全文获取类型
收费全文 | 1254篇 |
免费 | 93篇 |
国内免费 | 79篇 |
专业分类
化学 | 819篇 |
晶体学 | 9篇 |
力学 | 64篇 |
综合类 | 15篇 |
数学 | 142篇 |
物理学 | 377篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 31篇 |
2021年 | 37篇 |
2020年 | 48篇 |
2019年 | 39篇 |
2018年 | 36篇 |
2017年 | 35篇 |
2016年 | 58篇 |
2015年 | 58篇 |
2014年 | 82篇 |
2013年 | 70篇 |
2012年 | 92篇 |
2011年 | 106篇 |
2010年 | 63篇 |
2009年 | 56篇 |
2008年 | 79篇 |
2007年 | 63篇 |
2006年 | 54篇 |
2005年 | 42篇 |
2004年 | 56篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 24篇 |
2000年 | 29篇 |
1999年 | 14篇 |
1998年 | 16篇 |
1997年 | 4篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1966年 | 3篇 |
1936年 | 1篇 |
1863年 | 1篇 |
排序方式: 共有1426条查询结果,搜索用时 15 毫秒
951.
Hongna Wang Xiaoqiang Jia Xue Wang Zhengxi Zhou Jianping Wen Jinli Zhang 《Applied Mathematical Modelling》2014
A three-dimensional CFD model was developed in this work to simulate hydrodynamic characteristics of a gas–liquid two-phase stirred tank with two six-bladed turbines and four baffles, coupling of the Multiple Size Group model to determine bubble size distribution. Important hydrodynamic parameters of the multi-phase system such as volume-averaged overall and time-averaged local gas holdups and axial liquid velocities along time and transversal courses were simulated and analyzed in detail, under varied operating conditions (inlet air flow rate and impeller rotation speed). Model predictions of local transient gas holdup and liquid velocity distributions on vertical and horizontal sections of the tank were also carried out. The overall flow patterns were discussed in detail to assess the mixing. Bubble size distributions were further predicted to reveal the unique properties of gas phase. Experimental measurements of overall gas holdups and local axial liquid velocities were used to validate the developed model. 相似文献
952.
Francisco Marcellán Misael Marriaga Teresa E. Pérez Miguel A. Piñar 《Acta Appl Math》2018,153(1):81-100
We consider Koornwinder’s method for constructing orthogonal polynomials in two variables from orthogonal polynomials in one variable. If semiclassical orthogonal polynomials in one variable are used, then Koornwinder’s construction generates semiclassical orthogonal polynomials in two variables. We consider two methods for deducing matrix Pearson equations for weight functions associated with these polynomials, and consequently, we deduce the second order linear partial differential operators for classical Koornwinder polynomials. 相似文献
953.
Nian Tang Chao Yang Zhenbang Pi Qing Han 《Journal of Physics and Chemistry of Solids》2010,71(3):258-405
Single-crystalline α-MnO2 nanorods have been successfully synthesized by a novel hydrothermal method based on the redox reactions between the permanganate anion MnO4- and H2O in mixture containing KMnO4 and HNO3. The products have been characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR) and Brunauer-Emmett-Teller (BET). The results prove that the grain size of α-MnO2 nanorods with the surface area ∼95.2 m2 g−1 is homogeneous with diameters ranging from 10 to 20 nm. The electrochemical property of the material shows that compared with the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the as-prepared α-MnO2 nanorods is increased by 70.4%, 104.1% and 135.7% at different constant currents of 50, 250 and 500 mA g−1, respectively. 相似文献
954.
We present a fast algorithm using Gröbner basis to compute the dimensions of subfield subcodes of Hermitian codes. With these algorithms we are able to compute the exact values of the dimension of all subfield subcodes up to q ≤ 32 and length up to 215. We show that some of the subfield subcodes of Hermitian codes are at least as good as the previously known codes, and we show the existence of good long codes. 相似文献
955.
Let \({T_\alpha }\) denote the rotation \({T_\alpha }x = x + \alpha \) (mod 1) by an irrational number α on the additive circle T = [0, 1). Let β 1, …, β d be d ≥ 1 parameters in [0, 1). One of the goals of this paper is to describe the ergodic properties of the cocycle (taking values in ? d+1) generated over \({T_\alpha }\) by the vectorial function Ψ d+1(x):= (φ(x), φ(x+β 1), …, φ(x+β d )), with φ(x) = {x}?½. It was already proved in [LeMeNa03] that Ψ2 is regular for α with bounded partial quotients. In the present paper we show that Ψ2 is regular for any irrational α. For higher dimensions, we give sufficient conditions for regularity. While the case d = 2 remains unsolved, for d = 3 we provide examples of non-regular cocycles Ψ4 for certain values of the parameters β 1, β 2, β 3. We also show that the problem of regularity for the cocycle Ψ d+1 reduces to the regularity of the cocycles of the form \({\Phi _d} = {({1_{[0,{\beta _j}]}} - {\beta _j})_{j = 1, \ldots ,d}}\) (taking values in ? d ). Therefore, a large part of the paper is devoted to the classification problems of step functions with values in ? d . 相似文献
956.
We determine a 2-codimensional para-CR structure on the slit tangent bundle T0 M of a Finsler manifold(M,F) by imposing a condition regarding the almost paracomplex structure P associated to F when restricted to the structural distribution of a framed para-f-structure.This condition is satisfied when(M,F) is of scalar flag curvature(particularly constant) or if the Riemannian manifold(M,g) is of constant curvature. 相似文献
957.
The magnetic property of double doped manganite Nd0.5(1+x)Ca0.5(1−x)Mn(1−x)CrxO3 with a fixed ratio of Mn3+:Mn4+=1:1 has been investigated. For the undoped sample, it undergoes one transition from charge disordering to charge ordering (CO) associated with paramagnetic (PM)-antiferromagnetic (AFM) phase transition at T<250 K. The long range AFM ordering seems to form at 35 K, rather than previously reported 150 K. At low temperature, an asymmetrical M-H hysteresis loop occurs due to weak AFM coupling. For the doped samples, the substitution of Cr3+ for Mn3+ ions causes the increase of magnetization and the rise of Tc. As the Cr3+ concentration increases, the CO domain gradually becomes smaller and the CO melting process emerges. At low temperature, the FM superexchange interaction between Mn3+ and Cr3+ ions causes a magnetic upturn, namely, the second FM phase transition. 相似文献
958.
959.
本文证明了四元数分析中的有界区域G上的非齐次Dirac方程u=f的分布解T_Gf,当f∈L_P(G),P>4时,在G上具有Holder连续性,讨论了超球和双圆柱上的方程u=f的Riemann-Hilbert边值问题,给出了可解条件和通解的积分表示,并且还证明了通解的Holder连续性。 相似文献
960.
A generating function for nonstandard orthogonal polynomials involving differences: the Meixner case
In this paper we deal with a family of nonstandard polynomials orthogonal with respect to an inner product involving differences.
This type of inner product is the so-called Δ-Sobolev inner product. Concretely, we consider the case in which both measures appearing in the inner product correspond
to the Pascal distribution (the orthogonal polynomials associated to this distribution are known as Meixner polynomials).
The aim of this work is to obtain a generating function for the Δ-Meixner–Sobolev orthogonal polynomials and, by using a limit process, recover a generating function for Laguerre–Sobolev
orthogonal polynomials. 相似文献