全文获取类型
收费全文 | 344篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 127篇 |
力学 | 2篇 |
综合类 | 1篇 |
数学 | 62篇 |
物理学 | 173篇 |
出版年
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 29篇 |
2012年 | 39篇 |
2011年 | 37篇 |
2010年 | 31篇 |
2009年 | 19篇 |
2008年 | 21篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 5篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有365条查询结果,搜索用时 0 毫秒
71.
Norbert Polat 《Czechoslovak Mathematical Journal》2001,51(3):477-492
For an end and a tree T of a graph G we denote respectively by m() and m
T
() the maximum numbers of pairwise disjoint rays of G and T belonging to , and we define tm() := min{m
T(): T is a spanning tree of G}. In this paper we give partial answers — affirmative and negative ones — to the general problem of determining if, for a function f mapping every end of G to a cardinal f() such that tm() f() m(), there exists a spanning tree T of G such that m
T
() = f() for every end of G. 相似文献
72.
Nanosecond pulse generation in an erbium-doped fiber laser (EDFL) passively mode-locked by a silver nanoparticle(SNP)-based saturable absorber(SA) is experimentally demonstrated. The SA is fabricated by depositing a nanosized SNP layer onto the surface of polyvinyl alcohol film through the thermal evaporation process. By inserting the SA into an EDFL cavity, stable mode-locked operation is achieved at 1561.5 nm with the maximum pulse energy up to 52.3 nJ. The laser operates at a pulse repetition frequency of 1.0 MHz with a pulse width of 202 ns. These results suggest that SNPs could be developed as an effective SA for mode-locking pulse generation. 相似文献
73.
Harun Karsli 《Mathematical Methods in the Applied Sciences》2019,42(16):5190-5198
The concern of this paper is to continue the investigation of convergence properties of nonlinear approximation operators, which are defined by Karsli. In details, the paper centers around Urysohn‐type nonlinear counterpart of the Bernstein operators. As a continuation of the study of Karsli, the present paper is devoted to obtain Voronovskaya‐type theorems for the Urysohn‐type nonlinear Bernstein operators. 相似文献
74.
We consider the initial value problem for the Klein‐Gordon equation in de Sitter spacetime. We use the central difference scheme on the temporal discretization. We also discretize the spatial variable using the finite element method with implicit and the Crank‐Nicolson schemes for the numerical solution of the initial value problem. In order to show the accuracy for the results of the solutions, we also examine the finite difference methods. We observe that the numerical results obtained by using these methods are compatible. 相似文献
75.
Norbert Polat 《Discrete Mathematics》2009,309(8):2119-2133
A graph G has the Median Cycle Property (MCP) if every triple (u0,u1,u2) of vertices of G admits a unique median or a unique median cycle, that is a gated cycle C of G such that for all i,j,k∈{0,1,2}, if xi is the gate of ui in C, then: {xi,xj}⊆IG(ui,uj) if i≠j, and dG(xi,xj)<dG(xi,xk)+dG(xk,xj). We prove that a netlike partial cube has the MCP if and only if it contains no triple of convex cycles pairwise having an edge in common and intersecting in a single vertex. Moreover a finite netlike partial cube G has the MCP if and only if G can be obtained from a set of even cycles and hypercubes by successive gated amalgamations, and equivalently, if and only if G can be obtained from K1 by a sequence of special expansions. We also show that the geodesic interval space of a netlike partial cube having the MCP is a Pash-Peano space (i.e. a closed join space). 相似文献
76.
Polat Narin Ece Kutlu-Narin Gokhan Atmaca Beyza Sarikavak-Lisesivdin Sefer B. Lisesivdin Ekmel Ozbay 《Surface and interface analysis : SIA》2022,54(5):576-583
Metal–organic chemical vapor deposition (MOCVD) is one of the best growth methods for GaN-based materials as well-known. GaN-based materials with very quality are grown the MOCVD, so we used this growth technique to grow InAlN/GaN and AlN/GaN heterostructures in this study. The structural and surface properties of ultrathin barrier AlN/GaN and InAlN/GaN heterostructures are studied by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. Screw, edge, and total dislocation densities for the grown samples have been calculated by using XRD results. The lowest dislocation density is found to be 1.69 × 108 cm−2 for Sample B with a lattice-matched In0.17Al0.83N barrier. The crystal quality of the studied samples is determined using (002) symmetric and (102) asymmetric diffractions of the GaN material. In terms of the surface roughness, although reference sample has a lower value as 0.27 nm of root mean square values (RMS), Sample A with 4-nm AlN barrier layer exhibits the highest rough surface as 1.52 nm of RMS. The structural quality of the studied samples is significantly affected by the barrier layer thickness. The obtained structural properties of the samples are very important for potential applications like high-electron mobility transistors (HEMTs). 相似文献
77.
Interaction forces between alumina surfaces were measured using an AFM-colloid probe method at different pHs. For an alpha-alumina-sapphire system at acidic pH, the force curve exhibited a well-defined repulsive barrier and an attractive minimum. At basic pH, the interactive force was repulsive at all separations with no primary minimum. Lateral force measurements under the same conditions showed that frictional forces were nearly an order of magnitude smaller at basic pH than those observed at acidic pH. This behavior was attributed to the hydration of the alumina surface. Normal and lateral force measurements with the strongly hydrated rho-alumina surfaces supported these findings. 相似文献
78.
N.F.Zulkipli M.Batumalay F.S.M.Samsamnun M.B.H.Mahyuddin E.Hanafi T.F.T.M.N.Izam M.I.M.A.Khudus S.W.Harun 《中国物理快报》2019,(7)
Nanosecond pulse generation is demonstrated in a mode-locked erbium-doped fiber laser(EDFL) utilizing a samarium oxide(Sm_2O_3) film. The Sm_2O_3 film exhibits a modulation depth of 33%, which is suitable for modelocking operation. The passively pulsed EDFL operates stably at 1569.8 nm within a pumping power from 109 to 146 m W. The train of generated output pulses has a pulse width of 356 nm repeated at a fundamental frequency of 0.97 MHz. The average output power of 3.91 m W is obtained at a pump power of 146 m W, corresponding to 4.0 nJ pulse energy. The experimental result indicates that the proposed Sm_2O_3 saturable absorber is viable for the construction of a flexible and reliably stable mode-locked pulsed fiber laser operating in the 1.5 m region. 相似文献
79.
Neslihan Ekinci R. Polat 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,91(2):155-160
This work reports on an alternative method for the determination of element concentrations in human milk. Energy dispersive X-ray fluorescence (EDXRF) spectrometer with an annular Am241 and Fe55 sources was applied for the analysis of human milk samples. A sample preparation method suitable for the EDXRF analysis was described. The results were presented in Table 1. Energy dispersive X-ray fluorescence technique has been successfully used for the determination of calcium and other elements in human milk. For this reason, the experimental approach and the analytical method used in this study appear adequate for the purpose and can therefore be exploited for similar investigations. 相似文献
80.
Na-Cs混合蒸汽中的碰撞能量合并已在[2]中研究过。当在池中充入缓冲气体后,碰撞过程出现新的特点,缓冲气体增大了Na(3P)和Cs(6S)间的能量转移,这可从测量由Na(3P)/Cs(6P)和Cs(6P)/Cs(5D)碰撞而被布居的高能级所发射的荧光得到证实。得到三体碰撞速率系数k3=5.9×10-27cm6s-1。 相似文献