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161.
A semi-field experiment was carried out in two peach orchards in northern Italy to assess mortality due to predators and parasitoids
on the exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in comparison with the native coccinellid Adalia bipunctata L. (Coleoptera: Coccinellidae). The experiments were conducted in cages to avoid the possible escape of the exotic ladybird
(not yet established in Italy). Two kinds of cage experiments were included: ‘exclusion cages’ (access by walking predators
impeded) and ‘free cages’ (walking predators free to enter). The cages, containing all the stages of the two ladybird species,
were placed in two localities and left for 24 h. All ladybird stages used for the semi-field experiments came from a laboratory
rearing. The eggs of H. axyridis experienced less mortality than those of A. bipunctata. The ant workers were the most frequent predators in ‘free cages’ but A. bipunctata cannibalism on eggs was also detected. Larvae of both coccinellid species were predated equally but larval predation of L1
and L2 was higher in comparison to predation of L3 and L4. Pupae and adults of both exotic and native ladybirds were never
attacked by predators. Predation on younger larval stages was higher in the ‘free cages’ in comparison with ‘exclusion cages’.
No ladybird parasitisation was observed. The ‘free cage’ technique seems to provide a standardised and realistic estimation
of predation impact but more studies are needed to evaluate ladybird parasitisation in semi-field conditions. 相似文献
162.
Kaouri K. Maini P. K. Skourides P. A. Christodoulou N. Chapman S. J. 《Journal of mathematical biology》2019,78(7):2059-2092
Journal of Mathematical Biology - Calcium signalling is one of the most important mechanisms of information propagation in the body. In embryogenesis the interplay between calcium signalling and... 相似文献
163.
Gehring AJ Sun D Kennedy PT Nolte-'t Hoen E Lim SG Wasser S Selden C Maini MK Davis DM Nassal M Bertoletti A 《Journal of virology》2007,81(6):2940-2949
CD8 T cells exert their antiviral function through cytokines and lysis of infected cells. Because hepatocytes are susceptible to noncytolytic mechanisms of viral clearance, CD8 T-cell antiviral efficiency against hepatotropic viruses has been linked to their capacity to produce gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha). On the other hand, intrahepatic cytokine production triggers the recruitment of mononuclear cells, which sustain acute and chronic liver damage. Using virus-specific CD8 T cells and human hepatocytes, we analyzed the modulation of virus-specific CD8 T-cell function after recognition peptide-pulsed or virally infected hepatocytes. We observed that hepatocyte antigen presentation was generally inefficient, and the quantity of viral antigen strongly influenced CD8 T-cell antiviral function. High levels of hepatitis B virus production induced robust IFN-gamma and TNF-alpha production in virus-specific CD8 T cells, while limiting amounts of viral antigen, both in hepatocyte-like cells and naturally infected human hepatocytes, preferentially stimulated CD8 T-cell degranulation. Our data document a mechanism where virus-specific CD8 T-cell function is influenced by the quantity of virus produced within hepatocytes. 相似文献
164.
Infestation with Ostrinia nubilalis (Hb.), the European corn borer (ECB) can be detected by using different sampling techniques in the field and statistical models aimed to assess the development time of ECB larvae and crop damage. An appropriate monitoring for this polyphagous species to show a relationship between the kind of sampling or a model and the subsequent damage in a particular crop, is very difficult. Sex pheromone traps, generally, are also not reliable for monitoring ECB. The possibility of employing new types of traps baited with a sex pheromone and a maize kairomone, the phenylacetaldheyde (PAA) (multibaited traps) was investigated. In sweet corn, trapping experiments were conducted over a 2-year period with two kinds of cone traps (XLa and XLb) set up at the borders of fields (four replicates). ECB attacks of first and second generation larvae were evaluated in the corn ears as a percentage of damage and using a damage index (DI). A correlation was found between the number of females caught per trap and either the percentage of damaged ears (r = 0.73 for XLa; r = 0.65 for XLb) and the DI (r = 70 for XLa; r = 0.60 for XLb). Conversely, the number of males caught per trap was not correlated with ECB larval damage. A linear model of multiple correlation fitted to the data of simultaneous captures of males and females showed that the coefficients were not higher than simple correlation. The correlation coefficients obtained by fitting a curvilinear response surface were higher (r = 0.81 for XLa and r = 0.84 for XLb, respectively, related to percentage of damaged ears; r = 0.79 for XLa and r = 0.76 for XLb, respectively, related to DI) thus indicating that the simultaneous counting of males and females in cone traps can be an efficient and simple monitoring tool. 相似文献
165.
Role of fibroblast migration in collagen fiber formation during fetal and adult dermal wound healing 总被引:2,自引:0,他引:2
Paul D. Dale Jonathan A. Sherratt Philip K. Maini 《Bulletin of mathematical biology》1997,59(6):1077-1100
Adult dermal wounds, in contrast to fetal wounds, heal with the formation of scar tissue. A crucial factor in determining
the degree of scarring is the ratio of types I and III collagen, which regulates the diameter of the combined fibers. We developed
a reaction-diffusion model which focuses on the control of collagen synthesis by different isoforms of the polypeptide transforming
growth factor-β (TGFβ). We used the model to investigate the current controversy as to whether the fibroblasts migrate into
the wound from the surrounding unwounded dermis or from the underlying subcutaneous tissue. Numerical simulations of a spatially
independent, temporal model led to a value of the collagen ratio consistent with that of healthy tissue for the fetus, but
corresponding to scarring in the adult. We investigated the effect of topical application of TGFβ and show that addition of
isoform 3 reduces scar tissue formation, in agreement with the experiment. However, numerical solutions of the reaction-diffusion
system do not exhibit this sensitivity to growth factor application. Mathematically, this corresponds to the observation that
behind healing wavefront solutions, a particular healed state is always selected independent of transients, even though there
is a continuum of possible positive steady states. We explain this phenomenon using a caricature system of equations, which
reflects the key qualitative features of the full model but has a much simpler mathematical form. Biologically, our results
suggest that the migration into a wound of fibroblasts and TGFβ from the surrounding dermis alone cannot account for the essential
features of the healing process, and that fibroblasts entering from the underlying subcutaneous tissue are crucial to the
healing process. 相似文献
166.
Debbie L. Benson Philip K. Maini Jonathan A. Sherratt 《Journal of mathematical biology》1998,37(5):381-417
. The Turing bifurcation is the basic bifurcation generating spatial pattern, and lies at the heart of almost all mathematical
models for patterning in biology and chemistry. In this paper the authors determine the structure of this bifurcation for
two coupled reaction diffusion equations on a two-dimensional square spatial domain when the diffusion coefficients have a
small explicit variation in space across the domain. In the case of homogeneous diffusivities, the Turing bifurcation is highly
degenerate. Using a two variable perturbation method, the authors show that the small explicit spatial inhomogeneity splits
the bifurcation into two separate primary and two separate secondary bifurcations, with all solution branches distinct. This
splitting of the bifurcation is more effective than that given by making the domain slightly rectangular, and shows clearly
the structure of the Turing bifurcation and the way in which the!
var
ious solution branches collapse together as the spatial variation is reduced. The authors determine the stability of the solution
branches, which indicates that several new phenomena are introduced by the spatial variation, including stable subcritical
striped patterns, and the possibility that stable stripes lose stability supercritically to give stable spotted patterns..
Received: 10 January 1996/Revised version: 3 July 1996 相似文献
167.
We present two modelling frameworks for studying dynamic anistropy in connective tissue, motivated by the problem of fibre alignment in wound healing. The first model is a system of partial differential equations operating on a macroscopic scale. We show that a model consisting of a single extracellular matrix material aligned by fibroblasts via flux and stress exhibits behaviour that is incompatible with experimental observations. We extend the model to two matrix types and show that the results of this extended model are robust and consistent with experiment. The second model represents cells as discrete objects in a continuum of ECM. We show that this model predicts patterns of alignment on macroscopic length scales that are lost in a continuum model of the cell population. 相似文献
168.
For many years Turing systems have been proposed to account for spatial and spatiotemporal pattern formation in chemistry and biology. We extend the study of Turing systems to investigate the rôle of boundary conditions, domain shape, non-linearities, and coupling of such systems. We show that such modifications lead to a wide variety of patterns that bear a striking resemblance to pigmentation patterns in fish, particularly those involving stripes, spots and transitions between them. Using the Turing system as a metaphor for activator—inhibitor models we conclude that such a mechanism, with the aforementioned modifications, may play a rôle in fish patterning. 相似文献
169.
Debbie L. Benson Jonathan A. Sherratt Philip K. Maini 《Bulletin of mathematical biology》1993,55(2):365-384
Diffusion driven instability in reaction-diffusion systems has been proposed as a mechanism for pattern formation in numerous
embryological and ecological contexts. However, the possible effects of environmental inhomogeneities has received relatively
little attention. We consider a general two species reaction-diffusion model in one space dimension, with one diffusion coefficient
a step function of the spatial coordinate. We derive the dispersion relation and the solution of the linearized system. We
apply our results to Turing-type models for both embryogenesis and predator-prey interactions. In the former case we derive
conditions for pattern to be isolated in one part of the domain, and in the latter we introduce the concept of “environmental
instability”. Our results suggest that environmental inhomogeneity could be an important regulator of biological pattern formation. 相似文献
170.
P. K. Maini 《Journal of mathematical biology》1989,27(5):507-522
We investigate a cell-haptotaxis model for the generation of spatial and spatio-temporal patterns in one dimension. We analyse the steady state problem for specific boundary conditions and show the existence of spatially hetero-geneous steady states. A linear analysis shows that stability is lost through a Hopf bifurcation. We carry out a nonlinear multi-time scale perturbation procedure to study the evolution of the resulting spatio-temporal patterns. We also analyse the model in a parameter domain wherein it exhibits a singular dispersion relation. 相似文献