全文获取类型
收费全文 | 2243篇 |
免费 | 52篇 |
国内免费 | 196篇 |
专业分类
化学 | 1081篇 |
晶体学 | 5篇 |
力学 | 183篇 |
数学 | 402篇 |
物理学 | 436篇 |
综合类 | 384篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 27篇 |
2021年 | 34篇 |
2020年 | 46篇 |
2019年 | 55篇 |
2018年 | 47篇 |
2017年 | 53篇 |
2016年 | 71篇 |
2015年 | 81篇 |
2014年 | 97篇 |
2013年 | 136篇 |
2012年 | 124篇 |
2011年 | 176篇 |
2010年 | 153篇 |
2009年 | 188篇 |
2008年 | 194篇 |
2007年 | 161篇 |
2006年 | 127篇 |
2005年 | 98篇 |
2004年 | 97篇 |
2003年 | 56篇 |
2002年 | 50篇 |
2001年 | 44篇 |
2000年 | 29篇 |
1999年 | 31篇 |
1998年 | 36篇 |
1997年 | 40篇 |
1996年 | 27篇 |
1995年 | 28篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
排序方式: 共有2491条查询结果,搜索用时 15 毫秒
1.
Tracing is a method of assigning flows in an electricity network to particular generators and loads, assuming perfect mixing at each node. It can be used to assign costs to transmission users. We show that the resulting allocation is equal to the Shapley value of an equivalent co-operative game. 相似文献
2.
H. Maekawa K. Tsubakihara A. Ohnishi 《The European Physical Journal A - Hadrons and Nuclei》2007,33(3):269-272
We study the hyperon-nucleus potential with distorted-wave impulse wave approximation (DWIA) using the Green's function method.
In order to include the nucleon and hyperon potential effects in Fermi averaging, we introduce the local optimal momentum
approximation of target nucleons. We can describe the quasi-free Λ , Σ and Ξ production spectra in a better way than in the
standard Fermi-averaged t -matrix treatments. 相似文献
3.
This paper studied the cost allocation for the unfunded liability in a defined benefit pension scheme incorporating the stochastic phenomenon of its returns. In the recent literature represented by Cairns and Parker [Insurance: Mathematics and Economics 21 (1997) 43], Haberman [Insurance: Mathematics and Economics 11 (1992) 179; Insurance: Mathematics and Economics 13 (1993) 45; Insurance: Mathematics and Economics 14 (1994) 219; Insurance: Mathematics and Economics 14 (1997) 127], Owadally and Haberman [North American Actuarial Journal 3 (1999) 105], the fund level is modeled based on the plan dynamics and the returns are generated through several stochastic processes to reflect the current realistic economic perspective to see how the contribution changed as the cost allocation period increased. In this study, we generalize the previous constant value assumption in cost amortization by modeling the returns and valuation rates simultaneously. Taylor series expansion is employed to approximate the unconditional and conditional moments of the plan contribution and fund level. Hence the stability of the plan contribution and the fund size under different allocation periods could be estimated, which provide valuable information adding to the previous works. 相似文献
4.
“Optimization of aircraft maintenance/support infrastructure using genetic algorithms—level of repair analysis” 总被引:4,自引:0,他引:4
Level of repair analysis (LORA) is an approach used during the design stage of complex equipment for analysis of the cost
effectiveness of competing maintenance strategies. LORA is carried as a part of the life cycle cost and cost of ownership
analysis and plays a significant role in minimizing the life cycle cost and cost of ownership of the capital equipment. Since
many purchasing decisions of complex equipment are based on cost of ownership, it has become essential to carry out LORA to
compete in the market. In this paper, we develop a mathematical model for LORA and propose a solution methodology based on
genetic algorithms. The concept is illustrated using a hypothetical aircraft engine. 相似文献
5.
In this article, by introducing characteristic singular integral operator and associate singular integral equations (SIEs), the authors discuss the direct method of solution for a class of singular integral equations with certain analytic inputs. They obtain both the conditions of solvability and the solutions in closed form. It is noteworthy that the method is different from the classical one that is due to Lu. 相似文献
6.
杨祖彬 《重庆工商大学学报(自然科学版)》1991,(4)
本文根据缓冲包装五步设计法,包装设计的目的(保护产品、方便储运、促进销售),运输包装的基本要求,探讨了运输包装的设计过程. 相似文献
7.
We wish to report synthesis of perfluorinated functionalized, branched ethers from their hydrocarbon analogues by direct fluorination. Yields up to 90%, with high purities, have been obtained at ambient temperature and pressure. This technique will likely develop into a new general method for producing perfluorinated, hyperbranched and dendritic polymers. 相似文献
8.
9.
It is generally in a firm’s interest for its supply chain partners to invest in innovations. To the extent that these innovations either reduce the partners’ variable costs or stimulate demand for the end product, they will tend to lead to higher levels of output for all of the firms in the chain. However, in response to the innovations of its partners, a firm may have an incentive to opportunistically increase its own prices. The possibility of such opportunistic behavior creates a hold-up problem that leads supply chain partners to underinvest in innovation. Clearly, this hold-up problem could be eliminated by a pre-commitment to price. However, by making an advance commitment to price, a firm sacrifices an important means of responding to demand uncertainty. In this paper we examine the trade-off that is faced when a firm’s channel partner has opportunities to invest in either cost reduction or quality improvement, i.e. demand enhancement. Should it commit to a price in order to encourage innovation, or should it remain flexible in order to respond to demand uncertainty. We discuss several simple wholesale pricing mechanisms with respect to this trade-off. 相似文献
10.
An efficient technique for drag reduction uses dilute solutions of a few p.p.m. of polymers. A possible reduction in drag of up to 80% is achieved. Several experimental observations have been made which tend to indicate that the polymers modify the turbulence structures within the buffer layer. Flow visualisations have shown that the changes consist of a weakening of the strength of the streamwise vortices. Existing literature reveals no attempts of numerical simulation of this phenomenon. In this paper an approach is pursued by using a constitutive equation which relates the elongation viscosity to the local properties of the flow. According to this model this viscosity is large in zones where the amount of strain rate is greater than the amount of vorticity, and is zero when the vorticity exceeds the strain rate. Simulations have been performed in a “minimal channel” to give good resolution with a limited number of grid points. The accuracy of the method is tested by comparison with the results of other techniques. For simulations with polymers, quantitative comparisons cannot be made, but the results reproduce the qualitative outputs of the experiments. The mean streamwise velocity is modified in the buffer layer; the peak of the streamwise turbulent intensity, in wall units, increases and its maximum moves far from the wall; and the vertical turbulent intensity is largely reduced in the wall region. An interesting outcome from both the simulation and the experiments is that the strength of the longitudinal vortices is reduced when the polymers are present. 相似文献