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1.
2.
Summary Meiotic progeny of Chlamydomonas reinhardtii normally receive chloroplast genomes only from the mt
+ parent. However, exceptional zygotes, which transmit the chloroplast genomes of both parents or, more rarely, only those of the mt
- parent, arise at a low frequency. Mutations at the mt
+-linked mat-3 locus were found previously to elevate the transmission of chloroplast genomes from the mt-parent, resulting in a much higher than normal frequency of exceptional zygotes. In this paper we demonstrate that an ultraviolet-sensitive nuclear mutation mapping at the uvsE1 locus, which is unlinked to mating type, also promotes chloroplast genome transmission from the mt
- parent. This mutant, which was previously shown to reduce recombination of nuclear genes in meiosis, acts synergistically which the mat3-3 mutation to produce an extremely high frequency of exceptional zygotes. Through the use of restriction fragment length polymorphisms existing in the chloroplast genomes of C. reinhardtii and the interfertile strain C. smithii, we show that chloroplast DNA fragments from the mt
- parent normally begin to disappear shortly after zygote formation. However, this process appears to be blocked totally in the absence of wild-type uvsE1 and mat-3 gene products. Our findings are consistent with the hypothesis that both gene products contribute to the mechanism responsible for uniparental inheritance of the chloroplast genome from the mt
+ parent. 相似文献
3.
Summary Spontaneous mitotic intragenic and intergenic recombination at various sites is enhanced 10 to 100 fold in the methyl methanesulfonate (MMS)-sensitive mutants mms9-1, mms13-1, and mms21-1 of Saccharomyces cerevisiae. All three mutants show elevated rates of spontaneous mutation. Sporulation is reduced in diploids homozygous for any of the three mutations, and a deficiency in meiotic recombination and meiotic chromosome segregation is observed. Pleiotropic effects on cell viability, growth rate, and radiation sensitivity, in combination with the alterations in recombination and mutagenesis displayed by mutant strains, suggest that the MMS9, MMS13, and MMS21 genes play important roles in DNA replication and/or genetic recombination. 相似文献
4.
E. Coppin-Raynal 《Current genetics》1982,5(1):57-63
Summary The hypersensitivity to paromomycin dis played by the su
1–60 suppressor, which was thought to be a ribosomal ambiguity mutation, was used to isolate a new antisuppressor, AS
71. This antisuppressor is not specific for ribosomal suppressors, since it is able to act on putative tRNA-type suppressors. Compared to the wild-type, the AS
7-1 mutation produces an increased resistance to paromomycin. In addition, it was found to stop the sporulation process. In the polyuridylic acid-dependant assay, the paromomycin induced misreading was shown to be higher on su
1–60 ribosomes and lower on ribosomes from AS
7–1 mutant and AS
7S-1-su
1–60 double mutant than on wild-type ribosomes. These data confirm that su
1–60 and AS
7-1 mutants are ribosomal mutants involved in the control of translational fidelity. 相似文献
5.
Summary Extracts of S. cerevisiae cells can catalyze homologous recombination between plasmids in vitro. Extracts prepared from rad50, rad52 or rad54 disruption mutants all have reduced recombinational activity compared to wild-type. The rad52 and rad54 extracts are more impaired in the recombination of plasmids containing double-strand breaks than of intact plasmids, whereas rad50 extracts are deficient equally for both types of substrate. The nuclease RhoNuc (previously designated yNucR), encoded by the RNC1 (previously designated NUC2) gene and regulated by the RAD52 gene, is not required for recombination when one substrate is single-stranded but is essential for the majority of recombination events when both substrates are double-stranded. Furthermore, elimination of this nuclease restores recombination in rad52 extracts to levels comparable to those in wild-type extracts. 相似文献
6.
C. Strazielle P. Krémarik J.-F. Ghersi-Egea R. Lalonde 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,121(1):35-45
Lurcher mutant mice are characterized by massive degeneration of cerebellar Purkinje cells and granule cells and by deficits in motor
coordination. Regional brain variations of cytochrome oxidase (CO) activity were analyzed to identify those brain regions
with abnormal metabolic activity as a secondary consequence of the cerebellar atrophy and to establish the relationship between
CO activity and motor deficits. Lurcher mutants had higher CO activity in all three cerebellar deep nuclei than normal littermate controls of the same background
strain. Higher CO activity was also found in Lurcher mutants in brain regions directly connected to the cerebellum, such as the lateral vestibular nucleus, the cochlear nucleus,
the red nucleus, the ventrolateral thalamus, the dorsal raphe, the interpeduncular nucleus, and the inferior colliculus. By
contrast, there was a sharp decrease in CO activity in the inferior olive. As for brain regions not directly connected to
the cerebellum, higher CO activity was observed in the trigeminal motor nucleus and the CA1 molecular layer of the hippocampus,
which highlights probable transsynaptic alterations as a secondary consequence of cerebellar atrophy. A positive correlation
between CO activity in the red nucleus and latencies before falling in two motor-coordination tests indicates that a compensatory
increase of metabolic activity in a cerebellar efferent region is associated with improved behavior.
Received: 15 September 1997 / Accepted: 3 March 1998 相似文献
7.
Theophylline and 3-isobutyl-1-methylxanthine, two cyclic nucleotide phosphodiesterase inhibitors, when fed to wild-typeDrosophila adults, cause the rapid decay of learning index after training in a shock-odor learning paradigm. The drugs practically do not affect the olfactory acuity of flies, hence they influence the learning/memory process itself. The time courses of memory decay resemble those of the memory mutantsrutabaga andamnesiac and, to a lesser extent,dunce
2 anddunce
M11. Theophylline further deteriorates the learning performance ofdunce
M11. Biochemical characterization of the inhibition of the two major phosphodiesterase isoenzymes inDrosophila by theophylline predicts only a slight inhibition of these enzymesin vivo, in accordance with the unchanged level of cAMP in wild-type fly heads during drug feeding. 8-Phenyltheophylline, an adenosine receptor antagonist in mammals, slightly retards memory decay in the wild-type. It is suggested that alkylxanthines induce memory decay inDrosophila by interfering with cAMP dynamics at more than one point of its metabolism.This work was supported by Grants OTKA and OKKFT Tt to P.F. 相似文献
8.
Cloning and expression of surface antigens from occult chronic hepatitis B virus infections and their recognition by commercial detection assays 总被引:6,自引:0,他引:6
Jeantet D Chemin I Mandrand B Tran A Zoulim F Merle P Trepo C Kay A 《Journal of medical virology》2004,73(4):508-515
Occult hepatitis B virus (HBV) infections show little or no serological markers of viral infection, including the absence of hepatitis B surface antigen (HBsAg) which is the main marker of ongoing HBV infection. Such infections can be important in the context of blood and/or organ donations. To study whether mutations contribute to HBsAg seronegativity, S gene sequences from such patients were amplified and cloned. Sequencing revealed 12 clones from seven different patients which contained potentially important mutations. The sequences were subcloned into an expression vector and mutant HBsAgs were expressed in cell culture. The capacity of three HBsAg detection assays to recognise the mutant HBsAgs was studied. Three categories were found: mutant HBsAgs that are not recognised by the assays, those that are recognised as well as wild-type (WT) antigen and an intermediate category where detection of the mutant HBsAgs is reduced with respect to WT. Most of the isolates fall into the second category. Mutations can therefore contribute to HBsAg seronegativity in occult HBV infections, but in most cases the explanation is probably the low level of viral replication. 相似文献
9.
The influence of the DNA repair genePSO3 on photoactivated psoralen-induced meiotic recombination, gene conversion, reverse mutation, and on survival, was assayed in diploid strains ofSaccharomyces cerevisiae homozygous for the wild-type or thepso3-1 mutant allele. Sporulation was normal in thepso3-1 diploid. Wild-type and mutant strains had the same sensitivity to photoactivated monofunctional psoralen (3-CPs+UVA) in meiosis-uncommitted and meiosis-committed stages. The mutant showed higher sensitivity to photoactivated bifunctional psoralen (8-MOP+UVA) during all stages of the meiotic cycle. Mutation induction by 3-CPs+UVA or 8-MOP+UVA in meiosis-committed cells revealed no significant differences between wild-type and thepso3-1 mutant. The status of thePSO3 gene has no influence on the kinetics of induction of gene conversion and crossing-over after 3-CPs+UVA treatment in meiosis-committed cells: gene conversion was blocked while recombination was induced. After treatment with 8-MOP+UVA gene conversion was also blocked in both strains while crossing-over could only be observed in meiosis-committed wild-type cells. 相似文献
10.
Dr. Hans de Vries Jenny C. de Jonge Peter van't Sant Etienne Agsteribbe Annika Arnberg 《Current genetics》1981,3(3):205-211
Summary [E35], an extranuclear mutant of Neurospora crassa has all the phenotypic characteristics of the stopper mutants (De Vries et al. 1980). In the present work, the mitochondrial DNA as well as the mitochondrial translation products are characterized further. The primary mutational event appears to have been the deletion of about 4 kbp from the wild-type genome. Moreover, after prolonged vegetative growth the mutant accumulates an 8-m circular mtDNA, which was demonstrated both by electronmicroscopy and by restriction enzyme analysis. Hence, the mutant contains two populations of aberrant mitochondrial DNA, the smaller of which is an amplification of the rRNA-tRNA part of the larger. We propose that the primary deletion has generated a signal in the larger DNA which can cause premature termination of replication at the deletion site, and subsequent circularization of the unfinished daughter molecule. Finally, the deleted part may contain a determinant for synthesis of a protein of 11 kDal. The function of this protein, which is not a subunit of the F0 ATPase, is not yet known.Abbreviations (k)bp
(kilo)basepairs
- kDal
kilodalton
- mt
mitochondrial 相似文献