全文获取类型
收费全文 | 9106篇 |
免费 | 1091篇 |
国内免费 | 1166篇 |
专业分类
化学 | 7053篇 |
晶体学 | 155篇 |
力学 | 361篇 |
综合类 | 91篇 |
数学 | 1160篇 |
物理学 | 2543篇 |
出版年
2024年 | 9篇 |
2023年 | 88篇 |
2022年 | 156篇 |
2021年 | 238篇 |
2020年 | 272篇 |
2019年 | 282篇 |
2018年 | 229篇 |
2017年 | 262篇 |
2016年 | 390篇 |
2015年 | 398篇 |
2014年 | 468篇 |
2013年 | 609篇 |
2012年 | 751篇 |
2011年 | 827篇 |
2010年 | 586篇 |
2009年 | 517篇 |
2008年 | 663篇 |
2007年 | 559篇 |
2006年 | 546篇 |
2005年 | 476篇 |
2004年 | 400篇 |
2003年 | 353篇 |
2002年 | 381篇 |
2001年 | 287篇 |
2000年 | 236篇 |
1999年 | 214篇 |
1998年 | 130篇 |
1997年 | 123篇 |
1996年 | 76篇 |
1995年 | 90篇 |
1994年 | 64篇 |
1993年 | 77篇 |
1992年 | 82篇 |
1991年 | 74篇 |
1990年 | 57篇 |
1989年 | 46篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 38篇 |
1985年 | 44篇 |
1984年 | 30篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 134 毫秒
61.
62.
63.
应用密度矩阵方程计算了四能级原子系统中三阶非线性极化率随信号光和探针光频率失谐的变化关系。结果表明,由于量子干涉对信号光强度的敏感性,使四能级原子介质的交叉Kerr非线性作用大大增强,与三能级系统相比,四能级原子介质的Kerr非线性系数可增强两个数量级。 相似文献
64.
In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
65.
A numerical simulation is performed to investigate the flow induced by a sphere moving along the axis of a rotating cylindrical container filled with the viscous fluid. Three‐dimensional incompressible Navier–Stokes equations are solved using a finite element method. The objective of this study is to examine the feature of waves generated by the Coriolis force at moderate Rossby numbers and that to what extent the Taylor–Proudman theorem is valid for the viscous rotating flow at small Rossby number and large Reynolds number. Calculations have been undertaken at the Rossby numbers (Ro) of 1 and 0.02 and the Reynolds numbers (Re) of 200 and 500. When Ro=O(1), inertia waves are exhibited in the rotating flow past a sphere. The effects of the Reynolds number and the ratio of the radius of the sphere and that of the rotating cylinder on the flow structure are examined. When Ro ? 1, as predicted by the Taylor–Proudman theorem for inviscid flow, the so‐called ‘Taylor column’ is also generated in the viscous fluid flow after an evolutionary course of vortical flow structures. The initial evolution and final formation of the ‘Taylor column’ are exhibited. According to the present calculation, it has been verified that major theoretical statement about the rotating flow of the inviscid fluid may still approximately predict the rotating flow structure of the viscous fluid in a certain regime of the Reynolds number. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
66.
A new numerical method called linearized and rational approximation method is presented to solve non‐linear evolution equations. The utility of the method is demonstrated for the case of differentiation of functions involving steep gradients. The solution of Burgers' equation is presented to illustrate the effectiveness of the technique for the solution of non‐linear evolution equations exhibiting nearly discontinuous solutions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
67.
Siaw-Lynn Ng 《Designs, Codes and Cryptography》2003,30(1):5-19
Deciding whether a matroid is secret sharing or not is a well-known open problem. In Ng and Walker [6] it was shown that a matroid decomposes into uniform matroids under strong connectivity. The question then becomes as follows: when is a matroid m with N uniform components secret sharing? When N = 1, m corresponds to a uniform matroid and hence is secret sharing. In this paper we show, by constructing a representation using projective geometry, that all connected matroids with two uniform components are secret sharing 相似文献
68.
In this paper, the problem of estimating the covariance matrix of the elliptically contoured distribution (ECD) is considered. A new class of estimators which shrink the eigenvalues towards their arithmetic mean is proposed. It is shown that this new estimator dominates the unbiased estimator under the squared error loss function. Two special classes of ECD, namely, the multivariate-elliptical t distribution and the ε-contaminated normal distribution are considered. A simulation study is carried out and indicates that this new shrinkage estimator provides a substantial improvement in risk under most situations. 相似文献
69.
Summary The stability constants of Eu3+ and Am3+ with the site specific humic acid (YKHA) have been determined. The humic acid has been extracted from the soil of Yongkwang
area belonging geologically to the Okchon Basin of the Korean Peninsula, where the nuclear power plant is located. The total
carboxylate capacity, the acidity constant (pKa), and the binding constants with Eu3+ and Am3+ have been determined for humic acid. 相似文献
70.
The polycrystalline sample of layered compound FePS_3 has been investigated by using M?ssbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below T_N=120.5±1K. The M?ssbauer spectra below T_N indicate that the magnetization axis is perpendicular to the layer of FePS_3, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect. 相似文献