全文获取类型
收费全文 | 786篇 |
免费 | 36篇 |
国内免费 | 7篇 |
专业分类
化学 | 484篇 |
晶体学 | 2篇 |
力学 | 66篇 |
数学 | 78篇 |
物理学 | 199篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 24篇 |
2020年 | 29篇 |
2019年 | 44篇 |
2018年 | 51篇 |
2017年 | 40篇 |
2016年 | 50篇 |
2015年 | 31篇 |
2014年 | 60篇 |
2013年 | 79篇 |
2012年 | 81篇 |
2011年 | 90篇 |
2010年 | 42篇 |
2009年 | 42篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有829条查询结果,搜索用时 31 毫秒
71.
Water activity measurements by isopiestic method have been carried out on the aqueous solutions of alanine + tri-potassium citrate (K3Cit) over a range of temperatures at atmospheric pressure. From these measurements, values of the vapor pressure of solutions were determined. The effect of temperature on the vapor–liquid equilibrium of alanine + K3Cit + H2O systems has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson and NRTL models. The agreement between the correlations and the experimental data is good. 相似文献
72.
In this paper the superstability of the Cauchy equation can be proved for complex valued functions on commutative semigroup under some suitable conditions. Furthermore, in this note, we give a partial affirmative answer to problem 18, in the 31st ISFE. 相似文献
73.
We extend a hybrid DSMC/Navier–Stokes (NS) approach to unify the DSMC and the NS simulators in one framework capable of solving the mixed non‐equilibrium and near‐equilibrium flow regions efficiently. Furthermore, we use a one‐way state‐based coupling (Dirichlet–Dirichlet boundary‐condition coupling) to transfer the required information from the continuum region to the rarefied one. The current hybrid DSMC–NS frame is applied to the hypersonic flows over nanoflat plate and microcylinder cases. The achieved solutions are compared with the pure DSMC and NS solutions. The results show that the current hybrid approach predicts the surface heat transfer rate and shear stress magnitudes very accurately. Some important conclusions can be drawn from this study. For example, although the shock wave region would be a non‐equilibrium region, it is not necessary to use a pure DSMC simulator to solve it entirely. This is important when the researchers wish to predict the surface properties such as velocity slip, temperature jump, wall heat flux rate, and friction drag magnitudes accurately. Our investigation showed that our hybrid solution time would be at least 40% (for the flat plate) and 35% (for the cylinder) of the time that must be spent by a pure DSMC solver to attain the same accuracy.Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
74.
This presented study is to make comparison of cross sections to produce 117Sb and 90Nb via different reactions with particle incident energy up to 70 MeV as a part of systematic studies on particle-induced activations on enriched Sn, Y2O3 and ZrO2 targets, theoretical calculation of production yield, calculation of required thickness of target and suggestion of optimum reaction to produce Antimony-117 and Niobium-90. 相似文献
75.
The density, sound velocity, and conductivity measurements were performed on aqueous solutions of sodium dodecyl sulfate (C12H25SO4Na) or sodium dodecyl sulfonate (C12H25SO3Na) in the absence and presence of poly(ethylene glycol) (PEG) at different temperatures. Changes in the apparent molar volumes and isentropic compressibilities upon micellization were derived using a pseudophase-transition approach and the infinite dilution apparent molar properties of the monomer and micellar form of C12H25SO4Na and C12H25SO3Na were determined. Variations of the critical micelle concentrations (CMCs) of both surfactants in the solutions investigated with temperature were obtained from which thermodynamic parameters of micellization were estimated. It was found that at low temperature the micelle formation process is endothermic and therefore, this process must be entropically driven. However, upon increasing the temperature, the enthalpic factor becomes more significant and, at temperatures higher than 303.15 K the micellization is enthalpy driven. The interactions between C12H25SO4Na/C12H25SO3Na and PEG were studied and it was found that sodium alkyl sulfonates were seen to interact more weakly than their sulfate analogues. 相似文献
76.
J. Sadeghi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):453-457
In this paper we discuss interacting particles in an
external magnetic field. By comparing the Schr?dinger equation of
three interacting particles with the associated Laguerre differential
equation, we obtain the energy spectrum which corresponds to
indices ni and mi. Finally by using the so called
factorization method we obtain the raising and lowering operators.
These operators are supersymmetric structures related to the
Hamiltonian partner. Also these
operators lead to the realization of Heisenberg Lie superalgebras with two, four and six supercharges. 相似文献
77.
The Friedel-Crafts acylation of aromatic compounds with carboxylic acids was investigated in the presence of Tf2O. The reaction was carried out efficiently and very rapidly under mild reaction conditions without the need of any catalyst. 相似文献
78.
Motivated by the recent work of Elizalde et al. [E. Elizalde, S. Nojiri, S.D. Odintsov, D. Saez–Gomez, V. Faraoni, Phys. Rev. D 77 (2008) 106005], we generalize their work to the non-flat case. We consider a universe filled with matter and show that it is possible to obtain both inflation and accelerated expansion at late times by using a single scalar field. Realistic examples are worked out in order to illustrate this fact. Then we extend the problem to the interacting case. 相似文献
79.
Bahareh Sadeghi Mohammad Maleki Zeinab Kamali Homa Almasieh 《Numerical Methods for Partial Differential Equations》2023,39(2):1652-1671
Advection equations with delay are appeared in the modeling of the dynamics of structured cell populations. In this article, we construct an efficient two-dimensional multistep collocation method for the numerical solution of a class of advection equations with delay. Equations with aftereffect and equations with both aftereffect and retardation of a state variable are considered. Computability of the algorithm and convergence properties of the proposed numerical method are analyzed for solutions in appropriate Sobolev spaces, and it is shown that the proposed scheme enjoys the spectral accuracy. Numerical examples are given and comparison with other existing methods in the literature is made to demonstrate the efficiency, superiority and high accuracy of the presented method. 相似文献
80.
Acta Mathematica Sinica, English Series - In this paper we are concerned with absolute, relative and Tate Tor modules. In the first part of the paper we generalize a result of Avramov and... 相似文献