全文获取类型
收费全文 | 352篇 |
免费 | 12篇 |
国内免费 | 20篇 |
专业分类
384篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 43篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 22篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有384条查询结果,搜索用时 15 毫秒
11.
Natural products provide a unique element of molecular diversity and biological functionality and they are still indispensable for drug discovery. The polyketides, comprising a large and structurally diverse family of bioactive natural products, have been isolated from a group of mycelia-forming Gram-positive microorganisms, the actinomycetes. Relatively high amino acid sequence identity of the actinomycetes type I polyketide synthases (PKSs) was used to design three degenerate primer pairs for homology-based PCR detection of novel PKS genes, with particular interest into PKSs involved in biosynthesis of immunosuppressive-like metabolites. The stepdown PCR method, described here, enables fast insight into the PKS arsenal within actinomycetes. Designed primers and stepdown PCR were applied for the analysis of two natural isolates, Streptomyces sp. strains NP13 and MS405. Sequence analysis of chosen clones revealed the presence of two distinctive sequences in strain Streptomyces sp. NP13, but only one of these showed homology to PKS-related sequences. On analysing PCR amplicons derived from Streptomyces sp. strain MS405, three different PKS-related sequences were identified demonstrating a potential of designed primers to target PKS gene pool within single organism. 相似文献
12.
Survivin as a target for new anticancer interventions 总被引:66,自引:0,他引:66
Survivin is a member of the inhibitor of apoptosis protein (IAP) family, that has been implicated in both control of cell division and inhibition of apoptosis. Specifically, its anti-apoptotic function seems to be related to the ability to directly or indirectly inhibit caspases. Survivin is selectively expressed in the most common human neoplasms and appears to be involved in tumor cell resistance to some anticancer agents and ionizing radiation. On the basis of these findings survivin has been proposed as an attractive target for new anticancer interventions. Several preclinical studies have demonstrated that down-regulation of survivin expression/function, accomplished through the use of antisense oligonucleotides, dominant negative mutants, ribozymes, small interfering RNAs and cyclin-dependent kinase inhibitors, increased the apoptotic rate, reduced tumor-growth potential and sensitized tumor cells to chemotherapeutic drugs with different action mechanisms and gamma-irradiation in in vitro and in vivo models of different human tumor types. 相似文献
13.
The use of synthetic oligonucleotides and their analogs to block gene expression by binding the complementary RNA sequences in cells, the antisense principle, has been limited by poor uptake of the agents by cells in culture. This review describes attempts to harness by chemical conjugation the ability of certain peptides that may cross membranes to enhance the cellular uptake of oligonucleotides. These include fusogenic and hydrophobic peptides, nuclear localization signals, receptor targeting and translocating peptides, and various combinations. We also outline briefly some popular methods of peptide–oligonucleotide conjugation. Finally, we review the use of noncovalent peptide additives and the recent studies of conjugates of peptide nucleic acid (PNA) with peptides. 相似文献
14.
15.
目的:研究I组代谢型谷氨酸受体(mGluRs)反义寡核苷酸对谷氨酸钠(Glu)引起的小鼠大脑皮层神经元损伤的保护作用。方法:以细胞乳酸脱氢酶(LDH)漏出、光镜下细胞形态变化为指标,观察培养液中加入Glu引起的神经元损伤及mGluRl反义寡核苷酸或mGluR5反义寡核苷酸的保护作用;用免疫细胞化学检测神经元mGlulα仪和mGluR5表达。结果:实验显示0.1mmol.L-1的谷氨酸钠可明显造成神经元损伤,使LDH漏出增加(P<0.01),mGluRl反义寡核苷酸或mGluR5反义寡核苷酸6μmol.L-1和8μmol.L-1可明显拮抗Glu引起的神经元损伤,使LDH漏出显著减少(P<0.01);免疫组化实验证实体外培养神经元mGluRlα和mGluR5阳性表达。结论:mGluRl反义寡核苷酸和mGluR5反义寡核苷酸可对抗Glu引起的皮层神经元损伤。 相似文献
16.
为研究云南野生蔷薇属中的NBS类抗病基因,根据已知抗病基因NBSLRR序列中的保守区域设计简并引物,利用RTPCR技术从云南悬钩子蔷薇中进行体外扩增,获得了对应区域的cDNA片段,回收、克隆这些特异片段,测序分析,共得到4个含有NBSLRR保守结构域的抗病基因同源序列(RGAs),分别命名为AC9、AC39、AC50和AC68。它们与已报道的11个NBS类抗病基因相应区段的氨基酸序列相似性为5.4%~79.2%,其中这4个RGAs片段与Mi、RPS2、Pib和RPM1基因聚为一类。表明这4条RGAs序列可进一步用作悬钩子蔷薇抗病候选基因的分子筛选及遗传图谱的构建。 相似文献
17.
Yunfei Bi Qinzheng Zhao Wenkai Yan Mengxue Li Yuxi Liu Chunyan Cheng Lu Zhang Xiaqing Yu Ji Li Chuntao Qian Yufeng Wu Jinfeng Chen Qunfeng Lou 《The Plant journal : for cell and molecular biology》2020,102(1):178-186
Chromosome painting is a powerful technique for chromosome and genome studies. We developed a flexible chromosome painting technique based on multiplex PCR of a synthetic oligonucleotide (oligo) library in cucumber (Cucumis sativus L., 2n = 14). Each oligo in the library was associated with a universal as well as nested specific primers for amplification, which allow the generation of different probes from the same oligo library. We were also able to generate double‐stranded labelled oligos, which produced much stronger signals than single‐stranded labelled oligos, by amplification using fluorophore‐conjugated primer pairs. Oligos covering cucumber chromosome 1 (Chr1) and chromosome 4 (Chr4) consisting of eight segments were synthesized in one library. Different oligo probes generated from the library painted the corresponding chromosomes/segments unambiguously, especially on pachytene chromosomes. This technique was then applied to study the homoeologous relationships among cucumber, C. hystrix and C. melo chromosomes based on cross‐species chromosome painting using Chr4 probes. We demonstrated that the probe was feasible to detect interspecies chromosome homoeologous relationships and chromosomal rearrangement events. Based on its advantages and great convenience, we anticipate that this flexible oligo‐painting technique has great potential for the studies of the structure, organization, and evolution of chromosomes in any species with a sequenced genome. 相似文献
18.
《Nucleosides, nucleotides & nucleic acids》2013,32(12):1911-1927
To improve antisense oligonucleotide penetration inside cells, conjugates of oligonucleotides and cell‐penetrating peptides, covalently linked through a phosphoramide bond, were prepared by a fragment coupling approach in the liquid phase. Two methods were used for this synthesis, i.e., phosphorylation of a peptide amino group by an oligonucleotide terminal phosphate 1‐hydroxybenzotriazole ester in aqueous media or condensation of phosphate and amino groups in presence of triphenylphosphine, 2,2′‐dithiopyridine and 4‐dimethylaminopyridine in organic media. Several oligonucleotides, including a 18‐mer antisense oligodeoxyribonucleotide complementary to an internal coding region of the reporter gene of the green fluorescent protein (GFP) were prepared. Peptides derived from the third helix of the homeodomain of Antennapedia, the influenza envelope hemagglutinin subunit as well as melittin and polymyxin B were used for the conjugates' synthesis. The peptides with various amino acid composition were chosen to confirm that these coupling methods are of a general use. 相似文献
19.
《Nucleosides, nucleotides & nucleic acids》2013,32(5-8):623-627
Abstract Preparation of the nucleoside analogues 1 and incorporation of 1, B = T, in deoxyribooligonucleotides by the phosphoramidite method is described. A two-step deprotection procedure was developed to reduce cleavage of the modified allylic unit. The binding properties of the modified oligonucleotides towards complementary DNA and RNA has been evaluated by Tm measurements showing a ΔTm of ?2 to ?6.5°C per modification. An oligonucleotide with two modifications at the 3′-end showed considerable resistance towards cleavage by a 3′-exonuclease. No antiviral activity against HIV-1 or HSV-1 was found for 1, B = G or T, or for any of the trihydroxy derivatives 5. 相似文献
20.
Julio C. González-Olvera Eva González-Jasso Alejandra Rojas-Molina 《Nucleosides, nucleotides & nucleic acids》2013,32(9):642-655
AbstractDegradation of 2′-deoxyribonucleosides in 0.5?M aqueous pyrrolidine at 110?°C proceeds at different rates, ordered as deoxyuridine?>?deoxyadenosine?>?deoxycytidine?>?deoxyguanosine ??deoxythymidine. Deoxyadenosine degradation produces the free base, adenine, while deoxycytidine by deamination produces deoxyuridine, and then uracil. The solvolysis of deoxyadenosine has an activation energy of 23.3?kcal/mol. Ammonolysis is slower than pyrrolidinolysis for deoxyadenosine, but faster for deoxyguanosine. In pyrrolidinolysis of the trinucleotides, d-TGT and d-TAT, the guanine moiety reacts faster than the adenine moiety. These trends are interpreted in terms of the ionization of the guanine moieties under basic conditions, rendering them less susceptible to nucleophilic attack. 相似文献