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   13966篇
  免费   671篇
  国内免费   665篇
林业   2044篇
农学   1048篇
基础科学   479篇
  1473篇
综合类   5024篇
农作物   956篇
水产渔业   380篇
畜牧兽医   1580篇
园艺   1224篇
植物保护   1094篇
  2024年   110篇
  2023年   378篇
  2022年   507篇
  2021年   516篇
  2020年   490篇
  2019年   625篇
  2018年   384篇
  2017年   484篇
  2016年   498篇
  2015年   514篇
  2014年   589篇
  2013年   850篇
  2012年   897篇
  2011年   805篇
  2010年   592篇
  2009年   772篇
  2008年   574篇
  2007年   562篇
  2006年   491篇
  2005年   454篇
  2004年   515篇
  2003年   389篇
  2002年   403篇
  2001年   319篇
  2000年   389篇
  1999年   251篇
  1998年   206篇
  1997年   188篇
  1996年   310篇
  1995年   211篇
  1994年   185篇
  1993年   142篇
  1992年   136篇
  1991年   111篇
  1990年   95篇
  1989年   60篇
  1988年   72篇
  1987年   28篇
  1986年   25篇
  1985年   28篇
  1984年   22篇
  1983年   24篇
  1982年   16篇
  1981年   18篇
  1980年   18篇
  1979年   30篇
  1978年   15篇
  1975年   1篇
  1956年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 471 毫秒
71.
利用废弃的食用油油壶制成棉铃虫诱捕器,可提高诱蛾的效果。挡板距诱捕器器口的距离以3cm的效果最佳。与常规水钵、水盆诱捕器相比较,全年诱蛾总量分别增加116.3%和减少79.8%,但诱蛾灵敏度均高出18.72%。  相似文献   
72.
Based on current agroecological theory and IPM practices, this review explores the role of traditional practices, involving site selection, soil management, timing of planting and harvesting, crop resistance, intercropping, weed management, harvest residue management, post-harvest management, natural enemies management, mechanical control, repellents and traps in the natural regulation of potential pests. In synthesis, the literature suggests that although pest management professionals focus their efforts on pest control, the preventative approach taken by traditional farmers is more effective. Potential constraints to the implementation of this preventive pest management approach include:(1) lack of integration of ecological theory and pest management, (2) lack of cooperation among social and biological scientists, and (3) lack of real efforts to work with farmers as equals and support mechanisms that protect their knowledge. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
73.
辣椒疫病发病主导因素及综合防治技术研究   总被引:2,自引:0,他引:2  
通过3a在多年辣椒重茬地的田间试验及调查研究,基本明确了辣椒疫病发生与灌水方法、栽培方式、降水、中心病株的出现等主导因素的关系。提出了栽培防病、化学治疗的综防技术,达到控病增产的目的。  相似文献   
74.
笋用竹害虫天敌资源研究   总被引:1,自引:0,他引:1  
本文报道了浙江省笋用竹害虫天敌资源调查的结果,共查明天敌资源44种,经鉴定属于螳螂目1科2种,半翅目1科2种,蛇蛉目1科1种,脉翅目1科2种,鞘翅目2科9种,双翅目2科2种,膜翅目9科22种;蛛形纲蜱螨目1科1种,蜘蛛目3科3种,指出了天敌的寄主和分布。  相似文献   
75.
本文采用5%OV-17为色谱柱固定相,以邻苯二甲酸二正戊酯为内标物,用FID检测器对2%甲嘧磷 马粉剂进行定量分析,甲基嘧啶磷、马拉硫磷的标准偏差分别为0.027、0.011,变异系数分别为2.40%、0.99%; 甲基嘧啶磷回收率为99.5%-100.3%,马拉硫磷的回收率为98.9%~99.8%o该方法方便、快捷、准确。  相似文献   
76.
Weed:spring barley competition for applied nitrogen in pig slurry   总被引:2,自引:0,他引:2  
Summary The experiments were carried out in the two spring barley fields of the organic six-course cattle:crop rotation at Foulumgaard, Denmark. The weed density was 300 and 1800 plants m−2 respectively. Pig slurry was applied by hand in microplots by four methods: broadcasting followed by incorporation, or injected in bands to depths of 5, 10 or 15 cm. Spring barley and weeds were sampled separately six times during the tillering and elongation phase of the spring barley. The effect of application method on dry-matter (d.m.) production, nitrogen uptake and recovery of applied nitrogen in the spring barley and the weeds is reported. Slurry banding halved the weed d.m. and weed N uptake compared with broadcasting, irrespective of weed density. Weeds recovered up to 12% of the applied nitrogen, which made them a significant competitor when the slurry was broadcast and incorporated. Banding by direct injection reduced the slurry:soil contact and the weed:crop competition balance for applied nitrogen moved in favour of the crop. Thus, the crop recovery of applied nitrogen at the end of the sampling period was increased from approximately 45% for broadcast and incorporated to approximately 50% for injected slurry, and coincidental weed recovery was reduced to a maximum of 5%. As the nitrogen supply normally affects plant d.m. production, banding of slurry might well improve crop competitiveness and its tolerance to mechanical weed control.  相似文献   
77.
有效碳数法研究及其在农药气相色谱分析中的应用   总被引:2,自引:0,他引:2  
有机化合物结构与其所含有的有效碳数有一定的关系,本文给出了20类结构化合物及其所含有有效碳数的关系,并对理论计算值和实测值进行了比较,结果十分接近,利用有效碳数法可以设计农药分析实验方案和无标样的情况下测定农药杂质含量。  相似文献   
78.
通过在21日龄的肉用仔鸡饲料中添加丝兰属植物提取物(其有效成分为丝兰皂角苷),研究丝兰属植物提取物对降低鸡舍中氨气浓度和提高肉仔鸡生产性能的效果。试验结果表明,试验组鸡舍内氨气平均浓度为4.75mg/L,对照组鸡舍内氨气平均浓度为13.80mgl/L,试验组比对照组鸡舍内氨气平均浓度降低了9.05mg/L,经t检验,两鸡舍内氨气平均浓度差异显著(P<0.05),并且试验组比对照组饲料报酬提高了8.92%。  相似文献   
79.
Leaf explants of Caladium ‘Pink Cloud’ were cultured in vitro on MS medium containing various auxins (NAA, IBA, IAA, 2,4,5-T and 2,4-D) in combination with cytokinin (BA). NAA gave the most vigorous in vitro propagation of this plant, and only 15% of the plants were leaf-colour variants on the medium containing 0.5 μmol NAA. Leaf colour variation was observed in all plants regenerated on the medium containing 2,4-D at 0.5–4.5 μmol. In hormone-free medium, only a few leaf-colour variants (6%) occurred, but the rate of plant regeneration was very low. Application of 0.5 μmol NAA together with 4.5 μmol BA seemed to be the most appropriate for in vitro propagation of Caladium ‘Pink Cloud’ with only a few leaf-colour variants.  相似文献   
80.
In order to optimise production of the edible flower buds produced by myoga (Zingiber mioga Roscoe) a greater understanding of the growth and development of the plant and factors influencing flower initiation and development are required. The vegetative growth phase in myoga was characterised by a distinct period of pseudostem development from the planted rhizome piece followed by an extended period of rhizome growth from both the base of pseudostems and the planted rhizome piece. The transition from pseudostem formation to the initiation of rhizome growth occurred at the same time as the dry weight of the planted rhizome piece ceased to decline. Flower bud initiation and development occurred over an extended period, beginning soon after the commencement of new rhizome growth and ending prior to foliage senescence. Flower buds were observed at the terminal meristem of first, second, third and fourth order rhizomes. Increasing temperatures stimulated both increased vegetative growth and flower bud initiation and development. Low flower bud yields recorded under conditions of low temperature were the result of reduced rate of floral initiation and not abortion of flower buds. Increased shading of plants grown under glasshouse conditions resulted in reduced flower bud yield and similarly the response resulted from decreased initiation rather than abortion.  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