programme should maintain mean contributions of stocked fish no greater than 30% per year class over a 45‐year stocking period, coupled with at least 10 effective breeders in the hatchery replaced annually, to maintain current levels of genetic diversity estimated in the wild population. The IBM is a useful tool for hatchery managers to guide responsible stock enhancement. 相似文献