全文获取类型
收费全文 | 6025篇 |
免费 | 480篇 |
国内免费 | 2篇 |
出版年
2023年 | 15篇 |
2022年 | 39篇 |
2021年 | 69篇 |
2020年 | 50篇 |
2019年 | 54篇 |
2018年 | 80篇 |
2017年 | 71篇 |
2016年 | 117篇 |
2015年 | 190篇 |
2014年 | 267篇 |
2013年 | 349篇 |
2012年 | 352篇 |
2011年 | 395篇 |
2010年 | 267篇 |
2009年 | 257篇 |
2008年 | 353篇 |
2007年 | 376篇 |
2006年 | 347篇 |
2005年 | 352篇 |
2004年 | 316篇 |
2003年 | 296篇 |
2002年 | 314篇 |
2001年 | 74篇 |
2000年 | 67篇 |
1999年 | 94篇 |
1998年 | 111篇 |
1997年 | 89篇 |
1996年 | 80篇 |
1995年 | 62篇 |
1994年 | 63篇 |
1993年 | 67篇 |
1992年 | 55篇 |
1991年 | 62篇 |
1990年 | 45篇 |
1989年 | 63篇 |
1988年 | 51篇 |
1987年 | 35篇 |
1986年 | 47篇 |
1985年 | 38篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 58篇 |
1981年 | 34篇 |
1980年 | 36篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 26篇 |
1976年 | 19篇 |
1975年 | 25篇 |
1974年 | 15篇 |
排序方式: 共有6507条查询结果,搜索用时 390 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.
In vitro growth of murine T cells. IV. Use of T-cell growth factor to clone lymphoid cells 总被引:3,自引:0,他引:3
Murine bone marrow cells can suppress the in vitro primary antibody response of normal spleen cells without apparent cytotoxicity. The bone marrow cells suppress the response to both T-dependent (SRBC) and T-independent (DNP-Ficoll) antigens. When bone marrow cells are fractionated on a sucrose density gradient, the suppressive activity is found in the residue rather than the lymphocyte fraction. The suppressive activity is either unaffected or enhanced by treatment with anti-T- and anti-B-cell serums. Pretreatment of mice with phenylhydrazine which reduces the number of pre-B cells did not reduce the suppressive activity of their bone marrow cells. Suppressive activity is abolished by irradiation of the marrow cells in vitro with 1000 R prior to assay. The activity is present in the marrow of thymus deficient (nude) mice, infant mice, and mice which have been made polycythemic by transfusion. Furthermore, the suppressor cell can phagocytize iron carbonyl particles, is slightly adherent to plastic and Sephadex G-10, and can bind to EA monolayers. We conclude that the suppressor cell is not a mature lymphocyte or granulocyte nor a member of the erythrocytic series, but is likely to be an immature cell possibly of the myeloid series. We speculate on the physiologic role of this cell. 相似文献
14.
15.
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
16.
Roland Nagel 《当今生物学》1990,20(6):299-304
17.
18.
19.
Deletion analysis of the internal signal-anchor domain of the human asialoglycoprotein receptor H1. 总被引:7,自引:0,他引:7
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The human asialoglycoprotein receptor H1 is a single-spanning membrane protein with the amino terminus facing the cytoplasm and the carboxy terminus exposed on the exoplasmic side of the plasma membrane. It has been shown earlier that the transmembrane segment, residues 38-65, functions as an internal signal directing protein synthesis to the endoplasmic reticulum and initiating membrane insertion. This process is co-translational and mediated by signal recognition particle (SRP). To identify subsegments within this region containing the signal information, we prepared deletion mutants at the level of the cDNA and analysed them in a wheat germ in vitro translation system with microsomes as the target membrane. Insertion and membrane anchoring were judged by the glycosylation of the protein, its resistance to exogenous protease and the extent to which it can be extracted from the microsomes by alkaline treatment. It was found that very small deletions already reduce the stability of membrane anchoring. However, nearly half of the transmembrane domain can be deleted, both from the amino-terminal and from the carboxy-terminal side, without completely abolishing membrane insertion. Several mutants, although not inserted, still interact with SRP. The results support the notion that the main feature of a signal sequence is a hydrophobic stretch of sufficient length (10-12 residues in our sequence), and indicate that recognition by SRP is not sufficient for membrane insertion. 相似文献
20.
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