首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   308篇
  免费   11篇
  国内免费   13篇
林业   101篇
农学   11篇
基础科学   15篇
  63篇
综合类   102篇
农作物   3篇
水产渔业   1篇
畜牧兽医   26篇
园艺   3篇
植物保护   7篇
  2023年   5篇
  2022年   4篇
  2021年   5篇
  2020年   5篇
  2019年   12篇
  2018年   8篇
  2017年   12篇
  2016年   20篇
  2015年   14篇
  2014年   9篇
  2013年   24篇
  2012年   19篇
  2011年   22篇
  2010年   16篇
  2009年   23篇
  2008年   18篇
  2007年   16篇
  2006年   14篇
  2005年   16篇
  2004年   11篇
  2003年   7篇
  2002年   4篇
  2001年   8篇
  2000年   6篇
  1999年   4篇
  1998年   1篇
  1997年   2篇
  1996年   4篇
  1995年   7篇
  1994年   4篇
  1993年   2篇
  1992年   4篇
  1991年   2篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
排序方式: 共有332条查询结果,搜索用时 718 毫秒
11.
秸秆焚烧现状与对策探讨   总被引:4,自引:0,他引:4  
就我国当前秸秆焚烧问题展开探讨研究,通过深入分析当前秸秆焚烧现状,探讨问题产生的客观原因,并有针对性地提出可行性对策,为我国秸秆资源化进程提供参考。  相似文献   
12.
生物质型煤与无烟散煤在烟叶烘烤中的应用效果对比   总被引:2,自引:0,他引:2  
2010年在云南曲靖进行了生物质型煤与无烟散煤的对比研究,通过试验分析了不同类型燃料的燃烧效率、添加次数与耗煤量,以及对烤后烟叶质量、烘烤经济效益的影响.研究结果表明:生物质型煤升温均衡,主要表现在烘烤定色阶段和干筋阶段;生物质型煤稳温效果好,主要表现在变黄期关键温度点38℃和定色期47℃,但总体耗煤量大、加煤频繁;燃...  相似文献   
13.
秸秆露天焚烧排放的TSP等污染物清单   总被引:28,自引:5,他引:28  
根据2000—2003年各省市农作物的产量,估算了农业秸秆的总量;结合从有关文献查阅的排放因子,计算了各年份我国大陆秸秆露天焚烧所排放的TSP、PM10、SO2、NOX、NH3、CH4、EC、OC、VOC、CO、CO2的总量及各省市的排放清单,并进一步细化到县、区级行政区。研究表明,由于经济发展水平和生活习惯的不同,秸秆露天焚烧排放的污染物在地区间的分布极不均衡,排放量较大的包括华东、东北地区的各省市;单位排放污染物量较高的地区由东北至华东呈带状分布。  相似文献   
14.
介绍曲靖市森林防火现状及火烧防火线技术应用概况.阐述森林火烧防火线作业的最佳时期选择、工作程序、人员组织、任务分配、设备配置以及作业程序等.  相似文献   
15.
特种黑木炭是用柞、槲烧制的具有较高密度的木炭。影响黑木炭密度的主要因素有原料含水率和径级、干燥与炭化速度、炭窑窑形及精炼。本文还对烧制特种黑木炭过程中的具体操作技术要点进行了详尽的论述。  相似文献   
16.
Zhalong Nature Reserve is located in the border areaof Qiqihaer City, Fuyu County, Lindian County andTailai County of Heilongjiang Province. The area ofthe reserve is 210 000 ha. The reserve is the firstnature reserve for protecting wetland and crane inChina. There were more than 300 red-crownedcranes here at the very most. Zhalong Nature Reserveis situated at the Songnen Plain, the lower stream ofthe Wuyuer River. It is the biggest nature reserve inChina that takes crane and wetland …  相似文献   
17.
据样地调查,该25年生杉木人工林群落的植物有41科84属120种,群落的外貌特征以包括藤本在内的高位芽占绝对优势,叶特征以革质,单叶,中小型叶为主,由于该群落的幼树层以米储和木荷等占优势,若让其自然发展或杉木林采伐后不炼山,并排除其它人为干扰,该群落将向与常绿阔叶林采伐前的群落类型相似的方向演替。  相似文献   
18.
In order to investigate the pyrolytic characteristics of the burning residue of fire-retardant wood, a multifunctional fire-resistance test oven aimed at simulating the course of a fire was used to burn fire-retardant wood and untreated wood. Samples at different distances from the combustion surface were obtained and a thermogravimetric analysis (TG) was applied to test the prrolytic process of the burning residue in an atmosphere of nitrogen. The results showed that: 1) there was little difference between fire-retardant wood and its residue in the initial temperature of thermal degradation. The initial temperature of thermal degradation of the combustion layer in untreated wood was higher than that in the no burning wood sample; 2) the temperature of the flame retardant in fire-retardant wood was 200°C in the differential thermogravimetry (DTG). The peak belonging to the flame retardant tended to dissipate during the time of burning; 3) for the burning residue of fire-retardant wood, the peak belonging to hemicellulose near 230°C in the DTG disappeared and there was a gentle shoulder from 210 to 240°C; 4) the temperature of the main peaks of the fire-retardant wood and its burning residue in DTG was 100°C lower than that of the untreated wood and its burning residue. The rate of weight loss also decreased sharply; 5) the residual weight of fire-retardant wood at 600°C clearly increased compared with that of untreated wood. Residual weight of the burning residue increased markedly as the heating temperature increased when burning; 6) there was a considerable difference with respect to the thermal degradation temperature of the no burning sample and the burning residue between fire-retardant wood and untreated wood. __________ Translated from Journal of Beijing Forestry University, 2006, 28(3): 133–138 [译自: 北京林业大学学报]  相似文献   
19.
We followed the establishment and growth response of 13 commercial tree species to canopy opening, above-ground biomass removal, and experimental burns of low and high intensities in a lowland dry forest in Bolivia. Three patterns of response to treatments were observed among the most abundant commercial tree species. (1) Shade-intolerant species regenerated mostly from seed and had the highest survival and growth rates following high-intensity burns. (2) Shade-tolerant species were abundant in gap control and plant removal treatments. Treatments had little effect on the height growth of these species. (3) Individuals of root sprouting species were most abundant following plant removal and low-intensity burn treatments. Treatments had little effect on the height growth of these species. The wide variation in species responses to gap treatments found in this study not only reinforces the concept that species are distributed along a continuum of shade-tolerance levels, but that other aspects of species biology, such as seed dispersal type or sprouting behavior, further differentiate regeneration strategies. The variety of regeneration strategies found among the species at this forest site will require a flexible management scheme that mixes more intensive silvicultural treatments such as prescribed burning with less intensive treatments.  相似文献   
20.
杉木人工林地力维持及更新技术研究   总被引:4,自引:0,他引:4  
通过对土壤和杉木幼林调查分析结果表明 ,炼山、全垦初期表层土壤水分物理状况得到一定的改善 ,速效性养分大量增加 ;1年后 ,土壤表层水分物理性能变差 ,速效养分流失 ,土壤肥力逐渐下降。不同营林措施组合处理的杉木幼林生长 ,在树高、胸径、单株材积平均生长量上有差异 ,经方差分析 ,胸径、单株材积生长量有显著性差异 ,而树高生长量差异不显著  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号