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31.
Smith G Grenfell BT Isham V Cornell S 《International journal for parasitology》1999,29(1):77-91; discussion 93-4
Deterministic and stochastic models are used to examine the evolution of anthelmintic resistance among trichostrongylid parasites of domestic ruminants. We find that the relative selection pressures exerted by chemoprophylactic (preventive) control strategies, chemotherapeutic (salvage) control strategies, and regimens involving "under-dosing" are critically dependent on a variety of host and parasite parameters (particularly host immunity and grazing behaviour, parasite fecundity, and the survival of the free-living stages on the pasture). Chemoprophylactic strategies are not necessarily more likely to exert a stronger selection pressure than chemotherapeutic strategies. Similarly, as one reduces dosage levels, there is a range of dose levels where under-dosing promotes resistance and a range of dose levels where under-dosing impedes resistance. The most dangerous dose is either that necessary to kill all the susceptible homozygotes, or that necessary to kill all the susceptible homozygotes and all the heterozygotes. Which one prevails depends upon model parameters. The stochastic formulation indicates that spatial heterogeneity in transmission may be a significant force in promoting the spread of resistant genotypes--at least when infection is at low levels. 相似文献
32.
van Hoek AH; van Alen TA; Sprakel VS; Hackstein JH; Vogels GD 《Molecular biology and evolution》1998,15(9):1195-1206
The 18S and 5.8S rDNA genes and the internal transcribed spacers ITS-1 and
ITS-2 of ciliates living in the hindgut of frogs, millipedes, and
cockroaches were analyzed in order to study the evolution of intestinal
protists. All ciliates studied here belong to the genus Nycrotherus.
Phylogenetic analysis revealed that these ciliates from a monophyletic
group that includes the distantly related anaerobic free-living
heterotrichous ciliates Metopus palaeformis and Metopus contortus. The
intestinal ciliates from the different vertebrate and invertebrate hosts
are clearly divergent at the level of their rDNA repeats. This argues for
the antiquity of the associations and a predominantly vertical
transmission. This mode of transmission seems to be controlled primarily by
the behavior of the host. The different degrees of divergence between
ciliates living in different strains of one and the same cockroach species
most likely reflect the different geographical origins of the hosts. In
addition, host switches must have occurred during the evolution of
cockroaches, since identical ciliates were found only in distantly related
hosts. These phenomena prevent the reconstruction of potential cospeciation
events.
相似文献
33.
Expression of lauroyl-acyl carrier protein thioesterase in brassica napus seeds induces pathways for both fatty acid oxidation and biosynthesis and implies a set point for triacylglycerol accumulation 总被引:1,自引:0,他引:1 下载免费PDF全文
Expression of a California bay lauroyl-acyl carrier protein thioesterase (MCTE) in developing seeds of transgenic oilseed rape alters the fatty acid composition of the mature seed, resulting in up to 60 mol% of laurate in triacylglycerols. In this study, we examined the metabolism of lauric acid and 14C-acetate in developing seeds of oilseed rape that express high levels of MCTE. Lauroyl-CoA oxidase activity but not palmitoyl-CoA oxidase activity was increased several-fold in developing seeds expressing MCTE. In addition, isocitrate lyase and malate synthase activities were six- and 30-fold higher, respectively, in high-laurate developing seeds. Control seeds incorporated 14C-acetate almost entirely into fatty acids, whereas in seeds expressing MCTE, only 50% of the label was recovered in lipids and the remainder was in a range of water-soluble components, including sucrose and malate. Together, these results indicate that the pathways for beta-oxidation and the glyoxylate cycle have been induced in seeds expressing high levels of MCTE. Although a substantial portion of the fatty acid produced in these seeds is recycled to acetyl-CoA and sucrose through the beta-oxidation and glyoxylate cycle pathways, total seed oil is not reduced. How is oil content maintained if lauric acid is inefficiently converted to triacylglycerol? The levels of acyl carrier protein and several enzymes of fatty acid synthesis were increased two- to threefold at midstage development in high-laurate seeds. These results indicate that a coordinate induction of the fatty acid synthesis pathway occurs, presumably to compensate for the lauric acid lost through beta-oxidation or for a shortage of long-chain fatty acids. 相似文献
34.
A Kunche MA Kiresur A Ananthaneni VS Guduru HK Puneeth B Bagalad 《Biotechnic & histochemistry》2017,92(8):547-551
Tumors of the oral cavity include combinations of hard and soft tissues that may be difficult to identify using routine hematoxylin and eosin (H & E) staining. Although combination stains can demonstrate hard and soft tissues, trichrome stains, such as VanGieson and Masson, cannot differentiate dental hard tissues, such as dentin, cementum and osteoid. Modified Gallegos (MGS) and verdeluz orange G-acid fuchsin (VOF) stains can differentiate components of teeth. We used 10 tissue sections of decalcified bone and 10 pathologic tissue sections that contained different calcified tissues including peripheral ossifying fibroma, odontoma, central ossifying fibroma and cemento-ossifying fibroma. Sections were stained with H & E, VOF or MGS. H and E stained both hard tissues pink. VOF stained bone purple-red, cementum red and collagen blue. MGS stained bone green-blue, cementum red and collagen blue. VOF staining intensity and differentiation was better than MGS staining. VOF staining demonstrated hard tissue components distinctly and exhibited good contrast with the surrounding connective tissue. VOF also is a simple, single step, rapid staining procedure. 相似文献
35.
36.
Estimation of the incidence of HIV infection 总被引:1,自引:0,他引:1
V Isham 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1989,325(1226):113-121
The aim of the method of 'back projection' is to provide estimates of the number of new infections with the human immunodeficiency virus (HIV) as a function of time, by using the numbers of diagnoses of the acquired immune deficiency syndrome (AIDS) together with information on the distribution of the incubation period between infection and diagnosis. Here, the method is investigated with particular reference to cases of HIV infection and AIDS in the United Kingdom. 相似文献
37.
Mohammad Sarwar Jamal Srikanth Ravichandran Noor Jailkhani Samrat Chatterjee Raina Dua Kanury VS Rao 《BMC systems biology》2010,4(1):169
Background
Engagement of the antigen receptor on immature B-lymphocytes leads to cell cycle arrest, and subsequent apoptosis. This is an essential process for eliminating self reactive B cells during its different stages of development. However, the mechanism by which it is achieved is not completely understood. 相似文献38.
We contribute to the discussion of causes and effects of aggregation (overdispersion) of macroparasite counts, focussing
particularly upon the effects of clumped infections and parasite-induced host mortality. The simple nonlinear stochastic model
for the evolution of the parasite load of a single host, investigated in Isham (1995), is extended to allow three parasite
stages (larval, mature and offspring), and to allow durations of these stages to be non-exponentially distributed. As in the
earlier work, exact algebraic results are possible, providing insight into the aggregation mechanisms, as long as the only
source of interaction between host and parasites is an excess host mortality linearly related to the parasite load. Results
are obtained on the distribution of parasite lad and on host survival. In particular, although parasite-induced host mortality
is usually thought of as a process that reduces parasite aggregation (Anderson and Gordon 1982), it is shown that, for this
model, parasite-induced host mortality cannot cause the index of dispersion to fall below unity. Host heterogeneity and disease
control are also discussed. An approximation based on moment assumptions appropriate to a specially-constructed multivariate
negative binomial distribution is proposed. This approximation, which is applicable to other processes, and an alternative
based on the multivariate normal distribution are compared with exact results.
Received: 17 December 1998 / Revised version: 2 June 1999 相似文献
39.
We investigate the effect of spatial aggregation in the infection dynamics of nematode parasites in ruminants. We show that
a high degree of spatial aggregation is likely to lead to a dramatically enhanced rate of invasion by drug-resistant strains.
Received: 13 December 1999 / Revised version: 3 April 2000 / Published online: 4 October 2000 相似文献
40.