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41.
In March 2009, we documented the death of one member of a triplet polar bear (Ursus maritimus) litter at its den site in the southern Beaufort Sea (SBS) of Alaska. We used a self-contained video camera unit to document
activity between den emergence and departure. All three cubs showed low activity levels relative to other cubs observed, and
one died within one week of den emergence. Necropsy confirmed that the dead cub had a low body weight and was malnourished.
Capture later confirmed that the two surviving cubs were also undersized. Polar bear cub survival is influenced by many factors
including litter size and sea ice conditions. Triplet litters are often smaller and suffer higher mortality rates than singletons
and twins. This cub was not only a triplet but also born following 2 years of record minimum sea ice extent, both of which
may have played a role in this cub’s demise. 相似文献
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Induction of the nodA promoter of Rhizobium leguminosarum Sym plasmid pRL1JI by plant flavanones and flavones. 总被引:24,自引:16,他引:8 下载免费PDF全文
S A Zaat C A Wijffelman H P Spaink A A van Brussel R J Okker B J Lugtenberg 《Journal of bacteriology》1987,169(1):198-204
An expression vector containing the Rhizobium leguminosarum nodA promoter cloned in front of the Escherichia coli lacZ gene was used to characterize the properties of the R. leguminosarum nodA gene-inducing compound(s) present in sterile root exudate of the host plant Vicia sativa L. subsp. nigra (L.). The major inducing compound was flavonoid in nature, most likely a flavanone. The commercially available flavonoids naringenin (5,7,4'-trihydroxyflavanone), eriodictyol (5,7,3'4'-tetrahydroxyflavanone), apigenin (5,7,4'-trihydroxyflavone), and luteolin (5,7,3',4'-tetrahydroxyflavone) induced the nodA promoter to the same level as the root exudate. On the basis of chromatographic properties, it was concluded that none of these compounds is identical to the inducer that is present in root exudate. The induction of the nodA promoter by root exudate and by the most effective inducer naringenin was very similar, as judged from the genetic requirements and the kinetics of induction. 相似文献
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T. Ritsema A. M. Gehring A. R. Stuitje K. M. G. M. van der Drift I. Dandal R. H. Lambalot C. T. Walsh J. E. Thomas-Oates B. J. J. Lugtenberg H. P. Spaink 《Molecular & general genetics : MGG》1998,257(6):641-648
The nodulation protein NodF of Rhizobium shows 25% identity to acyl carrier protein (ACP) from Escherichia coli (encoded by the gene acpP). However, NodF cannot be functionally replaced by AcpP. We have investigated whether NodF is a substrate for various E. coli enzymes which are involved in the synthesis of fatty acids. NodF is a substrate for the addition of the 4′-phosphopantetheine
prosthetic group by holo-ACP synthase. The Km value for NodF is 61 μM, as compared to 2 μM for AcpP. The resulting holo-NodF serves as a substrate for coupling of malonate
by malonyl-CoA:ACP transacylase (MCAT) and for coupling of palmitic acid by acyl-ACP synthetase. NodF is not a substrate for
β-keto-acyl ACP synthase III (KASIII), which catalyses the initial condensation reaction in fatty acid biosynthesis. A chimeric
gene was constructed comprising part of the E.coliacpP gene and part of the nodF gene. Circular dichroism studies of the chimeric AcpP-NodF (residues 1–33 of AcpP fused to amino acids 43–93 of NodF) protein
encoded by this gene indicate a similar folding pattern to that of the parental proteins. Enzymatic analysis shows that AcpP-NodF
is a substrate for the enzymes holo-ACP synthase, MCAT and acyl-ACP synthetase. Biological complementation studies show that
the chimeric AcpP-NodF gene is able functionally to replace NodF in the root nodulation process in Vicia sativa. We therefore conclude that NodF is a specialized acyl carrier protein whose specific features are encoded in the C-terminal
region of the protein. The ability to exchange domains between such distantly related proteins without affecting conformation
opens exciting possibilities for further mapping of the functional domains of acyl carrier proteins (i. e., their recognition
sites for many enzymes).
Received: 22 September 1997 / Accepted: 31 October 1997 相似文献
47.
Some properties of a d-glutamic acid auxotroph of Escherichia coli B were studied. The mutant cells lysed in the absence of d-glutamic acid. Murein synthesis was impaired, accompanied by accumulation of uridine-5'-diphosphate-N-acetyl-muramyl-l-alanine (UDP-MurNac-l-Ala), as was shown by incubation of the mutant cells in a cell wall medium containing l-[(14)C]alanine. After incubation of the parental strain in a cell wall medium containing l-[(14)C]glutamic acid, the acid-precipitable radioactivity was lysozyme degradable to a large extent. Radioactive UDP-MurNac-pentapeptide was isolated from the l-[(14)C]glutamic acid-labeled parental cells. After hydrolysis, the label was exclusively present in glutamic acid, the majority of which had the stereo-isomeric d-configuration. Compared to the parent the mutant incorporated less l-[(14)C]glutamic acid from the wall medium into acid-precipitable material. Lysozyme degraded a smaller percentage of the acid-precipitable material of the mutant than of that of the parent. No radioactive uridine nucleotide precursors could be isolated from the mutant under these conditions. Attempts to identify the enzymatic defect in this mutant were not successful. The activity of UDP-MurNac-l-Ala:d-glutamic acid ligase (ADP; EC 6.3.2.9) (d-glutamic acid adding enzyme) is not affected by the mutation. Possible pathways for d-glutamic acid biosynthesis in E. coli B are discussed. 相似文献
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There is a need for safe medications that can effectively support recovery by treating symptoms of protracted abstinence that may precipitate relapse in alcoholics, e.g. craving and disturbances in sleep and mood. This proof-of-concept study reports on the effectiveness of gabapentin 1200 mg for attenuating these symptoms in a non-treatment-seeking sample of cue-reactive, alcohol-dependent individuals. Subjects were 33 paid volunteers with current Diagnostic and Statistical Manual of Mental Disorders-IV alcohol dependence and a strength of craving rating 1 SD or greater for alcohol than water cues. Subjects were randomly assigned to gabapentin or placebo for 1 week and then participated in a within-subjects trial where each was exposed to standardized sets of pleasant, neutral and unpleasant visual stimuli followed by alcohol or water cues. Gabapentin was associated with significantly greater reductions than placebo on several measures of subjective craving for alcohol as well as for affectively evoked craving. Gabapentin was also associated with significant improvement on several measures of sleep quality. Side effects were minimal, and gabapentin effects were not found to resemble any major classes of abused drugs. Results suggest that gabapentin may be effective for treating the protracted abstinence phase in alcohol dependence and that a randomized clinical trial would be an appropriate next step. The study also suggests the value of cue-reactivity studies as proof-of-concept screens for potential antirelapse drugs. 相似文献
50.
John A Babraj Niels BJ Vollaard Cameron Keast Fergus M Guppy Greg Cottrell James A Timmons 《BMC endocrine disorders》2009,9(1):1-8