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1.
2.
Harish Kumar Jayant B. Udgaonkar 《Protein science : a publication of the Protein Society》2021,30(4):785
Amyloid fibrillar aggregates isolated from the brains of patients with neurodegenerative diseases invariably have post‐translational modifications (PTMs). The roles that PTMs play in modulating the structures and polymorphism of amyloid aggregates, and hence their ability to catalyze the conversion of monomeric protein to their fibrillar structure is, however, poorly understood. This is particularly true in the case of tau aggregates, where specific folds of fibrillar tau have been implicated in specific tauopathies. Several PTMs, including acetylation at Lys 280, increase aggregation of tau in the brain, and increase neurodegeneration. In this study, tau‐K18 K280Q, in which the Lys 280 → Gln mutation is used to mimic acetylation at Lys 280, is shown, using HX‐MS measurements, to form fibrils with a structural core that is longer than that of tau‐K18 fibrils. Measurements of critical concentrations show that the binding affinity of monomeric tau‐K18 for its fibrillar counterpart is only marginally more than that of monomeric tau‐K18 K280Q for its fibrillar counterpart. Quantitative analysis of the kinetics of seeded aggregation, using a simple Michaelis–Menten‐like model, in which the monomer first binds and then undergoes conformational conversion to β‐strand, shows that the fibrils of tau‐K18 K280Q convert monomeric protein more slowly than do fibrils of tau‐K18. In contrast, monomeric tau‐K18 K280Q is converted faster to fibrils than is monomeric tau‐K18. Thus, the effect of Lys 280 acetylation on tau aggregate propagation in brain cells is expected to depend on the amount of acetylated tau present, and on whether the propagating seed is acetylated at Lys 280 or not. 相似文献
3.
Wolfgang Witt Peter Hampel Klaus Böcker Angelika Mertsching 《Archives of microbiology》1989,151(2):154-158
Divalent cations activate the lysophospholipase and transacylase reactions catalyzed by the same enzymes in the yeast Saccharomyces cerevisiae. The activation was observed at neutral pH, but not at the pH optimum of lysophospholipase/transacylase, near 3.5. Adenine nucleotides, especially AMP and ADP, are strong inhibitors of the same group of enzymes. Half maximal inhibition by AMP was found at a concentration of about 20 M. The inhibition by nucleotides in low concentrations is enhanced by divalent cations. 相似文献
4.
5.
Germline integration of moloney murine leukemia virus at the Mov13 locus leads to recessive lethal mutation and early embryonic death 总被引:33,自引:0,他引:33
Rudolf Jaenisch Klaus Harbers Angelika Schnieke Jürgen Löhler Ilya Chumakov Detlev Jähner Doris Grotkopp Evelyn Hoffmann 《Cell》1983,32(1):209-216
Thirteen mouse substrains genetically transmitting the exogenous Moloney murine leukemia virus (M-MuLV) at a single locus (Mov locus) have been derived previously. Experiments were performed to investigate whether homozygosity at the Mov loci would be compatible with normal development. Animals heterozygous at an Mov locus were mated, and the genotype of the offspring was analyzed. From parents heterozygous at the loci Mov1 to Mov12, respectively, homozygous offspring were obtained with the expected Mendelian frequency. In contrast, no homozygous offspring or embryos older than day 15 of gestation were obtained from parents heterozygous at the Mov13 locus. When pregnant Mov13 females at day 13 and day 14 of gestation were analyzed, approximately 25% of the embryos were degenerated. Genotyping revealed that these degenerated embryos were invariably homozygous and the normal appearing embryos were either heterozygous or negative for M-MuLV. These results suggest that integration of M-MuLV at the Mov13 locus leads to insertion mutagenesis, resulting in embryonic arrest between day 12 and day 13 of gestation. It is possible that the Mov13 locus represents a gene or gene complex involved in the early embryonic development of the mouse. 相似文献
6.
The enantioseparation of the sherry aroma components 5-oxo-4-hydroxyhexanoic acid γ-lactone (solerone) and 4,5-dihydroxyhexanoic acid γ-lactone (solerole) is achieved, using Chiraspher (Merck) as the chiral HPLC phase and the optical purity ascertained directly by HRGC with heptakis(3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin (Lipodex D) as the chiral stationary phase. The absolute configurations of 4,5-dihydroxyhexanoic acid γ-lactones are assigned by 1H-NMR spectral data of diastereomeric α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) esters, according to Mosher's model. Sensory qualities of the isomers are given. 相似文献
7.
Determination of the pressure in the water-conducting vessels of intactNicotiana rustica L. plants showed that the pressure probe technique gave less-negative values than the Scholander-bomb method. Even though
absolute values of the order of −0.1 MPa could be directly recorded in the xylem by means of the pressure probe, pressures
between zero and atmospheric were also frequently found. The data obtained by the pressure probe for excised leaves showed
that the Scholander bomb apparently did not read the actual tension in the xylem vessles ofNicotiana plants. The possibility that the pressure probe gave false readings was excluded by several experimental controls. In addition,
cavitation and leaks either during the insertion of the microcapillary of the pressure probe, or else during the measurements
were easily recognized when they occurred because of the sudden increase of the absolute xylem tension to that of water vapour
or to atmospheric, respectively. Tension values of the same order could also be measured by means of the pressure probe in
the xylem vessels of pieces of stem cut from leaves and roots under water and clamped at both ends. The magnitude of the absolute
tension depended on the osmolarity of the bathing solution which was adjusted by addition of appropriate concentrations of
polyethylene glycol. Partial and uniform pressurisation of plant tissues or organs, or of entire plants (by means of the Scholander
bomb or of a hyperbaric chamber, respectively) and simultaneous recording of the xylem tension using the pressure probe showed
that a 1∶1 response in xylem pressure only occurred under a few circumstances. A 1∶1 response required that the xylem vessels
were in direct contact with an external water reservoir and/or that the tissue was (pre-)infiltrated with water. Corresponding
pressure-probe measurements in isolated vascular bundles ofPlantago major L. orP. lanceolata L. plants attached to a Hepp-type osmometer indicated that the magnitude of the tension in the xylem vessels was determined
by the external osmotic pressure of the reservoir. These and other experiments, as well as analysis of the data using classical
thermodynamics, indicated that the turgor and the internal osmotic pressure of the accessory cells along the xylem vessels
play an important role in the maintenance of a constant xylem tension. This conclusion is consistent with the cohesion theory.
In agreement with the literature (P.E. Weatherley, 1976, Philos. Trans. R. Soc. London Ser. B23, 435–444; 1982, Encyclopedia of plant physiology, vol. 12B, 79-109), it was found that the tension in the xylem of intact
plants under normal and elevated ambient pressure (as measured with the pressure probe) under quasi-stationary conditions
was independent of the transpiration rate over a large range, indicating that the conductance of the flow path must be flow-dependent. 相似文献
8.
Benoît F. Morel Meghan A. Burke Jayant Kalagnanam Susan A. McCarthy David J. Tweardy Penelope A. Morel 《Bulletin of mathematical biology》1996,58(3):569-594
The cytokines are the information superhighway of the immune system. They are an important component of the integrated behavior
of the system. In order to be able to have a good understanding of the immune system, we must be able to model the effect
of cytokines and their combined effect. This work is a step in that direction. We study the combined effect of two cytokines:
interleukin-2 (IL-2) and interleukin-4 (IL-4) on some cells of the immune system.
Interleukin-2 and interleukin-4 are important growth and differentiation factors for B and T cells. Interleukin-4 antagonizes
the effect of interleukin-2 on B cells and some T cells while it synergizes with interleukin-2 on other T cells. We build
a mathematical model of the interaction of both cytokines on T and B cells as a building block toward a model of the Th1/Th2
cross-regulation. The response of a given cell to the combination of interleukin-2 and interleukin-4 is shown to involve competing
dynamical effects which can lead to either antagnostic or synergistic combined effect.
Author to whom correspondence should be addressed at Department of Engineering and Public Policy. Work supported by NIH grant
nv: Ai31427. 相似文献
9.
10.
Butler Michael J. Aphale Jayant S. DiZonno Michele A. Krygsman Phyllis Walczyk Eva Malek Lawrence T. 《Journal of industrial microbiology & biotechnology》1994,13(1):24-29
Summary We have investigated the aminopeptidase activities present inStreptomyces lividans strains. The majority of these activities proved to be intracellular with multiple active species. Two aminopeptidase P genes were identified to be responsible for the ability to hydrolyze amino terminal peptide bonds adjacent to proline residues. Two other broad spectrum aminopeptidases were found to display homology at both the DNA and protein levels. One showed significant homology to PepN proteins, particularly around the putative zinc-binding residues which are important for catalysis. The second broad spectrum activity was not analyzed in detail but showed a different spectrum of substrate specificity to that of PepN. 相似文献