全文获取类型
收费全文 | 17985篇 |
免费 | 1054篇 |
国内免费 | 676篇 |
专业分类
林业 | 4147篇 |
农学 | 594篇 |
基础科学 | 1290篇 |
2326篇 | |
综合类 | 6756篇 |
农作物 | 683篇 |
水产渔业 | 1052篇 |
畜牧兽医 | 1265篇 |
园艺 | 317篇 |
植物保护 | 1285篇 |
出版年
2024年 | 94篇 |
2023年 | 301篇 |
2022年 | 340篇 |
2021年 | 501篇 |
2020年 | 567篇 |
2019年 | 652篇 |
2018年 | 429篇 |
2017年 | 521篇 |
2016年 | 664篇 |
2015年 | 560篇 |
2014年 | 972篇 |
2013年 | 1151篇 |
2012年 | 1479篇 |
2011年 | 1477篇 |
2010年 | 1119篇 |
2009年 | 1192篇 |
2008年 | 1083篇 |
2007年 | 1113篇 |
2006年 | 921篇 |
2005年 | 891篇 |
2004年 | 696篇 |
2003年 | 595篇 |
2002年 | 434篇 |
2001年 | 410篇 |
2000年 | 337篇 |
1999年 | 232篇 |
1998年 | 176篇 |
1997年 | 164篇 |
1996年 | 135篇 |
1995年 | 107篇 |
1994年 | 77篇 |
1993年 | 62篇 |
1992年 | 66篇 |
1991年 | 63篇 |
1990年 | 35篇 |
1989年 | 46篇 |
1988年 | 31篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
丰富的森林资源促进了第2次世界大战结束后日本经济的恢复和高速发展。此后,林产品市场供求、生产经营和产业政策发生了重大变化。文中分析了日本森林资源和森林经营现状、木材供求和森林功能多样化的趋势,以及林业政策、经营管理和技术创新的动向,以期为理论研究和业务决策提供参考。日本在经济高速增长期过后,木材需求量减少,自给率维持低位。近年来,日本林木进入集中主伐利用期,社会对森林生态环保需求增大,森林经营面临着规模过小、国有林缺乏经营活力、年轻劳动力减少等问题。日本森林经营管理创新的重点包括提高科技贡献率、改革林业特别是国有林的生产经营体制、提升森林在生态与环境和经济减贫等多方面价值。目前,上述创新已经效果初现,也是今后日本林业改革发展的主要方向。 相似文献
992.
Miriam Cotillas Santi Sabat Carlos Gracia Josep Mª Espelta 《Forest Ecology and Management》2009,258(7):1677-1683
Climate change is one of the major challenges for ecosystem conservation. One of the most vulnerable areas to climate change is the Mediterranean Basin which is expected to suffer important changes in temperature and precipitation in the next few decades, leading to a warmer and dryer climate. Therefore, it is necessary to determine species-specific responses to increased drought to predict possible future changes in the structure and composition of Mediterranean forests, as well as to identify appropriate management strategies to mitigate these effects.The main aim of this study has been to experimentally simulate the effects of a 15% reduction in annual rainfall on the survival and growth of two co-occurring Mediterranean oaks with contrasting leaf-habit (the evergreen Quercus ilex spp. ilex and the winter-deciduous Quercus cerrioides) and, to assess whether traditional selective thinning carried out in these mixed oak coppices (i.e. selection of one to few stems per stump) can modify the consequences of rainfall reduction.Soil moisture decreased under the rainfall reduction level while it increased in the thinned plots. Reduced rainfall did not influence tree mortality, but did lead to species-specific effects on height growth: no changes were observed in Q. ilex while height growth rate of Q. cerrioides decreased (c.a. 20%). Selective thinning improved tree growth (c.a. 50%) in stands both under natural and, and to a lesser extent, under reduced rainfall conditions. Nevertheless, the positive effects of thinning rapidly declined during our three years experiment, probably because the vigorous resprouting of thinned stumps.Our results show that the forecasted reduction in annual rainfall for the Western Mediterranean Basin can constrain the growth of some deciduous oaks in mixed oak coppices. Traditional selective thinning can increase soil moisture and encourage tree growth, thus partially mitigating this effect. However, the transient results observed in this experiment suggest the need to reconsider the intensity and the frequency of this traditional management practice in light of new climatic scenarios. 相似文献
993.
Demand for non-timber forest products: Surveys of urban consumers and sellers in Switzerland 总被引:2,自引:0,他引:2
In recent years, worldwide socioeconomic, ecological, and cultural changes have led to a paradigm shift in forestry and forest management. Some years ago, most forest enterprises exclusively focused on wood production, whereas today, forest management is expected to be multifunctional and economically as well as socially and ecologically sustainable [Harrison, S., Herbohn, J., Niskanen, A., 2002. Non-industrial, smallholder, small-scale and family forestry: what's in a name? Small-scale Forest Economics. Management and Policy 1 (1), 1–11; Schmithuesen, F., 2004. Forest policy developments in changing societies — political trends and challenges to research. Towards the sustainable use of Europe's forests: Forest ecosystems and landscape research: Joensuu: European Forest Institute, Proc., vol. 49, pp. 87–99]. In this context, non-timber forest products (NTFPs) such as forest honey, mushrooms, or berries could gain importance as an additional source of income for the forestry sector. To assess the market potential of NTFPs in Switzerland, two corresponding surveys were conducted. A consumer survey (N = 897) conducted in six cities in Switzerland investigated the purchase of Swiss NTFPs, consumer preferences, and demand potentials. An additional survey of sellers of NTFPs (N = 105) looked at these aspects from a complementary perspective. The results showed that there is a high esteem and considerable demand potential for such products among urban consumers. Food products were mentioned most frequently. Both consumers and sellers considered quality and environmental friendliness the most important attributes of NTFPs. Structural and organizational innovations and considerable marketing efforts and sales promotion would be required to expand the market for Swiss NTFP, however. Our results indicate that certification of the products' origin, environmental performance, and quality could support such efforts and that recreational and ecological forest services have a synergetic potential for the marketing of NTFPs. 相似文献
994.
The shamba system involves farmers tending tree saplings on state-owned forest land in return for being permitted to intercrop
perennial food crops until canopy closure. At one time the system was used throughout all state-owned forest lands in Kenya,
accounting for a large proportion of some 160,000 ha. The system should theoretically be mutually beneficial to both local
people and the government. However the system has had a chequered past in Kenya due to widespread malpractice and associated
environmental degradation. It was last banned in 2003 but in early 2008 field trials were initiated for its reintroduction.
This study aimed to: assess the benefits and limitations of the shamba system in Kenya; assess the main influences on the
extent to which the limitations and benefits are realised and; consider the management and policy requirements for the system’s
successful and sustainable operation. Information was obtained from 133 questionnaires using mainly open ended questions and
six participatory workshops carried out in forest-adjacent communities on the western slopes of Mount Kenya in Nyeri district.
In addition interviews were conducted with key informants from communities and organisations. There was strong desire amongst
local people for the system’s reintroduction given that it had provided significant food, income and employment. Local perceptions
of the failings of the system included firstly mismanagement by government or forest authorities and secondly abuse of the
system by shamba farmers and outsiders. Improvements local people considered necessary for the shamba system to work included
more accountability and transparency in administration and better rules with respect to plot allocation and stewardship. Ninety-seven
percent of respondents said they would like to be more involved in management of the forest and 80% that they were willing
to pay for the use of a plot. The study concludes that the structural framework laid down by the 2005 Forests Act, which includes
provision for the reimplementation of the shamba system under the new plantation establishment and livelihood improvement
scheme (PELIS) [It should be noted that whilst the shamba system was re-branded in 2008 under the acronym PELIS, for the sake
of simplicity the authors continue to refer to the ‘shamba system’ and ‘shamba farmers’ throughout this paper.], is weakened
because insufficient power is likely to be devolved to local people, casting them merely as ‘forest users’ and the shamba
system as a ‘forest user right’. In so doing the system’s potential to both facilitate and embody the participation of local
people in forest management is limited and the long-term sustainability of the new system is questionable. Suggested instruments
to address this include some degree of sharing of profits from forest timber, performance related guarantees for farmers to
gain a new plot and use of joint committees consisting of local people and the forest authorities for long term management
of forests.
相似文献
Peter DorwardEmail: |
995.
Long range (or strategic) planning is an important tool for forest management to deal with the complex and unpredictable future.
However, it is the ability to make meaningful predictions about the rapidly changing future that is questioned. What appears
to be particularly neglected is the question of the length of time horizons and the limits (if any) to these horizons, despite
being considered one of the most critical factors in strategic planning. As the future creation of values lies within individual
responsibility, this research empirically explored the limits (if any) of individual foresters’ time horizons. To draw comparisons
between countries with different traditions in forest management planning, data were collected through telephone surveys of
forest managers in the state/national forest services of the Netherlands and Germany. In order to minimize other cultural
differences, the research in Germany concentrated on the federal state of Nordrhein-Westfalen, which has considerable similarities
with the Netherlands, e.g. in topography, forest types and forest functions. The results show that, in practice, 15 years
appears to be the most distant horizon that foresters can identify with. This is in sharp contrast to the time horizons spanning
decades and even generations that are always said to exist in forestry. The “doctrine of the long run”—the faith in the capacity
of foresters to overcome the barriers of the uncertain future and look ahead and plan for long-range goals—which in many countries
still underlies traditional forest management, can therefore be rejected.
相似文献
Heiner SchanzEmail: |
996.
通过二类资源清查数据,分别从林地面积、林种、树种、龄组等方面对流溪河林场森林资源动态变化进行了分析和评价,并对林杨林业的发展提出建议。 相似文献
997.
998.
根据1976年播后出苗率和成苗率调查,1987--1990年油松毛虫灾害对油松林分的影响,及1991年和2003年丁营飞播区森林资源清查资料,通过调查数据对比分析,丁营飞播区播后林分变化规律,符合近自然林业发展规律。面向整个丁营飞播区生态系统,依据近自然林业经营理念,研究丁营飞播区经营管理措施,实现林业经营目标的最大化。 相似文献
999.
以佛山市一环快速干线绿化养护工程为例,提出了城市环线快速干线的绿化养护管理技术,为类似工程提供参考。
相似文献
1000.
计划烧除的作用与应用研究综述 总被引:2,自引:0,他引:2
计划烧除是管理森林可燃物、预防森林火灾发生的有效方法,同时也是防治病虫害、促进山林复壮更新的重要措施。文章回顾了计划烧除在国内外的发展历史,阐述了计划烧除的应用及研究,总结出实施计划烧除的主要技术及操作程序,论述了国内目前计划烧除应用研究中存在的问题及发展前景。 相似文献