全文获取类型
收费全文 | 4057篇 |
免费 | 257篇 |
国内免费 | 363篇 |
专业分类
林业 | 827篇 |
农学 | 292篇 |
基础科学 | 191篇 |
551篇 | |
综合类 | 1978篇 |
农作物 | 309篇 |
水产渔业 | 96篇 |
畜牧兽医 | 252篇 |
园艺 | 76篇 |
植物保护 | 105篇 |
出版年
2024年 | 13篇 |
2023年 | 37篇 |
2022年 | 97篇 |
2021年 | 110篇 |
2020年 | 131篇 |
2019年 | 124篇 |
2018年 | 82篇 |
2017年 | 145篇 |
2016年 | 198篇 |
2015年 | 161篇 |
2014年 | 227篇 |
2013年 | 214篇 |
2012年 | 307篇 |
2011年 | 313篇 |
2010年 | 231篇 |
2009年 | 284篇 |
2008年 | 261篇 |
2007年 | 295篇 |
2006年 | 268篇 |
2005年 | 211篇 |
2004年 | 151篇 |
2003年 | 144篇 |
2002年 | 101篇 |
2001年 | 80篇 |
2000年 | 75篇 |
1999年 | 66篇 |
1998年 | 63篇 |
1997年 | 52篇 |
1996年 | 46篇 |
1995年 | 40篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 28篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 19篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有4677条查询结果,搜索用时 174 毫秒
992.
993.
刨花楠、花梨木、乐东拟单性木兰嫩枝扦插繁殖试验 总被引:6,自引:0,他引:6
对刨花楠、花梨木、乐东拟单性木兰3树种当年生半木质化嫩枝采用不同生根促进剂及浓度的扦插试验表明:3树种的嫩枝扦插成活率、生根率、生根系数、生根数量及根长等生根性状均有显著差异,不同树种对各生根剂及浓度反应不一,3树种较佳的处理组合是:刨花楠:ABT3生根剂,浓度500 mg·kg-1,可使扦插成活率达56.7%,生根率达56.7%,平均根数为6.7条, 平均最长根长9.2cm;花梨木:IBA生根剂,浓度为100 mg·kg-1,可使扦插成活率达53.3%,生根率达53.3%,平均根数为4.6条,平均最长根长为14.2cm;乐东拟单性木兰:NAA生根剂,浓度为100 mg·kg-1,可使扦插成活率达76.7%,生根率达53.6%,平均根数为3.2条,平均最长根长为6.4cm. 相似文献
994.
Acetylation of wood was carried out in acetic anhydride only, acetic anhydride/xylene 1:1 (v/v), and acetic anhydride/pyridine 4:1 (v/v) solutions. The antishrink efficiency (ASE), hygroscopic properties, vibrational properties, and bending strength were compared among the three reaction solutions. The ASE was a simple function of weight gain (WG); the equilibrium moisture content at a given WG differed among the reaction solutions. Based on this fact and the results of repeated water soaking and oven-drying tests, it was found that the bulking effect was a major factor, and that decreased hygroscopicity contributes only slightly to the dimensional stabilization by acetylation. The difference in equilibrium moisture content among reaction solutions appears more significant in block samples than wood meal, probably due to the fiber-to-fiber bonds in the former. The tendencies for change in the specific Youngs modulus and the loss tangent differed among reaction solutions, whereas in the static bending test the difference was not marked.Part of this report was represented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002 相似文献
995.
996.
滇西北亚高山地区黄背栎林植被演替过程中的林地土壤化学响应 总被引:2,自引:0,他引:2
探讨了滇西北亚高山地区黄背栎林植被演替过程中林地土壤化学性质的变化。研究结果表明:在该植物群落不同的植被演替阶段,其林地土壤的化学性质与之相响应。随着其植被的正向演替,林地土壤各项化学指标均向良性发展:土壤的pH值逐渐降低;土壤有机质、全N及水解N含量均呈上升趋势;速效K含量在演替顶极前期达最大含量,到演替顶极期有所下降;速效P含量在演替过程中有所变化,但随其植被演替的变化不明显,没有一定的规律性;林地上层土壤养分增加较之下层土壤增加率要大。该地区土壤化学性质变化与其群落的良性发展呈正相关。 相似文献
997.
Keiko Sakai Masahiro Matsunaga Kazuya Minato Fumiaki Nakatsubo 《Journal of Wood Science》1999,45(3):227-232
The impregnation of various simple phenolic and natural polycyclic compounds into wood was investigated from the viewpoints of vibrational property and dimensional stabilizing effect. When simple phenolic compounds were impregnated, the loss tangent (tan ) in the longitudinal direction increased linearly with increasing weight gain. Meanwhile, among the natural polycyclic compounds hematoxylin decreased the tan drastically by impregnation. It was suggested that the five hydroxyl groups and the pyran ring oxygen in the hematoxylin molecule contribute to formation of the crosslinkage-type hydrogen bonds between wood components. The rigidity of hematoxylin molecules may also be important. By impregnation of about 10% catechol, resorcinol, and saligenin, a 40% level of antiswelling efficiency (ASE) was attained, although a significant dimensional stabilizing effect was not observed after impregnation of natural polycyclic compounds.Part of this work has been published as a Rapid Communication inMokuzai Gakkaishi 43(12). It was also presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 相似文献
998.
京北山区板栗林生态系统养分元素含量特征分析 总被引:3,自引:0,他引:3
对北京北部山区板栗林生态系统5种主要养分元素N、P、K、Ca和Mg的含量测定的结果表明:地上各部分中不同养分元素在不同器官中的含量特点各不相同;但在根系中含量特征相同,即不同养分元素的含量均随着根系直径的增大而降低,且在根干中的含量最低。板栗林现存生物量5种养分元素贮存量为315.38kg/hm^2,在干中的贮存量最大,占养分总贮存量的36.75%,各器官中养分元素贮存量排序是干>枝>根>叶>花>果苞>果。5种养分元素中以Ca的贮存量最大,占总养分贮存量的33.45%,各元素贮存量排序为Ca>N>K>Mg>P。 相似文献
999.
浅论我国集体林产权法律制度 总被引:1,自引:0,他引:1
文章从法制的角度分析了我国集体林产权问题,介绍了林业发达国家发展集体林、私有林产权制度的基本经验,结合我国集体林的具体林情,阐述了在市场经济条件下,进一步完善我国集体林产权法律制度的相关问题。 相似文献
1000.
A forest property represents benefits to the owner, the nature of which varies between resident and non-resident owners. Forest
owners’ associations can be considered as an arrangement to increase the benefit from forest ownership by helping the forest
owner to increase profitability. Thus, it can be assumed that associated forest owners value forest property benefits differently
to non-associated owners. This study examines differences between members and non-members, and residents and non-residents,
with respect to how they value the various forest property benefits. Responses from a landholder survey reveal differences
concerning forestry income, maintaining contact with native locality, and keeping up a tradition in forestry. It is concluded
that a challenge for the associations is to develop the organisation in accordance with the forest owners’ dissimilar property
interests. 相似文献