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We have isolated mutants of Rous sarcoma virus from an unmutagenized stock of the Schmidt-Ruppin strain of Rous sarcoma virus. These mutants induce only a "partial" transformation, and the transformation properties induced show unusual properties or combinations. Cells infected with mutant CU2 have a unique "blebby" morphology, have lost surface fibronectin, form very small colonies in soft agar, and are nearly normal with respect to adhesiveness and hexose transport. Cells infected with mutant tsCU11 have a nearly normal morphology, but grow well in soft agar. Cells infected with mutant CU12 have a fusiform morphology, intermediate levels of hexose transport and fibronectin, and form very large colonies in soft agar. Because the appearance of the different parameters of transformation is dissociated in these mutant-infected cells, these data are interpreted as supporting a model in which the transforming protein pp60src interacts with more than one primary target in generating the transformed phenotype. All of the mutants display levels of pp60src kinase activity less than that of the wild type. In the case of mutant CU12, the lower kinase activity is in part a consequence of a lower steady-state amount of pp60src inside the cell.  相似文献
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The complete nucleotide sequence of the mRNA for the outer membrane lipoprotein from Escherichia coli has been determined. All the ribonuclease T1 and ribonuclease A fragments obtained from the mRNA were connected with DNA sequencing of restriction endonuclease fragments of the cloned lipoprotein gene. The mRNA consists of 322 nucleotides, and there are 38 and 50 nucleotides in the 5' and 3' end untranslated regions, respectively. The mRNA has several unique features: (a) Out of 50 possible codons for 15 amino acids in the prolipoprotein only 25 codons are used, and all of these appear to be read by the major isoaccepting species of tRNAs for individual amino acids. (b) In the first 64 nucleotides from the 5' end, there are no obvious secondary structures. On the other hand, between the 65th nucleotide and the 3' end, 85% of the nucleotides are involved in the formation of secondary structures, with nine stable stem-and-loop structures. (c) There are many repeating sequences including one repeat of 40 nucleotides. (d) There are a few other features which could be important for efficient translation of the mRNA.  相似文献
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The most important function of carotenoid pigments, especially beta-carotene in higher plants, is to protect organisms against photooxidative damage (G. Britton, in T. W. Goodwin, ed., Plant Pigments--1988, 1988; N. I. Krinsky, in O. Isler, H. Gutmann, and U. Solms, ed., Carotenoids--1971, 1971). beta-Carotene also functions as a precursor of vitamin A in mammals (G. A. J. Pitt, in I. Osler, H. Gutmann, and U. Solms, ed., Carotenoids--1971, 1971). The enzymes and genes which mediate the biosynthesis of cyclic carotenoids such as beta-carotene are virtually unknown. We have elucidated for the first time the pathway for biosynthesis of these carotenoids at the level of enzyme-catalyzed reactions, using bacterial carotenoid biosynthesis genes. These genes were cloned from a phytopathogenic bacterium, Erwinia uredovora 20D3 (ATCC 19321), in Escherichia coli and located on a 6,918-bp fragment whose nucleotide sequence was determined. Six open reading frames were found and designated the crtE, crtX, crtY, crtI, crtB, and crtZ genes in reference to the carotenoid biosynthesis genes of a photosynthetic bacterium, Rhodobacter capsulatus; only crtZ had the opposite orientation from the others. The carotenoid biosynthetic pathway in Erwinia uredovora was clarified by analyzing carotenoids accumulated in E. coli transformants in which some of these six genes were expressed, as follows: geranylgeranyl PPiCrtB----prephytoene PPiCrtE----phytoeneCrtI---- lycopeneCrtY----beta-caroteneCrtZ----zeaxanthinCrtX--- -zeaxanthin-beta- diglucoside. The carotenoids in this pathway appear to be close to those in higher plants rather than to those in bacteria. Also significant is that only one gene product (CrtI) for the conversion of phytoene to lycopene is required, a conversion in which four sequential desaturations should occur via the intermediates phytofluene, zeta-carotene, and neurosporene.  相似文献
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The ompF gene codes for a major outer membrane protein whose expression is positively regulated by the ompR and envZ genes. Two sets of promoter deletions, upstream deletions and downstream deletions, were generated in vitro, and the promoter function was studied by connecting them with the tet genes. One of the hybrid genes thus constructed had a functioning ompF-tet hybrid promoter. The 107 base-pair fragment was found to be functioning as the ompF promoter, 90 nucleotides upstream and 17 nucleotides downstream of the mRNA start site that was also determined in this study. The start site was preceded by a convenient Pribnow box. Although the sequence at the -35 region had a low degree of homology to the consensus sequence, analyses of the hybrid promoter suggested that this region is involved in the promoter function in relation to the Pribnow box. They also indicated that the domain responsible for regulation by the ompR gene is located within the -35 region and its upstream region.  相似文献
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SALL1 is a mammalian homolog of the Drosophila region-specific homeotic gene spalt (sal); heterozygous mutations in SALL1 in humans lead to Townes-Brocks syndrome. We have isolated a mouse homolog of SALL1 (Sall1) and found that mice deficient in Sall1 die in the perinatal period and that kidney agenesis or severe dysgenesis are present. Sall1 is expressed in the metanephric mesenchyme surrounding ureteric bud; homozygous deletion of Sall1 results in an incomplete ureteric bud outgrowth, a failure of tubule formation in the mesenchyme and an apoptosis of the mesenchyme. This phenotype is likely to be primarily caused by the absence of the inductive signal from the ureter, as the Sall1-deficient mesenchyme is competent with respect to epithelial differentiation. Sall1 is therefore essential for ureteric bud invasion, the initial key step for metanephros development.  相似文献
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The terminal structure of a linear plasmid pSLA2 , which was isolated from Streptomyces rochei , was analysed. The 5' ends of pSLA2 DNA were blocked by the association of a protein probably covalently bonded with the DNA. This block is removed by alkali treatment and blunt ends with 5'-phosphate and 3'-hydroxy termini were released. The two terminal fragments of pSLA2 were cloned and the nucleotide sequence was determined. An inverted terminal repetition of 614 bp was found along with the presence of further interrupted homologous sequences beyond this area up to 800 bp. These are the first inverted terminal repeat sequences found in microbial linear plasmids.  相似文献
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