全文获取类型
收费全文 | 199篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
林业 | 68篇 |
农学 | 16篇 |
基础科学 | 9篇 |
27篇 | |
综合类 | 88篇 |
农作物 | 1篇 |
水产渔业 | 8篇 |
园艺 | 1篇 |
植物保护 | 3篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 17篇 |
2011年 | 24篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 12篇 |
2007年 | 21篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 11篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 7篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 234 毫秒
61.
白族民居大门集中体现了白族建筑的精华,在白族民居中占有十分重要的位置.通过对其形成背景、结构形式、个性化装饰及文化内涵的研究,进一步解读白族民居的门文化. 相似文献
62.
讨论了现代生活中住宅卫生间(浴室)内存在的用电危险,以及做局部等电位联结的必要性;阐明了如何正确地设计局部等电位联结,并例举了一些设计中典型的错误做法及防范措施。 相似文献
63.
以关中地区村镇住宅为对象,通过实地调查、问卷及电话调查等方式,侧重调查了村镇住宅的建造特点和抗震性能,同时选取了该地区典型的两层砌体结构住宅,采用PKPM系列软件进行抗震性能分析,根据抗震验算结果,对结构提出改进设计方案。 相似文献
64.
昆明市住宅小区中植物物种多样性现状及分析 总被引:1,自引:0,他引:1
调查了昆明市的70个住宅小区,小区绿化共用植物203种,隶属76科,146属,分析了植物物种丰富度、组成、出现频率、群落结构,比较了常绿树种和落叶树种多样性、乡土植物和外来植物多样性以及观赏部位的多样性,进而探讨住宅小区绿化中的植物多样性问题,并提出改进建议. 相似文献
65.
适宜炭化温度及时间改善生物质成型炭品质 总被引:2,自引:3,他引:2
为制备品质特性较佳的成型炭块,对螺杆挤出的生物质高密度成型燃料进行炭化,试验研究了炭化温度(400、450、500、550和600℃)、升温速率(2、6和10℃/min)和保持时间(60、120和180 min)对成型炭块的工业分析成分、热值和力学强度等品质指标的影响。随着炭化温度的提高,成型炭块的炭得率、挥发分含量降低,固定碳含量提高,热值增大;炭化温度550℃时热值达到最大值,为31.04 MJ/kg,抗压强度和抗跌碎强度均较好。升温速率对成型炭块的力学性能影响较大,升温速率越小,抗压强度越大;升温速率为2℃/min时,成型炭块表面裂纹少,抗压强度达最大值,为439.8 k Pa;相应地,抗跌碎强度亦较佳,为95.5%。保持时间为120 min时成型炭块具有较高的热值29.63 MJ/kg,较大的抗压强度192.1 k Pa和较好的抗跌碎强度96.7%,过长或过短的保持时间都不利于成型炭块品质的提升。 相似文献
66.
After "SARS", people introspect on the human settlement, and the health conception becomes the focal point of attention.The thermal environment is the important content of the human settlement and a good thermal environment is the premise of healthy city, healthy residence and people's health.In this paper, the property and affection of the thermal environment are analyzed and the principle and the way to improve the thermal environment of city residence are investigated.All play an important role in the healthy human settlement. 相似文献
67.
68.
Andrew P. Butcher 《Asia Pacific viewpoint》2004,45(2):255-278
Abstract: This paper considers the convergence of immigration/globalisation and education in New Zealand. The issues of immigrant students at Epsom Normal Primary School were raised nationally in 1995, and this incident serves as a useful departure point to consider some of the challenges involved in bridging the gap between immigration and education. Educational immigration is a notion used by Belich (2001) amongst others, to suggest that immigrants arrive in New Zealand in order to bypass full cost fees paid by international students. This notion, while useful, is challenged. Research undertaken in North Shore City as well as official immigration figures show the complexities of the issue: immigrant communities may be indirect recruiters of these students, but there are also an increasing number of international students becoming permanent residents. Either way, education providers face particular challenges with migrant students, not only in terms of English language abilities, but also in the lack of financial incentive migrant students give to an education provider relative to international students’ contributions. These micro issues are placed in perspective when returning to considering the transient nature of many young migrants exploring opportunities in a globalised world. 相似文献
69.
70.
Forests cover one-third of the Earth’s land surface and account for 30-40% of soil carbon (C). Despite numerous studies, questions still remain about the factors controlling forest soil C turnover. Present understanding of global C cycle is limited by considerable uncertainty over the potential response of soil C dynamics to rapid nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application. Here, we present a 15-year-long field study and show an average increase of 14.6% in soil C concentration in the 0-5 cm mineral soil layer in N fertilized (defined as N+ hereafter) sub-plots of a second-rotation Pinus radiata plantation in New Zealand compared to control sub-plots. The results of 14C and lignin analyses of soil C indicate that N additions significantly accelerate decomposition of labile and recalcitrant soil C. Using an annual-time step model, we estimated the soil C turnover time. In the N+ sub-plots, soil C in the light (a density < 1.70 g cm−3) and heavy fractions had the mean residence times of 23 and 67 yr, respectively, which are lower than those in the control sub-plots (36 and 133 yr in the light and heavy fractions, respectively). The commonly used lignin oxidation indices (vanillic acid to vanillin and syringic acid to syringaldehyde ratios) were significantly greater in the N+ sub-plots than in the control sub-plots, suggesting increased lignin decomposition due to fertilization. The estimation of C inputs to forest floor and δ13C analysis of soil C fractions indicate that the observed buildup of surface soil C concentrations in the N+ sub-plots can be attributed to increased inputs of C mass from forest debris. We conclude that long-term N additions in productive forests may increase C storage in both living tree biomass and soils despite elevated decomposition of soil organic matter. 相似文献