全文获取类型
收费全文 | 6834篇 |
免费 | 387篇 |
国内免费 | 405篇 |
专业分类
林业 | 2771篇 |
农学 | 280篇 |
基础科学 | 200篇 |
502篇 | |
综合类 | 2644篇 |
农作物 | 315篇 |
水产渔业 | 32篇 |
畜牧兽医 | 292篇 |
园艺 | 360篇 |
植物保护 | 230篇 |
出版年
2024年 | 19篇 |
2023年 | 73篇 |
2022年 | 147篇 |
2021年 | 171篇 |
2020年 | 153篇 |
2019年 | 222篇 |
2018年 | 145篇 |
2017年 | 231篇 |
2016年 | 278篇 |
2015年 | 247篇 |
2014年 | 384篇 |
2013年 | 384篇 |
2012年 | 547篇 |
2011年 | 488篇 |
2010年 | 429篇 |
2009年 | 421篇 |
2008年 | 364篇 |
2007年 | 396篇 |
2006年 | 364篇 |
2005年 | 318篇 |
2004年 | 202篇 |
2003年 | 202篇 |
2002年 | 166篇 |
2001年 | 183篇 |
2000年 | 135篇 |
1999年 | 131篇 |
1998年 | 119篇 |
1997年 | 93篇 |
1996年 | 83篇 |
1995年 | 90篇 |
1994年 | 86篇 |
1993年 | 75篇 |
1992年 | 70篇 |
1991年 | 53篇 |
1990年 | 61篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 16篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1963年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有7626条查询结果,搜索用时 46 毫秒
61.
62.
Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf
leaf water potential
- soil
soil water potential
- DSC
daily stem contraction
- LVDT
linear variable displacement transducer
- PET
potential evapotranspiration 相似文献
63.
Although there has been increasing research on the adoption of agroforestry technologies over the last decade, few such studies have assessed uptake over a long period and many are based on a single snapshot in time. Furthermore, most of these studies have mainly looked at non-adopters and adopters: only recently have social scientists considered testers. A further category of users neglected in adoption studies has been re-adopters of technologies. Studying this group provides an interesting and more nuanced understanding of adoption and re-adoption. Methodologically, most adoption studies use quantitative methods and fail to link their findings to wider socio-economic, political and institutional settings. This paper presents a study of the dynamics of improved tree fallow use by farmers in Siaya and Vihiga districts of western Kenya over a period of eight years. It uses both qualitative and quantitative data to critically discuss the motivations of adopters, testers/rejecters and re-adopters. The results show that the process of adoption is highly dynamic and variable with farmers planting improved fallows and discontinuing or re-adopting them due to a whole range of factors, of which soil fertility improvement is just one. These factors included incentives from projects, the tying of adoption to credit programmes, prestige, participation in seminars/tours and the availability of a seed market from projects promoting improved fallows. Farmers planting improved fallows for such reasons may be termed ‘pseudo-adopters’. There were significant differences in adoption between the two districts, with more farmers in Siaya planting improved fallows than in Vihiga. A majority of farmers in Vihiga (53%) who were given seed never planted improved fallows, even though they had been exposed to the technology. Some 40% of farmers in Siaya and 38% in Vihiga planted improved fallows but later rejected them. This has some important implications for research and development. For improved fallow technologies to be attractive to farmers, they must provide other tangible economic benefits besides soil fertility improvement. This presents a challenge to researchers who must better attune themselves to the needs and demands of farmers if they wish to see their research findings widely adopted. 相似文献
64.
自压式树状管网的两级优化设计模型与神经优化设计 总被引:4,自引:0,他引:4
建立了自压式树状管网两级优化设计模型,并用人工神经网络法实现树状管网非线性规划模型的快速求解。采用的人工神经网络技术的两级优化设计模型在适用范围、求解速度和获得最优解能力上,均优于单一的非线性规划模型和线性规划模型,是实现树状管网全局优化设计的一条新途径。 相似文献
65.
故障树分析法(FTA)是一种将系统故障形成的原因由总体到部分按倒立树形状逐级细化的分析方法,是一种对系统设计、故障分析和排除非常有效的方法。为此,应用故障树分析方法对联合收割机液压系统进行了分析,根据液压系统结构以及组件与系统之间的逻辑关系,绘制了系统的故障树,并通过结构函数表示了各种因素对系统状态的影响。 相似文献
66.
67.
68.
69.
70.
通过对台湾杉和秃杉两种珍稀树种的引种栽培,就台湾杉和秃杉两种珍稀树种从种子(球果)到幼苗的整个发展过程,以及种子和苗木的生产技术做了细致的探索性研究,并就培育出的幼苗进行观察、记载和绘制成图;经定植3 a后评价引种成败。研究结果可为杉科台湾杉属的系统发育和亲缘关系方面的研究提供理论基础;也可为用材林造林、园林绿化树种提供参考和对这两种珍稀树种继续引种栽培提供实践依据。 相似文献