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   545篇
  免费   75篇
  国内免费   60篇
林业   87篇
农学   115篇
基础科学   15篇
  38篇
综合类   194篇
农作物   50篇
水产渔业   47篇
畜牧兽医   63篇
园艺   29篇
植物保护   42篇
  2024年   6篇
  2023年   16篇
  2022年   41篇
  2021年   40篇
  2020年   39篇
  2019年   44篇
  2018年   28篇
  2017年   40篇
  2016年   40篇
  2015年   31篇
  2014年   33篇
  2013年   28篇
  2012年   41篇
  2011年   39篇
  2010年   17篇
  2009年   21篇
  2008年   24篇
  2007年   17篇
  2006年   10篇
  2005年   6篇
  2004年   11篇
  2003年   10篇
  2002年   7篇
  2001年   6篇
  2000年   3篇
  1999年   5篇
  1998年   3篇
  1997年   4篇
  1996年   8篇
  1995年   2篇
  1994年   4篇
  1993年   7篇
  1992年   8篇
  1991年   5篇
  1990年   4篇
  1989年   7篇
  1988年   3篇
  1987年   1篇
  1986年   5篇
  1985年   2篇
  1984年   3篇
  1982年   3篇
  1981年   2篇
  1980年   1篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
排序方式: 共有680条查询结果,搜索用时 15 毫秒
71.
辣椒若干性状的相关及通径分析   总被引:5,自引:0,他引:5       下载免费PDF全文
对辣椒的13个杂种一代及其16个亲本的总产量等16个性状进行分析,结果表明,辣椒的总产量与早期产量及果实胎座宽度呈显著正相关,与干物质含量呈显著负相关;单果重与胎座宽度及果肉厚度呈显著正相关,与单株果数呈显著负相关。株高与播种至花期天数,始花节位与播种至花期天数及维生素C含量与果实长度之间也呈显著正相关;单株果数对总产量的直接影响最大,果实胎座宽度及早期产量也对总产量有明显的直接影响,而其它性状则仅对总产量产生有限的直接影响。  相似文献   
72.
本文用多变量相关分析和通径分析方法,对豫州褐壳蛋鸡5个品系产蛋性能方面的性状进行相关分析,结果表明,将开产日龄,40周龄平均蛋重和40周龄产蛋数,作为蛋鸡早期选种指标是适宜的。  相似文献   
73.
为了解贵州小果油茶的自然变异情况,以贵州黎平和榕江的5个居群30个小果油茶优良单株为研究对象,测定并分析果高、果形、高径比、果皮厚度、单个果重、单果中籽粒数、籽粒重和出籽率等8个种实性状,采用多重比较、变异系数、相关性分析、聚类分析和Shannon-Weiner多样性指数等方法,分析小果油茶种实性状的多样性及群体间和群体内的变异特征与变异规律。结果表明:小果油茶不同种实性状的多样性指数为1.014~2.242,种实性状多样性高,在群体间和群体内均存在丰富的变异;经相关分析,小果油茶的果皮厚度与出籽率呈极显著负相关,果高与果径、果形指数、果皮厚度和单果籽粒数呈极显著正相关;表型性状聚类结果与居群分布一致。  相似文献   
74.
石灰岩地区土壤水分对木豆表型可塑性的影响   总被引:6,自引:0,他引:6  
研究了土壤相对含水量分别为27.65%,19.47%,12.14%和7.66%水分条件下木豆(Cajannus cajan)幼苗生长和形态的表型可塑性。结果表明:木豆幼苗的根、叶、茎生物量以及株高、冠幅直径都在土壤相对含水量为12.14%的条件下最高;随着土壤含水量的增加,分配到枝和根的生物量随之增加,分配到叶的生物量减少;当土壤相对含水量从7.66%升到12.14%时,须根数目增加,土壤相对含水量再提高时,情况则相反。这些结果说明木豆幼苗的适宜水分生态位是较干旱的土壤环境,木豆幼苗通过器官生物量分配和形态结构调整来适应干旱胁迫。  相似文献   
75.
The effects of modified heavy metal (HM) availability on the microbial community structure and on the microbe-mediated degradation of herbicide isoproturon (IPU) were evaluated in soil with a long-term HM contamination. The fate of 14C-ring labelled IPU was investigated for over 60 days under controlled microcosm conditions. Phosphate mineral apatite and a water solution of Pb, Zn, and Cd salts were previously homogeneously mixed into the soil material to reduce and to increase the proportion of bioavailable HM, respectively. The availability of Pb, Zn, and Cd was determined by HM fractionation and plant uptake 110 days after the addition of amendments, shortly before IPU addition. Apatite treatment reduced the availability of HM, but did not affect the microbial biomass and the microbial community structure on the genotype level (total soil DNA-RAPD). However, it changed the microbial community structure on the phenotype level, based on the composition of phospholipid fatty acids (PLFA) at the end of the degradation experiment. The degradation of IPU did not change. In contrast to apatite treatment, HM supplementation increased the bioavailability of Pb, Zn and Cd, which resulted in biomass reduction and changes of microbial community structure on the genotypic (total soil DNA-RAPD) and phenotypic (PLFA) level. Increased bioavailability of HM also significantly reduced the rate of IPU degradation and mineralisation. The total mineralisation over a period of 60 days decreased from 12 to 5% of initial 14C. Increased HM bioavailability did not influence the degradation pathways and kinetics of IPU.  相似文献   
76.
测定了60-75日龄杜洛克×施格杂交1代仔猪9项血液化学性状,估测了血液性状间及其性状与日增重的表型相关。并在此基础上进行通径分析。结果表明:血清Se,Cu,AKP含量与日增重呈显著相关(相关系数分别为0.4757~(**),0.4125~(**),-0.3698~*);AKP,Se,Cu,GSH-PX的含量与日增重通径系数分别为-0.8416,0.5006,0.4904,0.4099,均达显著水平。因而,AKP,Se,Cu,GSH-PX可作为影响瘦肉型生长肥育猪的相对重要性状。  相似文献   
77.
V MAHELKA 《Weed Research》2006,46(1):82-90
Response to flooding intensity in three closely related taxa, Elytrigia repens, E. intermedia and their hybrid was studied. Plants were exposed to three intensities of flooding for a 30‐day period. Response to flooding intensity was estimated by measuring dry mass of the following: total biomass, above‐ground living biomass, above‐ground dead biomass, below‐ground biomass, rhizome and root mass and by the allocation of dry mass into rhizomes and root:shoot ratio. Reduction of nearly all the biomass compartments with increasing flooding intensity was observed in the three taxa. All three taxa can thus be regarded as flood‐intolerant. Based on the parameters measured, E. repens is regarded as the relatively most flooding‐tolerant, E. intermedia as the least tolerant, while the hybrid displayed intermediate flooding tolerance. The higher flooding tolerance in E. repens was likely related to its ability to accumulate a sufficient mass of rhizomes before flooding, due to higher regeneration ability. E. repens also displayed the highest phenotypic plasticity, as deduced from the reaction norms constructed for total biomass and rhizome mass of particular clones of the three taxa studied. This indicates that, on the species level, E. repens is better adapted to changing environmental conditions and it can be expected to colonize flooded soils. Both Elytrigia species also occur as weeds: E. intermedia grows in agricultural environments in warm regions, while E. repens infests many different types of habitats. Where they co‐occur, hybridization between them may lead to the enrichment of their gene pools with genes responsible for survival of the parental species under extreme conditions; their weedy potential may thus be enhanced.  相似文献   
78.
The consumption of products made from Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.) has increased in recent years in Japan. Increased consumer demand has led to recognition of the need for early varieties of this crop with high and stable yields. In order to accomplish this, more information is needed on the genetic mechanisms affecting earliness and yield. We conducted genetic analysis of 3 agronomic traits (days to flowering, plant height and total seed weight per plant) to segregate F2 and F3 populations derived from a cross between Tartary buckwheat cultivars ‘Hokuriku No. 4’ and ‘Ishisoba’. Broad-sense heritability estimates for days to flowering, plant height and total seed weight were 0.70, 0.62 and 0.75, respectively, in F3 population. Narrow-sense heritability for total seed weight (0.51) was highest, followed by heritability for days to flowering (0.37), with heritability for plant height (0.26) lowest. Later flowering was associated with increased plant height and higher yields. From the F4 generation, we identified twelve candidate plants with earlier maturity and reduced plant height compared to ‘Hokuriku No. 4’, but almost the same total seed weight. These results suggest that hybridization breeding using the single seed descent (SSD) method is an effective approach for improving agronomic characteristics of Tartary buckwheat.  相似文献   
79.
新疆甜瓜地方品种资源的表型遗传多样性   总被引:6,自引:0,他引:6  
 通过分析121份新疆甜瓜地方品种32个形态性状的数据,对其进行遗传多样性和亲缘关系研究。结果表明:121份新疆地方品种在蔓分支数、叶片长度、主蔓粗度、果实质量和果肉厚度等5个表型性状上差异显著;不同地区的地方品种之间在叶片长度、叶柄长度、果肉质地和风味等4个表型性状上差异显著,而在其余性状上差异不显著;121个新疆地方品种表型性状Shannon’s遗传多样性指数达0.74,不同地区地方品种的遗传多样性差异明显,新疆可能与栽培甜瓜的次生起源中心有关。121个地方品种的Euclidean遗传距离的平均值为0.42 ± 0.13,其中‘哈密野瓜’与其它地方品种的亲缘关系最远,遗传距离平均为0.76 ± 0.11。聚类分析结果表明:‘哈密野瓜’被单独聚为一个类群,其可能具有完全不同的遗传背景;其余地方品种被聚为3个类群和7个亚群,不同类群或亚群间的亲缘关系较远,各类群或亚群可能具有相互独立的遗传背景。‘哈密野瓜’属于野生甜瓜亚种Cucumis melo L. ssp. agrestis,其余地方品种属于C. melo L. var. cantalupensis和C. melo L. var. inodorus两个栽培变种。  相似文献   
80.
基于远缘杂交技术路线,以中国沙棘优良单株MK-88-01、HF-88-05为母本,俄罗斯栽培种阿列依及蒙古大果沙棘乌兰格木子代优良雄株为父本,开展了中国沙棘与蒙古沙棘2个亚种间杂交育种研究。结果发现:杂种子代性状分化严重,棘刺数、百果质量、果实产量等最重要的几项经济指标的遗传分化程度最大。选育出3个优良杂种单株,其树高均显著高于父本,2年生枝棘刺数均为3个,与母本中国沙棘相比,棘刺数大量减少。优良杂种单株百果质量与单株产量分别达26.33 29.33 g、2.00 2.50 kg,比母本中国沙棘分别提高31.34%46.30%、66.67%108.33%。杂交子代具有单株生长量越大,其果实与种子表型指标就越小的变化规律,与母本中国沙棘体大果小、父本蒙古沙棘体小果大的表型特征相吻合。  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