全文获取类型
收费全文 | 8201篇 |
免费 | 1134篇 |
国内免费 | 628篇 |
专业分类
化学 | 1792篇 |
晶体学 | 149篇 |
力学 | 642篇 |
综合类 | 57篇 |
数学 | 1202篇 |
物理学 | 2043篇 |
无线电 | 4078篇 |
出版年
2024年 | 14篇 |
2023年 | 79篇 |
2022年 | 102篇 |
2021年 | 108篇 |
2020年 | 125篇 |
2019年 | 120篇 |
2018年 | 99篇 |
2017年 | 202篇 |
2016年 | 247篇 |
2015年 | 209篇 |
2014年 | 424篇 |
2013年 | 464篇 |
2012年 | 562篇 |
2011年 | 497篇 |
2010年 | 439篇 |
2009年 | 496篇 |
2008年 | 710篇 |
2007年 | 787篇 |
2006年 | 549篇 |
2005年 | 545篇 |
2004年 | 561篇 |
2003年 | 439篇 |
2002年 | 299篇 |
2001年 | 235篇 |
2000年 | 204篇 |
1999年 | 192篇 |
1998年 | 175篇 |
1997年 | 159篇 |
1996年 | 125篇 |
1995年 | 128篇 |
1994年 | 96篇 |
1993年 | 88篇 |
1992年 | 105篇 |
1991年 | 62篇 |
1990年 | 42篇 |
1989年 | 46篇 |
1988年 | 40篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 7篇 |
1979年 | 21篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1974年 | 3篇 |
排序方式: 共有9963条查询结果,搜索用时 15 毫秒
71.
考虑二阶非线性椭圆型微分方程∑^n_{i,j}∂/∂x_i{A_{i,j}(x,y)∂/∂x_j}+q(x)f(y)=0 (E),其中q(x)在外区域 Ω∈R\+n上变号. 利用偏Riccati变换和积分平均技巧, 建立了方程(E)所有解振动的充分准则. 相似文献
72.
73.
Navier-Stokes方程带Backtracking技巧的两重网格算法 总被引:3,自引:1,他引:2
1 引 言考虑二维不可压 Navier-Stokes方程: 相似文献
74.
This paper presents the mathematical approach for the abnormal multiplication of plankton. An abnormal multiplication can be expressed as an unstable problem and the stability of the system is investigated by introducing eigenvalues of a mathematical equation. The stability of the system can be judged by an eigenvalue based on the Lyapunov's stability theory. In this paper, the Arnoldi‐QR method is used to obtain eigenvalues and eigenvectors of the system. The mode superposition method is employed to create spatial distribution needed to analyse the stability. To obtain the objective eigenvalue, the parameter identification technique is employed. The finite element method is used for the discretization in space. Lake Kasumigaura, which is located in Ibaraki Prefecture in Japan, is selected and actual data in 1975, 1976, 1991 and 2000 are used in order to investigate the stability of the specified lake in Japan. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
75.
The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan 相似文献
76.
The optical nonlinearities of Cu(mpo)2 [formula = C10H8N2CuO2S2] complex have firstly been investigated by using the Z-scan technique with a nanosecond-pulsed Nd:YAG laser at its second harmonic (532 nm) radiation. The nonlinear optical absorption and refraction coefficients of Cu(mpo)2 have been measured with the different on-axial peak irradiances I
0 at the waist ranging from 0.48 to 5.66 GW/cm2. The nonlinear transmittance characteristics exhibit the near resonant two-photon absorption (TPA) at 532 nm and are explained by a population redistribution model. The nonlinear absorption originates from the near resonant TPA while the mechanism of the nonlinear refraction is the near resonant TPA transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant TPA. 相似文献
77.
J. Haslinger T. Kozubek K. Kunisch G. Peichl 《Journal of Mathematical Analysis and Applications》2004,290(2):665-685
This contribution combines a shape optimization approach to free boundary value problems of Bernoulli type with an embedding domain technique. A theoretical framework is developed which allows to prove continuous dependence of the primal and dual variables in the resulting saddle point problems with respect to the domain. This ensures the existence of a solution of a related shape optimization problem in a sufficiently large class of admissible domains. 相似文献
78.
Techniques and Apparatus for Measuring Rotational Core Losses of Soft Magnetic Materials 总被引:1,自引:0,他引:1
In many situations such as the cores of a rotating electrical machine and the T joints of a multiphase transformer, the local flux density varies with time in terms of both magnitude and direction, i.e. the flux density vector is rotating. Therefore, the magnetic properties of the core materials under the rotating flux density vector excitation should be properly measured, modeled and applied in the design and analysis of these electromagnetic devices. This paper presents an extensive review on the development of techniques and apparatus for measuring the rotational core losses of soft magnetic materials based on the experiences of various researchers in the last hundred years. 相似文献
79.
航空放射性遥感系统采用航空γ能谱仪,在空中飞行探测地表放射性,能够快速进行大面积环境放射性调查。结合已经开始进行的首次大面积航空放射性遥感调查工作,简要介绍了航空放射性遥感系统构成、核探测γ能谱测量和数据处理技术。对系统转换因子刻度和剥离系数刻度方法进行了讨论,并对初步应用情况进行了总结。 相似文献
80.
This paper defines a set of material compatibility constraints for use in order promising mixed integer programs. The constraints always represent a necessary condition for compatibility and, in certain cases, are both necessary and sufficient. The underlying analysis represents incompatibilities using bipartite graphs and applies results from the perfectly matchable subgraph polytope. 相似文献