全文获取类型
收费全文 | 221596篇 |
免费 | 2699篇 |
国内免费 | 1324篇 |
专业分类
化学 | 122957篇 |
晶体学 | 3231篇 |
力学 | 8921篇 |
综合类 | 61篇 |
数学 | 24492篇 |
物理学 | 65957篇 |
出版年
2020年 | 1762篇 |
2019年 | 1913篇 |
2018年 | 2512篇 |
2017年 | 2558篇 |
2016年 | 3680篇 |
2015年 | 2437篇 |
2014年 | 3552篇 |
2013年 | 8907篇 |
2012年 | 7717篇 |
2011年 | 9429篇 |
2010年 | 6686篇 |
2009年 | 6481篇 |
2008年 | 8811篇 |
2007年 | 8924篇 |
2006年 | 8402篇 |
2005年 | 7726篇 |
2004年 | 6886篇 |
2003年 | 6062篇 |
2002年 | 5992篇 |
2001年 | 6716篇 |
2000年 | 5078篇 |
1999年 | 3674篇 |
1998年 | 3045篇 |
1997年 | 3014篇 |
1996年 | 3020篇 |
1995年 | 2629篇 |
1994年 | 2726篇 |
1993年 | 2587篇 |
1992年 | 2840篇 |
1991年 | 2902篇 |
1990年 | 2711篇 |
1989年 | 2621篇 |
1988年 | 2564篇 |
1987年 | 2505篇 |
1986年 | 2526篇 |
1985年 | 3302篇 |
1984年 | 3362篇 |
1983年 | 2808篇 |
1982年 | 3049篇 |
1981年 | 2820篇 |
1980年 | 2612篇 |
1979年 | 2796篇 |
1978年 | 3006篇 |
1977年 | 3039篇 |
1976年 | 3065篇 |
1975年 | 2796篇 |
1974年 | 2913篇 |
1973年 | 2966篇 |
1972年 | 2324篇 |
1971年 | 1850篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
The method of nonlinear moments, when used to solve the Boltzmann equation, necessitates the calculation of collision integral
matrix elements. The matrix elements are hard to calculate numerically, especially at large indices. The asymptotics of the
matrix elements are constructed. In terms of the model of pseudopower particle interaction, a formula free of summation is
derived. This makes it possible to find the asymptotic behavior of linear and nonlinear elements when two indices are large.
For an arbitrary interaction cross section, asymptotic expansions of linear and nonlinear matrix elements in one index are
obtained. For Maxwellian molecules, asymptotic formulas are derived for three large indices. 相似文献
52.
The fine-structure parameters of a series of configurations of the first ion of indium and the gyromagnetic ratios in intermediate coupling are calculated by a semiempirical method in the single-configuration approximation. 相似文献
53.
Lobanovsky L. S. Troyanchuk I. O. 《Journal of Experimental and Theoretical Physics》2003,96(2):331-334
Journal of Experimental and Theoretical Physics - The magnetoresistance effect in the SmCu3Mn4O12 compound with a perovskite-like structure is investigated for the first time. It is found that an... 相似文献
54.
A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
55.
This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two‐equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k–εmodel, the realizable k–εmodel, the standard k–ωmodel and the shear‐stress‐transport (SST) k–ωmodel. It has found that the realizable k–εturbulence model used with enhanced wall functions and near‐wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
56.
V. L. Bychkov L. P. Grachev I. I. Esakov A. A. Ravaev K. V. Khodataev 《Technical Physics》2004,49(7):833-838
A longitudinal dc electric discharge in a submerged high-pressure supersonic air jet is described. Photographs of the discharge
are provided. The experimental voltage across the discharge gap and the discharge current are given for two resistances of
the resistor that limits the discharge current over a certain range of the discharge channel length along the air flow. The
current-voltage discharge characteristic is provided at a constant discharge length. The main discharge characteristics are
obtained from a comparison of the experimental and theoretical results calculated on the basis of the simplest model. 相似文献
57.
Oksengendler B. L. Karimov M. Yunusov M. C. Karakhodzhaev A. K. 《Russian Physics Journal》2004,47(7):790-791
Russian Physics Journal - 相似文献
58.
Dmitry S. Zimnitsky Tatiana L. Yurkshtovich Pavel M. Bychkovsky 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4785-4791
Samples of oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity were obtained by the oxidation of native and mercerized cellulose with a solution of nitrogen(IV) oxide in CCl4. A detailed characterization of these OC samples was performed. The effect of oxidation conditions (concentration of N2O4 in the solution and oxidation time) and starting cellulose material on OC characteristics (carboxyl, carbonyl and nitrogen content, degree of crystallinity and polymerization, surface area and swelling, and acidic properties) was investigated. Reactivity in the oxidation process was higher in mercerized cellulose than in native cellulose. The action of dilute solutions (10–15%) of N2O4 did not affect the degree of crystallinity of cellulose samples. Under these conditions, the oxidation took place mainly in amorphous regions and on the surface of crystallites. Oxidation in a concentrated (40%) N2O4 solution led to the destruction of crystallites, which increased the surface area and swelling of cellulose in water. The surface area and the swelling of OC samples increased with a decrease in the index of crystallinity. The acidic properties of OC were shown to increase with an increase of swelling in water. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4785–4791, 2004 相似文献
59.
Strain hardening of polycarbonate in the glassy state: Influence of temperature and molecular weight
L. E. Govaert T. A. Tervoort 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2041-2049
This study is concerned with the temperature and molecular weight dependence of the strain-hardening behavior of polycarbonate. It is shown that the strain-hardening modulus reduces with increasing temperature and decreasing molecular weight. This result is interpreted in terms of temperature accelerated relaxation of the entanglement network. Moreover, it is shown that frozen-in orientations, induced by homogeneous deformations above the glass transition temperature, lead to anisotropic yield behavior that can be fully rationalized (and modelled) in terms of a superimposed stress contribution of the prestrained network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2041–2049, 2004 相似文献
60.
Rachel L. McSwain Alison R. Markowitz Kenneth R. Shull 《Journal of Polymer Science.Polymer Physics》2004,42(20):3809-3821
To develop a greater understanding of interfacial interactions between a semicrystalline polymer and a glassy polymer, adhesion tests were performed on very thin layers of poly(ethylene oxide) (PEO) sandwiched between two layers of poly(tetramethyl bisphenol A polycarbonate) (TMPC). The tests were designed to provide intimate contact between the surfaces while they were heated above the melting point of the PEO and cooled back to room temperature. A contact mechanics approach, based on the Johnson, Kendall, and Roberts theory, was used to determine values of the energy release rate describing the energetic driving force for crack propagation within the interfacial region. The ability to measure crack propagation at large values of the energy release rate was limited by rupture of the silicone elastomer that was used to provide a sufficiently compliant matrix for the adhesion experiment. By cycling the tensile stress at relatively low loading levels, we were able to measure fatigue crack propagation at values of the energy release rate that did not result in failure of the elastomer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3809–3821, 2004 相似文献