全文获取类型
收费全文 | 4557篇 |
免费 | 265篇 |
国内免费 | 151篇 |
专业分类
林业 | 435篇 |
农学 | 449篇 |
基础科学 | 112篇 |
378篇 | |
综合类 | 2086篇 |
农作物 | 176篇 |
水产渔业 | 106篇 |
畜牧兽医 | 702篇 |
园艺 | 352篇 |
植物保护 | 177篇 |
出版年
2024年 | 10篇 |
2023年 | 84篇 |
2022年 | 144篇 |
2021年 | 237篇 |
2020年 | 227篇 |
2019年 | 201篇 |
2018年 | 105篇 |
2017年 | 166篇 |
2016年 | 250篇 |
2015年 | 245篇 |
2014年 | 335篇 |
2013年 | 319篇 |
2012年 | 716篇 |
2011年 | 293篇 |
2010年 | 266篇 |
2009年 | 210篇 |
2008年 | 176篇 |
2007年 | 136篇 |
2006年 | 110篇 |
2005年 | 116篇 |
2004年 | 84篇 |
2003年 | 76篇 |
2002年 | 44篇 |
2001年 | 41篇 |
2000年 | 30篇 |
1999年 | 29篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 139篇 |
1995年 | 8篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
排序方式: 共有4973条查询结果,搜索用时 31 毫秒
101.
102.
103.
104.
以纪念女性为主的园林是中国历史园林的特殊类型,理清其营建的动因和经验,是传承中国园林文化的重要补充。纪念唐代女诗人薛涛的望江楼公园,其兴建、发展、造景等方面与薛涛的人生经历、个性品行紧密结合。基于历史文献梳理和园林空间分析,剖析了望江楼公园的发展变迁历程,归纳了针对薛涛的园林景观的纪念性造景手法,从遗迹、植物、建筑、活动等方面分析了女诗人薛涛与望江楼公园之间相辅相成的关系。 相似文献
105.
J.-P. Rossi J.-C. Samalens D. Guyon I. van Halder H. Jactel P. Menassieu D. Piou 《Forest Ecology and Management》2009
Bark beetles are notorious pests of natural and planted forests causing extensive damage. These insects depend on dead or weakened trees but can switch to healthy trees during an outbreak as mass-attacks allow the beetle to overwhelm tree defences. Climatic events like windstorms are known to favour bark beetle outbreaks because they create a large number of breeding sites, i.e., weakened trees and for this reason, windthrown timber is generally preventively harvested and removed. In December 1999, the southwest of France was struck by a devastating windstorm that felled more that 27 million m3of timber. This event offered the opportunity to study large-scale spatial pattern of trees attacked by the bark beetle Ips sexdentatus and its relationship with the spatial location of pine logs that were temporally stored in piles along stand edges during the post-storm process of fallen tree removal. The study was undertaken in a pure maritime pine forest of 1300 ha in 2001 and 2002. We developed a landscape approach based on a GIS and a complete inventory of attacked trees. During this study more than 70% of the investigated stands had at least one tree attacked by I. sexdentatus . Spatial aggregation prevailed in stands with n≥15 attacked trees. Patches of attacked trees were identified using a kernel estimation procedure coupled with randomization tests. Attacked trees formed patches of 500–700 m2 on average which displayed a clumped spatial distribution. Log piles stemming from the sanitation removals were mainly distributed along the large access roads and showed an aggregated spatial pattern as well. The spatial relationship between patches of attacked trees and log pile storage areas was analyzed by means of the Ripley’s statistic that revealed a strong association at the scale of the studied forest. Our results indicated that bark beetle attacks were facilitated in the vicinity of areas where pine logs were stored. The spatial extent of this relationship was >1000 m. Similar results were obtained in 2001 and 2002 despite differences in the number and spatial distribution of attacked trees. The presence of a strong “facilitation effect” suggests that log piles should be removed quickly in order to prevent outbreaks of bark beetles. 相似文献
106.
107.
A survey of forestry practices and attitudes was undertaken in four communities in Leyte, the Philippines, to improve understanding
of the social and economic factors affecting small-scale forestry development. The survey had three main data collection activities
— initial focus group discussions (FGDs), household interviews, and reporting and validation FGDs. A team of enumerators was
selected for household interviews which consisted of both males and females, to avoid potential problems of unwillingness
of people to talk with those of the opposite gender. The interviewers were also required to be able to speak local dialects
(Cebuano and Waray Waray), the survey questionnaires being administered in these dialects. Various methods were used to gain
the support and assistance of local government units and barangay captains. Some difficulty was experienced by the survey
team in the first community due to barangay elections at the time of the survey, and the requirement by the University of
Queensland Ethics Committee that respondents sign a consent form. This requirement was found to be not culturally appropriate
for the Leyte smallholder communities. Offering goods at the end of the interview was found to be of limited value for encouraging
participation in the survey. Provision of food and drinks were found to encourage FGD participants to express their views,
but too much alcohol had a negative effect. The importance of providing comprehensive feedback to respondents and involving
them and other stakeholders in development of policy recommendations was apparent. These survey experiences provide valuable
insights which are not generally available in textbooks on sample surveys, and provide lessons for planning and conducting
smallholder community survey into natural resource management issues. 相似文献
108.
对20年生马尾松人工林生物量的研究表明,全林生物量38.42吨/公顷,间伐后年生产量6.49吨/公顷林木根量5.73吨/公顷,相对生长率19.0%,净同化率0.253公斤/米~2·年,生产力水平偏低。林分抚育间伐后,林木的生物生产力得到提高。建立了林木各器官干重与直径树高的8个相关方程,相关系数均在0.92以上。通过叶面积及其生长函数分析,林分密度过高,生长速率降低,建议及时合理地调节林分密度。 相似文献
109.
A study was conducted to assess the role and effectiveness of community organisers in supporting the development of people’s
organisations in achieving community-based forest management objectives in Leyte Province Philippines. Community organisers
were found to be effective in forming people’s organisations (POs), motivating people to participate in voluntary activities
organised by POs and encouraging cohesiveness among PO members. Community organisers manage to raise the level of environmental
awareness and knowledge of members of people’s organisations, develop leadership interest and skills, create various livelihood
opportunities and provide direction and facilitate the establishment of large tree plantations. However, the short duration
of community organisers’ contracts (typically two years) is insufficient to establish mature and cohesive POs prepared to
assume management on their own, including the management of tree plantations. Further, lack of training and funding support,
low wages, delayed payment of salaries and limited time to work with people’s organisations, as well as the pressure to produce
tangible outputs such the establishment of large tree plantations, prevents them from placing greater emphasis on the development
and empowerment of the people. 相似文献
110.
蔬菜种植农户对无公害农药的认知和购买意愿——基于河北省120家菜农的调查分析 总被引:1,自引:0,他引:1
为了考察我国农户对无公害农药的接受程度,从源头上保障农产品质量,笔者以河北省为例,通过问卷调查和访谈具体考察了蔬菜种植农户对无公害农药的认知程度和购买意愿.研究表明,户主年龄、文化程度、居住地到中心城市的距离是影响农户对无公害农药认知的重要因素;而无公害农药的价格、土地的获得成本、种植面积和市场检测机制直接决定着农户对无公害农药的购买意愿. 相似文献