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We have analyzed micrococcal nuclease (MNase) DNA cleavage patterns at the sequence level by examining 2.3 X 10(3) base-pairs of data derived from the Drosophila melanogaster 44D larval cuticle locus. Within this region, MNase preferentially cleaved 140 sites. Clusters of these sites appear to generate the preferential MNase eukaryotic DNA cleavage sites seen on agarose gels at roughly 100 to 300 base-pair intervals. These clusters of preferential cleavage sites rarely occur within gene coding regions. The analysis revealed that duplex DNA sequences preferentially cleaved by MNase are generally determined by a single strand sequence: d(A-T)n, where n greater than or equal to 1, flanked by a 5' dC or dG. Cleavage of the other strand is generally staggered 5' by several nucleotides and occurs even if such sequences are absent on that strand. An empirical predictive DNA cleavage model derived from a statistical analysis of the sequence level data was applied to seven eukaryotic gene loci of known sequence. The predicted patterns were in good general agreement with the previously observed eukaryotic gene/spacer cleavage pattern. Statistical analysis also revealed that sites of predicted preferential DNA cleavage occur less frequently in protein coding regions than for randomized sequences of the same length and nucleotide content. Comparison of the MNase cleavage patterns to the sequence-dependent pattern of binding energies between duplex DNA strands indicates that MNase preferentially cleaves sequences with low helix stability.  相似文献   
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Elevation in intracellular Ca2+ acting via protein kinase C (PKC) is shown to regulate tight junction resistance in T84 cells, a human colon cancer line and a model Cl secretory epithelial cell. The Ca2+ ionophore A23187, which was used to increase the intracellular Ca2+ concentration, caused a decrease in tight junction resistance in a concentration- and time-dependent manner. Dual Na+/mannitol serosal-to-mucosal flux analysis performed across the T84 monolayers treated with 2 μm A23187 revealed that A23187 increased both fluxes and that in the presence of ionophore there was a linear relationship between the Na+ and mannitol fluxes with a slope of 56.4, indicating that the decrease in transepithelial resistance was due to a decrease in tight junction resistance. Whereas there was no effect of 0.1 μm A23187, 1 or 2 μm produced a 55% decrease in baseline resistance in 1 hr and 10 μm decreased resistance more than 80%. The A23187-induced decrease in tight junction resistance was partially reversible by washing 3 times with a Ringer's-HCO3 solution containing 1% BSA. The A23187 effect on resistance was dependent on intracellular Ca2+; loading the T84 cells with the intracellular Ca2+ chelator BAPTA significantly reduced the decrease in tight junction resistance caused by A23187. This intracellular Ca2+ effect was mediated by protein kinase C and not calmodulin. While the protein kinase C antagonist H-7 totally prevented the action of A23187 on tight junction resistance, the Ca2+/calmodulin inhibitor W13 did not have any effect. Sphingosine, another inhibitor of PKC, partially reduced the A23187-induced decline in tight junction resistance. The PKC agonist PMA mimicked the A23187 effect on resistance, although the effect was delayed up to 1 hr after exposure. In addition, however, PMA also caused an earlier increase in resistance, indicating it had an additional effect in addition to mimicking the effect of elevating Ca2+. The effects of a phospholipase inhibitor (mepacrine) and of inhibitors of arachidonic acid metabolism (indomethacin for the cyclooxygenase pathway, NDGA for the lipoxygenase pathway, and SKF 525A for the epoxygenase pathway) on the A23187 action were also examined. None of these agents altered the A23187-induced decrease in resistance. Monolayers exposed to 2 μm A23187 for 1 hr were stained with fluorescein conjugated phalloidin, revealing that neighboring cells did not part one from another and that A23187 did not have a detectable effect on distribution of F-actin in the perijunctional actomyosin ring. The results indicate that elevation in intracellular Ca2+ decreases tight junction resistance in the T84 monolayer, acting through protein kinase C by a mechanism which does not involve visible changes in the perijunctional actomyosin ring. Received: 14 July 1995/Revised: 25 September 1995  相似文献   
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The molecular evolution of mammalian Y-linked DNA sequences is of special interest because of their unique mode of inheritance: most Y- linked sequences are clonally inherited from father to son. Here we investigate the use of Y-linked sequences for phylogenetic inference. We describe a comparative analysis of a 515-bp region from the male sex- determining locus, Sry, in 22 murine rodents (subfamily Murinae, family Muridae), including representatives from nine species of Mus, and from two additional murine genera--Mastomys and Hylomyscus. Percent sequence divergence was < 0.01% for comparisons between populations within a species and was 0.19%-8.16% for comparisons between species. Our phylogenetic analysis of 12 murine taxa resulted in a single most- parsimonius tree that is highly concordant with phylogenies based on mitochondrial DNA and allozymes. A total evidence tree based on the combined data from Sry, mitochondrial DNA, and allozymes supports (1) the monophyly of the subgenus Mus, (2) its division into a Palearctic group (M. musculus, M. domesticus, M. spicilegus, M. Macedonicus, and M. spretus) and an Oriental group (M. cookii++, M. cervicolor, and M. caroli), and (3) sister-group relationships between M. spicilegus and M. macedonicus and between M. cookii and M. cervicolor. We argue that Y- chromosome DNA sequences represent a valuable new source of characters for phylogenetic inference.   相似文献   
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During sequence analysis of the first intron of the human c-fms oncogene, we identified an open reading frame encoding the ribosomal protein L7 (RPL7). The presence of this sequence within intron 1 of the c-fms gene was confirmed by Southern blot hybridization and by sequence analysis of two independent cosmid clones (cos2-e and cos1-22) that span the human genomic c-fms locus. The RPL7 sequence was detected in a region of sequence overlapped by the cos2-e and cos1-22 cosmid clones but oriented opposite to the c-fms gene. We demonstrated that the sequence is identical to the full-length RPL7 cDNA sequence, but lacks any recognizable introns, has a 30-bp poly(A) tail, and is bracketed by two perfect direct repeats of 14 bp. We also showed that despite the fact that the 5′ flanking region of the RPL7 sequence contains a potential TATA box upstream of an intact open reading frame, this pseudogene (RPL7P) is not actively transcribed.  相似文献   
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Crystal structures of the Ser/Thr phosphatase calcineurin (protein phosphatase 2B) have recently been solved by X-ray crystallography, both in the free-protein state, and complexed with the immunophilin/immunosuppressant FKBP12/FK506. Core elements of the calcineurin phosphatase have been found to be similar to the corresponding elements of Ser/Thr phosphatase 1 and purple acid phosphatase. The structures provide a basis for understanding calcineurin inhibition by a ternary complex of immunophilin and immunosuppressant proteins.  相似文献   
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A range of emerging technologies are expected to play a significant role in agricultural improvement in the next 20 years. Some are only now being explored, but others have already produced significant results. Recent progress in the tissue culture and genetic engineering of crop plants has opened the door to: (1) large scale and rapid propagation of genetically uniform plants from elite materials; (2) the selection of novel and improved varieties using somaclonal variation technology; (3) the development of new hybrids between different cultivars and species by means of protoplast fusion and (4) the use of recombinant DNA to introduce new genetic material into plant cells. It is expected that, by the year 2000, a wide range of crops will be affected by these advances in biotechnology.  相似文献   
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The nucleotide sequence of the tmr locus from the nopaline-type pTi T37 plasmid of Agrobacterium tumefaciens was determined. Examination of this sequence allowed us to identify an open reading frame of 720 nucleotides capable of encoding a protein with a derived molecular weight of 27025 d. Comparison of the pTi T37 tmr sequence with the published sequence of the pTi Ach5 tmr locus shows over 88% homology in the 240 bases 5' to the translational initiation codon and over 91% homology in the coding sequences. The 3' nontranslated regions show less than 50% homology as expected for the 3' regions of divergent related genes. The possible significance of areas of conserved sequences, particularly in the 5' regulatory regions, is discussed.  相似文献   
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Several lines of experimental evidence are presented suggesting that the L antigens in low potassium (LK) sheep red cells are associated with separate Na(+)K(+) pump flux is distinct from the action of anti-L(l) on K(+) leak flux, implying that K(+) leak transport sites may not be converted into active pumps by the L antiserum. Treatment of LK red cells with trypsin completely abolished both the stimulation of K(+) pump flux and the enhancement of the rate of ouabain binding brought about by anti- L. That this effect is due to a total destruction of the L(p) determinant associated with the LK pump was evident from the complete failure of anti-L(p) to bind to trypsinized LK red cells. The L(p) antigen can be effectively protected against the trypsin attack by prior incubation with anti-L, indicating that the sites for antibody binding and trypsin action may be closely adjacent at the structural level. Trypsin treatment, however, did not interfere with anti-L(l) reducing ouabain insensitive K(+) leak influx, nor did it prevent binding of anti-L(ly), the hemolytically active L antibody which is probably identical with anti-L(l). The functional independence of the L(p) and L(l) sites was documented by the observation that anti-L(l) still reduced K(+) leak influx in LK cells with experimentally induced high potassium concentrations, at which K(+) pump flux is fully suppressed, whether or not anti-L(p) was binding to the L(p) antigen associated with the LK pump.  相似文献   
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