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101.
Isolation of gamma-tocotrienol dimers from Hevea latex 总被引:2,自引:0,他引:2
102.
S4-alpha mRNA translation regulation complex. II. Secondary structures of the RNA regulatory site in the presence and absence of S4 总被引:15,自引:0,他引:15
The secondary structure of the Escherichia coli alpha mRNA leader sequence has been determined using nucleases specific for single- or double-stranded RNA. Three different length alpha RNA fragments were studied at 0 degrees C and 37 degrees C. A very stable eight base-pair helix forms upstream from the ribosome initiation site, defining a 29 base loop. There is evidence for base-pairing between nucleotides within this loop and for a "pseudo-knot" interaction of some loop bases with nucleotides just 3' to the initiation codon, forming a region of complex structure. A weak helix also pairs sequences near the 5' terminus of the alpha mRNA with bases near the Shine-Dalgarno sequence. Affinity constants for the translational repressor S4 binding different length alpha mRNA fragments indicate that most of the S4 recognition features must be contained within the main helix and hairpin regions. Binding of S4 to the alpha mRNA alters the structure of the 29 base hairpin region, and probably melts the weak pairing between the 5' and 3' termini of the leader. The pseudo-knot structure and the conformational changes associated with it provide a link between the structures of the S4 binding site and the ribosome binding site. The alpha mRNA may therefore play an active role in mediating translational repression. 相似文献
103.
Mariotti D.; Davey M. R.; Draper J.; Freeman J.P.; Cocking E. C. 《Plant & cell physiology》1984,25(3):473-482
Seedlings of the forage legume Medicago sativa formed crowngall tumours at low frequency following inoculation with octopineand nopaline strains of Agrobacterium tumefaciens. There occurreda plant variety-bacterial strain specificity with respect totumorigenesis, some Medicago varieties failing to develop tumoursfollowing inoculation. In comparison, all bacterial strainstested incited tumours on stem explants of Nicotiana tabacumcv. Xanthi. DNA-DNA hybridization revealed a simple T-DNA patternin an uncloned and cloned Medicago tumour incited by the octopinestrain ACH5, protoplast cloning indicating the T-DNA copy numberto be about 5 copies per genome. Comparison of the T-DNA ofoctopine positive and octopine negative B6 tumours showed acorrelation between absence of part of the T-DNA and loss ofopine synthesis. Although non-transformed tissues of Medicagoreadily regenerate plants, this ability was suppressed in transformedtissues.
1Present address: Centro Miglioramento Genetica Piante Foraggere,Facolt? di Agraria, Borgo XX Giugno, 06100 Perugia, Italy (Received September 14, 1983; Accepted February 7, 1984) 相似文献
104.
Lorraine A. Draper Karen Grainger Lucy H. Deegan Paul D. Cotter Colin Hill R. Paul Ross 《Molecular microbiology》2009,71(4):1043-1054
Lantibiotics are antimicrobial peptides that possess great potential as clinical therapeutic agents. These peptides exhibit many beneficial traits and in many cases the emergence of resistance is extremely rare. In contrast, producers of lantibiotics synthesize dedicated immunity proteins to provide self-protection. These proteins have very specific activities and cross-immunity is rare. However, producers of two peptide lantibiotics, such as lacticin 3147, face the unusual challenge of exposure to two active peptides (α and β). Here, in addition to establishing the contribution of LtnI and LtnFE to lacticin 3147 immunity, investigations were carried out to determine if production of a closely related lantibiotic (i.e. staphylococcin C55) or possession of LtnI/LtnFE homologues could provide protection. Here we establish that not only are staphylococcin C55 producers cross-immune to lacticin 3147, and therefore represent a natural repository of Staphylococcus aureus strains that are protected against lacticin 3147, but that functional immunity homologues are also produced by strains of Bacillus licheniformis and Enterococcus faecium . This result raises the spectre of resistance through immune mimicry, i.e. the emergence of lantibiotic-resistant strains from the environment resulting from the possession/acquisition of immunity gene homologues. These phenomena will have to be considered carefully when developing lantibiotics for clinical application. 相似文献
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Simon Firek David J. Martin Michael R. Roberts Faye Sturgess Rod Scott John Draper 《The Plant journal : for cell and molecular biology》1996,10(3):569-578
To assess the potential advantages of a transposon-tagging system based on gametophyte-specific transposition a fusion between the anther-specific Arabidopsis thaliana apg promoter and the maize Ac transposase gene was constructed and introduced into tobacco. The ability of this transposase source to activate Ds transposition in a developmentally controlled manner was monitored by crossing to plants harbouring the cell autonomous excision marker gene construct, Ds —SPT. A number of fully green, streptomycin-resistant seedlings resulting from germinal transposition events were observed in the progeny of apg -TPase x Ds —SPT F1 plants. Streptomycin-resistant sectors were not observed in either F1 seedlings or F2 progeny, indicating a complete lack of somatic excision. Further crosses of apg —TPase sources to plants containing Ds—bar herbicide selection excision marker constructs gave reproducible gametophytic excision frequencies of up to 0.3%. Sequencing of Ds excision sites from F2 seedlings derived from single F1 plants revealed various sequence alterations in the original Ds insertion 'footprint' indicative of independent Ds excision events. Independent re-insertion was confirmed by Southern analysis of F2 siblings. It is concluded that apg -controlled Ac transposase expression activates male gametophyte-specific Ds transposition. 相似文献
108.
Characterization of human embryonic stem cell lines by the International Stem Cell Initiative 总被引:1,自引:0,他引:1
International Stem Cell Initiative Adewumi O Aflatoonian B Ahrlund-Richter L Amit M Andrews PW Beighton G Bello PA Benvenisty N Berry LS Bevan S Blum B Brooking J Chen KG Choo AB Churchill GA Corbel M Damjanov I Draper JS Dvorak P Emanuelsson K Fleck RA Ford A Gertow K Gertsenstein M Gokhale PJ Hamilton RS Hampl A Healy LE Hovatta O Hyllner J Imreh MP Itskovitz-Eldor J Jackson J Johnson JL Jones M Kee K King BL Knowles BB Lako M Lebrin F Mallon BS Manning D Mayshar Y McKay RD Michalska AE 《Nature biotechnology》2007,25(7):803-816
The International Stem Cell Initiative characterized 59 human embryonic stem cell lines from 17 laboratories worldwide. Despite diverse genotypes and different techniques used for derivation and maintenance, all lines exhibited similar expression patterns for several markers of human embryonic stem cells. They expressed the glycolipid antigens SSEA3 and SSEA4, the keratan sulfate antigens TRA-1-60, TRA-1-81, GCTM2 and GCT343, and the protein antigens CD9, Thy1 (also known as CD90), tissue-nonspecific alkaline phosphatase and class 1 HLA, as well as the strongly developmentally regulated genes NANOG, POU5F1 (formerly known as OCT4), TDGF1, DNMT3B, GABRB3 and GDF3. Nevertheless, the lines were not identical: differences in expression of several lineage markers were evident, and several imprinted genes showed generally similar allele-specific expression patterns, but some gene-dependent variation was observed. Also, some female lines expressed readily detectable levels of XIST whereas others did not. No significant contamination of the lines with mycoplasma, bacteria or cytopathic viruses was detected. 相似文献
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