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为了消除非线性因素对相位生成载波解调结果的干扰,降低相位生成载波解调过程中低通滤波器的频响特性对相位生成载波解调结果的影响,该文提出了一种基于扩展卡尔曼滤波椭圆参数估计的相位生成载波微分交叉相乘解调方法。该方法在综合考虑各种非线性因素对相位生成载波微分交叉相乘解调结果的影响的基础上,对传统的相位生成载波微分交叉相乘解调过程进行了改进。经过计算机仿真和实验验证,该文所提出的扩展卡尔曼滤波微分交叉相乘方法能够有效地抑制非线性因素对相位生成载波解调结果的干扰,相比传统的相位生成载波微分交叉相乘方法,其信噪比提高了35.0 d B,总谐波失真降低了30.7 dB,信噪谐波比提高了31.0 dB,且扩展卡尔曼滤波微分交叉相乘方法受解调过程中低通滤波器频响特性的影响较小。 相似文献
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Numerical simulations and laboratory measurements have been used to illuminate the interaction of a moving shock wave impacting
on metallic grids at various shock strengths and grid solidities. The experimental work was carried out in a large scale shock
tube facility while computational work simulated the flow field with a time-dependent inviscid and a time-dependent viscous
model. The pressure drop measured across the grids is a result of two phenomena which are associated with the impact of the
shock on the metallic grids. First are the reflection and refraction of the incoming shock on the grid itself. This appears
to be the main inviscid mechanism associated with the reduction of the strength of the transmitted shock. Second, viscous
phenomena are present during the reflection and refraction of the wave as well as during the passage of the induced flow of
the air through the grid. The experimental data of pressure drop across the grid obtained in the present investigation are
compared with those obtained from computations. The numerical results slightly overpredict the experimental data of relative
pressure drop which increases substantially with grid solidity at fixed flow Mach numbers. The processes of shock reflection
and refraction are continuous and they can be extended in duration by using thicker grids that will result in lower compression
rates of the structural loading and increase the viscous losses associated with these phenomena which will further attenuate
the impacting shock. Preliminary theoretical analysis suggests that the use of a graded porosity/solidity material will result
in higher pressure drop than a constant porosity/solidity material and thus provide effective blast mitigation.
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A four-level double-ladder atomic system with two upper states coupled to the excited state by a standing-wave trigger field is explored to generate photonic bandgap (PBG) structure. With the assistance of spontaneously generated coherence (SGC) from the two decay pathways, we can obtain single or double fully developed PBG when the trigger field is far away from resonance or resonant. While in the absence of SGC, the atomic medium becomes strong absorptive to the probe field, and therefore the resulting PBGs are severely malformed or even cannot be opened up. Numerical results show that the PBG structure is originated from the third-order cross Kerr nonlinear modulation between the probe and trigger fields. This mechanism differs from the recent schemes based on linear modulation. 相似文献
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Paolo Zanardo 《代数通讯》2015,43(1):158-173
Let R be a commutative ring and A be an R-module. The Mal'cev rank μ(A) of A is the sup of genN, where N ranges over the finitely generated submodules of A, and genN is the minimum number of generators of N. We prove that μ is both sub-additive and pre-additive as an invariant of Mod(R). Our main goal is to investigate μ for modules over pseudo-valuation domains. Specifically, we establish which pseudo-valuation domains R satisfy the property that an R-module of finite Mal'cev rank must be finitely generated. We split the class 𝒞 of pseudo-valuation domains as a union 𝒞 = 𝒞1 ∪ 𝒞2 ∪ 𝒞3 ∪ 𝒞4 of suitably defined subclasses, and prove that the property holds if and only if R ∈ 𝒞3 ∪ 𝒞4. In that case we can describe the R-modules A where μ(A) < ∞. We also show that, for R ∈ 𝒞4, there exist indecomposable R-modules of arbitrarily large finite Mal'cev rank. 相似文献
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The goal of the paper is to automatize the construction and parameterization of kinetic reaction mechanisms that can describe a set of experimentally measured concentration versus time curves. Using the framework and theorems of formal reaction kinetics, first, we build a set of possible mechanisms with a given number of measured and unmeasured (real or fictitious) species and reaction steps that fulfill some chemically reasonable requirements. Then we fit all the corresponding mass-action kinetic models and offer the best one to the chemist to help explain the underlying chemical phenomenon or to use it for predictions. We demonstrate the use of the method via two simple examples: on an artificial, simulated set of data and on a small real-life data set. The method can also be used to do a kind of lumping to generate a model that can reproduce the simulation results of a detailed mechanism with less species and thereby can largely accelerate spatially inhomogeneous simulations. 相似文献