全文获取类型
收费全文 | 21082篇 |
免费 | 1248篇 |
国内免费 | 767篇 |
专业分类
林业 | 6218篇 |
农学 | 639篇 |
基础科学 | 1323篇 |
2454篇 | |
综合类 | 7738篇 |
农作物 | 687篇 |
水产渔业 | 1050篇 |
畜牧兽医 | 1278篇 |
园艺 | 395篇 |
植物保护 | 1315篇 |
出版年
2024年 | 79篇 |
2023年 | 315篇 |
2022年 | 362篇 |
2021年 | 529篇 |
2020年 | 631篇 |
2019年 | 755篇 |
2018年 | 464篇 |
2017年 | 573篇 |
2016年 | 755篇 |
2015年 | 622篇 |
2014年 | 1141篇 |
2013年 | 1321篇 |
2012年 | 1787篇 |
2011年 | 1718篇 |
2010年 | 1260篇 |
2009年 | 1409篇 |
2008年 | 1246篇 |
2007年 | 1312篇 |
2006年 | 1140篇 |
2005年 | 1141篇 |
2004年 | 886篇 |
2003年 | 751篇 |
2002年 | 520篇 |
2001年 | 517篇 |
2000年 | 388篇 |
1999年 | 282篇 |
1998年 | 212篇 |
1997年 | 192篇 |
1996年 | 168篇 |
1995年 | 134篇 |
1994年 | 93篇 |
1993年 | 86篇 |
1992年 | 75篇 |
1991年 | 75篇 |
1990年 | 41篇 |
1989年 | 56篇 |
1988年 | 36篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
在林业生产的过程中,采用正确、合理的造林技术和抚育技术,能够提高造林成活率,确保林木健康生长,并在短时间内构建完善的林分结构。而科学的抚育管理,又能进一步挖掘林业发展潜力,提升林地质量和产量,为林业发展创造更多的空间。同时做好造林和森林抚育工作,能够有效地促进林业科学发展,更好地应对全球气候变化的挑战。 相似文献
102.
103.
104.
105.
对农垦齐齐哈尔管理局奶牛养殖小区的饲养经营模式及效益进行了调查,分析了奶牛小区建设给奶牛群带来的主要变化。通过分析不同模式奶牛小区生产经营状况,确定适合该地区奶牛业发展的奶牛小区经营模式。 相似文献
106.
运用贡献度随机森林方法(CRF)方法探讨公司债财务指标比率与其违约率的关系.运用连续属性离散化方法(OB)进行财务指标最优降维;运用WOE变换进行模型变量约简.研究表明,CRF模型的分类性能显著优于其他模型,测试集评估总体正确率达90.47%,AUC统计量、AR比率及K-S值分别提升了2.6%、7.6%、4.38%,变量贡献度量化了各财务指标对违约率影响,为诠释随机森林预测机制提供了依据. 相似文献
107.
108.
109.
Interest in planting urban food trees (UFTs) in public spaces is growing in popularity as a form of urban greening and a potential food source. Currently there is minimal research on the governance and policy aspects of integrating food trees into cities. To fill this gap, we investigated the characteristics of UFT site governance and how it compares to current urban forest governance. Semi-structured interviews were conducted with relevant municipal officials in Calgary, Edmonton, Toronto and Victoria about their perspectives and involvement with UFT sites in their city. A scan of policy documents was completed to supplement the interviews. The interviews were analyzed using a deductive coding framework based on the Policy Arrangement Approach. We found that key actors at the UFT sites were local organizations and site champions, with minimal municipal engagement. Most site resources provided by municipalities were in-kind. There are also basic knowledge gaps about how to care for UFTs. Currently municipal by-laws prohibit the harvesting and removal of plant material, and are at odds with the purpose of UFT sites, with few municipalities fully integrating UFTs in policies. The primary discussion around UFTs centre concerns for public health and safety, management, and use of public space with limited discussions of benefits. This research demonstrates the value of co-governance models to support UFTs, while a shift in focus from risks to benefits could encourage additional resources and policy integration. Further, including UFTs into policy would also support foraging and food tree maintenance in public spaces, and more fully reflect the plurality of urban forest engagement. 相似文献
110.
In this paper the results of the first comprehensive study on perception of and satisfaction with urban forests and green space in seven Southeast European cities are presented. The aims of the paper are to analyse 1) citizen perceptions of the current state of urban forests and green space in their cities, 2) to what extent current urban forests and green space meet their needs and how this can be improved. A cross-sectional study was conducted by using a common face-to-face survey questionnaire. Respondents were selected based on census data though a stratified sampling procedure by taking into account age, gender and city district (n = 384 in each city). The results showed that citizens genuinely care for urban forests and green space in their cities, but are not satisfied with their current state. The respondents found issues related to misbehaviour of other users, the presence and quality of facilities, as well as the presence and quality of management or maintenance the most pressing. There were more statistically significant differences than similarities between cities. Socioeconomic variables explained perceptions only to some extent. Citizens were very supportive of educational campaigns about the importance of urban forests and green space as well as of better enforcement of the existing regulations though having more community wardens that were expected to tackle current unsatisfactory situations. Urban planning and urban forest and green space management in these cities are facing many problems characteristic for post-socialist countries. Study findings are expected to contribute to decision making in urban planning and natural resource management. 相似文献