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31.
This paper concentrates on the state observation in bioprocesses when there is uncertainty on the process parameters and/or the process inputs. An interval observer is designed on the basis of the cooperativity properties of the model for a standard stirred tank bioreactor model with a single microbial growth and a kinetic model depending on the substrate concentration. Further assumptions are the (lower and upper) boundedness of the specific growth rate and the inlet substrate concentration. Mathematical analysis of the stability and convergence of the interval observer is performed both in absence and in presence of uncertainty on the measurements. It is shown in particular that when the process inputs are known, the static observation error on the unknown state is inversely proportional to one of the observer gains. The performance of the interval observer are also illustrated through numerical simulation. 相似文献
32.
Trapping crystal nucleation of cholesterol monohydrate: relevance to pathological crystallization 下载免费PDF全文
Crystalline nucleation of cholesterol at the air-water interface has been studied via grazing incidence x-ray diffraction using synchrotron radiation. The various stages of cholesterol molecular assembly from monolayer to three bilayers incorporating interleaving hydrogen-bonded water layers in a monoclinic cholesterol.H(2)O phase, has been monitored and their structures characterized to near atomic resolution. Crystallographic evidence is presented that this multilayer phase is similar to that of a reported metastable cholesterol phase of undetermined structure obtained from bile before transformation to the triclinic phase of cholesterol.H(2)O, the thermodynamically stable macroscopic form. According to grazing incidence x-ray diffraction measurements and crystallographic data, a transformation from the monoclinic film structure to a multilayer of the stable monohydrate phase involves, at least initially, an intralayer cholesterol rearrangement in a single-crystal-to-single-crystal transition. The preferred nucleation of the monoclinic phase of cholesterol.H(2)O followed by transformation to the stable monohydrate phase may be associated with an energetically more stable cholesterol bilayer arrangement of the former and a more favorable hydrogen-bonding arrangement of the latter. The relevance of this nucleation process of cholesterol monohydrate to pathological crystallization of cholesterol from cell biomembranes is discussed. 相似文献
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New germline mutations in the human retinoblastoma gene are known to arise preferentially on paternally derived chromosomes,
but the magnitude of that bias has not been measured. We evaluated 49 cases with a new germline mutation and found that in
40 cases (82%) the mutation arose on the paternally derived allele. We also evaluated 48 cases likely to have a somatic initial
mutation; in this group the initial mutation arose on paternal or maternal chromosomes with approximately equal frequency.
There was no statistically significant difference in the average age of fathers of children with new paternal germline mutations
from the average age of fathers of children with new maternal germline mutations or somatic initial mutations. Combining the
data with that from previous reports from other groups, the proportion of new germline mutations arising on a paternally derived
allele is 85% (based on 72 cases; 95% confidence interval = 76–93%). This number can be useful in the genetic counseling of
some families with retinoblastoma.
Received: 18 December 1996 / Accepted: 30 April 1997 相似文献
36.
Walter Rapaport 《The Western journal of medicine》1955,83(6):410-411
Neuropsychiatric disabilities are the number one problem in medicine. More specialists are needed in the field of neuropsychiatry. Better psychiatric orientation of nonpsychiatric physicians is needed and there must be infinitely more research into psychiatric problems. We need more adequately equipped and staffed hospitals, both private and public, to care for the problem, and an alerted public as well as a sympathetic, understanding medical profession. 相似文献
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We have evaluated codon usage bias in Drosophila histone genes and have
obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat
unit. This repeat contains genes for all five histone proteins (H1, H2a,
H2b, H3, and H4) and differs from the previously reported one by a second
EcoRI site. These D. hydei repeats have been aligned to each other and to
the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from
D. melanogaster. In each species, base composition at synonymous sites is
similar to the average genomic composition and approaches that in the small
intergenic spacers of the histone gene repeats. Accumulation of synonymous
changes at synonymous sites after the species diverged is quite high. Both
of these features are consistent with the relatively low codon usage bias
observed in these genes when compared with other Drosophila genes. Thus,
the generalization that abundantly expressed genes in Drosophila have high
codon bias and low rates of silent substitution does not hold for the
histone genes.
相似文献
40.
Influence of translational efficiency on the stability of the mRNA for ribosomal protein S20 in Escherichia coli. 总被引:4,自引:0,他引:4 下载免费PDF全文
A set of plasmids was constructed so as to contain point mutations which limit the efficiency and/or extent of translation of the gene for ribosomal protein S20. These plasmids were transformed into strains carrying mutations in the genes for polynucleotide phosphorylase (pnp-7), RNase E (rne-1), or both. Subsequently, the effect of translational efficiency on mRNA abundance and chemical half-life was determined. The data indicated that mutations altering translational efficiency also affected mRNA levels over a 10-fold range. This variation in mRNA abundance occurred independently of mutations in either RNase E or polynucleotide phosphorylase, both of which determine the stability of the S20 mRNAs. Moreover, a mutation at codon 15 which caused premature termination of translation of the S20 mRNA did not significantly reduce its stability in different genetic backgrounds. We propose a model in which initiation of translation competes for early steps in mRNA turnover, which could be the binding of RNase E itself or as a complex to one or more sites near the 5' terminus of the S20 mRNA. 相似文献