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   20261篇
  免费   1175篇
  国内免费   3065篇
林业   461篇
农学   2603篇
基础科学   124篇
  1078篇
综合类   8629篇
农作物   1890篇
水产渔业   1063篇
畜牧兽医   6334篇
园艺   1021篇
植物保护   1298篇
  2024年   91篇
  2023年   357篇
  2022年   751篇
  2021年   924篇
  2020年   946篇
  2019年   1026篇
  2018年   764篇
  2017年   1044篇
  2016年   1266篇
  2015年   1158篇
  2014年   1106篇
  2013年   1088篇
  2012年   1696篇
  2011年   1693篇
  2010年   1310篇
  2009年   1279篇
  2008年   1169篇
  2007年   1337篇
  2006年   1101篇
  2005年   887篇
  2004年   633篇
  2003年   520篇
  2002年   387篇
  2001年   381篇
  2000年   292篇
  1999年   254篇
  1998年   165篇
  1997年   128篇
  1996年   127篇
  1995年   88篇
  1994年   91篇
  1993年   71篇
  1992年   77篇
  1991年   56篇
  1990年   38篇
  1989年   44篇
  1988年   24篇
  1987年   27篇
  1986年   19篇
  1985年   6篇
  1984年   3篇
  1982年   7篇
  1981年   4篇
  1978年   1篇
  1977年   4篇
  1976年   1篇
  1963年   4篇
  1962年   10篇
  1956年   20篇
  1955年   23篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
991.
应用半矮生基因sd-1选育矮秆大库容量水稻新品系研究   总被引:1,自引:0,他引:1  
用大穗高秆品种Akenohoshi与半矮生粳型系统SC-TN1杂交后代F5的6个品系及其亲本为材料,比较分析了品系与亲本遗传性状的表现及其联系。结果表明,通过改善sd-1基因的遗传背景,使半矮生性及优良株型的特性与大库容量相结合是可能的,能够从中培育出有更高产量潜力的新品系  相似文献   
992.
陆地棉栽培品种的种子无菌发芽1~3天。将萌动种子的顶端分生组织培养在无激素或附加低浓度激素MS基本培养基上,直接再生完整小植株。从顶端分生组织到再生植株所需的最短培养时间约10天。顶端分生组织供体种芽的萌芽天数及其所连接的胚轴长度对植株再生频率有明显影响,但与品种的关系较小,不同品种均能获得再生植株。应用基因枪轰击法将CPTⅠ基因和NPTⅡ基因的重组质粒导入到棉花茎尖分生组织,培养获得卡那霉素抗性株。  相似文献   
993.
F. Lin    Y. Liu    L. Wang    X. Liu    Q. Pan 《Plant Breeding》2007,126(3):287-290
The gene Pi15 for resistance of rice to Magnaporthe grisea was previously mapped to a ≈0.7-cM region on chromosome 9. To further define the chromosomal region of the Pi15 locus, a contig spanning the locus was constructed, in silico , through bioinformatics analysis using a reference sequence of the cultivar 'Nipponbare'. One simple sequence repeat marker adopted from the International Rice Microsatellite Initiative and six candidate resistance gene (CRG) markers, developed from gene annotation of the reference sequence of the contig, were used for linkage analysis in a mapping population consisting of 504 extremely susceptible F2 plants. The Pi15 locus was delimited to a ≈0.5-cM region flanked by the markers CRG5 and CRG2 and co-segregated with the markers BAPi15782, CRG3 and CRG4, which was physically converted to a 44-kb interval.  相似文献   
994.
植物低温诱导蛋白和诱导基因研究新进展   总被引:7,自引:0,他引:7  
本文就近年来植物低温诱导蛋白和低温诱导基因的研究进展进行了概述,同时探讨了低温诱导蛋白和低温诱导基因与植物抗寒能力之间的关系。  相似文献   
995.
转Bt-CpTI-GNA基因棉花的研究   总被引:3,自引:2,他引:3  
采用农杆菌介导法将外源三价抗虫基因(Bt-CpTI-GNA)导入常规棉花品种中,获得转基因再生株,分子检测表明外源基因已在棉花体内表达,并遗传给后代材料。PCR分子检测与转化的标记基因和外源目的基因抗性三者极有规律性。其所携带的基因在转基因棉花中有分离现象,这可能是外源基因整合到受体棉株体内“基因沉默”而引起所致。  相似文献   
996.
为了研究绵羊细粒棘球蚴重要抗原基因Tetraspanin 1-TSP1(TSP1)和Tetraspanin 1-TSP6(TSP6)的功能,对Gen Bank中Eg基因组数据库检索,获得TSP1和TSP6的c DNA序列并设计特异性引物。以Eg头节为总RNA模板,进行RT-PCR,将PCR产物克隆到p MD19-T载体后测序并进行生物信息学分析。TSP1 c DNA全长792个核苷酸,编码263个氨基酸,该多肽含有3个潜在的N端糖基化位点,2个N端酰基化位点,与已登录的标准株TSP1基因序列(EG_11043)同源性为98.99%,其推导的氨基酸序列同源性为98.48%;TSP6 c DNA全长666个核苷酸,编码221个氨基酸,该多肽含有5个N端酰基化位点,1个酪氨酸激酶磷酸化位点,与已登录的标准株TSP6基因序列(EG_00715)同源性为98.18%,其推导的氨基酸序列同源性为85.07%。运用分子生物学软件对Eg TSP1和TSP6基因进行生物信息学分析,预测已知序列的蛋白质抗原的结构和表位,为疫苗的研发奠定了前期基础。  相似文献   
997.
Fusarium head blight (FHB) is a destructive disease of wheat worldwide. Sources of resistance to FHB are limited in wheat. Search for novel sources of effective resistance to this disease has been an urgent need in wheat breeding. Fusarium head blight resistance has been identified in relatives of wheat. Alien chromatin carrying FHB resistance genes has been incorporated into wheat through chromosome addition, substitution, and translocation. Relatives of wheat demonstrate a great potential to enhance resistance of wheat to FHB.  相似文献   
998.
M. Imtiaz    M. Ahmad    M. G. Cromey    W. B. Griffin  J. G. Hampton 《Plant Breeding》2004,123(5):401-404
Stripe rust of wheat caused by Puccinia striiformis West. f. sp. tritici presents a serious problem for wheat production worldwide, and identification and deployment of resistance sources to it are key objectives for many wheat breeders. Here we report the detection of simple sequence repeat (SSR) markers linked to the durable adult plant resistance of cv. ‘Otane’, which has conferred this resistance since its release in New Zealand in 1984. A double haploid population from a cross between ‘Otane’ and the susceptible cv. Tiritea’ was visually assessed for adult plant infection types (IT) in the glasshouse and field, and for final disease severity in the field against stripe rust pathotype 106E139A+. At least three resistance loci controlled adult plant resistance to stripe rust in this population. Quantitative trait loci (QTL) mapping results revealed that two of these, one on chromosome 7DS corresponds to the durable adult plant resistance gene Yr18 and other on chromosome 5DL were contributed from ‘Otane’; while the remaining one on chromosome 7BL, was contributed from the susceptible ‘Tiritea’. Interval mapping placed the ‘Otane’‐resistant segment near the centromere of chromosome 7DS at a distance of 7 cM from the SSR marker gwm44. The stability of QTL in the two environments is discussed. SSR gwm44 is potentially a candidate marker for identifying the durable resistance gene Yr18 in breeding programmes.  相似文献   
999.
Summary Seeds of early generations of three reciprocal congruity-backcross (CBC) pedigrees, developed by backcrossing Phaseolus vulgaris-P. acutifolius hybrids to each of the parent species in alternate generations, exhibited a preponderance of traits (size, shape, color, and pattern) of the cytoplasmic parent. The large size of Red Cloud (V1), the P. vulgaris parent common to all of the pedigrees, dominated pedigrees with V1 as the cytoplasmic parent, while the small size and rounded or square shapes of the tepary parents, wild P. acutifolius var. acutifolius PI 263590 or G400445 (A19), wild P. acutifolius var. latifolius PI 406622 (A10), or cultivated P. acutifolius var. latifolius Serowi PI 319443 (A9), were the majority phenotypes when P. acutifolius was the cytoplasmic parent. Continuing through the second cycle of CBC, that is the second backcross with each of the parent species or the fourth backcross, began an amelioration of the apparent cytoplasmic effect on gene expression, as reciprocal pedigrees became more alike, usually with intermediate expression of parental traits or the appearance of new traits. The large seed size of V1 was recovered in hybrids with P. acutifolius cytoplasm and the kidney shape of V1 became rare in hybrids with P. vulgaris cytoplasm. Although the tepary-bean parents represented two subspecies and both cultivated and wild P. acutifolius, the three sets of reciprocal-hybrid pedigrees with P. vulgaris Red Cloud are surprisingly similar. It may be that the exotic parent used to develop a CBC pedigree should be selected more for combining ability in the interspecific cross than for specific economic traits. While the number of generations (six or more) required to produce fertile, intermediate CBC hybrids (that did not require embryo rescue) may preclude routine use of this method by practical plant breeders, the crossability of advanced hybrids with both parental species and the amount of variability apparent in advanced-hybrids progenies suggests that CBC would be valuable for maintaining exotic germplasm in immediately useful forms.  相似文献   
1000.
Summary Linkages between molecular markers and genes involved in the expression of agronomical traits have already been described in all of the major crops. In most cases, the genetic model underlying the Quantitative Traits Loci (QTL) is discussed. Here, Restriction Fragment Length Polymorphisms (RFLPs) and Mapmaker-QTL have been used to pinpoint seven regions of the genome significantly correlated with four pigmentation qualitative traits of maize (Zea mays L.). Two of these, located on chromosomes 2 and 10, explain most of the variation of these traits. The R and B gene loci known to be involved in the regulation of the anthocyanin pathway map to the same regions and we suggest that these loci could be the candidate genes involved in the correlations detected with RFLPs. This type of result is in accordance with the hypothesis of the candidate gene which supposes that, if we have a very high density map of randomly-selected cDNA clones, it should theoretically be possible to associate a cloned genic sequence with a phenotypic trait where correlations are found.  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