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1.
Castanospermine: a potent inhibitor of sucrase from the human enterocyte-like cell line Caco-2 总被引:2,自引:0,他引:2
The addition of castanospermine (5-50 microM) to a culture medium of Caco-2 cells results in a specific suppression of sucrase activity without modification of the biosynthesis of the enzyme. This effect is due to a direct inhibiting effect of castanospermine on Caco-2 sucrase activity. This inhibition is time-dependent (half-maximum efficiency at 10 min for 100 nM), enhanced by preincubation (suggesting a strong interaction with the enzyme), dose-dependent (ED50 at 4 nM after 1 h preincubation period) and of the fully non-competitive type. The calculated Ki (2.6 nM) suggests that castanospermine is the most potent inhibitor of sucrase so far reported. 相似文献
2.
Qualitative and quantitative investigations on the hemolymph proteins in the adult firebrat Thermobia domestica were performed during an ovarian cycle in inseminated and noninseminated females. Variations of hemolymph protein concentration were determined by Lowry's method. In addition, the proteins were studied by gradient slab gel electrophoresis using nondenaturing conditions and microdensitometry. Besides five major protein fractions, which are present in both sexes, three female-specific protein bands (vitellogenins) are found in the hemolymph and in maturing oocytes. These vitellogenins have molecular masses of 430, 300 and 240 kiloDalton. In fact, associated with the main 300-kD band, there were two smaller bands (320 and 280 kD) indistinguishable by densitometric measurement. Quantitative changes of vitellogenins are linked to oocyte maturation. These proteins appeared in the hemolymph before ecdysis, at the same time as the first yolk granules in the basal oocytes. They increased after ecdysis during the intense vitellogenic phase and decreased during chorion formation. In noninseminated females, in which all maturing oocytes are resorbed before chorion formation, the level of the 300 kD vitellogenins remained lower than in inseminated females. The quantity of vitellogenins fell only after complete oosorption. Thus insemination caused changes in the relative quantities of the different vitellogenic proteins. 相似文献
3.
4.
Modulation of IL-4-induced human IgE production in vitro by IFN-gamma and IL-5: the role of soluble CD23 (s-CD23) 总被引:10,自引:0,他引:10
J Pène I Chrétien F Rousset F Brière J Y Bonnefoy J E de Vries 《Journal of cellular biochemistry》1989,39(3):253-264
IL-4 specifically induced IgE production by peripheral blood lymphocytes or by tonsil or spleen cells from healthy donors. IL-4-induced IgE synthesis was dependent on CD4+ T cells and monocytes and was blocked by IFN-gamma, IFN-alpha, and prostaglandin E-2 (PGE-2). These substances also inhibited IL-4-induced CD23 expression and subsequent release of soluble CD23 (s-CD23). In addition, IgE production was blocked by F(ab')2 fragments of an mAb against CD23. In contrast, IL-5 enhanced IL-4-induced IgE production, provided IL-4 was added at nonsaturating concentrations. This increase in IgE production correlated quantitatively with an enhanced release of s-CD23. Collectively, these results indicate that there is a correlation between s-CD23 release and IgE production. However, s-CD23 fractionated from supernatants of the lymphoblastoid cell line RPMI-8866 was ineffective in inducing IgE production in the absence of IL-4, but acted synergistically with suboptimal concentrations of IL-4. In addition, it is demonstrated that alloreactive T-cell clones produced varying concentrations of IL-4, IL-2, or IFN-gamma upon stimulation. Only supernatants of 2/4 of these T-cell clones induced a low degree of IgE synthesis, but in the presence of anti-IFN-gamma antibodies, all four supernatants induced a strong induction of IgE production. This IgE synthesis was blocked specifically by anti-IL-4 antibodies, indicating that IL-4 is the sole inducer of IgE synthesis. Our findings demonstrate that IL-4-induced IgE production involves complex interactions of T cells, B cells, and monocytes and is positively modulated by IL-5 and s-CD23 but down-regulated by IFN-gamma, IFN-alpha, and PGE-2, respectively. 相似文献
5.
F Rousset M Billaud D Blanchard C Figdor G M Lenoir H Spits J E De Vries 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(5):1490-1498
LFA-1 and LFA-3 expression is absent or low on Burkitt's lymphoma cell lines and low on the EBV-transformed B cell line UD61. Incubation of cells of BL2 and of UD61 with various concentrations of IL-4 resulted in induction of LFA-1 and LFA-3 expression in a dose dependent fashion. This effect was already observed after 16 h of incubation whereas maximal expression was obtained after 72 h. Induction of LFA-1 and LFA-3 expression seemed to be specific for IL-4, because IL-1, IL-2, IL-3, IFN-alpha, IFN-gamma and a low m.w. B cell growth factor were ineffective. LFA-1 and LFA-3 induction by IL-4 was blocked specifically by an anti-IL-4 antiserum. Induction of LFA-1 expression by IL-4 was furthermore confirmed at the specific LFA-1 beta-chain mRNA level. IL-4 was unable to induce LFA-1 expression on EBV-transformed lymphoblastoid cell lines of two LFA-1-deficient patients. BL2 grows as single cells, but induction of LFA-1 and LFA-3 expression by IL-4 was insufficient to induce homotypic cell adhesions and required PMA as a second signal. PMA alone did not induce LFA-1 antigen expression and was unable to induce adhesions between BL2 cells in the absence of IL-4 in 22 h assays. Addition of PMA to BL2 cells that expressed LFA-1 Ag upon incubation with IL-4 resulted in aggregate formation within 30 min. Adhesions between BL2 cells induced by IL-4 in combination with PMA were blocked by anti-LFA-1 beta or anti-LFA-1 alpha-chains mAb. In addition, these mAbs dispersed preformed aggregates of BL2 cells. Our results indicate that IL-4 can induce the adhesion molecules LFA-1 and LFA-3 on B cell lines, but that an additional activation signal provided by PMA was required for the induction of homotypic cell adhesions. 相似文献
6.
An exogenous albumin promoter can become silent in dedifferentiated hepatoma variants as well as intertypic hybrids 总被引:5,自引:0,他引:5
In order to evaluate the ability of an exogenous tissue-specific promoter to undergo the same dynamic changes in activity as the endogenous one, a 400-base pair fragment of the rat albumin proximal promoter, upstream of the bacterial gpt gene, has been introduced into rat hepatoma cells. Four clones containing a single integrated copy of the construct and producing substantial amounts of albumin and of xanthine phosphoribosyltransferase were isolated. These clones were subjected to two treatments known to result in silencing of the albumin gene: selection for dedifferentiated variants, and fusion with L-cell fibroblasts. In most cases, the albumin-negative progeny obtained no longer expressed the gpt gene: the exogenous promoter of 400 base pairs must contain the sequences required to respond to the mechanisms that block activity of the endogenous gene. However, exceptions were observed: the albumin-deficient variants of one clone remained xanthine phosphoribosyltransferase positive, and some of the albumin-negative hybrids from a different clone continued to produce xanthine phosphoribosyltransferase. These cases of dissociation in expression of the endogenous and the exogenous genes indicate that the site of integration of the alb-gpt construct in one clone renders the sequences insensitive to the mechanisms responsible for albumin gene silencing in dedifferentiated variants, and in the other clone to the mechanism of extinction. Consequently, the mechanisms causing gene silencing in variants and in intertypic hybrids must be different. 相似文献
7.
M. T. Nieto-Taladriz M. R. Perretant M. Rousset 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(1):81-88
The storage proteins of 64 F2-derived F6 recombinant inbred lines (RILs) from the bread wheat cross Prinqual/Marengo were analyzed. Parents differed at four loci: Gli-B1 (coding for gliadins), Glu-B1 (coding for HMW glutenin subunits), Glu-A3/Gli-A1 (coding for LMW glutenin subunits/gliadins) and Glu-D3 (coding for LMW glutenin subunits). The effect of allelic variation at these loci on tenacity, extensibility and dough strength as measured by the Chopin alveograph was determined. Allelic differences at the Glu-B1 locus had a significant effect on only tenacity. None of the allelic differences at either the Glu-A3/Gli-A1 or Glu-D3 loci had a significant effect on quality criteria. Allelic variation at the Gli-B1 locus significantly affected all of the dough properties. Epistatic effects between some of the loci considered contributed significantly to the variation in dough quality. Additive and epistatic effects each accounted for 15% of the variation in tenacity. Epistasis accounted for 15% of the variation in extensibility, whereas additive effects accounted for 4%. Epistasis accounted for 14% of the variation in dough strength, and additivity for 9%. The relative importance of epistatic effects suggest that they should be included in predictive models when breeding for breadmaking quality. 相似文献
8.
Translational frameshifting at the gag-pol junction of human immunodeficiency virus type 1 is not increased in infected T-lymphoid cells. 总被引:3,自引:2,他引:1
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A frameshift event is necessary for expression of the products of the pol gene in a number of retroviruses, including human immunodeficiency virus type 1 (HIV-1). The basic signals necessary for frameshifting consist of a shifty sequence in which the ribosome slips and a downstream stimulatory structure which can be either a stem-loop or a pseudoknot. In HIV-1, much attention has been paid to the frameshift site itself, and only recently has the role of the downstream structure been examined. Here we used a luciferase-based experimental system to analyze in vivo the cis and trans factors potentially involved in controlling frameshifting efficiency at the gag-pol junction of HIV-1. We demonstrated that high-level frameshifting is dependent on the presence of a palindromic region located downstream of the site where the frameshift event takes place. Frameshifting efficiencies were found to be identical in mouse fibroblasts and the natural host cells of the virus, i.e., CD4+ human lymphoid cells. Furthermore, no increase in frameshifting was observed upon virus infection. Previous observations have shown that viral infection leads to specific alteration of tRNAs involved in translation of shifty sites (D. Hatfield, Y.-X. Feng, B.J. Lee, A. Rein, J.G. Levin, and S. Oroszlan, Virology 173:736-742, 1989). The results presented here strongly suggest that these modifications do not affect frameshifting efficiency. 相似文献
9.
Wolbachia are strictly endocellular, vertically transmitted bacteria associated with insects and crustaceans. This group of parasites modify their hosts' reproduction so as to increase their own fitness. This paper reviews the variability of these parasitic alterations and their consequences for host biology and populations. Wolbachia induce cytoplasmic incompatibility (a characteristic apparently specific to Wolbachia) in several insects and one isopod crustacean; parthenogenesis (thelytoky) in haplo-diploid insects; feminization in various isopods. The consequences of these phenomena on speciation, population dynamics and genetic polymorphism are discussed. The variability of the mechanisms of host sex determination is one important factor responsible for the diversity of Wolbachia-host interactions. However, parasite characteristics, such as the capacity to disturb host mitosis, and the ability to be horizontally transferred between hosts, also appear to play a role in this diversity. 相似文献
10.
K. Michalova J. Jami J. -P. Rousset E. Ritz D. Bucchini 《Experimental cell research》1978,114(2):293-300
Metaphases collected from cultures grown for three cell cycles in 5-bromodeoxyuridine (BUdR) and then for one or two further cell cycles without BUdR show persistence of differentially FPG-stained chromatids. The cell cycle length is not altered by the presence of BUdR. After removal of BUdR, the cells synthesize DNA and incorporate mainly thymine, as demonstrated by density gradient analysis of DNA. Our observations suggest that chromatids with T-B DNA stain lightly after removal of BUdR, in contrast with their dark staining when cultures are maintained in BUdR. Thus, in any experimental condition, there is a correspondence between the nature (T-DNA or B-DNA) of the “old” DNA strands and the FPG-staining (dark or light) of the chromatids. 相似文献