全文获取类型
收费全文 | 571篇 |
免费 | 23篇 |
国内免费 | 35篇 |
专业分类
林业 | 155篇 |
农学 | 47篇 |
基础科学 | 70篇 |
133篇 | |
综合类 | 183篇 |
农作物 | 14篇 |
水产渔业 | 4篇 |
畜牧兽医 | 8篇 |
园艺 | 8篇 |
植物保护 | 7篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2017年 | 24篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 38篇 |
2013年 | 34篇 |
2012年 | 55篇 |
2011年 | 39篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 33篇 |
2007年 | 40篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 17篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有629条查询结果,搜索用时 15 毫秒
31.
杨木高温干燥过程中表层流变特性的研究 总被引:8,自引:2,他引:6
本文讨论了干燥温度分别为85℃、105℃、115℃和125℃时板材表层厚度为3mm处的木材横纹流变特性。结果表明:干燥过程中的总应变为干缩应变、弹性应变、粘弹性蠕变应变和机械吸附蠕变应变的代数和。木材在长时间、高温高湿的联合作用下,不仅表现出弹性、塑性,而且还表现出粘弹性。作者根据木材干燥应力模型理论,提出了在同一块板方材上能同时测定所建模型各应变参数的试验方法。 相似文献
32.
在包装、家具框架中L型构件是一种比较常见的结构形式.本文通过分析跨距对木塑L型构件结构强度和连接结构强度的影响,得出以下结论:跨距对木塑L型构件结构强度的影响非常显著,跨距越短,结构强度越大;跨距对连接结构强度影响也很大,跨距在190mm左右时,连接性能最好. 相似文献
33.
白杨刨片横纹压缩流变性能 总被引:4,自引:3,他引:4
用参数分离法对手工刨切的厚为0.8、0.5、0.35、0.25、0.15mm的白杨刨片进行了横纹压缩流变试验。结果表明,用上述几种厚度的刨片所分别叠成的厚约10mm的试件,其柔量大于厚度为10mm木块试件的柔量;刨片越薄,柔量越大。弹性变形及瞬间塑性变形的增长,意味着实木经过刨切,因反复受力而使木材高聚物分子及细胞壁组织都受到影响,并有一定程度的破坏。实木经过刨切成为薄片后再层叠起来所组成的试样,在横纹压缩流变性能方面所体现的变化,一定程度上与木块受压所发生的变化,在趋势上是一致的。然而,由于前者试样系由薄刨片层叠而成,因而在影响其流变性能的诸多因素中,尚有刨片厚度及刨片层叠方向二者明显的影响作用。 相似文献
34.
We made several buckling tests of wooden columns with intermediate slenderness ratios () and examined the empirical formulas. On the basis of the examination, we formulated an equation for predicting the buckling stress () of an intermediate wooden column. Sitka spruce (Picea sitchensis Carr.) and buna (Japanese beech, Fagus crenata BI.) were used for the studies. A compressive load was applied on the specimen supported with pin ends, and the buckling stress was predicted by the tangent modulus theory and two empirical equations: those of Tetmajer and Newlin-Gahagan. The predicted - relations were compared with the test results, and the applicability of these predictions were examined. Based on the comparisons, we formulated an equation that can predict the - relations of materials with various stress-strain characters in the plastic strain range. 相似文献
35.
36.
Effect of temperature and compression on the mechanical behavior of steam-treated wood 总被引:2,自引:0,他引:2
The mechanical behavior of steamed spruce wood changes dramatically with compression along the grain, the change being much more moderate perpendicular to the grain. The stiffness decrement due to increased temperature is greatest in the tangential material direction. The stiffness decrement due to compression is greatest along the grain. Compression to 80% compressive strain at 131°C inverts the order of the material directions regarding stiffness, the stiffness being the least along the grain. Plastic strain due to compression is greater at higher temperatures. The compression-induced decrement of stiffness along the grain is greater at higher temperatures, but the off-axis decrement of stiffness is less at higher temperatures. 相似文献
37.
A quasi-simple shear test, which is the most direct method for examining the shear properties of sheet metals, has been applied to measure the shear moduli of wood. Buna (Fagus crenata Blume) with variously sized shear regions was used for the test specimens. Strain gauges were mounted in the center of the shear regions to measure the shear strains. The shear tests were carried out to determine the shear moduli in the radial and tangential planes. Apparent shear moduli obtained from the experimental results were corrected by finite element method (FEM) simulation of the shear region, where both shearing and bending are produced. It was found that the corrected shear moduli are roughly independent of test conditions, and their values are in good agreement with the data obtained from bending-shear tests. This suggests that the method employed here can effectively estimate the shear moduli of wood.Part of this research was presented at the 50th Annual Meeting of the Society of Materials Science, Osaka, May 2001 相似文献
38.
39.
40.
使用1992~2011年的时间序列数据,采用线性几乎理想需求系统模型(LAIDS),重点检验了劳动力流动对农村居民消费结构的影响。研究发现,劳动力流动会使衣着、文教娱乐及服务、医疗消费有所增加,会减少食品、居住消费,对家用几乎没有影响。为此,应增加工资性收入,完善劳动力流动政策和供给结构。 相似文献