全文获取类型
收费全文 | 1016篇 |
免费 | 95篇 |
国内免费 | 38篇 |
专业分类
化学 | 99篇 |
晶体学 | 10篇 |
力学 | 596篇 |
综合类 | 12篇 |
数学 | 146篇 |
物理学 | 286篇 |
出版年
2023年 | 16篇 |
2022年 | 21篇 |
2021年 | 20篇 |
2020年 | 22篇 |
2019年 | 20篇 |
2018年 | 25篇 |
2017年 | 18篇 |
2016年 | 50篇 |
2015年 | 24篇 |
2014年 | 40篇 |
2013年 | 76篇 |
2012年 | 37篇 |
2011年 | 58篇 |
2010年 | 33篇 |
2009年 | 42篇 |
2008年 | 38篇 |
2007年 | 44篇 |
2006年 | 56篇 |
2005年 | 47篇 |
2004年 | 55篇 |
2003年 | 48篇 |
2002年 | 43篇 |
2001年 | 26篇 |
2000年 | 26篇 |
1999年 | 40篇 |
1998年 | 30篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 15 毫秒
41.
42.
This is one of the applications of Part (I), in which the angular stiffness, and the corresponding stress distributions of U-shaped bellows were discussed. The bellows
was divided into protruding sections, concave sections and ring plates for the calculation that the general solution (I) with its reduced form to ring plates were used respectively, but the continuity of the surface stresses and the meridian
rotations at each joint of the sections were entirely satisfied. The resent results were compared with those of the slender
ring shell solution proposed earlier by the authors, the standards of the Expansion Joint Manufacturers Association (EJMA),
the experiment and the finite element method. It is shown that the governing equation and the general solution (I) are very effective.
Contributed by HUANG Qian
Biography: ZHU Wei-ping (1962-) 相似文献
43.
Kristian Berland 《Superlattices and Microstructures》2011,50(4):411-418
A general, system-independent, formulation of the parabolic Schrödinger–Poisson equation is presented for a charged hard wall in the limit of complete screening by the ground state. It is solved numerically using iteration and asymptotic boundary conditions. The solution gives a simple relation between the band bending and sheet charge density at an interface. Approximative analytical expressions for the potential profile and wave function are developed based on properties of the exact solution. Specific tests of the validity of the assumptions leading to the general solution are made. The assumption of complete screening by the ground state is found be a limitation; however, the general solution provides a fair approximate account of the potential profile when the bulk is doped. The general solution is further used in a simple model for the potential profile of an AlN/GaN barrier structure. The result compares well with the solution of the full Schrödinger–Poisson equation. 相似文献
44.
Green emission can be identified as either a structured or a structureless emission. In the downward surface band bending region, the influence of defects on the continuous change in the 0-0 electronic transition was found to be a dominating factor that differentiates the characteristics of green emission. Such a change in the 0-0 electronic transition gives rise to the structureless green emission at higher energy, while the 0-0 electronic transition in the bulk of ZnO plays an important role resulting in structured green emission with lower energy. 相似文献
45.
46.
Polyakov V. A. Shlitsa R. P. Khitrov V. V. Zhigun V. I. 《Mechanics of Composite Materials》2001,37(2):91-106
The distribution of transverse stresses in the midlayer of a composite sandwich panel under multipoint loading is investigated. The stresses averaged across the thickness of a soft filler are estimated using a discrete model. Finite expressions for the compression of the filler along the length of the panel are derived by means of superposition of the local effects from the bending of face layers under an infinite system of transverse point forces constant across the panel thickness. The effects of compression and transverse extension of the filler, in the case of a high distribution frequency of these forces, i.e., when the distance between the forces is comparable to the panel thickness, are revealed. Compression of the panel by two systems of forces applied symmetrically or nonsymmetrically to the upper and lower faces is considered. The bending characteristics in the cases of loading with point forces and piecewise distributed loads are compared. The formulas obtained are used to determine the length of a small region on the panel surface for which the local effects from the distributed pressure and the point force are equivalent. The corresponding estimates are obtained in a closed form. The analysis, carried out with varied parameters of the structure, allows us to elucidate the peculiarities of the effect of discontinuous loads on the design characteristics in the local zones, using finite expressions derived by the operational method. 相似文献
47.
G. De Marchis 《Fiber and Integrated Optics》2013,32(3):277-317
Abstract Coherent lightwave techniques, when compared to direct detection techniques, offer nearly quantum noise limited sensitivity as well as fine tunability similar to that obtained at radio frequencies. These two aspects provide communication systems planners and engineers the means to better exploit the huge bandwidth of single mode optical fibers. Research activity in this field started in the early 1980s, and some laboratory experiments and field trials were performed by the end of the decade, showing that such techniques are suitable for transmitting multigigabit per second signals to distances well exceeding hundred kilometers. On the other hand, coherent multichannel, frequency division multiple access, local area networks have been proposed and experimented worldwide. This article will discuss the theoretical advantages and limitations of the various modulation and detection formats together with the state of the art. Moreover, some aspects, related to the introduction of coherent systems in local and metropolitan area networks, will be treated. Finally some experimental data will be provided and future evolution will be discussed. 相似文献
48.
电子通过wiggler产生的辐射,除了短波辐射在轴线附近也有较强的长波辐射,在与轴线夹 角1/γ处达到最大.推导出wiggler长波辐射公式,理论分析了这种辐射的特点,并且将 理论分析的结果与数值计算的结果进行了比较.对在红外波长范围内电子束通过弯转磁铁和wiggler时产生的辐射强度和光通量作了计算,结果表明wiggler下的辐射强度和光通量均强 于弯转磁铁.比较了弯转磁铁的边沿辐射、波荡器的渡越辐射和wiggler长波辐射,表明wigg ler在红外波长范围辐射的性能最优.
关键词:
wiggler
波荡器
弯转磁铁
长波辐射 相似文献
49.
In the paper, the bending stiffness and strength of multilayer structural elements in relation to the mechanical properties of layers and their number layout and sizes are investigated and the corresponding correlations are established. It is found that the most rational structure of a multilayer element in bending is a symmetric three-layer structure formed from two materials with the thickness of the core less than the half-thickness of the element. The values of normal stresses in the layers of a multilayer beam in bending depends on its bending stiffness and the position of layers relative to the neutral axis. The influence of the number of layers on the stiffness of the structural element and on the magnitude of normal stresses is insignificant. 相似文献
50.