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101.
Morten Gram Pedersen Alberto Maria Bersani Enrico Bersani 《Journal of mathematical chemistry》2008,43(4):1318-1344
Enzyme reactions play a pivotal role in intracellular signal transduction. Many enzymes are known to possess Michaelis–Menten
(MM) kinetics and the MM approximation is often used when modeling enzyme reactions. However, it is known that the MM approximation
is only valid at low enzyme concentrations, a condition not fulfilled in many in vivo situations. Recently the total quasi steady-state approximation (tQSSA) has been developed for enzymes with MM kinetics.
This new approximation is valid not only whenever the MM approximation is, but moreover in a greatly extended parameter range.
Starting from a single reaction and arriving at the mitogen activated protein kinase (MAPK) cascade, we give several examples
of biologically realistic scenarios where the MM approximation leads to quantitatively as well as qualitatively wrong conclusions,
and show that the tQSSA improves the accuracy of the simulations greatly.
相似文献
102.
103.
Thomas Parr Lancelot Da Costa Conor Heins Maxwell James D. Ramstead Karl J. Friston 《Entropy (Basel, Switzerland)》2021,23(9)
In theoretical biology, we are often interested in random dynamical systems—like the brain—that appear to model their environments. This can be formalized by appealing to the existence of a (possibly non-equilibrium) steady state, whose density preserves a conditional independence between a biological entity and its surroundings. From this perspective, the conditioning set, or Markov blanket, induces a form of vicarious synchrony between creature and world—as if one were modelling the other. However, this results in an apparent paradox. If all conditional dependencies between a system and its surroundings depend upon the blanket, how do we account for the mnemonic capacity of living systems? It might appear that any shared dependence upon past blanket states violates the independence condition, as the variables on either side of the blanket now share information not available from the current blanket state. This paper aims to resolve this paradox, and to demonstrate that conditional independence does not preclude memory. Our argument rests upon drawing a distinction between the dependencies implied by a steady state density, and the density dynamics of the system conditioned upon its configuration at a previous time. The interesting question then becomes: What determines the length of time required for a stochastic system to ‘forget’ its initial conditions? We explore this question for an example system, whose steady state density possesses a Markov blanket, through simple numerical analyses. We conclude with a discussion of the relevance for memory in cognitive systems like us. 相似文献
104.
基于eCK(extended Canetti-Krawczyk)模型的定义,针对eCK模型下证明安全的两个密钥交换协议进行了分析.结果显示两个密钥交换协议在eCK模型中都是不安全的,其中SAKA(secure authenticated key agree-ment)协议不能抵抗临时密钥泄露攻击也不能抵抗长期密钥泄露攻击,并且不具有前向安全性.另一个SHY(Shi-Huang-Yang)协议不能抵抗两方临时密钥同时泄露的攻击. 相似文献
105.
V. A. Merzlyakov 《International Applied Mechanics》2008,44(8):892-904
A method to determine the nonstationary temperature fields and the thermoelastoplastic stress-strain state of noncircular
cylindrical shells is developed. It is assumed that the physical and mechanical properties are dependent on temperature. The
heat-conduction problem is solved using an explicit difference scheme. The temperature variation throughout the thickness
is described by a power polynomial. For the other two coordinates, finite differences are used. The thermoplastic problem
is solved using the geometrically nonlinear theory of shells based on the Kirchhoff-Love hypotheses. The theory of simple
processes with deformation history taken into account is used. Its equations are linearized by a modified method of elastic
solutions. The governing system of partial differential equations is derived. Variables are separated in the case where the
curvilinear edges are hinged. The partial case where the stress-strain state does not change along the generatrix is examined.
The systems of ordinary differential equations obtained in all these cases are solved using Godunov's discrete orthogonalization.
The temperature field in a shell with elliptical cross-section is studied. The stress-strain state found by numerical integration
along the generatrix is compared with that obtained using trigonometric Fourier series. The effect of a Winkler foundation
on the stress-strain state is analyzed
Translated from Prikladnaya Mekhanika, Vol. 44, No. 8, pp. 79–90, August 2008. 相似文献
106.
107.
S. Zhu 《Journal of Polymer Science.Polymer Physics》1996,34(3):505-516
The formation of polyradical chains is an important feature in free radical polymer modification with crosslinking. The effect of these polyradicals on the prediction of the gel point is theoretically investigated using the method of moments. The polyradical model derived gives a criterion for gelation, xr W,0 = 1, which fully agrees with the Flory-Stockmayer classical theory. The validity of the widely used monoradical assumption and the stationary-state hypothesis in modeling of free radical gel formation is extensively examined by making comparisons to the polyradical model. It is found that both assumptions delay the prediction of the gel point. The magnitude of the discrepancies depends on the reaction conditions. Based on the calculations using a wide range of parameters, it is concluded that these two assumptions are acceptable provided Rin/KhaY1,0Y1,0 is smaller than 10?7. However, this condition can be easily violated in a typical polymer modification system. Therefore, the use of polyradical models is suggested. © 1996 John Wiley & Sons, Inc. 相似文献
108.
With the development of access network, 10G EPON has gained more and more attention. As its topology structure is point-to-multi-point and the downstream data is broadcasted, it will suffer from eavesdropping and masquerading attack. To eliminate these safety threats, this paper proposes an integrated security scheme including a bilateral authentication method and an encryption algorithm combined with one-way hash function. The authentication method can verify OLT and ONU during the registration process, preventing illegal users joining the network, and safely establish a secret key used for encrypting as well. The proposed scheme's security is based on the computational Diffie–Hellman assumption and the target collision resistant hash functions. The simulation results indicate that this mechanism is more suitable for practical use. 相似文献
109.
Zaixing Huang 《International Journal of Theoretical Physics》2008,47(11):2850-2861
It is generally considered that global gauge symmetry of an action integral over a finite spatial-temporal domain as a whole
holds in any subdomain of this domain. However, in this paper we demonstrate that when the so-called localized assumption
is no longer valid, the global gauge symmetry will break in the subdomain of this spatial-temporal domain, due to occurrence
of a new source called the nonlocal residual. The nonlocal residual is correlated with a gauge field and satisfies the zero
mean condition with respect to whole spatial-temporal domain. An example is given to support this conclusion. 相似文献
110.
IntroductionThegeometrizationofmechanicsisatendencyofthedevelopmentofcontinuummechanicsanddrawsextensiveatentionofresearchers... 相似文献