全文获取类型
收费全文 | 655篇 |
免费 | 41篇 |
国内免费 | 17篇 |
专业分类
化学 | 480篇 |
晶体学 | 1篇 |
力学 | 46篇 |
数学 | 101篇 |
物理学 | 85篇 |
出版年
2023年 | 4篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 28篇 |
2019年 | 43篇 |
2018年 | 40篇 |
2017年 | 29篇 |
2016年 | 68篇 |
2015年 | 38篇 |
2014年 | 40篇 |
2013年 | 102篇 |
2012年 | 58篇 |
2011年 | 45篇 |
2010年 | 39篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 28篇 |
2006年 | 7篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有713条查询结果,搜索用时 15 毫秒
81.
Dialkyl 2‐(alkylamino)‐4,9‐dihydro‐9‐oxocyclohepta[b]pyran‐3,4‐dicarboxylates are prepared in a one‐pot three‐component reaction of alkyl isocyanide, dialkyl acetylenedicarboxylate, and α‐tropolone (=2‐hydroxycyclohepta‐2,4,6‐trienone). The reaction proceeds smoothly at room temperature and under neutral conditions to afford tropolone derivatives in high yield. 相似文献
82.
83.
R. Mokhtari Moghari A. Akbarinia M. Shariat F. Talebi R. Laur 《International Journal of Multiphase Flow》2011
Heat transfer enhancement of a mixed convection laminar Al2O3–water nanofluid flow in an annulus with constant heat flux boundary condition has been studied employing two phase mixture model and effective expressions of nanofluid properties. The fluid flow properties are assumed constant except for the density in the body force, which varies linearly with the temperature (Boussinesq’s hypothesis), thus the fluid flow characteristics are affected by the buoyancy force. The Brownian motions of nanoparticles have been considered to determine the effective thermal conductivity and the effective dynamic viscosity of Al2O3–water nanofluid, which depend on temperature. Three-dimensional Navier–Stokes, energy and volume fraction equations have been discretized using the finite volume method while the SIMPELC algorithm has been introduced to couple the velocity–pressure. Numerical simulations have been presented for the nanoparticles volume fraction (?) between 0 and 0.05 and different values of the Grashof and Reynolds numbers. The calculated results show that at a given Re and Gr, increasing nanoparticles volume fraction increases the Nusselt number at the inner and outer walls while it does not have any significant effect on the friction factor. Both the Nusselt number and the friction coefficient at the inner wall are more than their corresponding values at the outer wall. 相似文献
84.
Gholamreza Talebi 《Indagationes Mathematicae》2019,30(4):741-743
The results in Section 4 of the paper “On the Taylor sequence spaces and upper boundedness of Hausdorff matrices and Nörlund matrices” that appeared in this journal (28 (3) (2017), 629–636) are valid only for those summability matrices whose absolute row sums do not exceed 1. For other summability matrices, the corrected results are presented and proved. 相似文献
85.
Nonlinear vibration mitigation of a flexible rotor shaft carrying a longitudinally dispositioned unbalanced rigid disc 总被引:1,自引:0,他引:1
Nonlinear Dynamics - This study is dedicated to investigate the nonlinear dynamics of a system composed of a flexible rotor shaft carrying a longitudinally dispositioned unbalanced rigid disc. The... 相似文献
86.
Let (an)n0 be a sequence of complex numbers, and, for n0, let
A number of results are proved relating the growth of the sequences(bn) and (cn) to that of (an). For example, given p0, if bn= O(np and for all > 0,then an=0 for all n > p. Also, given 0 < p < 1, then for all > 0 if and onlyif . It is further shown that, given rß > 1, if bn,cn=O(rßn), then an=O(n),where , thereby proving a conjecture of Chalendar, Kellay and Ransford. The principal ingredientsof the proogs are a Phragmén-Lindelöf theorem forentire functions of exponential type zero, and an estimate forthe expected value of e(X), where X is a Poisson random variable.2000 Mathematics Subject Classification 05A10 (primary), 30D15,46H05, 60E15 (secondary). 相似文献
87.
Javad Mashreghi Julian Ransford Thomas Ransford 《Journal of Functional Analysis》2018,274(11):3254-3262
We show that every linear functional on the Dirichlet space that is non-zero on nowhere-vanishing functions is necessarily a multiple of a point evaluation. Continuity of the functional is not assumed. As an application, we obtain a characterization of weighted composition operators on the Dirichlet space as being exactly those linear maps that send nowhere-vanishing functions to nowhere-vanishing functions.We also investigate possible extensions to weighted Dirichlet spaces with superharmonic weights. As part of our investigation, we are led to determine which of these spaces contain functions that map the unit disk onto the whole complex plane. 相似文献
88.
Javad Mashreghi Mostafa Nasri 《Nonlinear Analysis: Theory, Methods & Applications》2010,72(3-4):2086-2099
We develop a variant of Korpelevich’s method for solving variational inequality problems with pseudomonotone operators in Banach spaces. We establish the strong convergence of the sequence generated by the method under reasonable assumptions on the problem data. Finally, we justify the motivation of our theory by including compelling examples of infinite dimensional variational inequality problems for which our method is applicable. 相似文献
89.
In this paper, we introduce and study a new class of extended general nonlinear mixed variational inequalities and a new class of extended general resolvent equations and establish the equivalence between the extended general nonlinear mixed variational inequalities and implicit fixed point problems as well as the extended general resolvent equations. Then by using this equivalent formulation, we discuss the existence and uniqueness of solution of the problem of extended general nonlinear mixed variational inequalities. Applying the aforesaid equivalent alternative formulation and a nearly uniformly Lipschitzian mapping S, we construct some new resolvent iterative algorithms for finding an element of set of the fixed points of nearly uniformly Lipschitzian mapping S which is the unique solution of the problem of extended general nonlinear mixed variational inequalities. We study convergence analysis of the suggested iterative schemes under some suitable conditions. We also suggest and analyze a class of extended general resolvent dynamical systems associated with the extended general nonlinear mixed variational inequalities and show that the trajectory of the solution of the extended general resolvent dynamical system converges globally exponentially to the unique solution of the extended general nonlinear mixed variational inequalities. The results presented in this paper extend and improve some known results in the literature. 相似文献
90.
This paper proposes a tunable zeroth-order resonator on a composite right/left-handed transmission line consisting of a transversely magnetized ferrite substrate periodically loaded by microstrip inductors. Based on the propagation theory of edge guided modes, the analysis procedure of this structure is introduced. The numerical results demonstrate the tunability of the resonant frequency by changing the DC bias magnetic field applied to the ferrite. In contrast to previous work, the proposed structure is easy to design and fabricate and does not require a chip component. 相似文献