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   314篇
  免费   9篇
  国内免费   17篇
林业   33篇
农学   6篇
基础科学   5篇
  47篇
综合类   195篇
农作物   3篇
水产渔业   28篇
畜牧兽医   20篇
园艺   3篇
  2023年   2篇
  2021年   2篇
  2020年   3篇
  2019年   2篇
  2018年   6篇
  2017年   12篇
  2016年   7篇
  2015年   19篇
  2014年   17篇
  2013年   19篇
  2012年   29篇
  2011年   34篇
  2010年   27篇
  2009年   28篇
  2008年   26篇
  2007年   22篇
  2006年   16篇
  2005年   9篇
  2004年   6篇
  2003年   4篇
  2002年   6篇
  2001年   3篇
  2000年   4篇
  1999年   7篇
  1998年   4篇
  1997年   6篇
  1996年   3篇
  1995年   4篇
  1994年   3篇
  1993年   8篇
  1992年   1篇
  1985年   1篇
排序方式: 共有340条查询结果,搜索用时 15 毫秒
1.
周新年 《森林工程》1996,12(4):28-32
本文对福建省贮木场的发展历史进行扼要回顾,分析和评述了木材市场开放后福建省贮木场的现状,针对发展中存在的问题,并紧紧围绕经济发展的两个根本转变,对贮木场的发展出路提出看法。  相似文献   
2.
Aspects of intensive management practices such as high-yielding cultivars, narrow-row spacings and fungicide treatments could potentially increase cereal yields in regions with a short crop-growing season and occasionally dry and hot weather. A field experiment was carried out at McGill University, Canada for three years (1987 to 1989) to test the effects of triadimefon (1-[4-chlorophenoxy]-3,3-dimethyl-1-[1H-1,2,4-triazol-1-yl]-2-butanone, or Bayleton, a trade name) fungicide (0 vs. 140 g a.i. ha−1) and row spacing (10 vs. 20 cm) on the yield components, yield and other agronomic traits (spike emergence, days to maturity, leaf disease and plant height) of spring barley ( Hordeum vulgare L.) cv. Cadette, Laurier and Leger. A cultivar by row spacing interaction resulted in a 11 to 13.5 % increase in grain yield due to narrow rows for Laurier in two out of the three years and up to 16 % for Leger in one year. Over the three years grain yields were on average increased 6 to 12 % due to use of the narrower row spacing. Fungicide application to barley at the early heading stage effectively controlled leaf diseases without influence on yield components or grain yield. Our results indicate that some components of intensive management such as narrow row spacing can be applicable in regions with a short crop-growing season.  相似文献   
3.
专门化肉用种羊选定、引进后,通过适应性研究,在较大规模养羊业生产实践中。对现代集约化肉羊业的主要关键技术进行研究、完善和创新,组装集成并应用于生产。技术研究应用结果既为市场提供了大批专门化肉用种羊和优质安全的杂种肉羊,取得了高水平的研究成果及显著的经济效益和社会效益.又为我国目前正在迅速发展的集约化肉羊业提供了可靠的技术支持和理想的生产模式:从适宜的专门化肉羊品种到运用高效母羊快速扩繁技术.建立和完善有效的肉羊杂交利用体系,普遍应用种羊鲜、冻精生产大批肉用杂种羔羊,种植高产优质饲草及其科学加工调制和利用.建立严格兽医防疫制度.实行放牧 补饲或全舍饲的精细管理和集约化育肥,至生产优质、安全、标准肉羊,获得显著的经济效益和社会效益。  相似文献   
4.
“精明增长”是由西方国家针对城市蔓延提出的一种全新的城市发展理念,它倡导高效、集约、紧凑的城市发展模式,对于解决我国城市化进程中面临的诸多问题具有现实意义.该研究从城市增长的数量、强度、效益、循环和建设水平5个方面选取了8个指标建立城市精明增长现状测评体系,对长春市的精明增长现状进行测评.结果表明,长春市城市扩展速度较快,土地利用的集约度与强度均有待提高,但就城市经济发展、道路和公共交通现状来说,符合精明增长的发展方向.  相似文献   
5.
建设用地集约利用评价指标的权重确定方法研究   总被引:2,自引:0,他引:2  
基于建设用地集约利用评价指标,应用文献统计法和综合分析法,阐述了中国建设用地及建设用地集约利用评价指标权重赋权方法的现状,着重研究了各种权重确定方法在建设用地集约评价中的实践应用,并对其进行总结和讨论,探讨了建设用地集约利用评价指标权重确定方法的发展趋势.  相似文献   
6.
Use of ongrownArtemia in nursery culturing of the tiger shrimp   总被引:1,自引:0,他引:1  
Juvenile and adultArtemia produced in a semi flow-through culture system were used as food for postlarval shrimp. The growth performance of shrimp reared on such ongrownArtemia live prey is identical to the growth obtained when feeding newly hatchedArtemia. However, a significantly better stress resistance is obtained when the postlarvae are exposed to a low salinity in a stress test. Besides nutritional and energetic advantages, the use ofArtemia biomass for feeding postlarval shrimp also results in improved economics as expenses for cysts and weaning diets can be reduced.  相似文献   
7.
In the process of exploring ways to intensify crayfish culture, a growout system of individual cages (cells) was designed to determine the effects of gender and cell size on the growth of the red claw crayfish Cherax quadricarinatus. Cells of three different diameters—large (25 cm), medium (20 cm) and small (16 cm)—were used. When crayfish were stocked at a mean weight of approximately 10 g, growth rate of males was significantly higher than that of females. The growth rate of the males in the large cells was 0.31±0.14 g/day, while that of the females was 0.18±0.09 g/day. The size of the cell had significant influence on the weight of males. Male crayfish in the large and medium cells grew better than those in the small cells. When males were stocked at a higher mean weight (about 23 g), their mean weight after 206 days was higher in the large cells (69.28±15.72 g) than in the small cells (58.11±12.66 g), suggesting that the growth of large males was also affected by cell size. Regardless of cell size, male animals of this species grew faster than females under conditions of individual cells. This intensive culture method appears to present a powerful improvement in yields, by as much as two orders of magnitude, in comparison with communal cultures.  相似文献   
8.
净化育苗循环水生物流化床特性的研究   总被引:6,自引:1,他引:6  
战培荣 《水产学报》1998,22(4):328-333
比较了生物流化床与生物固定床的水净化特性,生物流化床氨氮负荷和硝化率提高3倍。用电子显微镜和营养琼脂培养法观察了流化床中生物粒子表面的细菌分布与生长情况,生物粒子表面生物膜丰富,均匀,生长繁殖快,活性好。在15万尾/m3的密度下,循环水培育鲤苗,15天体重达21.2mg,体长达12.58±0.94mm,成活率90%。  相似文献   
9.
The perch population in Lake Höytiäinen was intensively fished to reduce the density of the population and hence also the predation pressure by perch on vendace larvae. A hypothesis suggests that this predation can prevent recovery of commercially important vendace stock from a state of low-density. In the 1990s the density of the perch population in Lake Höytiäinen has increased, while the vendace stock has been sparse. Intensive fishing was conducted by professional fishermen with a paired bottom trawl, seine net, hoop net and small fish traps and by recreational fishermen with small fish traps. The size of perch population during the intensive fishing period was studied by test fishing with multi-mesh gillnets and the Leslie method in which trawl YPUE was regressed on the cumulative yield. The results suggest that the population size clearly diminished in the area where the fishing pressure was strongest. YPUE of test fishing decreased ca. 30% whereas the Leslie method gave almost a decrease twice as large as that of the former. Mean weight of perch increased in the trawl and test fishing catches during the intensive fishing period. The most effective fishing gear was trawl (62% of the total yield), but importance of trap net fishing by recreational fishermen was also high as they caught 22% of the total yield.  相似文献   
10.
为了进一步摸清散叶堆积烘烤技术对烤烟综合效益的影响,研究分析了2011年贵州正安县推广应用散叶堆积烘烤技术的相关数据.结果表明,散叶堆积烘烤相较常规挂竿烘烤,能省工节能、提质增效;其中,烤后烟均价、上等烟率和橘黄烟率分别提高0.33元/kg、5.78个百分点和3.52个百分点,杂色烟率降低0.97个百分点,烘烤环节用工成本降低0.53元/kg,能耗成本降低0.32元/kg,增加经济效益1.18元/kg.  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