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   313篇
  免费   24篇
  国内免费   21篇
林业   7篇
农学   38篇
基础科学   4篇
  65篇
综合类   87篇
农作物   17篇
水产渔业   2篇
畜牧兽医   55篇
园艺   45篇
植物保护   38篇
  2024年   4篇
  2023年   8篇
  2022年   14篇
  2021年   20篇
  2020年   18篇
  2019年   15篇
  2018年   6篇
  2017年   12篇
  2016年   14篇
  2015年   15篇
  2014年   20篇
  2013年   28篇
  2012年   37篇
  2011年   44篇
  2010年   17篇
  2009年   29篇
  2008年   6篇
  2007年   21篇
  2006年   18篇
  2005年   8篇
  2004年   4篇
排序方式: 共有358条查询结果,搜索用时 375 毫秒
1.
CALIS联合编目中410字段及其相关字段的正确著录   总被引:1,自引:1,他引:0  
用大量的例子对CALIS联合编目数据410字段度其相关字段的正确使用进行了说明.并概括归纳出使用这些字段的一些规律和方法。  相似文献   
2.
几种牧草对河西走廊盐渍化土壤改土培肥的效应研究   总被引:13,自引:2,他引:13  
在河西走廊盐渍化土地上种植老芒麦、扁穗冰草、碱茅和紫花苜蓿4种优质牧草,对盐渍化程度均有一定的改良效果.其中碱茅对盐渍化土壤的改土培肥效果最好,建植3年后的碱茅,与对照比较,0~20 cm土层中自然含水量增加125.99 g/kg,总孔度增加16.14%,容重降低0.27 g/cm3,pH值由8.43降到8.10,全盐含量降低52.90 g/kg,脱盐率达到76.12%,有机质增加3.67 g/kg,碱解氮含量增加18.63 mg/kg,速效磷和钾亦随之增加.  相似文献   
3.
利用生态足迹和生态承载力的理论和方法,以西北干旱绿洲农业区城市张掖为例,对其可持续发展状况及程度进行了评价和度量。结果表明:张掖市2009年人均生态足迹为3.798hm2,人均承载力为1.453hm2,人均生态赤字为2.345hm2。在此基础上,对张掖市的生态可持续发展进行了评价,并提出解决对策。  相似文献   
4.
甜叶菊栽培研究进展   总被引:1,自引:0,他引:1  
通过对品种、茬口、栽培措施及光照要求等方面的研究文献进行综述,归纳了目前甜叶菊栽培方面的研究动态和存在的问题,为今后甜叶菊的栽培研究提供参考。  相似文献   
5.
为了探究天仙子(Hyoscyamus niger L.)对禾本科牧草的化感作用,以天仙子和黑麦草(Lolium perenne L.)为材料,通过5个不同浓度天仙子种子浸提液(0,0.025,0.05,0.075,0.1 g·mL-1),对黑麦草种子萌发和幼苗生长进行处理,测定黑麦草种子萌发和幼苗生长情况。结果表明:不同浓度的天仙子种子浸提液对黑麦草种子萌发有极显著影响(P<0.01),随浸提液浓度增加,黑麦草萌发率和发芽指数显著降低(P<0.05);浸提液对黑麦草根长和地上、地下生物量有显著的影响(P<0.05),对株高影响不显著;不同浓度的天仙子种子浸提液处理下,黑麦草幼苗丙二醛、脯氨酸含量、相对电导率均随浸提液浓度的增加而增加,叶片中叶绿素含量则随浸提液浓度的增大而减小。综上所述,天仙子种子浸提液对黑麦草幼苗细胞膜具有一定的损伤作用,黑麦草植株通过细胞膜的变化而影响内部生理生化过程,以适应不利的环境。  相似文献   
6.
研究沼液作追肥对制种玉米产量及土壤化学性质的影响。文章以制种玉米为试验材料,采用计随机区组试验设,研究沼液追肥对制种玉米经济性状、产量、土壤化学性质、经济效益的影响。结果表明,T1(沼液1500kg·hm-2+142.50 kg N·hm-2)有机质含量最高,与其他处理间达到了显著差异;T1的土壤速效钾含量最高,达12.67 g·kg-1,与CK(150 kg N·hm-2),T2(沼液22500 kg·hm-2+138.75 kg N·hm-2)间达到了显著差异;土壤速效磷含量,土壤p H值,土壤电导率差异不显著;不同处理对穗行数,行粒数、穗粒重的影响差异不显著,T3(沼液30000 kg·hm-2+135 kg N·hm-2)千粒重最高,与CK,T2,T4(沼液37500 kg·hm-2+131.25 kg N·hm-2)间差异达到了显著水平;T2的产量,产值,经济效益最高。沼液做追肥可提高产量,降低生产成本,但必须和化肥配合施用。  相似文献   
7.
While there is strong evidence supporting retinal vascular pattern as a distinctive marker for sheep, it would be advantageous to get an insight into its robustness; in other words, to determine whether retinal recognition of young animals (lambs) can reach as good a matching performance as the one demonstrated for adult sheep. To this aim, a longitudinal study was devised to observe the evolution of matching scores (ms) of lamb retinal images (n = 38) acquired from 1 to 22 weeks after birth. It was observed that four lamb retinas (out of 38) underwent slight curving of one or two secondary arteries, which ceased by the time they were 6–8 weeks old. However, this slight artery curving did not affect matching performance. A random effects statistical model demonstrated that lamb age had an effect (P < 0.01) on the matching scores produced using this commercially available retinal recognition system. As lambs grew older (larger eyes) and they became easier to handle, retinal images of progressively better quality could be obtained in a more consistent way; and thus matching scores increased from an average of 86 at the first week of life, up to an average of 96 by week 8. Dunnett simultaneous tests of means indicated that no further improvement in matching score took place once lambs were at least 6–8 weeks old, meaning that the retinal image quality became by then optimal and consistent. Although the variable retinal image quality of younger lambs (1–4 weeks old) caused a reduction in matching score, they did not lead to false non-matches in any case (considering a cut-off matching score of 70 for acceptance of a positive match). Therefore, the results of these trials have shown that, with the available technology, retinal images can be used as a robust biometric marker of lambs from 1 week of age.  相似文献   
8.
Ethylene biosynthesis in kiwifruit, Actinidia chinensis ‘Sanuki Gold’ was characterized using propylene, an ethylene analog, and 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception. In fruit harvested between a young stage (66 days after pollination) (DAP) and an early commercial harvesting stage (143 DAP), 2 days of exposure to propylene were sufficient to initiate ethylene biosynthesis while in fruit harvested at commercial harvesting stage (154 DAP), 4 days of propylene treatment were required. This observation suggests that response of ethylene biosynthesis to propylene treatment in kiwifruit declined with fruit maturity. Propylene treatment resulted in up-regulated expression of AC-ACO1, AC-ACO2, AC-SAM1 and AC-SAM2, prior to the induction of AC-ACS1 and ethylene production, confirming that AC-ACS1 is the rate limiting step in ethylene biosynthesis in kiwifruit. Treatment of fruit with more than 5 μL L?1 of 1-MCP after the induction of ethylene production subsequently suppressed ethylene production and expression of ethylene biosynthesis genes. Treatment of fruit with 1-MCP at harvest followed with propylene treatment delayed the induction of ethylene production and AC-ACS1 expression for 5 days. These observations suggest that in ripening kiwifruit, ethylene biosynthesis is regulated by positive feedback mechanism and that 1-MCP treatment at harvest effectively delays ethylene production by 5 days.  相似文献   
9.
采用自编《大学生婚前同居观念调查问卷》,对328名在校大学生进行了抽样调查。结果显示:大学生对婚前同居现象的态度更加开放和宽容,但实际的婚前同居行为则比较理性和谨慎;男生比女生更愿意接受婚前同居行为;农村大学生比城市大学生更赞同婚前同居现象;赞同婚前同居的比率随年级的增高呈上升趋势,大四学生的赞同率最高;"试婚"和同伴影响是大学生选择或认同婚前同居的主要原因。  相似文献   
10.
立足河西学院人才与资源优势,从实际出发阐述了建立学校文库的意义和作用,并提出了建立文库的几点建议和措施。  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