全文获取类型
收费全文 | 1491篇 |
免费 | 51篇 |
国内免费 | 140篇 |
专业分类
林业 | 165篇 |
农学 | 82篇 |
基础科学 | 413篇 |
135篇 | |
综合类 | 740篇 |
农作物 | 28篇 |
水产渔业 | 37篇 |
畜牧兽医 | 54篇 |
园艺 | 11篇 |
植物保护 | 17篇 |
出版年
2024年 | 13篇 |
2023年 | 28篇 |
2022年 | 63篇 |
2021年 | 53篇 |
2020年 | 63篇 |
2019年 | 66篇 |
2018年 | 27篇 |
2017年 | 53篇 |
2016年 | 58篇 |
2015年 | 61篇 |
2014年 | 83篇 |
2013年 | 87篇 |
2012年 | 115篇 |
2011年 | 112篇 |
2010年 | 76篇 |
2009年 | 85篇 |
2008年 | 66篇 |
2007年 | 77篇 |
2006年 | 81篇 |
2005年 | 85篇 |
2004年 | 61篇 |
2003年 | 42篇 |
2002年 | 33篇 |
2001年 | 30篇 |
2000年 | 30篇 |
1999年 | 22篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 23篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
排序方式: 共有1682条查询结果,搜索用时 15 毫秒
31.
32.
中外人工用材林经营方式比较分析 总被引:2,自引:0,他引:2
首先对国内外人工用材林经营方式进行了分析, 进而提出通过林工贸一体化发挥产业间的协同效应, 实现人工用材林由分户经营向规模化经营的转变, 将成为我国人工用材林经营方式的发展趋势; 其次, 对我国人工用材林规模化经营的现实性进行了分析; 最后, 在探讨林工贸一体化实现规模化经营内在机理的基础上, 提出林工贸一体化经营是我国人工用材林规模化经营的实现途径。 相似文献
33.
钟荣丙 《中南林业科技大学学报(自然科学版)》2003,23(3):9-13
长沙、株洲、湘潭(以下简称长株潭)一体化建设是一项系统工程。以系统学理论为依据,分析了长株潭一体化的准确定位,探讨了长株潭一体化的合理实施步伐和推进时序,并且提出了建立长株潭一体化的合理的内部运行机制和优化外部条件的合理化建议。 相似文献
34.
35.
历史文化名城的滨水区建设成为近年来全球水资源开发重点项目。该研究结合生态经济运行规律和水资源转化机制作用原理,从发展链的点段式管理角度、线型管理角度和环型管理角度构建"水资源转化机制及生态经济耦合运行模型",进而创新资源开发规划理论和生态经济理论。
相似文献
36.
37.
Makoto ANDO 《中国林学(英文版)》2012,14(2):85-91
We studied the impact of stand density and forest floor humus removal on regeneration of Pinus densiflora in a mixed conifer and broad-leaved forest on the Daimonji-Yama Mountain,Kyoto,Japan.Three levels of stand density were set,i.e.,a clear-cut site,a heavily thinned site and a lightly thinned site.In each density treatment,comparisons were carried out between humus removal (A 0 -free)and humus intact(A 0 -intact)subplots.We counted the emergence of sown pine seeds and measured survival and growth of pine seedlings over the next four years.In addition,light conditions and the recovery of understory were monitored.Results show that thinning intensity and humus removal promoted the establishment and growth of seedlings.One exception,however,was that seedling growth was minimal in the heavily thinned A 0 -intact subplots.This was due to a strong response of understory vegetation growth on the treatment combination,which hindered the pine seedling growth.Furthermore,we found that the canopy openness measured at 1.3-m height remained at least 35%for the heavily thinned site in 2008.The results suggest that the removal of the A 0 layer after heavy thinning is the most effective and labor-saving operation for P.densiflora regeneration. 相似文献
38.
“庄园”是新农村建设和乡村振兴的重要载体。文章阐述了“庄园”经济的概念、主要特征和经营方针,归纳分析了“庄园”经济的组织型式和主要经营模式,提出了大力发展“庄园”经济的主要对策和建议。 相似文献
39.
This study examined the ability of an airborne laser scanner to identify individual trees in the canopy of a Chamaecyparis obtusa stand and investigated the relationship between the penetration rate of the laser pulses and stand attributes under different canopy conditions caused by different levels of thinning. Individual tree crowns were identified from a digital canopy model (DCM) derived from airborne laser scanner data by the watershed segmentation method. The identification rate of individual trees in blocks with heavy thinning (ratio of the basal area of the felled trees to the total basal area, hereinafter thinning ratio of the basal area, 38.0%), moderate thinning (30.4%), and no thinning was 95.3%, 89.2%, and 60.0%, respectively. Individual tree heights were estimated from the DCM values by local maximum filtering within identified individual crowns. Tree height in the three blocks was estimated with a root-mean-square error of 0.95, 0.65, and 0.68 m, respectively. Tree heights determined in a field survey were regressed against those estimated from the DCM, yielding coefficients of determination (r2) of 0.71, 0.87, and 0.85, respectively, for the blocks with heavy thinning, moderate thinning, and no thinning, respectively, and 0.86 overall. The respective penetration rates of the laser pulses through the canopy to the ground were 50.6%, 43.1%, and 9.2%. Regression of the laser pulse penetration rate against the thinning ratio of the basal area and against the total basal area of the remaining trees in 25 quadrats established in the blocks, yielded r2 values of 0.89 and 0.74, respectively. 相似文献
40.
伐区采集作业方式对森林生态环境的影响分析 总被引:9,自引:0,他引:9
通过分析伐区几种主要的采集作业方式对森林生态环境的影响,结果表明择伐和架空索道集材两种作业方式对森林生态环境的影响最小。 相似文献