全文获取类型
收费全文 | 740篇 |
免费 | 55篇 |
国内免费 | 47篇 |
专业分类
化学 | 154篇 |
力学 | 29篇 |
综合类 | 21篇 |
数学 | 360篇 |
物理学 | 278篇 |
出版年
2023年 | 16篇 |
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 11篇 |
2019年 | 17篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 35篇 |
2013年 | 35篇 |
2012年 | 49篇 |
2011年 | 43篇 |
2010年 | 34篇 |
2009年 | 48篇 |
2008年 | 50篇 |
2007年 | 45篇 |
2006年 | 38篇 |
2005年 | 25篇 |
2004年 | 27篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 21篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1969年 | 3篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有842条查询结果,搜索用时 15 毫秒
101.
TONG Jie DONG Yanwu 《声学学报:英文版》1993,(4)
In this paper, several mixtrue rules of sound velocity and their useful ness in characterizing the components of biomedium are analysed. It is pointed out that for characterizing the components of biomedium, the rules are compatible with each other under certain conditions, and the errors between each rule and real sound velocity are diffferent. It concludes that there is no general rule suitable for various media among above mentioned rules. 相似文献
102.
In this paper,we apply cellular automata rules,which can be given by a truth table,to human memory.We design each memory as a tracking survey mode that keeps the most recent three opinions.Each cellular automata rule,as a personal mechanism,gives the final ruling in one time period based on the data stored in one’s memory.The key focus of the paper is to research the evolution of people’s attitudes to the same question.Based on a great deal of empirical observations from computer simulations,all the rules can be classified into 20 groups.We highlight the fact that the phenomenon shown by some rules belonging to the same group will be altered within several steps by other rules in different groups.It is truly amazing that,compared with the last hundreds of presidential voting in America,the eras of important events in America’s history coincide with the simulation results obtained by our model. 相似文献
103.
In this article, we take the point of view that the light scalar meson a0(980) is a conventional qqstate, and calculate the coupling constants ga0ηπ0 and ga0ηπ0 with the light-cone QCD sum rules. The central value of the coupling constant ga0ηπ0 is consistent with that extracted from the radiative decay φ(1020) → a0(980)γ→ηπ0γ. The central value and lower bound of the decay width Γa0→ηπ0 =127+8448 MeV are compatible with the experimental data of the total decay width Γa0(980) = (50-100) MeV from the Particle Data Group with a very model dependent estimation (the decay width can be much larger), while the upper bound is too large. We give a possible explanation for the discrepancy between the theoretical calculation and experimental data. 相似文献
104.
This paper deals with the problem of multivariate copula density estimation. Using wavelet methods we provide two shrinkage procedures based on thresholding rules for which knowledge of the regularity of the copula density to be estimated is not necessary. These methods, said to be adaptive, have proved to be very effective when adopting the minimax and the maxiset approaches. Moreover we show that these procedures can be discriminated in the maxiset sense. We provide an estimation algorithm and evaluate its properties using simulation. Finally, we propose a real life application for financial data. 相似文献
105.
This paper presents new elimination rules for the single machine problem with general earliness and tardiness penalties subject to release dates. These rules, based on a Lagrangian decomposition, allow to drastically reduce the execution windows of the jobs. We measure the efficiency of these properties by integrating them in a branch-and-bound. Tests show that instances with up to 70 jobs without release dates, and up to 40 jobs with release dates, can be optimally solved within 1000 seconds. 相似文献
106.
This paper focuses on the cubature Kalman filters (CKFs) for the nonlinear dynamic systems with additive process and measurement noise. As is well known, the heart of the CKF is the third-degree spherical–radial cubature rule which makes it possible to compute the integrals encountered in nonlinear filtering problems. However, the rule not only requires computing the integration over an n-dimensional spherical region, but also combines the spherical cubature rule with the radial rule, thereby making it difficult to construct higher-degree CKFs. Moreover, the cubature formula used to construct the CKF has some drawbacks in computation. To address these issues, we present a more general class of the CKFs, which completely abandons the spherical–radial cubature rule. It can be shown that the conventional CKF is a special case of the proposed algorithm. The paper also includes a fifth-degree extension of the CKF. Two target tracking problems are used to verify the proposed algorithm. The results of both experiments demonstrate that the higher-degree CKF outperforms the conventional nonlinear filters in terms of accuracy. 相似文献
107.
One of the most important issues for aggregating preferences rankings is the determination of the weights associated with the different ranking places. To avoid the subjectivity in determining the weights, Cook and Kress (1990) [5] suggested evaluating each candidate with the most favorable scoring vector for him/her. With this purpose, various models based on Data Envelopment Analysis have appeared in the literature. Although these methods do not require predetermine the weights subjectively, some of them have a serious drawback: the relative order between two candidates may be altered when the number of first, second, …, kth ranks obtained by other candidates changes, although there is not any variation in the number of first, second, …, kth ranks obtained by both candidates. In this paper we propose a model that allows each candidate to be evaluated with the most favorable weighting vector for him/her and avoids the previous drawback. Moreover, in some cases, we give a closed expression for the score assigned with our model to each candidate. 相似文献
108.
M. A. Bokhari Asghar Qadir H. Al-Attas 《Numerical Functional Analysis & Optimization》2013,34(10):1120-1134
Some Gauss-type Quadrature rules over [0, 1], which involve values and/or the derivative of the integrand at 0 and/or 1, are investigated. Our work is based on the orthogonal polynomials with respect to linear weight function ω(t): = 1 ? t over [0, 1]. These polynomials are also linked with a class of recently developed “identity-type functions”. Along the lines of Golub's work, the nodes and weights of the quadrature rules are computed from Jacobi-type matrices with simple rational entries. Computational procedures for the derived rules are tested on different integrands. The proposed methods have some advantage over the respective Gauss-type rules with respect to the Gauss weight function ω(t): = 1 over [0, 1]. 相似文献
109.
Harald Hillebrecht Natascha Vojteer Vanessa Sagawe Kathrin Hofmann Barbara Albert 《无机化学与普通化学杂志》2019,645(3):362-369
Transparent and nearly colorless single crystals of r‐LiB13C2 were obtained by reaction of boron with Li2CO3 in a Cu melt at 1250–1300 °C. The structure analysis [R3 m, a = 5.6535(1), c = 12.5320(2) Å, 421 independent reflections, 22 parameters, R1 = 0.034, wR2 = 0.093] revealed a crystal structure that can be described as a filling variant of rhombohedral B13C2. Li+ is located in a void above or below the linear CBC unit. The site occupation is close to 50 % resulting in an electron‐precise composition according to Wade's rules if a positive charge is given to the CBC entity: Li+(B12)2–(CBC)+. The displacement parameters of the CBC unit indicate disorder in the [001] direction, that relates to the short Li–C distance and the partial occupation of the Li+ site. The composition is confirmed by EELS measurements of single crystals. Band gap calculations give a value of 2.94 eV, which is in agreement to the crystals being colorless. The evaluation of the electron density by application of the QTAIM formalism as proposed by Bader modifies the assignment pictured above according to Wade's rules. In agreement to the electronegativities the carbon atoms carry a negative charge (–2.31/–2.42) and the effective charges are: Li+0.81(B12)+2.02(CBC)–2.83. 相似文献
110.
James K.G. Watson 《Journal of Molecular Spectroscopy》2008,252(1):5-8
Hönl-London factors are the factors that give the dependence of spectroscopic line intensities on the rotational quantum numbers. Recently it has been shown that most tabulations of Hönl-London factors for singlet-singlet transitions do not allow for the special cases of Π-Σ and Σ-Π transitions, where a consideration of the parity symmetrisation shows that an extra factor of 2 is required. The present paper extends these considerations to multiplet transitions, in either pure Hund’s case a or pure Hund’s case b. 相似文献