全文获取类型
收费全文 | 18483篇 |
免费 | 1145篇 |
国内免费 | 636篇 |
专业分类
林业 | 11301篇 |
农学 | 200篇 |
基础科学 | 177篇 |
2175篇 | |
综合类 | 5534篇 |
农作物 | 94篇 |
水产渔业 | 40篇 |
畜牧兽医 | 158篇 |
园艺 | 277篇 |
植物保护 | 308篇 |
出版年
2024年 | 74篇 |
2023年 | 229篇 |
2022年 | 321篇 |
2021年 | 404篇 |
2020年 | 422篇 |
2019年 | 634篇 |
2018年 | 293篇 |
2017年 | 440篇 |
2016年 | 585篇 |
2015年 | 567篇 |
2014年 | 1001篇 |
2013年 | 948篇 |
2012年 | 1459篇 |
2011年 | 1338篇 |
2010年 | 1129篇 |
2009年 | 1182篇 |
2008年 | 1126篇 |
2007年 | 1238篇 |
2006年 | 1075篇 |
2005年 | 987篇 |
2004年 | 788篇 |
2003年 | 621篇 |
2002年 | 503篇 |
2001年 | 527篇 |
2000年 | 384篇 |
1999年 | 289篇 |
1998年 | 270篇 |
1997年 | 213篇 |
1996年 | 213篇 |
1995年 | 201篇 |
1994年 | 169篇 |
1993年 | 132篇 |
1992年 | 119篇 |
1991年 | 113篇 |
1990年 | 78篇 |
1989年 | 100篇 |
1988年 | 62篇 |
1987年 | 23篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
S. Hashimoto S. Ugawa K. Morisada M. Wattenbach P. Smith Y. Matsuura 《Soil Use and Management》2012,28(1):45-53
Forest management and climate change may have a substantial impact on future soil organic carbon (SOC) stocks at the country scale. Potential SOC in Japanese forest soils was regionally estimated under nine forest managements and a climate change scenario using the CENTURY ecosystem model. Three rotations (30, 50, 100 yr) and three thinning regimes were tested: no‐thinning; 30% of the trees cut in the middle of the rotation (e.g. 15 year in a 30‐yr rotation) and thinned trees all left as litter or slash (ThinLef) and the trees from thinning removed from the forest (ThinRem). A climate change scenario was tested (ca. 3 °C increase in air temperature and 9% increase in precipitation). The model was run at 1 km resolution using climate, vegetation and soil databases. The estimated SOC stock ranged from 1600 to 1830 TgC (from 6800 to 7800 gC/m2), and the SOC stock was largest with the longest rotation and was largest under ThinLef with all three rotations. Despite an increase in net primary production, the SOC stock decreased by 5% under the climate change scenario. 相似文献
122.
123.
以吉林省汪清林业局金仓林场2块面积为0.25 hm2的蒙古栎天然中龄林固定样地为对象,采用8个竞争指标,研究蒙古栎天然林种内、种间竞争状态。研究结果表明,该林分竞争激烈,蒙古栎与其他各树种存在种间竞争,但其主要竞争压力来自种内,种外竞争压力主要来自黑桦与白桦。其它树种的竞争主要为种间竞争。蒙古栎竞争能力处于中等,白桦与黑桦最强。各竞争指标结果存在差异性,但均能反映蒙古栎天然林竞争状态。蒙古栎竞争强度与胸径存在幂函数关系,竞争强度随个体大小的增大而减小。 相似文献
124.
125.
The species composition of wood-inhabiting fungi (polypores and corticoids) was investigated on 1138 spruce logs and 992 pine logs in 90 managed and 34 natural or near-natural spruce and pine forests in SE Norway.Altogether, the study included 290 species of wood-inhabiting fungi. Comparisons of logs with similar properties (standardized tree species, decay class, dimension class) in natural and managed forests showed a significant reduction in species number per log in managed spruce forests, but not in managed pine forests. The species number per log in managed spruce forests was 10-55% lower than on logs from natural spruce forests. The reduction was strongest on logs of large dimensions. A comparison of 200-400 spruce logs from natural and managed forests showed a 25% reduction in species richness corresponding to a conservative loss of ca. 40 species on a regional scale.A closer inspection revealed that species confined to medium and very decayed spruce logs were disfavored in managed forests, whereas species on early decay classes and decay generalists were unaffected. Similarly, species preferring large spruce logs were disfavored in managed forests. Forest management had strongest impact on low-frequent species in the spruce forests (more than 50% reduction), whereas common species were modestly affected. Corticoid fungi were more adversely affected than polypore fungi.These results indicate that wood-decaying fungi in pine forests are more adapted to forest disturbances than spruce-associated species. Management measures securing a continuous supply of dead wood are more important in spruce forests than in pine forests. 相似文献
126.
127.
社会林业与五指山的自然保护 总被引:1,自引:0,他引:1
五指山自然保护区是世界上现存地势最高的原始热带雨林之一,是我省目前面积最大的自然保护区,也是海南三大河流的发源地。但由于保护区横跨琼中、通什、保亭三县、市,紧邻保护区还生存着众多贫困的黎、苗族村民。因此,保护区与周边社区的联系是十分紧密的,社区的发展也直接影响到五指山热带天然林的保护。海南省林业局中德海南热带林保护和恢复项目在社会林业与五指山森林的保护上做出了有益的尝试,就在全省来说,也是首次对社会林业与森林保护上进行的探索。五指山地区社会林业的研究,对保护海南热带雨林也有着积极的意义。特对社会林业与五指山的森林保护进行了阐述、分析和设想。 相似文献
128.
浅谈森林资源保护中存在问题及对策 总被引:1,自引:0,他引:1
进一步规范森林资源管理和执法行为进一步加强森林资源林政管理队伍建设,采用先进技术,改善执法条件,进一步保持森林资源林政管理和执法队伍的稳定、全面提高森林资源林政管理和执法人员的素质外,还将积极采用新技术加强森林资源和林政管理,并进一步加大对森林资源林政管理的投入,以改善执法条件. 相似文献
129.
130.