全文获取类型
收费全文 | 5814篇 |
免费 | 450篇 |
国内免费 | 2篇 |
专业分类
6266篇 |
出版年
2023年 | 17篇 |
2022年 | 38篇 |
2021年 | 68篇 |
2020年 | 50篇 |
2019年 | 51篇 |
2018年 | 79篇 |
2017年 | 70篇 |
2016年 | 117篇 |
2015年 | 185篇 |
2014年 | 260篇 |
2013年 | 341篇 |
2012年 | 348篇 |
2011年 | 384篇 |
2010年 | 261篇 |
2009年 | 252篇 |
2008年 | 342篇 |
2007年 | 366篇 |
2006年 | 341篇 |
2005年 | 346篇 |
2004年 | 305篇 |
2003年 | 287篇 |
2002年 | 304篇 |
2001年 | 71篇 |
2000年 | 57篇 |
1999年 | 83篇 |
1998年 | 110篇 |
1997年 | 92篇 |
1996年 | 78篇 |
1995年 | 60篇 |
1994年 | 63篇 |
1993年 | 66篇 |
1992年 | 49篇 |
1991年 | 56篇 |
1990年 | 40篇 |
1989年 | 58篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 24篇 |
1982年 | 52篇 |
1981年 | 33篇 |
1980年 | 33篇 |
1979年 | 23篇 |
1978年 | 16篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 21篇 |
1974年 | 15篇 |
排序方式: 共有6266条查询结果,搜索用时 15 毫秒
11.
12.
Summary Phage adsorption tests and transfection by electroporation were carried out to decide whether phage-resistance in Lactococcus lactis subsp. lactis strain 4513-5 is based on intracellular or extracellular mechanisms. Using high voltage (12.5 kV/cm) electroporation, untreated phage DNA was introduced into phage-sensitive and phage-resistant cells. Since phages showed low adsorption frequencies on resistant bacteria, resistance is localized in the cell wall preventing phage DNA from entering the cell. This is the only mechanism responsible for the resistance of L. lactis subsp. lactis 4513-5 against its homologous phage P4513-K12 and non-homologous phages P05M-13 and P05M-47, but not against phage P530-7 and phage P530-12. In the case of the latter two phage strains, intracellular resistance mechanisms are involved and discussed. 相似文献
13.
14.
Markus Pech Thomas Spreter Roland Beckmann Birgitta Beatrix 《The Journal of biological chemistry》2010,285(25):19679-19687
Nascent polypeptide-associated complex (NAC) was identified in eukaryotes as the first cytosolic factor that contacts the nascent polypeptide chain emerging from the ribosome. NAC is present as a homodimer in archaea and as a highly conserved heterodimer in eukaryotes. Mutations in NAC cause severe embryonically lethal phenotypes in mice, Drosophila melanogaster, and Caenorhabditis elegans. In the yeast Saccharomyces cerevisiae NAC is quantitatively associated with ribosomes. Here we show that NAC contacts several ribosomal proteins. The N terminus of βNAC, however, specifically contacts near the tunnel exit ribosomal protein Rpl31, which is unique to eukaryotes and archaea. Moreover, the first 23 amino acids of βNAC are sufficient to direct an otherwise non-associated protein to the ribosome. In contrast, αNAC (Egd2p) contacts Rpl17, the direct neighbor of Rpl31 at the ribosomal tunnel exit site. Rpl31 was also recently identified as a contact site for the SRP receptor and the ribosome-associated complex. Furthermore, in Escherichia coli peptide deformylase (PDF) interacts with the corresponding surface area on the eubacterial ribosome. In addition to the previously identified universal adapter site represented by Rpl25/Rpl35, we therefore refer to Rpl31/Rpl17 as a novel universal docking site for ribosome-associated factors on the eukaryotic ribosome. 相似文献
15.
Roland Nagel 《当今生物学》1990,20(6):299-304
16.
17.
18.
Roland von Bothmer Maija Kotimäki Ib Linde-Laursen 《Plant Systematics and Evolution》1987,156(3-4):183-188
Hybrids between the Chinese endemic speciesPsathyrostachys huashanica
Keng and the SW. Asian speciesP. fragilis (Boiss.)Nevski (all 2n = 14) developed normally but were completely sterile. Meiotic analyses revealed a high chiasma frequency indicating that the two species as well asP. juncea (Fisch.)Nevski share the same basic genome (called N). The hybrid nature of the plants was established through karyotype analysis and Giemsa C-banding. 相似文献
19.
DNA fragments complementing theenvC mutation could be isolated by cloning chromosomal DNA in the vector pUH84. When the frequencies of transformation and the frequencies of restoring theenvC
+ phenotype were compared, the high copy number hybrid plasmids complemented with a frequency of 10–5. After subcloning theenvC-complementing DNA fragment into the low copy number plasmid pLG339, efficient complementation was achieved by spontaneous integration of the IS2 element ofEscherichia coli. By nucleotide sequence analysis, a potential promoter, a ribosome-binding site, and an unidentified reading frame were detected in the respective DNA fragment. 相似文献
20.
Abstract Four plasmids were constructed by associating Escherichia coli and yeast selection markers and replication origins to a structural gene coding for aminoglycoside phosphotransferase (APH(3')) controlled by different flanking sequences. We used the two bacterial genes of Tn5 (APH(3')II) and Tn903 (APH(3')I) as such and the chimeric pSVneo (APH(3')II) and pNOSneo (APH(3')II) constructs, functional in mammalian and plant cells, respectively. Yeast clones resistant to G418 were obtained with all plasmids except with that bearing the bacterial APH(3')II gene. The three plasmids harbouring the functional APH genes, however, conferred different levels of G418 resistance to yeast. 相似文献