全文获取类型
收费全文 | 1022篇 |
免费 | 158篇 |
国内免费 | 531篇 |
专业分类
化学 | 1107篇 |
晶体学 | 23篇 |
力学 | 23篇 |
综合类 | 19篇 |
数学 | 230篇 |
物理学 | 309篇 |
出版年
2023年 | 2篇 |
2022年 | 36篇 |
2021年 | 33篇 |
2020年 | 32篇 |
2019年 | 8篇 |
2018年 | 25篇 |
2017年 | 55篇 |
2016年 | 49篇 |
2015年 | 76篇 |
2014年 | 101篇 |
2013年 | 119篇 |
2012年 | 186篇 |
2011年 | 159篇 |
2010年 | 91篇 |
2009年 | 78篇 |
2008年 | 93篇 |
2007年 | 114篇 |
2006年 | 36篇 |
2005年 | 70篇 |
2004年 | 74篇 |
2003年 | 46篇 |
2002年 | 34篇 |
2001年 | 18篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 25篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有1711条查询结果,搜索用时 15 毫秒
181.
The lepton-number-violating decays of singly-charged Higgs bosons H^± are investigated in the minimal type-( Ⅰ+Ⅱ ) seesaw model with one SU(2)L Higgs triplet △ and one heavy Majorana neutrino N1 at the TeV scale. We find that the branching ratios B(H^+ → 1α^+υ^-) (for α = e,μ,τ) depend not only on the mass and mixing parameters of three light neutrinos υi (for i = 1, 2, 3) but also on those of N1. Assuming that the mass of N1 lies in the range of 200 GeV to 1 TeV, we figure out the generous interference bands for the contributions of υi and N1 to B(H^+→ 1α^+υ^-). We illustrate some salient features of such interference effects by considering three typical mass patterns of υi, and show that the relevant Majorana CP-violating phases can affect the magnitudes of B(H^+→ 1α^+υ^-)) in this parameter region. 相似文献
182.
Using ~ 14 × 10^6 ψ(2S) and ~ 58 × 10^ J/ ψ data collected at BES Ⅱ/BEPC, the branching fraction of ψ(2S)→Ω-Ω^+ is measured with about 5a statistical significance. The A electric dipole and ∧ decay parameter are studied using the decay J/ψ →∧∧→ ppπ^+π^-. Using (106±3)× 10^6 ψ(2S) decays collected at BESⅢ/BEPC Ⅱ, we have obtained some interesting physics results. The branching fractions of XcJ→π^0π^0, ηη are measured with precision improved. The mass and width of he(l^1P1) state, together with the branching fractions of Br(ψ(2S) →π^0hc) and Br(hc →γηc) are the first measurements. Surprisingly, the decays of Xc1→φφ, ωω, and ωφ are firstly observed in BESⅢ data. 相似文献
183.
In this paper,a dedicated synchrotron radiation (SR) mode for the BEPCⅡ with an emittance of 85 nm has been designed,including the linear lattice,chromaticity correction and dynamic aperture optimization.The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ .The effect of wigglers on the linear lattice was compensated and the total dynamic aperture including the wigglers’ nonlinear effect was estimated.The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits. 相似文献
184.
A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW. 相似文献
185.
We present an exact approach for solving the -interdiction median problem with fortification. Our approach consists of solving a greedy heuristic and a set cover problem iteratively that guarantees to find an optimal solution upon termination. The greedy heuristic obtains a feasible solution to the problem, and the set cover problem is solved to verify optimality of the solution and to provide a direction for improvement if not optimal. We demonstrate the performance of the algorithm in a computational study. 相似文献
186.
187.
无容量设施选址问题(Uncapacitated Facility Location Problem,UFLP)是一类经典的组合优化问题,被证明是一种NP-hard问题,易于描述却难于求解.首先根据UFLP的数学模型及其具体特征,重新设计了蝙蝠算法的操作算子,给出了求解UFLP的蝙蝠算法.其次构建出三种可行化方法,并将其与求解UFLP的蝙蝠算法和拉格朗日松弛算法相结合,设计了求解该问题的拉格朗日蝙蝠算法.最后通过仿真实例和与其他算法进行比较的方式,验证了该混合算法用来求解UFLP的可行性,是解决离散型问题的一种有效方式. 相似文献
188.
无容量限制设施选址问题(uncapacitated facility location problem, UFLP)是经典组合优化中NP-Hard问题之一,在诸多领域具有广泛的应用价值。本文首先研究UFLP的数学性质,并进行了数学证明。运用这些数学性质不仅可以确定某些设施必定开设或者关闭,还可以确定某些连接边是否在服务集中,从而缩小问题的规模,加快求解速度;在此基础上设计出一个新的基于上下界的回溯算法来求解UFLP。最后,通过一个示例进一步阐述该算法的原理,结果表明该算法具有明显的可行性和有效性。 相似文献
189.
Carlos Obreque Macarena Donoso Gabriel Gutiérrez Vladimir Marianov 《European Journal of Operational Research》2010
The Hierarchical Network Design Problem consists of locating a minimum cost bi-level network on a graph. The higher level sub-network is a path visiting two or more nodes. The lower level sub-network is a forest connecting the remaining nodes to the path. We optimally solve the problem using an ad hoc branch and cut procedure. Relaxed versions of a base model are solved using an optimization package and, if binary variables have fractional values or if some of the relaxed constraints are violated in the solution, cutting planes are added. Once no more cuts can be added, branch and bound is used. The method for finding valid cutting planes is presented. Finally, we use different available test instances to compare the procedure with the best known published optimal procedure, with good results. In none of the instances we needed to apply branch and bound, but only the cutting planes. 相似文献
190.
This paper considers the problem of locating a single facility in the presence of a line barrier that occurs randomly on a given horizontal route on the plane. The objective is to locate this new facility such that the sum of the expected rectilinear distances from the facility to the demand points in the presence of the probabilistic barrier is minimized. Some properties of the problem are reported, a solution algorithm is provided with an example problem, and some future extensions to the problem are discussed. 相似文献