全文获取类型
收费全文 | 1423篇 |
免费 | 140篇 |
国内免费 | 151篇 |
专业分类
林业 | 41篇 |
农学 | 42篇 |
基础科学 | 28篇 |
93篇 | |
综合类 | 694篇 |
农作物 | 7篇 |
水产渔业 | 751篇 |
畜牧兽医 | 27篇 |
园艺 | 9篇 |
植物保护 | 22篇 |
出版年
2024年 | 1篇 |
2023年 | 21篇 |
2022年 | 26篇 |
2021年 | 59篇 |
2020年 | 40篇 |
2019年 | 58篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 33篇 |
2015年 | 37篇 |
2014年 | 125篇 |
2013年 | 130篇 |
2012年 | 199篇 |
2011年 | 208篇 |
2010年 | 150篇 |
2009年 | 200篇 |
2008年 | 54篇 |
2007年 | 130篇 |
2006年 | 95篇 |
2005年 | 38篇 |
2004年 | 19篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有1714条查询结果,搜索用时 15 毫秒
1.
2.
2%氨基寡糖防治苹果花叶病 总被引:19,自引:0,他引:19
2001年8月应用2%氨基寡糖对苹果花叶病进行了田间防治试验 ,结果表明:2%氨基寡糖水剂稀释300、500倍液,对苹果花叶病防效达93.85%、89.42%。其防效比对照药剂20%病毒A 81.11%的防效高 ,比对照区增产21%、23% ,是防治苹果花叶病较理想的药剂 相似文献
3.
This short article reexamines Zhang et al., 2010 (Forest Policy and Economics 2010, 12, 223–230) who concluded that forest expansion in China will continue due to the high economic benefit of forest plantations. It is suggested that their conclusion rested on data mistakes and problematic calculation, and might be misleading. A more realistic calculation is made. 相似文献
4.
在分析了大连市中心区声环境功能区划调整必要性的基础上,全面评估了现有区划实施效果,以问题为导向提出了区划调整的方法体系,并阐述了区划调整结果的可行性,为城市环境噪声管理和防治提供科学依据。 相似文献
5.
6.
高校图书馆保存本的改革 总被引:2,自引:1,他引:1
于向前 《农业图书情报学刊》2010,22(6):108-110
高校图书馆保存本必须改革。文章指出保存本存在的问题以及改革的必要性、措施和意义,改革的有效措施是变保存本为特色馆藏。 相似文献
7.
柴油机曲轴有限元分析及结构优化设计 总被引:4,自引:1,他引:4
对一车用柴油机整体曲轴建立了符合实际情况的三维模型,采用有限元法对其进行了三维有限元分析,研究了整体曲轴的应力状态,并对其在交变载荷下的疲劳强度进行了校核。同时对曲轴结构参数,圆角形状优化和圆角应力分布等相关问题进行了探讨。最后对曲轴进行了模态分析。为柴油机曲轴的结构设计提供了有价值的理论依据。 相似文献
8.
The dynamic behavior of a fish cage collar in waves was investigated using a numerical model based on the finite element method. The floating collar and mooring system were divided into a series of line segments modeled by straight massless model segments with a node at each end. To verify the validity of the numerical model, research data from other authors were cited and compared with the simulated results, the comparison of results showed a good agreement. The numerical model was then applied to a dynamic simulation of a floating cage collar in waves to analyze its elastic deformation and mooring line tension. The simulated results indicated that the greatest deformation of the collar taken place in the position of the mooring line connection point when incident waves were in the same direction. An increase in the length of mooring line would help to decrease the mooring line tension of the collar. Furthermore, the effects of collar dimension, including collar circumference, pipe diameter in cross-section, and pipe thickness, on the dynamic behavior of the floating collar were discussed. The results of this study provided a better understanding of the dynamic behavior of the fish cage collar. 相似文献
9.
10.
In response to the increased demand for food in general and food fish in particular, offshore mariculture is faced with the technological challenge of providing a viable cage design concept that is able to function effectively in high-energy environments. The single-point-mooring (SPM) fish cage systems for offshore fish farming are gaining support due to their environmentally friendly and economically favorable characteristics. An SPM self-submersible cage design concept has been identified as a potential mariculture cage concept for offshore waters, and the success of this concept depends on the operational performance in the offshore environment. Therefore, the current paper investigates the submergence characteristics of such a cage system in regular waves with a following current. This work also investigates the possibility of manipulating the cage system to achieve the desired submergence under different environmental conditions. The analysis demonstrates good potential for the self-submersible SPM cage concept in the simulated load cases because the response of the cage system to increasing wave height implies considerable additional submergence for realistic environmental conditions in offshore sites. The results also suggest that the concept allows adequate flexibility for use of the cage system in a range of environmental conditions. 相似文献