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   383篇
  免费   18篇
  国内免费   61篇
林业   19篇
农学   83篇
基础科学   5篇
  27篇
综合类   194篇
农作物   55篇
水产渔业   16篇
畜牧兽医   41篇
园艺   14篇
植物保护   8篇
  2024年   1篇
  2023年   5篇
  2022年   21篇
  2021年   18篇
  2020年   13篇
  2019年   16篇
  2018年   11篇
  2017年   11篇
  2016年   30篇
  2015年   30篇
  2014年   29篇
  2013年   17篇
  2012年   33篇
  2011年   26篇
  2010年   23篇
  2009年   30篇
  2008年   18篇
  2007年   28篇
  2006年   20篇
  2005年   18篇
  2004年   14篇
  2003年   8篇
  2002年   9篇
  2001年   10篇
  2000年   13篇
  1999年   1篇
  1998年   2篇
  1997年   3篇
  1996年   1篇
  1994年   2篇
  1992年   1篇
排序方式: 共有462条查询结果,搜索用时 31 毫秒
1.
Fifty isolates of Crinipellis perniciosa originating from Theobroma cacao , Heteropterys acutifolia and Solanum lycocarpum , from six states within Brazil, were characterized through ERIC-PCR, representing the first application of this method for molecular characterization within C. perniciosa . Phenetic analysis of banding patterns revealed a separation of isolates on the basis of host of origin, with T. cacao -derived isolates showing only a 0·2 similarity level to a cluster comprising the isolates from H. acutifolia and S. lycocarpum . Considerable intraspecific variability was observed within C. perniciosa isolates from T. cacao , with distinct groups observed correlating with geographical origin. Given that a number of isolates from T. cacao from the Amazon region grouped with isolates from Bahia state, this work discusses the possibility that current C. perniciosa populations pathogenic on T. cacao in Bahia originated from the Amazon region, rather than from alternative host plants.  相似文献   
2.
为毕节大方圆珠半夏质量标准的建立提供参考,采用HPLC法对10批不同产地及不同采收时间的圆珠半夏进行了指纹图谱研究。结果表明:测定的10批半夏样品有23个共有峰,共有峰面积为91.6%~95.8%,相对峰面积的RSD为0.12%~0.40%;共有峰的相对保留时间从0.182~1.810min,相对保留时间的RSD在0.02%~0.10%。结论,该方法具有良好的稳定性和重复性,可用于圆珠半夏化学成分分析。  相似文献   
3.
为了研究SCoT分子标记技术对甜菜种质资源鉴定的可行性。利用80条SCoT引物对48份甜菜种质资源进行鉴别,同时对种质资源进行了遗传多样性分析和亲缘关系的鉴定。结果表明,80条SCoT引物中有6条能够扩增出清晰、且多态性高的条带,分别为SCoT1、SCoT12、SCoT13、SCoT14、SCoT17和SCoT23,其中引物SCoT1、SCoT12、SCoT14和SCoT23单独使用均可鉴别全部的48份种质资源,引物SCoT13和SCoT17共同使用可以鉴别48个种质资源;聚类分析结果表明,在遗传距离0.15处,95.8%的种质资源均聚为一类,从分子角度上表明甜菜种质资源遗传距离较小。本研究为利用SCoT分子标记技术鉴别甜菜种质资源、对种质资源进行亲缘关系鉴定、杂交组合亲本选配以及分子标记辅助育种等提供相关科学依据。  相似文献   
4.
Quality control and screening of active substances in traditional Chinese medicines have been performed using fingerprint analysis. The spectrum-effect relationship between chromatography fingerprints and efficacy of herbal drugs is considered as a potentially useful method for determining active ingredients in complex mixtures. The study was designed to develop a method for determining the bioactive components of a compound Chinese medicine called Tiefeng based on spectrum-effect relationships between high-performance liquid chromatography (HPLC) fingerprints and anticoccidial activities. Four peaks of the established HPLC fingerprint indicate the main bioactive components of this medicine. In addition, pharrnacodynamic atlas was defined and used to assess the anticoccidial activity of Tiefeng from different sources for the first time. We found that the level of anticoccidial activity of Tiefeng was consistent with the degree of similarity between the pharmacodynamic atlas and chromatogram of any sample. Furthermore, effect of this medicine was related with the main active constituents, along with the origin and the harvesting time.  相似文献   
5.
In the Gilgel Gibe catchment in Ethiopia, local farmers intensify land use on Planosols by adjusting a traditional soil burning practice known as guie. The burning practice used to be applied in a cycle of shifting cultivation. However, more recently, farmers burn small plots to make fertile seedbeds for Eucalyptus seedlings in the first year before these trees are transplanted to larger plots. The purpose of this research was to assess the physico‐chemical properties of Planosols that have been subjected to burning over the last 10 yrs and evaluate the contribution of guie to land‐use intensification of these soils. Transect studies and interviews of local farmers, followed by chemical, physical and micromorphological analyses of samples from selected plots were used to compare the soil properties of recently (0–2 yrs) and formerly (3–10 yrs) burnt Planosols with those of unburnt Planosols. The analytical results show that the burning practice improved nutrient availability in the first 2 yrs after guie. Increased amounts of exchangeable aluminium (Al) were reported in the long term. Charge fingerprints illustrate that the nutrient‐buffering capacity of the soil was high shortly after the practice but subsequently decreased with time. Given the population pressure on the formerly extensively used Planosols, it is argued that the current application of guie on small, localized plots for raising Eucalyptus seedlings is well adapted to the local socio‐economic context and promotes land‐use intensification on the Planosols. The increased exchangeable Al content of former Eucalyptus seedbeds merits further in‐depth research into the biophysical sustainability of the burning practice.  相似文献   
6.
Twelve types of gingko flavonoids were separated with SDS/n -C4 HgOH/n- C7 Hls/H2O microernlusion as developer on polyamide film. The polarity of the microemulsion was regulated through adding or reducing water. Compared with general mobile phase, the sensitivity of detection was improved markedly and the test results were satisfied. By means of HPTLC, fingerprint was argued on gingko flavonoids. It can meet the needs of simple and convenient, reasonable standard quality control methods.  相似文献   
7.
Fingerprint classification can provide an important indexing mechanism in a fingerprint database. An accurate and consistent classification can greatly reduce fingerprint matching time for large database. In the paper, by combining genetic algorithm and neural network is presented a fingerprint classification algorithm which is able to achieve an accurate classification. By inputting the global feature represented by directional image to three layer neural network trained by genetic algorithm, the fingerprints were classified into six categories: whorl, right loop, left loop, arch, double loop and undiscerning type successfully.  相似文献   
8.
玉米品种DNA指纹数据库构建的标准化规范   总被引:7,自引:0,他引:7  
为了保证玉米品种DNA指纹库构建的标准化,从建库标记、检测平台、试剂、样品、评估程序、数据整合、模式库、扩展库、随机盲测等九个方面进行了全面的规范:(1)通过对不同分子标记的比较,确定SSR标记作为建库标记;(2)通过对不同DNA指纹检测方法的比较,确定毛细管电泳结合多色荧光检测方法作为DNA指纹片段分析方法;(3)规范了DNA、引物、Taq酶等试剂质量,以保证数据的稳定性和可重复性;(4)规范了样品来源、样品类型及分析样品数量;(5)确定评估品种的数量及引物的取舍标准;(6)为解决不同来源DNA指纹数据的有效整合问题,提出了固定一套核心引物、提供标准品种、提供标准DNA、确定引物等位基因BIN、规定对异常带型数据处理方式、规定数据的编码方式等6个解决策略;(7)规范了构建模式库的材料名单、来源及构建方式;(8)规范了构建扩展库的材料来源及构建方式;(9)进行数据库数据随机盲测,以评估入库数据质量.以上规范将为不同单位合作开展大规模的DNA指纹库构建研究奠定基础.  相似文献   
9.
为筛选适宜贵州省栽培种植的优良品种,以Y10、ZY、Y42、QL、Y43、Y8、Y160、ZF等8个薏苡新材料为试验材料,以‘兴仁小白壳’为对照,采用SSR标记对8个材料间的亲缘关系进行了鉴定,随机区组设计进行品种比较试验。结果表明:将20对组合的SSR引物扩增结果进行聚类,遗传相似系数变化范围为0.467~0.922,供试材料间存在差异,说明这9个参试材料间各不相同;2015—2016年品种比较试验结果表明,Y10、ZY、Y42、QL、Y160与对照的产量比较均达到极显著水平,Y10 2年产量均最高,说明筛选出的Y10、ZY、Y42、QL、Y160薏苡新材料具有显著的优势,为薏苡新品种选育提供参考。  相似文献   
10.
作物DNA指纹库构建后,如何有效应用是亟待解决的问题.本研究首先设定品种间某(些)分子标记位点遗传距离大于零者为某(些)分子标记可鉴别的品种,分析DNA分子标记鉴别品种的能力;在此基础上,设定品种间某(些)分子标记位点最小遗传距离大者为优,筛选出鉴定参试品种所需的最少标记数.然后利用聚美分析,从20个SSR标记构建的48个玉米杂交种的指纹库中,可以筛选出鉴别能力最强的标记和鉴据别效果最优的标记组合.结果表明,该方法直观、易行、快速、高效,可为指纹图谱库的高效应用提供参考.  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