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   1031篇
  免费   51篇
  国内免费   155篇
林业   50篇
农学   108篇
  48篇
综合类   445篇
农作物   84篇
水产渔业   160篇
畜牧兽医   229篇
园艺   57篇
植物保护   56篇
  2024年   2篇
  2023年   5篇
  2022年   12篇
  2021年   18篇
  2020年   10篇
  2019年   8篇
  2018年   7篇
  2017年   20篇
  2016年   36篇
  2015年   27篇
  2014年   43篇
  2013年   47篇
  2012年   82篇
  2011年   112篇
  2010年   104篇
  2009年   116篇
  2008年   90篇
  2007年   109篇
  2006年   86篇
  2005年   79篇
  2004年   54篇
  2003年   49篇
  2002年   31篇
  2001年   24篇
  2000年   17篇
  1999年   10篇
  1998年   7篇
  1997年   9篇
  1996年   1篇
  1995年   9篇
  1994年   2篇
  1993年   3篇
  1992年   2篇
  1991年   1篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
  1981年   1篇
排序方式: 共有1237条查询结果,搜索用时 15 毫秒
81.
82.
The BRCA1 gene plays an important role in the development of human breast cancer, and recent research indicated that genetic variations of BRCA1 are also related to canine mammary tumors (CMTs). Here, using rapid amplification of cDNA ends (RACE), we cloned the 5′- and 3′-UTRs of BRCA1. By direct sequencing of the flanking sequences of the 5′- and 3′-UTRs of BRCA1, three previously unreported single-nucleotide polymorphisms (SNPs) were identified, two (−1228T >C, −1173C >T) in the putative promoter regions and one non-synonymous SNP (63449G >A) in exon 23. Compared with 16 normal samples, the sequences from 34 CMTs suggested that SNP (−1173C >T) was associated with the development of CMTs (odds ratio (OR)=2.57, 95% confidence interval (CI): 1.07–6.15).  相似文献   
83.
A cDNA encoding the subunit of thyrotropin (TSH) was isolated from a goldfish (Carassius auratus) pituitary gland cDNA library. By comparing the sequence with other teleost TSHs, a signal peptide of 19 amino acids and a mature hormone of 131 amino acids were predicted for goldfish TSH subunits. The resulting putative mature hormone of 131 amino acids had well-conserved cysteine positions and a putative N-linked glycosylation site; homology was 51–67% with TSHs from other teleosts, 38–43% with tetrapod TSHs, but only 27 and 29% with goldfish GTH-I and -II, respectively. We also examined the effects of thyroid hormones (TH) and thiourea (TU, an inhibitor of TH production) treatments on TSH and GTH subunit gene expressions in the goldfish pituitary gland. After thyroxine (T4) treatment, circulating T4 concentration increased and TSH mRNA level decreased. Supressing the amount of circulating T4 and triiodothyronine (T3) by TU treatment increased the TSH mRNA level. Moreover, T4 replacement therapy (simultaneous treatment of both TU and T4) caused a high level of circulating T4 and a low level of circulating T3, and a decrease in the TSH mRNA level. Thus, changing levels of circulating TH exert a negative feedback on the level of TSH subunit mRNA in goldfish in vivo. On the other hand, GTH subunit mRNA levels were not affected by changes in the levels of circulating TH.  相似文献   
84.
85.
We determined full-length cDNA of carp warm-temperature-acclimation-associated 65-kDa protein (Wap65). It encoded 439 amino acid residues with a signal peptide of 22 residues and showed an amino acid sequence identity of 88% to that of goldfish reported before (J. Biol. Chem. 1995. 270: 17087–17092). The number of potential N-linked glycosylation sites of carp Wap65 was two in contrast to three for goldfish. In addition, molecular mass determined by SDS-PAGE was apparently different from that of goldfish. These results suggest that the amount of oligosaccharide is different between the carp and goldfish protein. As in goldfish, carp Wap65 mRNA showed marked accumulation in hepatopancreas of the 30 °C- acclimated fish, which was 8-fold higher than that of the 10 °C-acclimated fish. Carp Wap65 showed 30% amino acid identity to mammalian hemopexins, which appeared to be considerably low in comparison with those among mammalian hemopexins (72 to 80%), or among carp Wap65 and rainbow trout hemopexin-like protein (70%). However, although mammalian hemopexins contain residues comprising the heme binding pocket, carp Wap65 lacked one of the two histidine residues to serve as heme axial ligands in hemopexins. Our data on carp protein substantiates the previous observation for goldfish and indicates that Wap65 might have some important functions in warm-temperature-acclimation of fish.  相似文献   
86.
The full-length cDNA, encoding the orange-spotted grouper β-actin and spanning 1920 bp including a poly (A) tail, was cloned from its brain cDNA library. The open reading frame encodes a protein of 375 amino acids. Sequence analysis indicated that it contained the typical structural features of cytoplasmic actins, and showed higher homology with other vertebrate β-actin than any other members of the actin family. The partial genomic sequence indicated that the organization of the β-actin gene in the orange-spotted grouper might also be conserved. Northern blot analysis indicated that it was expressed at high levels in the brain, spleen, adipose tissue, ovary, and liver, but at low levels in the gill filament and heart, and at a very low level in the kidney. The expression of β-actin gene in the skeletal muscle was barely detectable. These results indicated that the expression of the orange-spotted grouper β-actin gene showed significant variation in different tissues. Therefore, caution should be taken when using β-actin gene as an internal control in the normalization of gene expression among tissues. Whereas, semi-quantitative RT-PCR analysis indicated that treatment with 17α–methyltestosterone (MT) had little effect on the mRNA expression of β-actin gene in the in vitro incubated hypothalamus, pituitary, and ovary fragments of the orange-spotted grouper, suggesting β-actin can be used as an internal control for RT-PCR analysis of MT effects on gene expression in these tissues.  相似文献   
87.
草鱼生长激素cDNA基因的克隆及序列分析   总被引:1,自引:0,他引:1  
通过反转录PCR技术,从草鱼脑垂体的总RNA中获得一特异cDNA片段,经克隆后测序,结果表明,该片段长633bp,与报道的草鱼生长激素基因相比,有10个碱基的差异,而推导的蛋白质仅1个氨基酸残基的差异,推测为草鱼生长激素cDNA基因。  相似文献   
88.
乙醇酸氧化酶( glycolate oxidase,GLO)是植物光呼吸途径中的一种限速酶,催化羟乙酸盐氧化成乙醛酸盐和H2 O2,与植物的诱导抗病性密切相关。试验从已构建好的木奈( Prunus salicina Lindl.var.cordata J.Y.Zhang et al.)5个不同生长发育时期叶片的均一化全长cDNA文库中分离得到了一个乙醇酸氧化酶( GLO)基因,命名为PsGLO。序列分析表明,PsGLO基因cDNA全长为1531 bp,开放阅读框为1122 bp,编码374个氨基酸。氨基酸多重序列比对表明,该基因与陆地棉乙醇酸氧化酶基因相似性最高,为90%。荧光定量PCR分析表明, PsGLO基因在木奈叶中木奈叶芽、展开叶、幼叶、成熟叶、老叶5个不同生长发育时期中都有表达,其中,老叶中表达量最高,叶芽最低。  相似文献   
89.
[目的]研究溃疡病菌诱导下毛白杨防御相关基因的应答反应.[方法]以毛白杨为试验材料,用溃疡病菌对7月龄幼苗进行接种,提取诱导前后的毛白杨树皮mRNA,通过反转录生成cDNA,构建72 h差异表达的SSH-cDNA文库.随机挑选199个阳性克隆进行测序,将测序结果与NCBI基因库中序列进行比较,并对这些EST在dbEST数据库进行同源检索分析,利用RT-qPCR对文库中7个基因进行进一步分析.[结果] 172个EST找到了同源序列,其中有32个序列与防御相关.在毛白杨受到溃疡病菌诱导时,这些防御基因的表达量明显上升.[结论]该研究为开展毛白杨抗溃疡病重要功能基因的克隆和鉴定奠定了基础.  相似文献   
90.
采用差减抑制杂交技术(SSH)以1龄红狮头金鱼(Carassius auratus)的头瘤组织为检测子(Tester),40日龄红狮头金鱼幼鱼的头顶上皮组织为驱动子(Driver),构建金鱼头瘤相关基因的差减cDNA文库。以鲫管家基因α-tubilin为参照检测差减效率,结果表明该文库差减效率达210倍,效率较高。随机挑选阳性克隆进行接头特异引物的PCR检测,结果表明插入片段均在0.1~2.0kb之间。利用斑点杂交对PCR检测结果为单一条带的阳性克隆进行筛选并测序,获得高差异性的有效序列93条。通过生物信息学方法对文库序列进行比对、分类和注释,发现若干结缔形成基因和原癌/抑癌基因等与金鱼头瘤形成相关的功能基因,表明cDNA文库构建成功。  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