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   2517篇
  免费   138篇
  国内免费   218篇
林业   93篇
农学   848篇
  193篇
综合类   730篇
农作物   261篇
水产渔业   113篇
畜牧兽医   310篇
园艺   213篇
植物保护   112篇
  2024年   2篇
  2023年   21篇
  2022年   42篇
  2021年   66篇
  2020年   73篇
  2019年   77篇
  2018年   59篇
  2017年   81篇
  2016年   101篇
  2015年   112篇
  2014年   148篇
  2013年   121篇
  2012年   153篇
  2011年   214篇
  2010年   222篇
  2009年   220篇
  2008年   174篇
  2007年   155篇
  2006年   152篇
  2005年   123篇
  2004年   97篇
  2003年   85篇
  2002年   60篇
  2001年   66篇
  2000年   49篇
  1999年   42篇
  1998年   32篇
  1997年   19篇
  1996年   26篇
  1995年   21篇
  1994年   9篇
  1993年   6篇
  1992年   14篇
  1991年   8篇
  1990年   4篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1986年   1篇
  1984年   1篇
  1980年   1篇
  1963年   1篇
  1962年   1篇
  1955年   2篇
排序方式: 共有2873条查询结果,搜索用时 19 毫秒
41.
In this study, the cross‐amplification of a commercial multiplex set of 11 cattle (Bos taurus) microsatellites was tested on a panel of 35 European bison (Bison bonasus) individuals. After polymerase chain reaction optimization, all loci cross‐amplified successfully in investigated bisons. Number of alleles and observed and expected heterozygosity per locus are in the range of 2–4, 0.086–0.629 and 0.288–0.621 respectively. The availability of a heterologous set of multiplexed microsatellite markers derived from cattle opens an avenue for collecting profound genetic data for efficient conservation management strategies of the European bison.  相似文献   
42.
桃果肉颜色、果皮茸毛和花粉育性性状的分子标记   总被引:18,自引:2,他引:18  
 以91-42-51 ×瑞光2号的杂交后代共48个单株为试材, 采用集群分离分析法(BSA) , 对桃果实的有毛/无毛、白肉/黄肉以及无花粉/有花粉3 个性状进行了分子标记研究。研究获得SSR 标记UDP96-018 (300 bp) 与有毛性状连锁, 遗传距离4.5 cM, SSR标记UDP98-407 (680 bp) 与白肉性状连锁, 遗传距离为2.2 cM; 根据拟南芥雄性不育序列标记设计的引物扩增出的两个片段NNJ-I (600 bp ) 和NNJ-I (900 bp) 与桃无花粉性状之间的遗传距离为0 cM。这些标记的获得为桃分子标记辅助育种提供了有效的筛选手段。  相似文献   
43.
This research was conducted to assess polymorphism among local genotypes of common fig available in Jordan (one of countries of origin). Leaf samples were collected in spring for DNA isolation from 20 different local genotypes (5 cultivars and 15 landraces). Two more wild types and one foreign cultivar were included. The genotypes were assessed using the randomly amplified polymorphic DNA (RAPD) technique. Six of the 19 screened primers showed reproducible polymeric profiles. Out of 62 amplified bands, 48 were polymorphic (77%). They generated 1104 data entries (591 for present and 513 for absent bands). After determining Jaccard similarity index, some genotypes showed high genetic similarity (90% between F20 and F22), while other were less similar (3–18% between F11 and all other genotypes). Moreover, the primers were evaluated for their discriminating power, where primer RAPD06 showed the weakest power (0.431), while highest values of 0.989 and 0.996 were achieved for primers RAPD02 and RAPD13, respectively.  相似文献   
44.
选用鹌鹑上的12个微卫星位点,对随机选取朝鲜鹌鹑的40个个体进行多态性检测,共检测到55个等位基因,每个座位平均等位基因数为4.583个。该群体平均多态信息含量和平均杂合度分别为0.6945和0.7111,表明朝鲜鹌鹑属多态性较丰富的群体。  相似文献   
45.
To study the genetic variation in Iranian olive collections and some foreign olive cultivars, 47 accessions of 18 local cultivars from 6 olive collections of Iran (Roudbar, Zanjan, Ahvaz, Dezful, Kazeroon and Shiraz), were analyzed along with 30 imported cultivars using 16 microsatellite primer pairs. All the used microsatellite loci revealed polymorphism in the studied genotypes, except GAPU14 and GAPU113 markers. Fourteen microsatellite primers amplified 126 polymorphic alleles in the 87 selected olive accessions. The average number of alleles per locus was 9, ranging from 3 to 14. Polymorphic information content (PIC) was 0.85. The genetic similarity based on Jaccard coefficient ranged from 0.15 to 1. The genetic relationships among accessions were investigated using cluster analysis and principal component analysis (PCA). Most of the accessions with the same name were grouped together; some exceptions were also observed. As expected, close relationship was observed among accessions within same cultivar. Most of the Iranian olive accessions were clustered to a main distinct group. Two-dimensional scatter plot of principal component analysis revealed a clear separation of most of the Iranian olives from Syrian and other introduced cultivars. These suggest that Iranian cultivars have different origin related to West Mediterranean basin cultivars and have evolved independently from the others. Between and within Iranian and foreign cultivars (cultivars including three or more accessions) genetic diversity was analyzed using analysis of molecular variance (AMOVA). AMOVA revealed higher within cultivar genetic variation (62.76%) as compare to that between cultivar variations (37.24%). The intra- and inter-cultivar variance tested by permutation test showed significant genetic variation at both levels. The high level within cultivar genetic variance could be due to mislabeling and presence of homonyms in cultivars produced by vegetative propagation from original plants.  相似文献   
46.
RAPDs and SSRs were used to study the genetic diversity of Iranian almond cultivars and their relationship to important foreign cultivars and three related species. Eight unidentified almond Shahrodi cultivars and three wild almonds (Prunus communis, Prunus orientalis and Prunus scoparia) were also included. Of the primers tested, 42 (out of 80) RAPD and 18 (out of 26) SSR primers were selected for their reproducibility and high polymorphism. A total of 664 polymorphic RAPD bands were detected out of 729 bands. The number of presumed alleles revealed by the SSR analysis ranged from 3 to 10 alleles per locus with a mean value of 6.64 alleles per locus. Both techniques discriminated the genotypes very effectively, but only RAPDs were able to discriminate the cultivars Monagha and Sefied. Results demonstrated an extensive genetic variability within the tested cultivars as well as the value of SSR markers developed in peach for characterization of almond and related species of Prunus. Dice similarity coefficient was calculated for all pair wise comparisons and was used to construct a UPGMA dendrogram. For both markers a high similarity in dendrogram topologies was obtained although some differences were observed. All dendrograms, including that obtained by the combined use of both the marker data, depicted the phenetic relationships among the cultivars and species, depending upon their geographic region and/or pedigree information. Almond cultivars clustered with accession of P. communis showing their close relationship. P. orientalis and P. scoparia were clustered out of the rest of P. dulcis.  相似文献   
47.
Some species of the genusOrobanche are among the most devastating parasitic weeds, causing extensive damage in agricultural fields. Considering the difficult control due to seed longevity in the soil, small seed size, high fecundity and a subterranean phase that allows them to parasitize the host before they emerge and become evident, the development of diagnostic markers is highly recommended. In our study we identified potential molecular diagnostic markers from the plastid genome in order to distinguish among the most importantOrobanche species attacking crops in Andalusia, the southern region of the Iberian Peninsula. The study has consideredO. crenata, O ramosa andO. cumana causing serious losses in legumes, solanaceous crops and sunflower fields, respectively, andO. minor that, although abundant in Andalusia, has to our knowledge not yet been found parasitizing agricultural hosts. We amplified a non-coding region from the plastid genome, studied sequence differences among the amplified fragments and digested those of the same length with selected restriction enzymes. Here, we propose a molecular protocol to distinguish the main parasitic plants in crop fields of southern Spain. Different applications such as identification ofOrobanche seeds in soil or crop seed lots are discussed in order to offer right crop recommendations or to prevent new infestation of parasite-free fields. Recommendations for further development of these diagnostic markers are also considered. http://www.phytoparasitica.org posting Jan. 15, 2007.  相似文献   
48.
利用SRAP标记分析文心兰部分种质资源的遗传多样性,采用30对引物组合对33份文心兰种质进行扩增,从中筛选出19个多态性较高的引物组合,共产生277条多态性条带,平均每个引物组合产生14.6个多态性条带,相似系数在0.280~0.927。通过聚类分析发现,在值为0.37时,可将33份文心兰种质划分为4大类群。第Ⅰ类厚叶大花品种,第Ⅱ类为厚叶小花品种,第Ⅲ、第Ⅳ类均为类薄叶品种。 结果表明,文心兰种质的聚类与其遗传背景有很大的关系。  相似文献   
49.
The study was undertaken to assess the genetic effect of quantitative trait loci (QTLs) conferring heat tolerance at flowering stage in rice. A population consisting of 279 F2 individuals from the cross between 996, a heat tolerant cultivar and 4628, a heat-sensitive cultivar, was analyzed for their segregation pattern of the difference of seed set rate under optimal temperature condition and high temperature condition. The difference of seed set rate under optimal temperature condition and high temperature condition showed normal distribution, indicating the polygenic control over the trait. To identify main effect of QTL for heat tolerance, the parents were surveyed with 200 primer pairs of simple sequence repeats (SSR). The parental survey revealed 30% polymorphism between parents. In order to detect the main QTL association with heat tolerance, a strategy of combining the DNA pooling from selected segregants and genotyping was adopted. The association of putative markers identified based on DNA pooling from selected segregants was established by single marker analysis (SMA). The results of SMA revealed that SSR markers, RM3735 on chromosome 4 and RM3586 on chromosome 3 showed significant association with heat tolerance respectively, accounted for 17 and 3% of the total variation respectively. The heat tolerance during flowering stage in rice was controlled by multiple gene. The SSR markers, RM3735 on chromosome 4 and RM3586 on chromosome 3 showed significant association with heat tolerance respectively, accounted for 17 and 3% of the total variation respectively. The two genetic loci, especially for RM3735 on chromosome 4, can be used in marker-assistant-selected method in heat tolerance breeding in rice.  相似文献   
50.
ISSR和SRAP标记技术在葫芦科植物种质资源研究中的应用   总被引:1,自引:0,他引:1  
蹇黎 《长江蔬菜》2012,(2):13-16
阐述了简单重复序列间扩增(ISSR)和相关序列扩增多态性(SRAP)分子标记技术的基本原理和特点,综述与探讨了分子标记技术在葫芦科植物种质资源的亲缘关系鉴定与遗传多样性分析、分子遗传图谱的构建与目的性状基因的标记定位、基因库的构建和基因克隆、辅助育种选择及品种纯度鉴定等研究领域的广泛利用与推广,以期更合理高效地保护和利用葫芦科植物种质资源。  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