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   882篇
  免费   49篇
  国内免费   82篇
林业   117篇
农学   42篇
基础科学   16篇
  178篇
综合类   320篇
农作物   58篇
水产渔业   61篇
畜牧兽医   136篇
园艺   27篇
植物保护   58篇
  2024年   7篇
  2023年   8篇
  2022年   24篇
  2021年   31篇
  2020年   37篇
  2019年   29篇
  2018年   17篇
  2017年   29篇
  2016年   57篇
  2015年   34篇
  2014年   53篇
  2013年   53篇
  2012年   65篇
  2011年   93篇
  2010年   56篇
  2009年   75篇
  2008年   57篇
  2007年   62篇
  2006年   55篇
  2005年   21篇
  2004年   24篇
  2003年   17篇
  2002年   20篇
  2001年   9篇
  2000年   16篇
  1999年   12篇
  1998年   5篇
  1997年   10篇
  1996年   8篇
  1995年   6篇
  1994年   3篇
  1993年   3篇
  1992年   6篇
  1991年   3篇
  1990年   3篇
  1988年   1篇
  1986年   1篇
  1984年   1篇
  1977年   1篇
  1962年   1篇
排序方式: 共有1013条查询结果,搜索用时 15 毫秒
101.
为了解北方森林动物园观赏鸟类寄生蠕虫的感染情况,于2006年3~6月采用饱和盐水漂浮法和水洗沉淀法对园内12科158只观赏鸟的粪便进行了蠕虫虫卵检查,结果有32只鸟检出虫卵,感染率为20.3%,雉科、鹤科和鸭科的感染率分别为60%、35.7%和18.5%,检出的虫卵为蛔虫、毛细线虫和棘口吸虫卵。该调查为动物园制定鸟类驱虫方案奠定了基础。  相似文献   
102.
提出了一套解决北方地区冬季沼气使用难的技术方法,包括改进建池技术、添加沼气菌剂、加强保温措施等内容,可确保沼气池在冬季正常使用,平均产气量高于0.46m3/d。该方法简单有效、易于掌握、投资低廉,可以促进沼气池在北方地区的推广和利用。  相似文献   
103.
以马克思辩证唯物主义理论和科学发展观为基础,针对豫北地区强筋小麦育种面临的问题,探讨了强筋小麦育种技术体系。新麦系列优质强筋高产高效小麦品种的育种实践表明,新品种与栽培技术、产业加工的有机结合能够适应当前豫北地区的农业发展需要,值得借鉴和学习。  相似文献   
104.
于2016年4月和7月在乐清湾北部海域进行海洋环境调查,依据富营养化状态评价原则和营养状态指数(E)对乐清湾北部海域的富营养化现状进行评价。结果表明,NO3--N和NH4+-N是乐清湾海域无机氮的主要存在形式。乐清湾北部海域富营养化程度严重,整体处于磷中等限制潜在性富营养至磷限制潜在性富营养状态。究其原因是海湾位置结构、沿岸城镇带来的生产生活污水及水产养殖的规模及密度大。  相似文献   
105.
黑龙江省玉米大斑病菌生理小种的研究   总被引:4,自引:2,他引:4  
本文通过对黑龙江省西部玉米主产区及哈尔滨市农科院 试验地采集的30份玉米大斑病叶标本分离得到16个菌株,其中有5个菌株是从带有Ht1的自交系上分离的,寄主鉴定结果表明哈尔滨市存在有玉米大斑病2号生理小种,其他地区只分离到1号小种。  相似文献   
106.
北部冬麦区旱地小麦品种的演变规律   总被引:2,自引:0,他引:2  
为了给北部冬麦区旱地小麦育种提供参考,利用1986-2015年国家北部冬麦区旱地小麦长治区试点参试品种的试验资料,研究其演变规律,并对产量和主要农艺性状进行相关和通径分析。结果表明,28年间北部冬麦区旱地小麦品种产量呈逐年递增趋势,年平均遗传进展分别为68.163kg·hm~(-2)或1.57%。主要农艺性状演变的总趋势是,有效穗数和千粒重增加,穗粒数略有减少,株高降低,抽穗期和成熟期提前,灌浆期延长,其年平均遗传进展分别为0.18%、0.26%、-0.03%、-0.26%、-0.12%、-0.05%、0.17%。从产量及主要农艺性状变化趋势和变异情况及区域布局、气候条件和育种现状分析,选育抗旱节水性好、高产稳产适应性广的品种是北部冬麦区旱地小麦育种面临的挑战和最终目标。为了适应当前耕作制度、生产条件和气候变化的影响,北部冬麦区旱地品种选育应在加强品种抗旱节水性选择的基础上,通过适当降低株高增强抗倒性来进一步增加穗数,通过选育穗子较大、小穗数适中、结实性好的品种来提高穗粒数,通过选择灌浆期长且灌浆速率高的品种来提高品种的千粒重。  相似文献   
107.
本文介绍了创意农业和创意农业景观的内涵,并从农业生产方式,产品的特性和功能,园林的美化,文化的历史和主题,进行了创意农业的景观分类及其表达描述。通过对北大荒旱作农业创意园区的景观规划设计,探讨农业、景观、旅游相结合的创意农业新方式。  相似文献   
108.
Available water is typically the biggest constraint to spring wheat production in the northern Great Plains of the USA. The most common rotation for spring wheat is with summer fallow, which is used to accrue additional soil moisture. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, allowing for increased cropping intensity. We conducted a field trial from 1998 through 2003 comparing productivity and water use of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average most years, resulting in substantial drought stress to crops not following fallow. Preplant soil water, water use, and spring wheat yields were generally greater following summer fallow than wheat recropped after wheat or alternate crops. Water use and yield of wheat following summer fallow was greater than for chickpea or yellow mustard, the only other crops in the trial that followed summer fallow. Field pea performed best of all alternate crops, providing yields comparable to those of recropped spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region, at least during periods of below average precipitation. Following summer fallow, and despite drought conditions, zero tillage often provided greater amounts of soil water at planting compared to conventional tillage.  相似文献   
109.
In response to customer concerns related to gluten strength in commercial baking, the Canadian Grain Commission assessed whether the Canadian Short Process (CSP) test bake method was generating useful data related to intrinsic strength of wheat varieties. Assessment of CSP loaf volume data for Canadian variety trials spanning 2003 to 2013 showed very little correlation with dough strength parameters as measured by farinograph and extensigraph. A lean no time (LNT) test baking method was developed that can better discriminate genotypes and provide objective indicators of the effect of intrinsic dough strength on baking quality. From early method development, through method validation and verification using diverse sets of samples targeting different Canadian wheat classes and grown in three different crop years, results showed the LNT method to be more discriminating and easily adopted by other laboratories. In 2015, the LNT method was adopted as the method of choice in future Canadian variety registration trials. The LNT method is fast, simple and well-suited to high throughput test baking conditions encountered in the evaluation of large numbers of breeder lines. A new objective parameter, loaf top ratio, was also introduced and found to correlate well with dough strength and dough handling properties.  相似文献   
110.
A 2‐year whole‐farm system study compared the accumulation, utilization and nutritive value of grass in spring‐calving grass‐based systems differing in stocking rate (SR) and calving date (CD). Six treatments (systems) were compared over two complete grazing seasons. Stocking rates used in the study were low (2·5 cows ha?1), medium (2·9 cows ha?1) and high (3·3 cows ha?1), respectively, and mean CDs were 12 February (early) and 25 February (late). Each system had its own farmlet of eighteen paddocks and one herd that remained on the same farmlet area for the duration of the study. Stocking rate had a small effect on total herbage accumulation (11 860 kg DM ha?1 year?1), but had no effect on total herbage utilization (11 700 kg DM ha?1 year?1). Milk and milk solids (MS; fat + protein) production per ha increased by 2580 and 196 kg ha?1 as SR increased from 2·5 to 3·3 cows ha?1. Milk production per ha and net herbage accumulation and utilization were unaffected by CD. Winter feed production was reduced as SR increased. Increased SR, associated with increased grazing severity, resulted in swards of increased leaf content and nutritive value. The results indicate that, although associated with increased milk production per ha, grazed grass utilization and improved sward nutritive value, the potential benefits of increased SR on Irish dairy farms can only be realized if the average level of herbage production and utilization is increased.  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