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Evidence for an ascorbate shuttle for the transfer of reducing equivalents across chromaffin granule membranes 总被引:2,自引:0,他引:2
Adrenal chromaffin granules must shuttle reducing equivalents from the cytosol inward to reduce ascorbic acid oxidized during norepinephrine biosynthesis by intragranular dopamine-beta-hydroxylase. A transmembrane electron shuttle between the external (cytosolic) and intragranular ascorbate pools was demonstrated in vitro in intact bovine chromaffin granules undergoing tyramine- or dopamine-stimulated dopamine-beta-hydroxylase turnover. Incubation of intact chromaffin granules with tyramine results in a time-dependent decrease in reduced intragranular ascorbate and production of octopamine. The rate of ascorbate oxidation is a function of the extragranular concentrations of tyramine over the range 50 microM to 2 mM and is 95% inhibited by addition of the dopamine-beta-hydroxylase inhibitor disulfiram. The stoichiometry of octopamine synthesized/ascorbate oxidized closely approximates unity. The presence of extragranular dopamine also induces oxidation of intragranular ascorbate which is inhibited by blocking dopamine transport with reserpine. On the other hand, incubation with octopamine, which is also transported by the granules, causes no net decrease in reduced intragranular ascorbate. The presence of 400 microM extragranular ascorbate abolishes the observed tyramine-induced intragranular ascorbate oxidation. The addition of ascorbate extragranularly 30 min after addition of tyramine reverses the oxidation of intragranular ascorbate. The measurement of [14C]ascorbate distribution ratios in granule pellets and supernatants indicates that there is no transmembrane transport of ascorbate. Extravesicular NADH had no significant effect on matrix ascorbate levels during beta-hydroxylation. These data provide new in vitro evidence that chromaffin granules shuttle reducing equivalents inwardly from an extra- to an intravesicular ascorbate pool and that cytosolic ascorbate is the source of the intragranular reducing equivalents required during norepinephrine biosynthesis. 相似文献
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A cell culture assay for follicle-stimulating hormone 总被引:3,自引:0,他引:3
Cultured rat ovarian granulosa cells respond to follicle-stimulating hormone (FSH) by synthesizing and secreting plasminogen activator. The specificity of the response for FSH prompted us to explore the use of this system as an in vitro bioassay for FSH. The release of FSH by pituitary cell cultures has been examined by this method, as have been preparations of FSH of known biological activity. The results indicate that the granulosa cell system allows accurate, rapid, and convenient determinations of FSH activity. Furthermore, the method obviates metabolic clearance problems associated with whole animal assays and it is extremely sensitive: as little as 10(-15) mol (approximately 100 micronIU) of FSH can be detected. 相似文献
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Nucleotide sequence of the Pseudomonas fluorescens signal peptidase II gene (lsp) and flanking genes. 总被引:5,自引:3,他引:2 下载免费PDF全文
The lsp gene encoding prolipoprotein signal peptidase (signal peptidase II) is organized into an operon consisting of ileS and three open reading frames, designated genes x, orf149, and orf316 in both Escherichia coli and Enterobacter aerogenes. A plasmid, pBROC128, containing a 5.8-kb fragment of Pseudomonas fluorescens DNA was found to confer pseudomonic acid resistance on E. coli host cells and to contain the structural gene of ileS from P. fluorescens. In addition, E. coli strains carrying pBROC128 exhibited increased globomycin resistance. This indicated that the P. fluorescens lsp gene was present on the plasmid. The nucleotide sequences of the P. fluorescens lsp gene and of its flanking regions were determined. Comparison of the nucleotide sequences of the lsp genes in E. coli and P. fluorescens revealed two highly conserved domains in this enzyme. Furthermore, the five genes which constitute an operon in E. coli and Enterobacter aerogenes were found in P. fluorescens in the same order as in the first two species. 相似文献
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Gasim Omer Elkhalifa Abd-Elfarag Lukudu Emmanuel Arthur W. D. Edridge Stella van Beers Mohamed B. Sebit Michaël B. van Hensbroek Ente J. J. Rood 《PLoS neglected tropical diseases》2022,16(7)
BackgroundNodding syndrome (NS) is a progressive neurological disease that has been described in several sub-Saharan African counties, but South Sudan is considered the most affected. However, knowledge about the exact burden and the epidemiological risk factors of NS in South Sudan is lacking.ObjectiveTo determine the prevalence, distribution and epidemiological risk factors of NS in the Greater Mundri area, the epicenter of NS in South Sudan.MethodsA NS prevalence house-to-house survey was conducted in multiple villages between February 2018 and November 2019. Geographical distribution and clustering of NS cases was identified using spatial and binomial regression analysis. Epidemiological risk factors of NS were identified using univariate and multivariate models.ResultsOf the 22,411 persons surveyed in 92 villages, 607 (2.7%) persons with NS were identified, of which 114 (19%) were new-onset cases. The highest prevalence was found in Diko village with a prevalence of 13.7%. NS showed a significant spatial pattern with clustering of cases between adjacent households and along rivers. Risks factors for NS include all behaviors around rivers (drinking, cooking, handwashing and bathing) and exposure to poultry. On the other hand, ownership of mobile phone decreased the risk of NS. Many other factors, including prior ivermectin treatment and internal displacement were not associated with NS.ConclusionOur study demonstrates a very high burden of the NS disease in the Greater Mundri area, strengthens the association with rivers, and identified possible new clues for an underlying cause. 相似文献
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Sophie O. Vanwambeke Eric F. Lambin Markus P. Eichhorn Stéphane P. Flasse Ralph E. Harbach Linda Oskam Pradya Somboon Stella van Beers Birgit H. B. van Benthem Cathy Walton Roger K. Butlin 《EcoHealth》2007,4(1):37-51
Land-use change, a major constituent of global environmental change, potentially has significant consequences for human health
in relation to mosquito-borne diseases. Land-use change can influence mosquito habitat, and therefore the distribution and
abundance of vectors, and land use mediates human–mosquito interactions, including biting rate. Based on a conceptual model
linking the landscape, people, and mosquitoes, this interdisciplinary study focused on the impacts of changes in land use
on dengue and malaria vectors and dengue transmission in northern Thailand. Extensive data on mosquito presence and abundance,
land-use change, and infection risk determinants were collected over 3 years. The results of the different components of the
study were then integrated through a set of equations linking land use to disease via mosquito abundance. The impacts of a
number of plausible scenarios for future land-use changes in the region, and of concomitant behavioral change were assessed.
Results indicated that land-use changes have a detectable impact on mosquito populations and on infection. This impact varies
according to the local environment but can be counteracted by adoption of preventive measures. 相似文献
9.
The epidemiology of mycobacterium leprae: Recent insight 总被引:2,自引:0,他引:2
Stella M. van Beers Madeleine Y.L. de Wit Paul R. Klatser 《FEMS microbiology letters》1996,136(3):221-230
Abstract Leprosy is still a health problem in many countries. Because the causative organism, Mycobacterium leprae cannot be cultured in vitro, it is virtually impossible to assess exposure, and the onset of infection and disease. As a consequence, the chain of infection, considered as the relationships between M. leprae , transmission and human host, is poorly understood. Here, we discuss a number of organism-, host- and environmental-related factors which may be incriminated in the dynamic process of the development of leprosy disease. The use of modern molecular and immunological tools has become a valuable addition to epidemiological research. Understanding of the epidemiology of leprosy is a prerequisite for effective control of the disease. 相似文献
10.
van Beers RJ Baraduc P Wolpert DM 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2002,357(1424):1137-1145
Neural signals are corrupted by noise and this places limits on information processing. We review the processes involved in goal-directed movements and how neural noise and uncertainty determine aspects of our behaviour. First, noise in sensory signals limits perception. We show that, when localizing our hand, the central nervous system (CNS) integrates visual and proprioceptive information, each with different noise properties, in a way that minimizes the uncertainty in the overall estimate. Second, noise in motor commands leads to inaccurate movements. We review an optimal-control framework, known as 'task optimization in the presence of signal-dependent noise', which assumes that movements are planned so as to minimize the deleterious consequences of noise and thereby minimize inaccuracy. Third, during movement, sensory and motor signals have to be integrated to allow estimation of the body's state. Models are presented that show how these signals are optimally combined. Finally, we review how the CNS deals with noise at the neural and network levels. In all of these processes, the CNS carries out the tasks in such a way that the detrimental effects of noise are minimized. This shows that it is important to consider effects at the neural level in order to understand performance at the behavioural level. 相似文献