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511.
A likely function of the Lambda FI gene product (gpFI) is condensation of developmental forms of the bacteriophage DNA in the host cell. Several characteristics of gpFI support this hypothesis: it is similar in its structure and properties toE. coli NS proteins whose involvement in the bacterial DNA condensation has been established and it comigrates with DNA during fractionation of host cell lysate through a sucrose gradient. 相似文献
512.
In this work we discuss different factors governing coil-globule coexistence in the compaction process of DNA. We initially
analyse the role played by fluctuations in the degree of binding of an external compacting agent in the conformational behavior
of the chain backbone. The analysis relies both on Monte Carlo simulation results and simple statistical approaches. Compacting
agents of various binding characteristics are taken into consideration and the degree of charge neutralization upon the chain
is related to conformational indicators. Selected model systems comprising stiff chains in the presence of multivalent ions
are employed to assess intrinsic single-chain conformational fluctuation, in the presence of external agents but not resulting
from differences in binding. It is shown that trends found for a variety of compacting agents, including the extension of
the coil-globule coexistence regions, can be ratio-nalised on the basis of this analysis. 相似文献
513.
Increased adult body size in Drosophila raised at lower temperatures could be attributed both to an increase in the cell volume and cell number. It is not clear, however, whether increased cell size is related to (or even caused by) increased nuclear volume and genome size (or configuration). Experiments with Drosophila melanogaster stocks (Oregon-R and w1118) raised at 16, 22, 24, and 28 °C resulted in larger adult body and wing size with lower temperature, while eye size was less affected. The increase in wing size reflected an increase in cell size in both males and females of both stocks. The nucleus size, genome size, and DNA condensation of adult flies, embryos, and Schneider 2 cells (S2 cells, of larval origin) were estimated by flow cytometry. In both adult flies and S2 cells, both nucleus size and DNA condensation varied with temperature, while DNA content appears to be constant. From 12% to 18% of the somatic cells were tetraploid (4C) and 2–5% were octoploid (8C), and for the Oregon strain we observed an increase in the fraction of polyploid cells with decreasing temperature. The observed increase in body size (and wing size) at low temperatures could partly be linked with the cell size and DNA condensation, while corresponding changes in the haploid genome size were not observed. 相似文献
514.
J. Bordas L. Perez-Grau M. H. J. Koch M. C. Vega C. Nave 《European biophysics journal : EBJ》1986,13(3):175-185
Model calculations on the superstructure of uncondensed and condensed chromatin are presented. It is found that agreement between the calculated X-ray solution scattering patterns and the experimental observations can be reached with the assumptions that: a) The uncondensed chromatin fibre in solution has a helix-like structure, with a pitch of ca. 33.0 nm, a helical diameter of ca. 20.0 nm and 2.75–3.25 nucleosomes per turn. b) The most condensed state of the chromatin fibre in solution is best represented by a helix-like structure with ca. 2.56 nucleosomes per turn, a pitch of ca. 3.0 nm and a helical diameter of ca. 27.0 nm. 相似文献
515.
Lasonolide A (LSA) is a natural product with high and selective cytotoxicity against mesenchymal cancer cells, including leukemia, melanomas and glioblastomas. Here, we reveal that LSA induces rapid and reversible premature chromosome condensation (PCC) associated with cell detachment, plasma membrane smoothening and actin reorganization. PCC is induced at all phases of the cell cycle in proliferative cells as well as in circulating human lymphocytes in G0. It is independent of Cdk1 signaling, associated with cyclin B downregulation and induced in cells at LSA concentrations that are three orders of magnitude lower than those required to block phosphatases 1 and 2A in vitro. At the epigenetic level, LSA-induced PCC is coupled with histone H3 and H1 hyperphosphorylation and deacetylation. Treatment with SAHA reduced LSA-induced PCC, implicating histone deacetylation as one of the PCC effector mechanisms. In addition, PCC is coupled with topoisomerase II (Top2) and Aurora A hyperphosphorylation and activation. Inhibition of Top2 or Aurora A partially blocked LSA-induced PCC. Our findings demonstrate the profound epigenetic alterations induced by LSA and the potential of LSA as a new cytogenetic tool. Based on the unique cellular effects of LSA, further studies are warranted to uncover the cellular target of lasonolide A (“TOL”). 相似文献
516.
Huda Alsaeedi 《Luminescence》2023,38(5):527-535
Novel push–pull fluorescent molecules based on dicyanodihydrofuran that had marked molar extinction coefficients were created and described. The fluorophores were synthesized using the Knoevenagel condensation in arid pyridine at room temperature and acetic acid as a catalytic agent. In addition, a condensation reaction was performed for the activated methyl-containing dicyanodihydrofuran with a 3° amine-containing aromatic aldehyde. The molecular structures for the synthesized fluorophores were determined using various spectral techniques such as 1H or 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, and C, H, N analysis. Ultraviolet–visible (UV–vis) absorption and emission spectra of the prepared fluorophores revealed a high extinction coefficient, which was monitored to be affected by the type of the aryl (phenyl and thiophene)–vinyl bridge in conjugation with the 3° amine donor moiety. The substituents bonded to the tertiary amine, aryl, and alkyl groups, were found to affect the maximum absorbance wavelength. In addition, the synthesized dicyanodihydrofuran analogues were investigated to determine their antimicrobial effectiveness. Derivatives 2b , 4a , and 4b showed reasonable activity towards Gram-positive(+ve) bacteria rather than Gram-negative(−ve) bacteria relative to an amoxicillin drug reference. In addition, a molecular docking stimulation was performed to explore the binding interactions (PDB code: 1LNZ). 相似文献
517.
Dorota Rybaczek Aneta Żabka Anna Pastucha Janusz Maszewski 《Acta Physiologiae Plantarum》2008,30(5):663-672
A number of chemical agents known to influence the key cell cycle regulatory factors were used to assess the requirements
of hydroxyurea-treated root meristem cells of Vicia
faba for premature condensation of chromosomes (PCC). These included caffeine and 2-aminopurine (inhibitors of ATM/ATR sensor
kinases activated by DNA damage or stalled replication forks), inhibitors of protein kinases (staurosporine and wortmannin),
inhibitors of protein phosphatases (sodium vanadate and calyculin A), and other compounds like 1,2-dioctyl-sn-glycerol, an activator of protein kinase C, 5-azacytidine, an inhibitor of DNA methyltransferase, dithiothreitol and N-etylmaleimide, capable to up- and down-regulate the activity of Cdc25 phosphatase. Cytological parameters used to evaluate
quantitative aspects of PCC allowed us to discriminate various phenotypes of cells and, consistent with the extent of chromosomal
fragmentation, to classify them as S- or G2-PCC. Two significant aspects relevant to the induction of premature mitosis in
plants seem to emerge: one concerns the inverse relationship between the incidence of mitotic and PCC events, the other refers
to the extent with which a variety of chemical agents may activate mechanisms that override the S-M replication checkpoint.
1,2-dioctyl-sn-glycerol, an activator of protein kinase C in animal cells proved extremely effective in stimulation of PCC, in spite of
evident lack of molecular targets in plants. 相似文献
518.
Irene Coin 《Journal of peptide science》2010,16(5):223-230
After about one century of peptide chemistry, the main limitation to the accessibility of peptides and proteins via chemosynthesis is the arising of folding and aggregation phenomena. This is true not only for sequences above a critical length but also for several biologically relevant substrates that are relatively short yet form either highly folded structures (e.g. WW domains) or fibrils and aggregates after final deprotection (β‐amyloid peptide). Such so‐called difficult sequences may be more easily obtained via their corresponding depsipeptides (O‐acyl isopeptides), ester isomers that are often easier to assemble and purify, and are smoothly converted to the parent amides under mild conditions. The depsipeptide method is the most recent technique to improve the outcome of difficult syntheses, applicable to sequences containing residues of serine or threonine. A brief overview is presented about chemical aspects of the method, the steps that have been undertaken for its optimization, and the evaluation of its efficiency. Further applications of analogous principles to other critical topics in peptide synthesis such as condensation of peptide segments and solid‐phase synthesis of naturally occurring cyclodepsipeptides are addressed as well. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
519.
Curtis C Harnett Paul J Guerin Teresa Furtak Eric R Gauthier 《Cell biochemistry and function》2013,31(5):417-426
l ‐Glutamine (Gln) starvation rapidly triggers apoptosis in Sp2/0‐Ag14 (Sp2/0) murine hybridoma cells. Here, we report on the role played by the stress‐activated kinase p38 mitogen‐activated protein kinase (MAPK) in this process. p38 activation was detected 2 h after Gln withdrawal and, although treatment with the p38 inhibitor SB203580 did not prevent caspase activation in Gln‐starved cells, it reduced the occurrence of both nuclear condensation/fragmentation and apoptotic body formation. Similarly, transfection of Sp2/0 cells with a dominant negative p38 MAPK reduced the incidence of nuclear pyknosis and apoptotic body formation following 2 h of Gln starvation. Gln withdrawal‐induced apoptosis was blocked by the overexpression of the anti‐apoptotic protein Bcl‐xL or by the caspase inhibitor Z‐VAD‐fmk. Interestingly, Bcl‐xL expression inhibited p38 activation, but Z‐VAD‐fmk treatment did not, indicating that activation of this MAPK occurs downstream of mitochondrial dysfunction and is independent of caspases. Moreover, the anti‐oxidant N‐acetyl‐l ‐cysteine prevented p38 phosphorylation, showing that p38 activation is triggered by an oxidative stress. Altogether, our findings indicate that p38 MAPK does not contribute to the induction of apoptosis in Gln‐starved Sp2/0 cells. Rather, Gln withdrawal leads to mitochondrial dysfunction, causing an oxidative stress and p38 activation, the latter contributing to the formation of late morphological features of apoptotic Sp2/0 cells. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
520.