全文获取类型
收费全文 | 364篇 |
免费 | 17篇 |
国内免费 | 29篇 |
专业分类
林业 | 73篇 |
农学 | 41篇 |
基础科学 | 29篇 |
58篇 | |
综合类 | 113篇 |
农作物 | 15篇 |
水产渔业 | 22篇 |
畜牧兽医 | 34篇 |
园艺 | 9篇 |
植物保护 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 21篇 |
2013年 | 16篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 28篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 23篇 |
2006年 | 29篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有410条查询结果,搜索用时 15 毫秒
71.
72.
Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae . Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20°C, but not at 24°C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12–20°C, 10 h at 8°C, 16 h at 6°C or 24 h at 4°C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16°C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16°C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20°C and to 26 days as temperature decreased to 4°C. At 8°C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6°C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12–16°C, and decreased as temperature decreased to 8°C or increased to 20°C. At temperatures from 8 to 20°C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by 'lesions' (both log10 -transformed) at different temperatures. 相似文献
73.
Maria-Elisabeth Krautwald-Junghanns DrMedVet Friedrich Schumacher AR DrMed Bernd Tellhelm AOR DrMedVet 《Veterinary radiology & ultrasound》1993,34(6):382-390
In the last 21 /2 years, 288 grey parrot and amazon species with symptoms of respiratory disease clinically were presented to the clinic for avian medicine at the Justus-Liebig-University in Giessen. Ventro-dorsal and latero-lateral radiographs were taken from all birds; radiologic signs of lower respiratory tract disease were noted. Radiographs were normal in 55 of the birds. The results of the radiographic examination for the remaining 233 birds were compared with the necropsy results of terminally ill parrots, with the results of laboratory examinations/endoscopy/and/or with an examination by computed tomography. Thoracic radiographs were evaluated for occurring radiological abnormalities pertaining to the respiratory tract. The frequency of these lesions and their association with a disease process and/or specific etiology was noted. 相似文献
74.
75.
D.B. Ndumu R. Baumung M. Wurzinger A.G. Drucker A.M. Okeyo D. Semambo J. Slkner 《Livestock Science》2008,113(2-3):234-242
Ankole cattle are well known for their massive white horns and red coat colour. These characteristics are attributed to centuries of cultural breeding practices. Two experiments with traditional cattle keepers were carried out at a governmental Ankole nucleus farm in south-western Uganda to identify phenotypic characteristics as well as production and fitness traits which are important indigenous selection criteria. Forty one body measurements each were taken from 15 bulls and 35 cows and phenotypic characteristics were described in detail. In the first experiment 12 groups of 6 to 8 cattle keepers were invited to rank several groups of 4–5 animals according to their preference for a breeding bull or cow based on phenotype alone. In the second experiment the ranking was based on phenotype and a hypothetical life history that was randomly assigned to each animal on each day of experiment. The history included milk yield (on own performance for cows and that of the dam for bulls), fertility of the animal and its sire as well as events of East Coast Fever. For analysis, Generalized Multinomial Logit Models were fitted. To compare different models the likelihood-based pseudo R square measure was used. The results indicate that, in the selection of cows, performance and fitness traits are emphasized by the cattle keepers while in the selection of bulls, the phenotypic appearance of the animal plays an important role. Individual fertility followed by milk performance are the main criteria for selecting cows, resistance to East Coast Fever was of highest importance in bulls. In both sexes a dark red coat colour was highly rated. The study indicates that the methodology of preference ranking combining phenotype and a hypothetical life history may provide insight into indigenous selection criteria of stock owners elsewhere. 相似文献
76.
77.
灌区混凝土建筑物老化病害评估指标及其标准的研究 总被引:5,自引:0,他引:5
刘柏青 《中国农村水利水电》1998,(5):16-18
在大量、普通调查的基础上,进行了认真的统计、分析、计算与分类,广泛参考建筑、水利方面有关研究文献、规范,研究并提出了以评价可靠性(含安全性、适用性、耐久性)为基本内容的灌区混凝土建筑物老化病害评估准则;提供了各准则的评估指标体系内容;制定了主要指标体系的标准。为数以万计的中小型水工建筑物老化病害评估提供了参考依据。 相似文献
78.
79.
运用改进的原型进化法设计和开发通用的县级森林资源管理信息系统(general forest resource management information system for forest bureau on county-level,简称GFRMIS),并将该系统应用到广西壮族自治区武鸣县.GFRMIS具有通用性、标准规范性、地方兼容性、继承性和系统功能易于扩展维护等特点.改进的原型进化法不但能够延长软件的使用周期,而且可提高系统的实用性和扩展性,是一种较好的软件开发模式. 相似文献
80.
森林可持续经营标准和森林认证标准的比较分析* 总被引:4,自引:0,他引:4
在介绍森林可持续经营标准和森林认证标准的概念和产生背景的基础上 ,从目的、内容、性质、倡导机构、尺度等方面对两者进行了比较分析 ,认为两者的目的都是为了实现森林可持续经营 ,但在内容、性质和倡导机构方面互为补充。许多国家已经制定了这两类标准并正在积极试验中 ,中国的这两类标准也已被报送到有关部门审批。随着全球经济一体化进程的加快 ,森林认证正在从欧美经济发达地区向亚非地区扩展。不同森林认证体系标准之间的互认是当前的热点 ,而增加森林经营单位水平可持续经营标准的可操作性非常关键。 相似文献