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61.
Some properties of purified phospholipase D and especially the effect of amphipathic substances 总被引:11,自引:10,他引:1
1. The soluble phospholipase D of cabbage was purified by heat treatment, acetone precipitation and electrophoresis on a density gradient of aqueous glycerol. 2. The purified enzyme slowly attacked a lecithin suspension whereas ultrasonically treated lecithin was hydrolysed more rapidly. 3. Diethyl ether stimulated the hydrolysis of both the lecithin suspension and ultrasonically treated lecithin. 4. Ca2+ was essential for the hydrolysis (optimum about 0·04m); it could not be replaced by Mg2+ or cationic amphipathic substances. 5. The reaction had a sharp pH optimum at pH5·4, irrespective of the physical form of the lecithin substrate or the activator used. 6. Anionic amphipathic substances such as dodecyl sulphate, phosphatidic acid, triphosphoinositide and monocetyl phosphoric acid, were potent activators of the reaction: other acidic lipids were relatively inactive. 7. Cationic amphipathic substances inhibited the hydrolysis; however, they also reversed the inhibition caused by using an excess of anionic amphipathic substance as activator. 8. The activation produced by amphipathic substances could not be correlated with their effect on the ζ-potential or size of the substrate particles. 9. The addition of activating anionic amphipaths to lecithin induces the latter to adsorb enzyme from solution. In the absence of Ca2+ the enzyme is denatured on the highly negatively charged surface, but in the presence of Ca2+ (or Mg2+) it is protected from denaturation. It is suggested that this adsorption is an essential prerequisite for ready enzymic hydrolysis. 10. The hydrolysis of lecithin by the enzyme was strongly inhibited by protamine sulphate (0·1mg./ml.) and by choline and ethanolamine. 11. Ultrasonically treated phosphatidylethanolamine, or mixed particles of phosphatidylethanolamine plus dodecyl sulphate, were slowly attacked by the enzyme provided that Ca2+ was present. 相似文献
62.
K Kaneko J Milic-Emili M B Dolovich A Dawson D V Bates 《Journal of applied physiology》1966,21(3):767-777
63.
`Phosphatido-peptide'-like complexes formed by the interaction of calcium triphosphoinositide with protein 总被引:4,自引:0,他引:4
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R. M. C. Dawson 《The Biochemical journal》1965,97(1):134-138
1. The sodium salt of triphosphoinositide partitions in the upper polar phase in a biphasic chloroform-methanol-water system similar to that of Folch et al. (1957). 2. On the addition of 2mug.atoms of Ca(2+) or Mg(2+) per mumole of triphosphoinositide the phospholipid passes entirely into the lower non-polar phase as the dicalcium or dimagnesium salt. 3. When serum albumin is included in the biphasic system, some of the dicalcium (dimagnesium) triphosphoinositide becomes attached to the protein material at the interface. 4. The affinity of Ca(2+) for triphosphoinositide is 2-2.5 times as great as that of Mg(2+) and the salt is not dissociated appreciably by equimolar amounts of EDTA or cyclohexane-1,2-diaminetetra-acetate. 5. When dicalcium triphosphoinositide is mixed with serum albumin a complex is formed which is insoluble in chloroform-methanol (2:1, v/v) but which dissolves completely when 0.25% (v/v) of concentrated hydrochloric acid is added. 6. On homogenizing a chloroform-methanol solution of dicalcium triphosphoinositide with guinea-pig liver the phospholipid becomes quantitatively attached to the insoluble residue, but it can be completely extracted from this with acidified chloroform-methanol. 7. The relevance of these observations to the significance of the phosphatido-peptide-complexes extracted from brain is discussed. 相似文献
64.
J H Linehan C A Dawson R D Bongard T A Bronikowski D L Roerig 《Journal of applied physiology》1989,66(6):2617-2628
The influence of plasma albumin binding of the synthetic angiotensin-converting enzyme (ACE) substrate [3H]benzoyl-phenylalanyl-alanyl-proline (BPAP) on BPAP hydrolysis by pulmonary endothelial ACE was studied in isolated rabbit lungs perfused with a salt solution containing either 5% bovine serum albumin (BSA) or 5% dextran. The single-pass indicator-dilution method was used to measure the fraction (M) of [3H]BPAP hydrolyzed. Lung M was greater with albumin-free perfusate than when BSA was present. M decreased as the time (ti) that the BPAP was in contact with the BSA before reaching the lung was increased, suggesting that some BSA binding sites for BPAP were not in equilibrium during bolus transit through the lungs. The M vs. ti data were correlated using a model incorporating both rapid and slow binding kinetics of BPAP and BSA. For the slow BPAP-BSA interaction, the dissociation rate constant was approximately 0.015 s-1, and the fraction of the BPAP bound to these slowly equilibrating sites at equilibrium was approximately 22%. The results indicate that transient plasma protein binding kinetics can affect lung BPAP hydrolysis. 相似文献
65.
Gary W. Arendash William J. Millard Ralph Dawson Jr. Adrian J. Dunn Edwin M. Meyer 《Neurochemical research》1989,14(11):1113-1118
Young adult rats received either unilateral or bilateral ibotenic acid infusions in their nucleus basalis, destroying most of the cholinesterase-staining neurons in that region. Cerebral cortex levels of choline acetyltransferase, somatostatin, neuropeptide Y, and monoamines were then assayed 2.5 and 10 months after bilateral lesions, or, 2.5, 10, and 14 months after unilateral lesions. Entorhinal and cerebral cortex levels of several amino acid transmitters were also measured. As expected, choline acetyltransferase activity was decreased in the frontal cortex ipsilateral to the ibotenic acid infusion in unilaterally or bilaterally lesioned animals. Parietal cortex concentrations of somatostatin and neuropeptide Y were altered by lesioning in a complicated, time-dependent manner. Thus, while unilateral lesions transiently decreased or had no effect on these neuropeptide levels, bilateral lesions elevated the level of each neuropeptide by over 100% at 10 months. Other cortical transmitter systems investigated appeared to be less affected by nucleus basalis-lesions. Unilateral lesions had no effect on prefrontal cortex norepinephrine, serotonin, or dopamine content at 14 months post-lesioning. These different neurochemical effects of unilateral and bilateral nucleus basalis lesions may be important for developing a model for the trans-synaptic effects of cortical cholinergic deafferentation. 相似文献
66.
Seasonal water uptake and movement in root systems of Australian phraeatophytic plants of dimorphic root morphology: a stable isotope investigation 总被引:12,自引:0,他引:12
A natural abundance hydrogen stable isotope technique was used to study seasonal changes in source water utilization and water movement in the xylem of dimorphic root systems and stem bases of several woody shrubs or trees in mediterranean-type ecosystems of south Western Australia. Samples collected from the native treeBanksia prionotes over 18 months indicated that shallow lateral roots and deeply penetrating tap (sinker) roots obtained water of different origins over the course of a winter-wet/summer-dry annual cycle. During the wet season lateral roots acquired water mostly by uptake of recent precipitation (rain water) contained within the upper soil layers, and tap roots derived water from the underlying water table. The shoot obtained a mixture of these two water sources. As the dry season approached dependence on recent rain water decreased while that on ground water increased. In high summer, shallow lateral roots remained well-hydrated and shoots well supplied with ground water taken up by the tap root. This enabled plants to continue transpiration and carbon assimilation and thus complete their seasonal extension growth during the long (4–6 month) dry season. Parallel studies of other native species and two plantation-grown species ofEucalyptus all demonstrated behavior similar to that ofB. prionotes. ForB. prionotes, there was a strong negative correlation between the percentage of water in the stem base of a plant which was derived from the tap root (ground water) and the amount of precipitation which fell at the site. These data suggested that during the dry season plants derive the majority of the water they use from deeper sources while in the wet season most of the water they use is derived from shallower sources supplied by lateral roots in the upper soil layers. The data collected in this study supported the notion that the dimorphic rooting habit can be advantageous for large woody species of floristically-rich, open, woodlands and heathlands where the acquisition of seasonally limited water is at a premium. 相似文献
67.
A Familial Factor Independent of CAG Repeat Length Influences Age at Onset of Machado-Joseph Disease 总被引:3,自引:0,他引:3
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Anita L. DeStefano L. Adrienne Cupples Patricia Maciel Claudia Gaspar Joao Radvany David M. Dawson Lewis Sudarsky Lee Corwin Paula Coutinho Patrick MacLeod Jorge Sequeiros Guy A. Rouleau Lindsay A. Farrer 《American journal of human genetics》1996,59(1):119-127
Machado-Joseph disease (MJD) is a late-onset, progressive, neurodegenerative disorder caused by the expansion of an unstable trinucleotide (CAG) repeat sequence in a novel gene (MJD1) on chromosome 14. Previous studies showed that age at onset is negatively correlated with the number of CAG repeat units, but only part of the variation in onset age is explained by CAG repeat length. Ages at onset and CAG repeat lengths of 136 MJD patients from 23 kindreds of Portuguese descent were analyzed, to determine whether familial factors independent of CAG repeat length modulate age at onset of MJD. Correlation among sibs for onset age adjusted for CAG repeat length was .43, which indicates that an environmental or genetic factor common to sibs influences onset age. Positive correlations were also observed for avuncular (r = .22) and first-cousin pairs (r = .28), which supports the hypothesis that a genetic factor is influencing age at onset. Commingling analysis of onset ages adjusted for CAG repeat length identified three distributions in this population of affected individuals. Further studies of a much larger sample are needed to determine whether these distributions represent the influence of a genetic or environmental factor. 相似文献
68.
Meiotic Recombination Initiated by a Double-Strand Break in Rad50Δ Yeast Cells Otherwise Unable to Initiate Meiotic Recombination
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Meiotic recombination in Saccharomyces cerevisiae is initiated by double-strand breaks (DSBs). We have developed a system to compare the properties of meiotic DSBs with those created by the site-specific HO endonuclease. HO endonuclease was expressed under the control of the meiotic-specific SPO13 promoter, creating a DSB at a single site on one of yeast's 16 chromosomes. In Rad(+) strains the times of appearance of the HO-induced DSBs and of subsequent recombinants are coincident with those induced by normal meiotic DSBs. Physical monitoring of DNA showed that SPO13::HO induced gene conversions both in Rad(+) and in rad50Δ cells that cannot initiate normal meiotic DSBs. We find that the RAD50 gene is important, but not essential, for recombination even after a DSB has been created in a meiotic cell. In rad50Δ cells, some DSBs are not repaired until a broken chromosome has been packaged into a spore and is subsequently germinated. This suggests that a broken chromosome does not signal an arrest of progression through meiosis. The recombination defect in rad50Δ diploids is not, however, meiotic specific, as mitotic rad50 diploids, experiencing an HO-induced DSB, exhibit similar departures from wild-type recombination. 相似文献
69.
For either clinical or research purposes, the timing of the nocturnal onset in production of the urinary melatonin metabolite 6-sulfatoxymelatonin (UaMT6s-onset), has been proposed as a reliable and robust marker of circa-dian phase. However, given that most circadian rhythms show cycle-to-cycle variability, the statistical reliability of phase estimates obtained from a single study using UaMT6s-onset remains to be determined. Following 2 weeks of sleep diary and wrist actigraphy, 15 young, healthy good sleepers participated in four UaMT6s sampling sessions spaced 1 day apart. During the sampling sessions subjects remained indoors under low light conditions and hourly urine samples were collected from 19:00 to 02:00 h. Samples were subsequently assayed for UaMT6s using standard radioimmunographic techniques. UaMT6s-onset was determined by the time at which melatonin production exceeded the average of three proceeding trials by 100%. Sleep onset times were derived from sleep diary and actigraphic measures taken before the melatonin collection nights. We found that there was no significant variation between nights in group mean UaMT6s-onset times, and intraindividual variability was small. In addition, UaMT6s-onset times were highly and significantly correlated between nights (grand mean r = 0.804). Our results suggest that within 95% confidence interval limits, individual UaMT6s-onset estimates obtained from a single night UaMT6s-onset study can be used to predict subsequent UaMT6s-onset times within ±97 min. A close temporal relationship was also found between the timing of UaMT6s-onset and sleep onset. Overall, our results suggest that under entrained conditions single-session UaMT6s-onset studies can provide reliable individual UaMT6s-onset phase estimates and that the protocol described in this study is a practical and noninvasive methodology. (Chronobiology International, 13(6), 411-421, 1996) 相似文献
70.
Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
相似文献