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111.
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113.
Three antibodies that recognize distinct fucose epitopes were used to study
fucosylation during growth and development of Dictyostelium discoideum.
mAb83.5 is known to recognize an undefined "fucose epitope" on several
proteins with serine-rich domains, while mAb CAB4, and a component of
anti-horse-radish peroxidase, specifically recognize Fucalpha1,6GlcNAc and
Fucalpha1,3GlcNAc residues respectively in the core of N-linked
oligosaccharides. We show that mAb 83.5 defines a new type of
O-glycosylation. Serine-containing peptides incubated with GDPbeta[3H]Fuc
and microsomes formed two fucosylated products. A neutral product
accounting for 30% of the label did not react with the antibody, while the
rest of the label was incorporated into a charged product which contained
all the mAb83.5 reactive material. beta- Elimination of the labeled peptide
or endogenous products produced [3H]Fuc-1-P, indicating phosphodiester
linkage to serine. Fucbeta-1-P and GDP-betaFuc at 100 microM blocked
mAb83.5 binding to endogenous and peptide products, but their alpha-linked
anomers did not. Electrospray ionization mass spectra of the neutral and
anionic labeled products showed major peaks of mass units corresponding to
O-Fuc-Ser peptide and O-Fuc-phospho-Ser peptide, respectively. The activity
of Fuc- phosphotransferase exactly paralleled the accumulation of reactive
glycans during growth and development. The expressions of N-glycan core
Fucalpha1,6GlcNAc and Fucalpha1,3GlcNAc and their respective fucosyl
transferase activities were also synchronous, but their developmental
regulation differed from one another. Fucalpha1, 6GlcNAc was expressed
maximally during growth but declined during development. In contrast core
Fucalpha1,3GlcNAc epitopes were expressed almost exclusively during
development. These findings provide direct evidence for a novel type of
O-phosphofucosylation, demonstrate the existence of an O- fucosyl
transferase, and identify two different types of core fucosylation in the
N-glycans of Dictyostelium.
相似文献
114.
Evidence for an enhanced substrate requirement by marine mesophilic bacterial isolates at minimal growth temperatures 总被引:6,自引:0,他引:6
Bacterial isolates from the subtropical southeastern continental shelf were cultured in a matrix of temperature and substrate concentrations encompassing a range of temperature and substrate concentrations equal to and exceeding natural ones. At the annual minimum temperature, marine heterotrophic bacterial isolates required higher concentrations of dissolved substrates for active growth than are usually found in seawater. We show this to result from a nonlinear interaction of the combined effects of temperature and substrate concentration on bacterial growth and respiratory rate. As a result, bacterial and protozoan utilization of phytoplankton production during winter and early spring is low, permitting greater energy flow to zooplankton and benthic animals, while in late spring, summer, and fall, the microbial loop dominates energy flux and organic carbon utilization. Escherichia coli shows a similar nonlinear response to temperature at minimal substrate concentrations, albeit at a higher range of concentrations than were utilized by the marine isolates. Thus, bacteria from subtropical regions are shown to have a differential growth response near the minimum temperature for growth, depending on the concentration of available substrates.
Offprint requests to: W.J. Wiebe. 相似文献
115.
Preparations of the dissolved organic compounds released by photosynthesizing marine phytoplankton have been obtained with14carbon activities as high as 1.5 × 105 dpm/ml. The radioisotope content of the preparations resides wholly in dissolved organic compounds of low molecular weight (MW<3500), which are uncontaminated by residual14C-labeled inorganic carbon. The labeled compunds arise through photosynthetic fixation and do not appear to be products of cell lysis during the incubation or to originate from cell damage during the filtration step employed. 相似文献
116.
The release rate of dissolved organic carbon (DOC) by unialgal cultures and natural phytoplankton assemblages was constant over a wide range of dissolved inorganic carbon concentrations. DOC release was not proportional to the particulate organic carbon production rate. We postulate that intracellular DOC, fated for release, exists either as a separate pool from that leading to particulate organic carbon production or that there is active metabolic control on one portion of a common pool. 相似文献
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The role of progesterone metabolites in breast cancer: potential for new diagnostics and therapeutics 总被引:6,自引:3,他引:3
Wiebe JP Lewis MJ Cialacu V Pawlak KJ Zhang G 《The Journal of steroid biochemistry and molecular biology》2005,93(2-5):201-208
Proliferative changes in the normal breast are known to be controlled by female sex steroids. However, only a portion of all breast cancer patients respond to current estrogen based endocrine therapy, and with continued treatment nearly all will become unresponsive and experience relapse. Therefore, ultimately for the majority of breast carcinomas, explanations and treatments based on estrogen are inadequate. Recent observations indicate that 5α-pregnane and 4-pregnene progesterone metabolites may serve as regulators of estrogen-responsive as well as unresponsive human breast cancers. The conversion of progesterone to the 5α-pregnanes is increased while conversion to the 4-pregnenes is decreased in breast carcinoma tissue, as a result of changes in progesterone metabolizing 5α-reductase, 3α-hydroxysteroid oxidoreductase (3α-HSO) and 20α-HSO activities and gene expression. The 5α-pregnane, 5α-pregnane-3,20-dione (5αP) stimulates, whereas the 4-pregnene, 3α-hydroxy-4-pregnen-20-one (3αHP), inhibits cell proliferation and detachment, by modulation of cytoskeletal and adhesion plaque molecules via the MAP kinase pathway and involving separate and specific plasma membrane-based receptors. The promotion of breast cancer appears to be related to changes in in situ concentrations of cancer-inhibiting and cancer-promoting progesterone metabolites. New diagnostic and therapeutic possibilities for breast cancer are suggested. 相似文献