全文获取类型
收费全文 | 159746篇 |
免费 | 8013篇 |
国内免费 | 16392篇 |
专业分类
林业 | 18832篇 |
农学 | 22489篇 |
基础科学 | 13839篇 |
24430篇 | |
综合类 | 52349篇 |
农作物 | 8320篇 |
水产渔业 | 5719篇 |
畜牧兽医 | 22026篇 |
园艺 | 6448篇 |
植物保护 | 9699篇 |
出版年
2024年 | 220篇 |
2023年 | 1514篇 |
2022年 | 3974篇 |
2021年 | 5678篇 |
2020年 | 5316篇 |
2019年 | 4973篇 |
2018年 | 3617篇 |
2017年 | 5380篇 |
2016年 | 4929篇 |
2015年 | 6998篇 |
2014年 | 6862篇 |
2013年 | 8464篇 |
2012年 | 10455篇 |
2011年 | 11271篇 |
2010年 | 10933篇 |
2009年 | 10145篇 |
2008年 | 9695篇 |
2007年 | 10000篇 |
2006年 | 9156篇 |
2005年 | 8083篇 |
2004年 | 4021篇 |
2003年 | 3688篇 |
2002年 | 3188篇 |
2001年 | 3375篇 |
2000年 | 3520篇 |
1999年 | 3849篇 |
1998年 | 3494篇 |
1997年 | 3062篇 |
1996年 | 2824篇 |
1995年 | 2616篇 |
1994年 | 2291篇 |
1993年 | 2228篇 |
1992年 | 1832篇 |
1991年 | 1552篇 |
1990年 | 1335篇 |
1989年 | 1105篇 |
1988年 | 834篇 |
1987年 | 510篇 |
1986年 | 303篇 |
1985年 | 154篇 |
1984年 | 121篇 |
1983年 | 108篇 |
1982年 | 96篇 |
1981年 | 89篇 |
1980年 | 61篇 |
1979年 | 35篇 |
1965年 | 26篇 |
1964年 | 25篇 |
1963年 | 22篇 |
1956年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
101.
102.
103.
为了建立青蒿的SRAP最佳扩增体系,并筛选出SRAP多态性引物,本研究以青蒿叶片DNA为模板,采用正交试验设计,以Mg^2+、dNTP Mix、Taq DNA聚合酶、引物和DNA模板5种因素5个水平,对青蒿SRAP反应体系进行研究。结果表明,青蒿SRAP-PCR最佳反应体系为:引物0.6μmol/L、Mg^2+2.0 mmol/L、模板DNA 5.1 ng、Taq DNA聚合酶2.0 U、dNTPs 0.25 mmol/L,总体积为25μL。各因素对扩增反应均有不同影响,其中引物浓度的影响最大,dNTPs的影响最小。运用该体系对不同种质资源的青蒿进行验证,证明该体系稳定可靠,并在30个引物组合中筛选出了25对扩增条带清晰,多态性丰富的引物组合。这一结论为今后利用SRAP标记技术进行青蒿分子遗传学研究提供了科学依据。 相似文献
104.
105.
Ting Shi Yan-Yan Yu Jia-Jia Dai Yi-Ting Zhang Wen-Peng Hu Li Zheng Da-Yong Shi 《Marine drugs》2021,19(3)
The species Pseudogymnoascus is known as a psychrophilic pathogenic fungus with a ubiquitous distribution in Antarctica. Meanwhile, the study of its secondary metabolites is infrequent. Systematic research of the metabolites of the fungus Pseudogymnoascus sp. HSX2#-11, guided by the method of molecular networking, led to the isolation of one novel polyketide, pseudophenone A (1), along with six known analogs (2–7). The structure of the new compound was elucidated by extensive spectroscopic investigation and single-crystal X-ray diffraction. Pseudophenone A (1) is a dimer of diphenyl ketone and diphenyl ether, and there is only one analog of 1 to the best of our knowledge. Compounds 1 and 2 exhibited antibacterial activities against a panel of strains. This is the first time to use molecular networking to study the metabolic profiles of Antarctica fungi. 相似文献
106.
为探讨模拟气候变暖(增温2℃)和大气氮沉降(4 g·m-2·a-1)对入侵植物子代生长的影响,以中国和北美两种来源的加拿大一枝黄花子一代为研究对象,研究了子一代幼苗的生长和生物量分配的响应.结果表明:(1)增温降低中国来源加拿大一枝黄花的地上生物量,但提高其根冠比,增温降低北美来源加拿大一枝黄花的根冠比;(2)与北美来源加拿大一枝黄花相比,加氮对中国来源加拿大一枝黄花叶片数、地下生物量和总生物量的促进作用更大;(3)加氮促进加拿大一枝黄花地上生物量、地下生物量和总生物量的积累,但增温减缓了这种促进作用.这些结果表明,气候变暖可能会部分抵消氮沉降对加拿大一枝黄花子一代幼苗生长的促进作用. 相似文献
107.
Climate change has become a global issue influencing human survival and development while low‐carbon is the inevitable choice. As the world’s largest emitter of greenhouse gases, China has become an important force that influences the cooperation of climate change. China is a large agricultural country, and the rural carbon emissions have been gradually increasing. We consider rural neighborhood as an important space for the use of low‐carbon ideas to address climate change. There is no specific assessment system for a rural neighborhood. The studies of rural neighborhood low‐carbon mainly focus on the method of calculation carbon emissions. However, only quantifying rural carbon emissions is insufficient. In this paper, a low‐carbon evaluation indicator system has been proposed for rural neighborhood and Fuzzy Comprehensive Evaluation has been applied to get the low‐carbon degree. Considering the influence and feedback inside the indicator system, Analytic Network Process was applied to get the weights. Furthermore, a case study was carried out for the using of the proposed method in an eco‐village of China. Our practice has proved that the system is easy to operate in rural neighborhood. 相似文献
108.
Interaction effects between the agglomerative externalities affecting the survival of small startups
The purpose of this study is to identify the relationship between the survival of firms and the influence of agglomeration economies on firm location using a mixed effect Cox model considering random effects, given the industrial conditions of South Korea. Each agglomerative externality had a negative effect on the survival proportion of small startups except the related variety of the tertiary sector. However, the interaction effects between each externality and the location potential and among agglomerative externalities mostly played a complementary role to the survivability of startups; however certain effects reduced the survivability, and the effects were differentiated for each industrial sector. This study provides an advanced understanding of small firm performance after entry into the market in developing and developed nations. 相似文献
109.
110.
随着我国社会经济的发展,逐步暴露出了许多的生态环境问题。而为了维持生态的平衡,就要提高植树造林的力度,这其中碳汇造林就是植树造林工作的延伸。在碳汇造林中乡土阔叶树种发挥着重要作用,针对乡土阔叶树种在碳汇造林中的应用进行分析,对项目中出现的问题进行优化。 相似文献