全文获取类型
收费全文 | 12680篇 |
免费 | 749篇 |
国内免费 | 1363篇 |
专业分类
林业 | 2114篇 |
农学 | 731篇 |
基础科学 | 374篇 |
3289篇 | |
综合类 | 4858篇 |
农作物 | 703篇 |
水产渔业 | 863篇 |
畜牧兽医 | 1051篇 |
园艺 | 211篇 |
植物保护 | 598篇 |
出版年
2024年 | 186篇 |
2023年 | 402篇 |
2022年 | 546篇 |
2021年 | 599篇 |
2020年 | 591篇 |
2019年 | 658篇 |
2018年 | 422篇 |
2017年 | 710篇 |
2016年 | 759篇 |
2015年 | 627篇 |
2014年 | 669篇 |
2013年 | 901篇 |
2012年 | 929篇 |
2011年 | 940篇 |
2010年 | 723篇 |
2009年 | 722篇 |
2008年 | 641篇 |
2007年 | 679篇 |
2006年 | 559篇 |
2005年 | 457篇 |
2004年 | 338篇 |
2003年 | 256篇 |
2002年 | 221篇 |
2001年 | 196篇 |
2000年 | 152篇 |
1999年 | 157篇 |
1998年 | 138篇 |
1997年 | 110篇 |
1996年 | 96篇 |
1995年 | 77篇 |
1994年 | 62篇 |
1993年 | 71篇 |
1992年 | 72篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 19篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1962年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Fijian adolescents’ understanding and evaluation of climate change: Implications for enabling effective future adaptation 下载免费PDF全文
Pacific Island countries are particularly vulnerable to future manifestations of climate change due to high coastline‐to‐land‐area ratios, and high dependence of inhabitants on natural ecosystems. While everyone in the Pacific Islands should participate in climate change adaptation activities, it is the young people, given they are the generation likely to not only bear the burden of climate change, but to lead and live effective climate change adaptation activities and strategies specific to their region, the involvement of youth is critical. Pacific Island youths are often marginalised within traditional decision‐making hierarchies, therefore they are typically excluded from participating in meaningful discussions at community and government levels. Discussions were held with 30 adolescents aged 14–18 years in Fiji to explore knowledge and experiences regarding climate change. Participants revealed their dismay at their inability to talk to family – who they consider are not doing enough – about what they consider as appropriate responses to climate change, recommending the help of an authoritative outsider who could speak to their community leaders and family. Discussions also revealed that Fijian youth could not distinguish between changes in the climate and normal weather events, attesting to the importance of climate‐change education and awareness‐raising efforts within the Pacific Islands more generally. 相似文献
962.
多花木兰人工生态恢复植物群落种群竞争及其生态位研究 总被引:2,自引:1,他引:2
为了掌握常吉高速公路边坡多花木兰人工生态恢复植物群落的种间竞争和生态位等生长状况,运用Hegyi的单木竞争指数模型、Shannon-Wiener公式和Shoener公式对多花木兰人工植物群落的种内与种间竞争强度、生态位宽度与生态位重叠进行研究。结果表明:多花木兰种内竞争能力与个体的地径径级成正比,多花木兰竞争能力大于刺槐、小叶女贞,原有配置的马尾松等植物已经死亡;群落各种群生态位宽度的大小顺序为:多花木兰>刺槐>小叶女贞,分别为2.271、2.147、2.088;群落各种群的生态位重叠值较大,多花木兰和刺槐的生态位重叠值最大,为0.793,多花木兰和小叶女贞生态位重叠值最小,为0.632。多花木兰能够很好地适应高速公路边坡环境,群落中已经被淘汰的其他竞争力太弱的树种不适合与多花木兰混植。 相似文献
963.
Under the background of the new rural construction in China, it is an important scientific question and an urgent social task to construct the harmonious society and to achieve the sustainable regional development on how to construct concentrative residence and manage the human habitat environment in the fast industrializing and typically urbanizing area. This paper analyzed the problems in the construction of the human habitat envi- ronment in the rural area of southern Jiangsu, discussed the methodologies of planning and design for rural con- centrative residence, researched the human habitat environment improvement technologies, and put forward the resolution of the recycling community for the rural inhabitation, which aimed at demonstrating the practicing in rapidly urbanizing regions. 相似文献
964.
沂蒙山林区不同植物群落下土壤颗粒分形特征 总被引:2,自引:0,他引:2
运用土壤物理学和分形学原理与方法,研究了沂蒙山林区7种植物群落下的土壤颗粒组成与分形特征。结果表明:1)研究区土壤颗粒组成具有石质山地典型粗骨土的结构特征,各种植物群落的土壤中以粗砂粒含量最高,细砂粒含量次之,而石砾含量和粉黏粒含量较低;2)防护林群落具有显著地改善土壤颗粒组成和提高土壤颗粒分形维数的作用,其作用程度为针阔叶(赤松+麻栎)混交林依次高于阔叶林(刺槐纯林、麻栎纯林)和针叶林(赤松纯林);3)土壤颗粒分形维数与土壤中粉黏粒(粉粒及黏粒)含量呈极显著正相关,与细砂粒和粗砂粒含量呈显著的负相关,而与石砾含量的相关性不显著。研究成果可为沂蒙山区水土保持植被类型的合理选择与配置提供参考。 相似文献
965.
地基差异沉降时管道的纵向力学性状分析 总被引:6,自引:0,他引:6
软土地基的不均匀沉降将导致管道纵向力学性状的变化,产生破坏管道的应力响应,从而引发工程事故。针对地基产生差异沉降的实际管道,通过建立较为合理的力学模型,分析其受力特性,计算管道上的最大挠度、转角、弯矩及确定出应力集中的危险受力区域。通过对该结果的研究,绘制相应关系曲线,为解决由于地基不均匀沉降引起的管道渗漏和爆管等问题提供了一定的理论依据。 相似文献
966.
为了研究不同硬度等位基因与小麦籽粒淀粉组分含量及特性的关系,为小麦品质改良提供依据,以7个硬度Puroindoline b位点近等基因系为试材,研究了不同硬度基因型对小麦籽粒淀粉组分含量及特性的影响。结果表明,Pina-D1b/Pinb-D1a基因型的籽粒硬度值、支链淀粉含量最高;Pina-D1b/Pinb-D1a基因型的淀粉溶解度最高,而Pina-D1a/Pinb-D1d溶解度最低,两者差异达显著水平;不同基因型之间籽粒淀粉酶解力没有显著差异;冻融失水率以基因型Pina-D1a/Pinb-D1b最低,表明Pina-D1a/Pinb-D1b基因型冻融稳定性最好,可能较适宜冷冻食品的制作;对于抗性淀粉,Pina-D1a/Pinb-D1b基因型的抗性淀粉含量最高、Pina-D1a/Pinb-D1d最低,表明Pina-D1a/Pinb-D1b基因型有助于籽粒中抗性淀粉含量的提高。 相似文献
967.
为给茭白与鸭共作系统中适宜放养鸭密度提供参考依据,本研究通过大田试验,比较了茭白单作、茭白田放鸭300、375、450只/hm~2条件下茭白的生物学性状、产量和品质。结果表明:茭鸭共作能显著提高茭白后期叶片数、干物重及产量,并延缓茭白后期叶片衰败。放鸭密度从375只/hm~2增加至450只/hm~2时,茭白后期叶片衰败加快,且茭白产量不再增加。茭鸭共作显著提高茭白蛋白质、维生素C和氨基酸含量。茭鸭共作系统灌溉养殖池塘富营养化水4500 m~3/hm~2时,输入的N、P、K相当于99.75 kg尿素、38.25 kg过磷酸钙和83.55 kg氯化钾的养分含量。本试验条件下,茭白常规种植密度27795株/hm~2,田间适宜放鸭密度为375只/hm~2,可显著提高茭白产量及品质。 相似文献
968.
969.
文章分析了大姚核桃的经济价值,并从营建原则、栽植要领、土壤管理、肥料管理、水分管理和健康护理方面论述其培育技术。 相似文献
970.
Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin II: effects of processing parameters 总被引:1,自引:0,他引:1
To obtain high-strength phenol formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, the effects of resin content, preheating temperature, pressing temperature, and pressing speed on the compressive deformation of oven-dried low molecular weight PF resin-impregnated wood was investigated. With an increase of PF resin content, the Youngs modulus of the cell wall perpendicular to the fiber direction decreases, and collapse-initiating pressure decreases linearly with the Youngs modulus. This indicates that the occurrence of cell wall collapse is strain-dependent. By increasing preheating temperatures, the collapse-initiating pressure increases due to the increment of the Youngs modulus of the cell wall. An increase in pressing temperature results in the thermal softening of the cell wall and causes collapse at a lower pressure. The wood is compressed effectively despite accelerated resin curing. The pressing speed significantly affects the viscoelastic deformation of the cell wall and the wood is well deformed with decreasing pressing speed, although the differences in density and mechanical properties are relatively small after a pressure-holding period of 30min. In all the parameters examined in this study, the Youngs modulus and bending strength increase with increasing density. 相似文献