全文获取类型
收费全文 | 7159篇 |
免费 | 548篇 |
国内免费 | 5篇 |
出版年
2023年 | 39篇 |
2022年 | 68篇 |
2021年 | 143篇 |
2020年 | 89篇 |
2019年 | 119篇 |
2018年 | 147篇 |
2017年 | 121篇 |
2016年 | 224篇 |
2015年 | 363篇 |
2014年 | 430篇 |
2013年 | 446篇 |
2012年 | 621篇 |
2011年 | 519篇 |
2010年 | 360篇 |
2009年 | 279篇 |
2008年 | 369篇 |
2007年 | 431篇 |
2006年 | 320篇 |
2005年 | 354篇 |
2004年 | 315篇 |
2003年 | 283篇 |
2002年 | 266篇 |
2001年 | 73篇 |
2000年 | 49篇 |
1999年 | 69篇 |
1998年 | 93篇 |
1997年 | 65篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 43篇 |
1993年 | 46篇 |
1992年 | 45篇 |
1991年 | 37篇 |
1990年 | 32篇 |
1989年 | 33篇 |
1988年 | 37篇 |
1987年 | 47篇 |
1986年 | 28篇 |
1985年 | 39篇 |
1984年 | 44篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 21篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有7712条查询结果,搜索用时 31 毫秒
971.
Michael W. Bairu Wendy A. Stirk Karel Doležal Johannes van Staden 《Plant Cell, Tissue and Organ Culture》2008,95(3):373-379
The effect of the cytokinins mT (meta-topolin), mTR (meta-topolin riboside), MemT (meta-methoxy topolin) and MemTR (meta-methoxy topolin riboside) on micropropagation of banana cultivars ‘Williams’ and ‘Grand Naine’ was studied and compared to
BA (6-benzylaminopurine). In vitro cultures, at the third sub-culture level, were purchased from African Biotechnologies (Pty)
Ltd., South Africa. These were then sub-cultured on MS media containing 7.5, 15 and 30 μM of all the cytokinins tested. Results
recorded after 6 weeks of growth demonstrated that there were statistically significant differences between the parameters
analyzed for the treatments. Superior multiplication rates were recorded for mT and mTR treatments. This result was consistent when compared to BA at 22.2 μM (previously published standard concentration). Contrary
to previous findings with other species, these cytokinins inhibited rooting. The effect on somaclonal variation was not significantly
different when BA, mT and mTR were tested at the seventh multiplication cycle for ‘Williams’ banana. These results support the possible use of topolins
as an alternative to BA for Cavendish banana tissue culture. The role of these cytokinins on somaclonal variation however,
requires a more stringent investigation as the results obtained in this investigation could have been influenced by carry-over
effects from the initial cultures. 相似文献
972.
973.
Anna Kielak Agata S Pijl Johannes A van Veen George A Kowalchuk 《FEMS microbiology ecology》2008,63(3):372-382
To examine the relationship between plant species composition and microbial community diversity and structure, we carried out a molecular analysis of microbial community structure and diversity in two field experiments. In the first experiment, we examined bacterial community structure in bulk and rhizosphere soils in fields exposed to different plant diversity treatments, via a 16S rRNA gene clone library approach. Clear differences were observed between bacterial communities of the bulk soil and the rhizosphere, with the latter containing lower bacterial diversity. The second experiment focused on the influence of 12 different native grassland plant species on bacterial community size and structure in the rhizosphere, as well as the structure of Acidobacteria and Verrucomicrobia community structures. In general, bacterial and phylum-specific quantitative PCR and PCR-denaturing gradient gel electrophoresis revealed only weak influences of plant species on rhizosphere communities. Thus, although plants did exert an influence on microbial species composition and diversity, these interactions were not specific and selective enough to lead to major impacts of vegetation composition and plant species on below-ground microbial communities. 相似文献
974.
Bacterial communities associated with the brown alga Laminaria saccharina from the Baltic Sea and from the North Sea were investigated using denaturing gradient gel electrophoresis and 16S rRNA gene clone libraries. The rhizoid, cauloid, meristem and phyloid revealed different 16S rRNA gene denaturing gradient gel electrophoresis banding patterns indicating a specific association of bacterial communities with different parts of the alga. Associations with cauloid and meristem were more specific, while less specific associations were obtained from the old phyloid. In addition, seasonal and geographical differences in the associated communities were observed. Results from 16S rRNA gene libraries supported these findings. Bacterial phylotypes associated with the alga were affiliated with the Alphaproteobacteria (nine phylotypes), Gammaproteobacteria (nine phylotypes) and the Bacteroidetes group (four phylotypes). A number of bacteria associated with other algae and other marine macroorganisms were among the closest relatives of phylotypes associated with L. saccharina. 相似文献
975.
Mela F Fritsche K Boersma H van Elsas JD Bartels D Meyer F de Boer W van Veen JA Leveau JH 《FEMS microbiology ecology》2008,66(1):45-62
Plasmid pTer331 from the bacterium Collimonas fungivorans Ter331 is a new member of the pIPO2/pSB102 family of environmental plasmids. The 40 457-bp sequence of pTer331 codes for 44 putative ORFs, most of which represent genes involved in replication, partitioning and transfer of the plasmid. We confirmed that pTer331 is stably maintained in its native host. Deletion analysis identified a mini-replicon capable of replicating autonomously in Escherichia coli and Pseudomonas putida. Furthermore, plasmid pTer331 was able to mobilize and retromobilize IncQ plasmid pSM1890 at typical rates of 10(-4) and 10(-8), respectively. Analysis of the 91% DNA sequence identity between pTer331 and pIPO2 revealed functional conservation of coding sequences, the deletion of DNA fragments flanked by short direct repeats (DR), and sequence preservation of long DRs. In addition, we experimentally established that pTer331 has no obvious contribution in several of the phenotypes that are characteristic of its host C. fungivorans Ter331, including the ability to efficiently colonize plant roots. Based on our findings, we hypothesize that cryptic plasmids such as pTer331 and pIPO2 might not confer an individual advantage to bacteria, but, due to their broad-host-range and ability to retromobilize, benefit bacterial populations by accelerating the intracommunal dissemination of the mobile gene pool. 相似文献
976.
Navdaev A Heitmann V Desantana Evangelista K Mörgelin M Wegener J Eble JA 《Experimental cell research》2008,314(3):489-497
Using a recombinant mini-laminin-332, we showed that truncation of the three C-terminal amino acids of the gamma 2 chain, but not of the C-terminal amino acid of the beta 3 chain, completely abolished alpha 3 beta 1 integrin binding and its cellular functions, such as attachment and spreading. However, a synthetic peptide mimicking the gamma 2 chain C-terminus did not interfere with alpha 3 beta 1 integrin binding or cell adhesion and spreading on laminin-332 as measured by protein interaction assays and electric cell-substrate impedance sensing. Nor was the soluble peptide able to restore the loss of integrin-mediated cell adhesiveness to mini-laminin-332 after deletion of the gamma 2 chain C-terminus. These findings spoke against the hypothesis that the gamma 2 chain C-terminus of laminin-332 is a part of the alpha 3 beta 1 integrin interaction site. In addition, structural studies with electron microscopy showed that truncation of the gamma 2 chain C-terminus opened up the compact supradomain structure of LG1-3 domains. Thus, by inducing or stabilizing an integrin binding-competent conformation or array of the LG1-3 domains, the gamma 2 chain C-terminus plays an indirect but essential role in laminin-332 recognition by alpha 3 beta 1 integrin and, hence, its cellular functions. 相似文献
977.
Pina DG Stechmann B Shnyrov VL Cabanié L Haicheur N Tartour E Johannes L 《FEBS letters》2008,582(2):185-189
The homopentameric B-subunit of Shiga toxin (STxB) is used as a tool to deliver antigenic peptides and proteins to the cytosolic compartment of dendritic cells (DCs). In this study, a series of interface mutants of STxB has been constructed. All mutants retained their overall conformation, while a loss in thermal stability was observed. This effect was even more pronounced in trifluoroethanol solutions that mimic the membrane environment. Despite this, all mutants were equally efficient at delivering a model antigenic protein into the MHC class I-restricted antigen presentation pathway of mouse DCs, suggesting that the structural stability of STxB is not a key factor in the membrane translocation process. 相似文献
978.
Poirier S Mayer G Benjannet S Bergeron E Marcinkiewicz J Nassoury N Mayer H Nimpf J Prat A Seidah NG 《The Journal of biological chemistry》2008,283(4):2363-2372
The proprotein convertase PCSK9 gene is the third locus implicated in familial hypercholesterolemia, emphasizing its role in cardiovascular diseases. Loss of function mutations and gene disruption of PCSK9 resulted in a higher clearance of plasma low density lipoprotein cholesterol, likely due to a reduced degradation of the liver low density lipoprotein receptor (LDLR). In this study, we show that two of the closest family members to LDLR are also PCSK9 targets. These include the very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2) implicated in neuronal development and lipid metabolism. Our results show that wild type PCSK9 and more so its natural gain of function mutant D374Y can efficiently degrade the LDLR, VLDLR, and ApoER2 either following cellular co-expression or re-internalization of secreted human PCSK9. Such PCSK9-induced degradation does not require its catalytic activity. Membrane-bound PCSK9 chimeras enhanced the intracellular targeting of PCSK9 to late endosomes/lysosomes and resulted in a much more efficient degradation of the three receptors. We also demonstrate that the activity of PCSK9 and its binding affinity on VLDLR and ApoER2 does not depend on the presence of LDLR. Finally, in situ hybridization show close localization of PCSK9 mRNA expression to that of VLDLR in mouse postnatal day 1 cerebellum. Thus, this study demonstrates a more general effect of PCSK9 on the degradation of the LDLR family that emphasizes its major role in cholesterol and lipid homeostasis as well as brain development. 相似文献
979.
Woodall BP Nyström A Iozzo RA Eble JA Niland S Krieg T Eckes B Pozzi A Iozzo RV 《The Journal of biological chemistry》2008,283(4):2335-2343
Endorepellin, the C-terminal module of perlecan, has angiostatic activity. Here we provide definitive genetic and biochemical evidence that the functional endorepellin receptor is the alpha2beta1 integrin. Notably, the specific endorepellin binding to the receptor was cation-independent and was mediated by the alpha2 I domain. We show that the anti-angiogenic effects of endorepellin cannot occur in the absence of alpha2beta1. Microvascular endothelial cells from alpha2beta1(-/-) mice, but not those isolated from either wild-type or alpha1beta1(-/-) mice, did not respond to endorepellin. Moreover, syngeneic Lewis lung carcinoma xenografts in alpha2beta1(-/-) mice failed to respond to systemic delivery of endorepellin. In contrast, endorepellin inhibited tumor growth and angiogenesis in the wild-type mice expressing integrin alpha2beta1. We conclude that the angiostatic effects of endorepellin in vivo are mediated by a specific interaction of endorepellin with the alpha2beta1 integrin receptor. 相似文献
980.
Gross G van der Meulen J Snel J van der Meer R Kleerebezem M Niewold TA Hulst MM Smits MA 《FEMS immunology and medical microbiology》2008,54(2):215-223
Host-microorganism interactions in the intestinal tract are complex, and little is known about specific nonpathogenic microbial factors triggering host responses in the gut. In this study, mannose-specific interactions of Lactobacillus plantarum 299v with jejunal epithelium were investigated using an in situ pig Small Intestinal Segment Perfusion model. The effects of L. plantarum 299v wild-type strain were compared with those of two corresponding mutant strains either lacking the gene encoding for the mannose-specific adhesin (msa) or sortase (srtA; responsible for anchoring of cell surface proteins like Msa to the cell wall). A slight enrichment of the wild-type strain associated with the intestinal surface could be observed after 8 h of perfusion when a mixture of wild-type and msa-mutant strain had been applied. In contrast to the mutant strains, the L. plantarum wild-type strain tended to induce a decrease in jejunal net fluid absorption compared with control conditions. Furthermore, after 8 h of perfusion expression of the host gene encoding pancreatitis-associated protein, a protein with proposed bactericidal properties, was found to be upregulated by the wild-type strain only. These observations suggest a role of Msa in the induction of host responses in the pig intestine. 相似文献