全文获取类型
收费全文 | 17054篇 |
免费 | 1372篇 |
国内免费 | 816篇 |
专业分类
化学 | 330篇 |
晶体学 | 8篇 |
力学 | 3018篇 |
综合类 | 130篇 |
数学 | 12795篇 |
物理学 | 2961篇 |
出版年
2024年 | 36篇 |
2023年 | 176篇 |
2022年 | 139篇 |
2021年 | 251篇 |
2020年 | 465篇 |
2019年 | 450篇 |
2018年 | 459篇 |
2017年 | 450篇 |
2016年 | 443篇 |
2015年 | 406篇 |
2014年 | 707篇 |
2013年 | 1804篇 |
2012年 | 655篇 |
2011年 | 994篇 |
2010年 | 793篇 |
2009年 | 1097篇 |
2008年 | 1053篇 |
2007年 | 1007篇 |
2006年 | 920篇 |
2005年 | 715篇 |
2004年 | 660篇 |
2003年 | 637篇 |
2002年 | 645篇 |
2001年 | 530篇 |
2000年 | 512篇 |
1999年 | 469篇 |
1998年 | 400篇 |
1997年 | 372篇 |
1996年 | 285篇 |
1995年 | 192篇 |
1994年 | 184篇 |
1993年 | 168篇 |
1992年 | 122篇 |
1991年 | 106篇 |
1990年 | 94篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 48篇 |
1986年 | 46篇 |
1985年 | 70篇 |
1984年 | 101篇 |
1983年 | 50篇 |
1982年 | 67篇 |
1981年 | 65篇 |
1980年 | 58篇 |
1979年 | 57篇 |
1978年 | 54篇 |
1977年 | 33篇 |
1976年 | 27篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The processes of wave disturbance propagation in a supersonic boundary layer with self-induced pressure [1–4] are analyzed. The application of a new mathematical apparatus, namely, the theory of characteristics for systems of differential equations with operator coefficients [5–8], makes it possible to obtain generalized characteristics of the discrete and continuous spectra of the governing system of equations. It is shown that the discontinuities in the derivatives of the solution of the boundary layer equations are concentrated on the generalized characteristics. It is established that in the process of flow evolution the amplitude of the weak discontinuity in the derivatives may increase without bound, which indicates the possibility of breaking of nonlinear waves traveling in the boundary layer. 相似文献
992.
993.
Feng Xiqiao Yu Shouwen 《Acta Mechanica Solida Sinica》1995,8(2):121-132
By using the concept of domain of microcrack growth(DMG),themicromechanisms of damage in quasi-brittle materials subjected to triaxial either tensileor compressive loading are investigated and the complete strew-strain relation includingfour stages is obtained from micromechanical analysis.The regime of pre-peaknonlinear hardening corresponds to the distributed damage,i.e.the stable propagationof microcracks.After the attainment of the ultimate strength of load-bearing capacity,some microcracks experience the second unstable growth and the distributed damage istransmitted to the localization of damage.These analyses improve our understanding ofthe hardening and softening behaviors of quasi-brittle materials. 相似文献
994.
V. Yu. Aleksandrov 《Fluid Dynamics》2002,37(6):983-995
On the basis of a numerical analysis of the non-Navier-Stokes gas-dynamic equations for slow non-isothermal gas flows, the nonlinear thermomolecular pressure difference effect due to a large temperature gradient along the lateral surface of a capillary is investigated. It is shown that the magnitude of the effect is substantially different from the values calculated using the Navier-Stokes equations. For two models of molecular interaction (Maxwell molecules and hard spheres), the possibility of a quasi-one-dimensional interpretation of the effect for experimental estimation purposes is demonstrated. The solutions of the relaxation kinetic equation for flow in a plane capillary at small Knudsen numbers and the gas-dynamic equations for slow non-isothermal flows are compared and the range of their applicability is estimated. 相似文献
995.
钛合金TC-4在高应变率下的动态本构关系 总被引:1,自引:0,他引:1
利用分离式Hopkinson扭杆对钛合金TC-4进行了高应变率下动态剪切本构关系的实验研究。结果表明TC-4对应变率高度敏感,对应变率的敏感性随应变率的提高而增加。其动态应力应变关系呈线性强化形式。但动态强化模量随应变率的提高而略有减少。采用Malvern给出的过应力模式_p={exp[(1/)(-f())]-1}/b可以较好地描述TC-4的动态剪切本构关系。 相似文献
996.
It is shown that a perturbation argument that guarantees persistence of inertial (invariant and exponentially attracting) manifolds for linear perturbations of linear evolution equations applies also when the perturbation is nonlinear. This gives a simple but sharp condition for existence of inertial manifolds for semi-linear parabolic as well as for some nonlinear hyperbolic equations. Fourier transform of the explicitly given equation for the tracking solution together with the Plancherel's theorem for Banach valued functions are used. 相似文献
997.
Dr. H. Braun 《Rheologica Acta》1991,30(6):523-529
Using a power-law ansatz for the temperature dependence of the shear modulus on the level of internal variables, the thermorheological behavior is modeled for viscoelastic fluids of a special group of rheological constitutive equations (rate-type models). The model parameter introduced characterizes thermoelastic contributions. The relation between the model parameter and the physical quantities appearing in deformation processes is discussed. Based on the chosen temperature dependence of the shear modulus, thermodynamically consistent equations like the nonlinear rheological constitutive equation and the temperature equation are derived. The special cases of entirely entropy and energy elastic fluids are also considered. The thermorheological behavior (exo-, - or endothermal processes) of a viscoelastic fluid in a stress-growth experiment followed by relaxation is analyzed with respect to the model parameter. 相似文献
998.
A general nonlinear theory for the dynamics of elastic anisotropic plates undergoing moderate-rotation vibrations is presented. The theory fully accounts for geometric nonlinearities (moderate rotations and displacements) by using local stress and strain measures and an exact coordinate transformation, which result in nonlinear curvatures and strain-displacement expressions that contain the von Karman strains as a special case. The theory accounts for transverse shear deformations by using a third-order theory and for extensionality and changes in the configuration due to in-plane and transverse deformations. Five third-order nonlinear partial-differential equations of motion describing the extension-extension-bending-shear-shear vibrations of plates are obtained by an asymptotic analysis, which reveals that laminated plates display linear elastic and nonlinear geometric couplings among all motions. 相似文献
999.
J. M. Wiest 《Rheologica Acta》1989,28(1):4-12
A modification of the Giesekus constitutive equation is derived by incorporating (approximately, via the Peterlin approximation) the finite extensibility of polymer molecules into dumbbell kinetic theory along with the anisotropic hydrodynamic drag suggested by Giesekus. The constitutive equation that is obtained retains much of the simplicity of Giesekus' constitutive equation, but it involves terms that are cubic in the stress as well as those that are quadratic. It is shown that the constitutive equation quantitatively describes the steady elongational viscosity of the IUPAC polymer melt A (including the strain softening of the melt), but it cannot describe the elongational and shear viscosities simultaneously. It is also shown that the constitutive equation satisfies the Lodge-Meissner relation for shear strains less than unity. 相似文献
1000.
R. Steller 《Rheologica Acta》1985,24(2):134-142
Zusammenfassung Es werden theoretische und experimentelle Untersuchungen pulsierender Strömungen viskoelastischer Flüssigkeiten in einem kreisförmigen Kanal durchgeführt. Unter Voraussetzung einer eindimensionalen, isothermen und vollentwickelten Strömung in Anwesenheit sinusförmiger Druckgradientenschwankungen wird für die rheologische Zustandsgleichung von Bird-Carreau eine asymptotische Lösung erzielt. Die Ergebnisse weisen darauf hin, daß sowohl die relative Amplitude der Ausstoßschwankungen als auch die relative Änderung des mittleren Ausstoßes sich in einer allgemeinen Form darstellen läßt, die bezüglich der Temperatur und der relativen Amplitude der Druckgradientenschwankungen invariant ist. Die theoretischen Ergebnisse werden mit experimentellen Daten für ein Polyethylen niederer Dichte verglichen. Dabei wird eine gute Übereinstimmung der Theorie mit dem Experiment festgestellt.
Theoretical and experimental studies were carried out on the pulsating flow of viscoelastic liquids through a circular channel. By assuming the flow to be one-dimensional, isothermal, and fully developed and the Bird-Carreau constitutive equation to be applicable, an asymptotic solution was found. The results obtained indicate that both the relative amplitude of pulsation of the output and the relative change in the average output may be presented in a generalized form that is independent of the relative amplitude of the pressure pulsations and temperature. The theoretical results were verified experimentally for a low-density polyethylene. Good agreement was found between the theory and the experimental data.相似文献