全文获取类型
收费全文 | 53311篇 |
免费 | 6921篇 |
国内免费 | 5267篇 |
专业分类
化学 | 14279篇 |
晶体学 | 1039篇 |
力学 | 10623篇 |
综合类 | 823篇 |
数学 | 19651篇 |
物理学 | 19084篇 |
出版年
2024年 | 114篇 |
2023年 | 550篇 |
2022年 | 1113篇 |
2021年 | 1257篇 |
2020年 | 1465篇 |
2019年 | 1293篇 |
2018年 | 1336篇 |
2017年 | 1819篇 |
2016年 | 2038篇 |
2015年 | 1626篇 |
2014年 | 2740篇 |
2013年 | 3842篇 |
2012年 | 3158篇 |
2011年 | 3649篇 |
2010年 | 3087篇 |
2009年 | 3435篇 |
2008年 | 3441篇 |
2007年 | 3416篇 |
2006年 | 3116篇 |
2005年 | 2918篇 |
2004年 | 2449篇 |
2003年 | 2225篇 |
2002年 | 2026篇 |
2001年 | 1653篇 |
2000年 | 1581篇 |
1999年 | 1437篇 |
1998年 | 1342篇 |
1997年 | 1099篇 |
1996年 | 920篇 |
1995年 | 785篇 |
1994年 | 738篇 |
1993年 | 560篇 |
1992年 | 572篇 |
1991年 | 445篇 |
1990年 | 349篇 |
1989年 | 301篇 |
1988年 | 252篇 |
1987年 | 202篇 |
1986年 | 137篇 |
1985年 | 192篇 |
1984年 | 156篇 |
1983年 | 88篇 |
1982年 | 120篇 |
1981年 | 75篇 |
1980年 | 48篇 |
1979年 | 73篇 |
1978年 | 65篇 |
1977年 | 59篇 |
1976年 | 33篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
121.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
122.
对于任意秩有限总体,在二次损失下,有关文献已给出了线性可预测变量在齐次线性预测类中的唯一线性Minimax预测.本文在正态假设下,证明了这个线性Minimax预测也是线性可预测变量在一切预测类中的唯一Minimax预测. 相似文献
123.
M. A. Posypkin I. Kh. Sigal 《Computational Mathematics and Mathematical Physics》2006,46(12):2187-2202
The efficiency of parallel implementations of the branch-and-bound method in discrete optimization problems is considered. A theoretical analysis and comparison of two parallel implementations of this method is performed. A mathematical model of the computation process is constructed and used to obtain estimates of the maximum possible speedup. Examples of problems in which none of these two parallel implementations can speed up the computations are considered. 相似文献
124.
用三个关系式与Mathematica软件求第二类自然数幂和公式 总被引:1,自引:1,他引:0
首先介绍三个第二类自然数幂和关系式并对其中的两式给出证明,接着利用这些关系式与数学软件M athem atica4.0,给出求解第二类自然数幂和公式的若干机械计算方法. 相似文献
125.
Growth characteristics and surface morphology of boron carbide films fabricated by ablating a B4C target in high vacuum with a traditional KrF excimer laser and a high brightness hybrid dye/excimer laser system emitting at the same wavelength while delivering 700 fs pulses are compared. The ultrashort pulse processing is highly effective. Energy densities between 0.25 and 2 J cm−2 result in apparent growth rates ranging from 0.017 to 0.085 nm/pulse. Ablation with nanosecond pulses of one order of magnitude higher energy densities yields smaller growth rates, the figures increase from 0.002 to 0.016 nm/pulse within the 2-14.3 J cm−2 fluence window. 2D thickness maps derived from variable angle spectroscopic ellipsometry reveal that, when ablating with sub-ps pulses, the spot size rather than the energy density determines both the deposition rate and the angular distribution of film material. Pulse shortening leads to significant improvement in surface morphology, as well. While droplets with number densities ranging from 1 × 104 to 7 × 104 mm−2 deteriorate the surface of the films deposited by the KrF excimer laser, sub-ps pulses produce practically droplet-free films. The absence of droplets has also a beneficial effect on the stoichiometry and homogeneity of the films fabricated by ultrashort pulses. 相似文献
126.
H. P. Gunnlaugsson 《Hyperfine Interactions》2006,167(1-3):851-854
The general problem of finding a distribution in hyperfine interaction parameters from experimental Mössbauer spectra is outlined. Existing methods may lack flexibility to be easily applicable to simple problems. A line shape for hyperfine parameter distributions is given, which is based on linear segments in the probability function. This method is applied in the analysis of samples containing iron in a silicate glass. 相似文献
127.
Silvia Vogel 《Annals of Operations Research》2006,142(1):269-282
The paper considers upper semicontinuous behavior in distribution of sequences of random closed sets. Semiconvergence in distribution
will be described via convergence in distribution of random variables with values in a suitable topological space. Convergence
statements for suitable functions of random sets are proved and the results are employed to derive stability statements for
random optimization problems where the objective function and the constraint set are approximated simultaneously.
The author is grateful to two anonymous referees for helpful suggestions. 相似文献
128.
Jian‐guo Tang 《Mathematical Methods in the Applied Sciences》2006,29(11):1327-1338
An implicit iterative method is applied to solving linear ill‐posed problems with perturbed operators. It is proved that the optimal convergence rate can be obtained after choosing suitable number of iterations. A generalized Morozov's discrepancy principle is proposed for the problems, and then the optimal convergence rate can also be obtained by an a posteriori strategy. The convergence results show that the algorithm is a robust regularization method. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
129.
Boniface Nkemzi 《Mathematical Methods in the Applied Sciences》2006,29(9):1053-1080
This paper is concerned with the structure of the singular and regular parts of the solution of time‐harmonic Maxwell's equations in polygonal plane domains and their effective numerical treatment. The asymptotic behaviour of the solution near corner points of the domain is studied by means of discrete Fourier transformation and it is proved that the solution of the boundary value problem does not belong locally to H2 when the boundary of the domain has non‐acute angles. A splitting of the solution into a regular part belonging to the space H2, and an explicitly described singular part is presented. For the numerical treatment of the boundary value problem, we propose a finite element discretization which combines local mesh grading and the singular field methods and derive a priori error estimates that show optimal convergence as known for the classical finite element method for problems with regular solutions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
130.
高固体分羟基丙烯酸树脂的合成 总被引:1,自引:0,他引:1
以过氧化二苯甲酰(BPO)/过氧化二异丙苯(DCP)(质量比为2:3)为复合引发剂,二甲苯为溶剂,选用适量含羟基单体和分子量调节剂,以减缓树脂合成聚合反应中的自动加速现象,合成了分子量为3000-4000,多分散性指数d〈2的高固体分羟基丙烯酸树脂.该树脂与缩二脲多异氰酸酯(HDI)的配漆实验证明,所得漆膜鲜映性好、丰满度高、色泽好、雾影值低、综合性能较好. 相似文献