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1.
The sequences coding for DNA[cytosine-N4]methyltransferases MvaI (from Micrococcus varians RFL19) and Cfr9I (from Citrobacter freundii RFL9) have been determined. The predicted methylases are proteins of 454 and 300 amino acids, respectively. Primary structure comparison of M.Cfr9I and another m4C-forming methylase, M.Pvu II, revealed extended regions of homology. The sequence comparison of the three DNA[cytosine-N4]-methylases using originally developed software revealed two conserved patterns, DPF-GSGT and TSPPY, which were found similar also to those of adenine and DNA[cytosine-C5]-methylases. These data provided a basis for global alignment and classification of DNA-methylase sequences. Structural considerations led us to suggest that the first region could be the binding site of AdoMet, while the second is thought to be directly involved in the modification of the exocyclic amino group.  相似文献
2.
The complete nucleotide sequence (321 bp) of smr (staphylococcal multidrug resistance), a gene coding for efflux-mediated multidrug resistance of Staphylococcus aureus, was determined by using two different plasmids as DNA templates. The smr gene product (identical to products of ebr and qacC/D genes) was shown to be homologous to a new family of small membrane proteins found in Escherichia coli, Pseudomonas aeruginosa, Agrobacterium tumefaciens, and Proteus vulgaris. The smr gene was subcloned and expressed in S. aureus and E. coli and its ability to confer the multidrug resistant phenotype was demonstrated for two different lipophilic cation classes: phosphonium derivatives and quarternary amines. Expression of smr gene leads to the efflux of tetraphenylphosphonium and to a net decrease in the uptake of lipophilic cations. The deduced polypeptide sequence (107 amino acid residues, 11,665 kDa) has 46% hydrophobic residues (Phe, Ile, Leu, and Val) and 20% hydroxylic residues (Ser and Thr). Four transmembrane segments are predicted for smr gene product. Of the charged amino acid residues, only Glu 13 is located in a transmembrane segment. This Glu 13 is conserved in all members of the family of small membrane proteins. We propose a mechanism whereby exchange of protons at the Glu 13 is a key in the efflux of the lipophilic cation. This mechanism includes the idea that protons are transported to the Glu 13 via an appropriate chain of hydroxylic residues in the transmembrane segments of Smr.  相似文献
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Genetic recombination can be important evolutionarily in speeding the adaptation of organisms to new environments and in purging deleterious mutations. Here, we describe polymerase chain reaction (PCR), hybridization and DNA sequence-based evidence of six such exchanges between two strains of Helicobacter pylori during natural mixed infection of a patient in Lithuania. One parent strain contained the 37 kb long, virulence-associated cag pathogenicity island (PAI), and the other strain lacked this PAI. Most H. pylori from the patient had descended from the cag + parent, but had become cag during infection. This had resulted from transfer of DNA containing the 'empty site' allele from the cag strain and homologous recombination, not from excision of the cag PAI without DNA transfer. Other cases of recombination involved genes for an outer membrane protein ( omp 5 and omp 29; also called HP0227 and HP1342) and a putative phosphoenolpyruvate synthase ( ppsA  ; HP0121). Replacement of a short patch of DNA sequence (36–124 bp) was also seen. As the chance of forming any given recombinant is small, the abundance of recombinants in this patient suggests selection for particular recombinant genotypes during years of chronic infection. We suggest that genetic exchange among unrelated H. pylori strains, as documented here, is important because of the diversity of this gastric pathogen and its human hosts. Certain H. pylori recombinants may grow better in a given host than either parent. The vigour of growth, in turn, could impact on the severity of disease that infection can elicit.  相似文献
5.
This paper reports on the isolation of a novel class of plant serine/threonine protein kinase genes, MsK-1 , MsK-2 and MsK-3 . They belong to the superfamily of cdc2 -like genes, but show highest identity to the Drosophila shaggy and rat GSK-3 proteins (66–70%). All of these kinases share a highly conserved catalytic protein kinase domain. Different amino-terminal extensions distinguish the different proteins. The different plant kinases do not originate from differential processing of the same gene as is found for shaggy , but are encoded by different members of a gene family. Similarly to the shaggy kinases, the plant kinases show different organ-specific and stage-specific developmental expression patterns. Since the shaggy kinases play an important role in intercellular communication in Drosophila development, the MsK kinases are expected to perform a similar function in plants.  相似文献
6.
The Baltic Sea, a semi-enclosed brackish water region, has been inoculated by non-indigenous species for centuries. Today, much of its biological diversity is of foreign origin (i.e. xenodiversity), intentionally or unintentionally moved by humans over ecological and geographical barriers. As many as 98 introduced species have been recorded in the Baltic Sea and Kattegat. The role and abundance of much of the unique native brackish water fauna of the Baltic Sea are threatened by these non-indigenous species. The rate of primary introductions into the Baltic has increased since the 1950s; the secondary rate of spread of non-indigenous species within the basin varies from 30–480 km/year. We review here the invasion histories of the brown alga Sargassum muticum (introduced in the early 1990s), the mud snail Potamopyrgus antipodarum (1887), the barnacle Balanus improvisus (1844), the polychaetes Marenzelleria viridis (1985) and Polydora redeki (1963), the cladoceran Cercopagis pengoi (1992) and the mysid shrimp Hemimysis anomala (1962). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献
7.
Recent advances in cytogenetics of the Lolium/Festuca complex provide new opportunities for understanding and manipulating physiological mechanisms in complex quantitative traits such as stress resistance. The complex provides a valuable reserve for research and breeding since (a) it includes a wide range of valuable agronomic characters, (b) it has the capacity for intergeneric hybridization with promiscuous recombination, and its genomes, despite their close homology, have sufficient structural heterogeneity to allow Lolium and Festuca chromosomes to be discriminated using genomic in situ hybridization (GISH).Two alternative procedures are used to 'dissect' stress-resistance traits into their individual components both to determine their function and to physically map the relevant QTL(s) onto chromosome arms: (a) Festuca genes are introgessed into Lolium to improve stress resistance, (b) Lolium genes are introgressed into Festuca to reduce stress resistance. Whichever approach is used, alien introgressions can be detected by GISH and assigned to chromosome arms to create a physical map. Genes of interest may then be located more accurately following further recombination events which reduce the size of the relevant alien introgression.It has become obvious during the past years that genetic and physical maps are not directly comparable as chiasmata are not evenly distributed along the chromosome axis. By integrating physical maps created by GISH and genetic linkage-maps, the precise site of genes on a chromosome arm may be determined, and markers found which are tightly linked to the genes of interests, for future use in breeding programmes.Key words: Genomic in situ hybridization (GISH), physical mapping, Lolium/Festuca complex, stress resistance.   相似文献
8.
The Eco57I restriction endonuclease and methylase were purified to homogeneity from the E.coli RR1 strain carrying the eco57IRM genes on a recombinant plasmid. The molecular weight of the denaturated methylase is 63 kDa. The restriction endonuclease exists in a monomeric form with an apparent molecular weight of 104-108 kDa. R.Eco57I also possesses methylase activity. The methylation activities of both enzymes modify the outer A residue in the target sequence 5'CTGAAG yielding N6-methyladenine. M.Eco57I modifies both strands of the substrate while R.Eco57I modifies only one. Only the methylase enzyme is stimulated by Ca2+. The restriction endonuclease shows an absolute requirement for Mg2+ and is stimulated by AdoMet. ATP has no influence on either activity of the enzymes. The subunit structure and enzymatic properties of the Eco57I enzymes distinguish them from all other restriction-modification enzymes that have been described previously. Therefore, RM.Eco57I may be regarded as a representative of a novel class of restriction-modification systems, and we propose to classify it as type IV.  相似文献
9.
Graphite (GE) or printed graphite electrode (PGE) based biosensors containing recombinant fungal laccase Polyporus pinsitus (rPpL), and Myceliophthora thermophila (rMtL) were developed. The enzymes were immobilized using bovine serum albumin and glutaraldehyde. At pH 5.5 and -0.1 V, the calibration graphs of GE based biosensors were hyperbolic if pyrocatechol was used. The concentration of substrate that results in 50% of steady-state response (EC(50)) was 0.7 mM and sensitivity (S) was 3.8 mA/M. The sensitivity increased up to 4 A/M if larger amount of rPpL was used. The sensitivity of biosensors changed little during 9 days of exploitation, but decreased at longer time. The PGE based biosensors were mounted into the flow-through cell and calibrated under kinetic regime. EC(50) of the biosensors containing rPpL varied from 0.6 to 4.0 mM and sensitivity varied from 0.11 to 1.9 mA/M. The response of biosensor containing thermostable laccase rMtL was less, but response saturated at larger pyrocatechol concentration. The sensitivity changed little during 6 days. Both type of biosensors responded also to 1-naphthol, o-phenylenediamine, guaiacol, o-anizidine, benzidine. The experiments demonstrate recombinant laccases application to biosensor engineering and their use to phenol and related compound determination under steady-state and flow-through regimes.  相似文献
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