全文获取类型
收费全文 | 40414篇 |
免费 | 5256篇 |
国内免费 | 4152篇 |
专业分类
化学 | 11049篇 |
晶体学 | 962篇 |
力学 | 9625篇 |
综合类 | 569篇 |
数学 | 14701篇 |
物理学 | 12916篇 |
出版年
2024年 | 89篇 |
2023年 | 424篇 |
2022年 | 754篇 |
2021年 | 912篇 |
2020年 | 1172篇 |
2019年 | 1016篇 |
2018年 | 1024篇 |
2017年 | 1422篇 |
2016年 | 1637篇 |
2015年 | 1259篇 |
2014年 | 2071篇 |
2013年 | 2890篇 |
2012年 | 2490篇 |
2011年 | 2847篇 |
2010年 | 2418篇 |
2009年 | 2674篇 |
2008年 | 2583篇 |
2007年 | 2577篇 |
2006年 | 2357篇 |
2005年 | 2200篇 |
2004年 | 1880篇 |
2003年 | 1697篇 |
2002年 | 1516篇 |
2001年 | 1274篇 |
2000年 | 1189篇 |
1999年 | 1073篇 |
1998年 | 996篇 |
1997年 | 842篇 |
1996年 | 693篇 |
1995年 | 589篇 |
1994年 | 546篇 |
1993年 | 442篇 |
1992年 | 452篇 |
1991年 | 345篇 |
1990年 | 273篇 |
1989年 | 211篇 |
1988年 | 177篇 |
1987年 | 128篇 |
1986年 | 87篇 |
1985年 | 114篇 |
1984年 | 108篇 |
1983年 | 53篇 |
1982年 | 71篇 |
1981年 | 50篇 |
1980年 | 29篇 |
1979年 | 43篇 |
1978年 | 31篇 |
1977年 | 38篇 |
1976年 | 13篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
181.
A boundary element method for the calculation of noise barrier insertion loss in the presence of atmospheric turbulence 总被引:1,自引:0,他引:1
Yiu Wai Lam 《Applied Acoustics》2004,65(6):583-603
Atmospheric turbulence is an important factor that limits the amount of attenuation a barrier can provide in the outdoor environment. It is therefore important to develop a reliable method to predict its effect on barrier performance. The boundary element method (BEM) has been shown to be a very effective technique for predicting barrier insertion loss in the absence of turbulence. This paper develops a simple and efficient modification of the BEM formulation to predict the insertion loss of a barrier in the presence of atmospheric turbulence. The modification is based on two alternative methods: (1) random realisations of log-amplitude and phase fluctuations of boundary sources and (2) de-correlation of source coherence using the mutual coherence function (MCF). An investigation into the behaviours of these two methods is carried out and simplified forms of the methods developed. Some systematic differences between the predictions from the methods are found. When incorporated into the BEM formulation, the method of random realisations and the method of MCF de-correlation provide predictions that agree well with predictions by the parabolic equation method and by the scattering cross-section method on a variety of thin barrier configurations. 相似文献
182.
In this paper, based on the Lame function and Jacobi elliptic function, the perturbation method is appliedto some nonlinear evolution equations to derive their multi-order solutions. 相似文献
183.
184.
185.
L.G. Casado I. García T. Csendes V.G. Ruíz 《Journal of Optimization Theory and Applications》2003,118(1):27-43
Based on the investigation carried out in Ref. 1, this paper incorporates new studies about the properties of inclusion functions on subintervals while a branch-and-bound algorithm is solving global optimization problems. It is found that the relative place of the global minimum value within the inclusion function value of the objective function at the current interval indicates mostly whether the given interval is close to a minimizer point. This information is used in a heuristic interval rejection rule that can save a considerable amount of computation. Illustrative examples are discussed and an extended numerical study shows the advantages of the new approach. 相似文献
186.
D. Baleanu 《Czechoslovak Journal of Physics》2003,53(11):971-976
The variational formulation of the Schrödinger field was investigated and the applicability of the chain method was analyzed. Using Batalin-Fradkin-Tyutin formalism a gauge invariant theory was constructed. 相似文献
187.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
189.
190.
本文研究非线性算子方程F(x)=y的解,结合最速下降法,Newton-Landweber迭代格式及正则化思想,在F满足适当的条件下,构造出新的双循环迭代格式。本文对格式的收敛性进行了严格论证,并估计出迭代格式的收敛精度。 相似文献