全文获取类型
收费全文 | 2704篇 |
免费 | 104篇 |
国内免费 | 15篇 |
专业分类
化学 | 2125篇 |
晶体学 | 30篇 |
力学 | 30篇 |
数学 | 320篇 |
物理学 | 318篇 |
出版年
2023年 | 15篇 |
2022年 | 42篇 |
2021年 | 66篇 |
2020年 | 42篇 |
2019年 | 45篇 |
2018年 | 30篇 |
2017年 | 35篇 |
2016年 | 81篇 |
2015年 | 79篇 |
2014年 | 84篇 |
2013年 | 126篇 |
2012年 | 204篇 |
2011年 | 189篇 |
2010年 | 146篇 |
2009年 | 139篇 |
2008年 | 179篇 |
2007年 | 174篇 |
2006年 | 157篇 |
2005年 | 158篇 |
2004年 | 132篇 |
2003年 | 105篇 |
2002年 | 103篇 |
2001年 | 42篇 |
2000年 | 53篇 |
1999年 | 40篇 |
1998年 | 29篇 |
1997年 | 20篇 |
1996年 | 30篇 |
1995年 | 35篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1970年 | 1篇 |
1963年 | 1篇 |
1939年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有2823条查询结果,搜索用时 62 毫秒
1.
2.
Marcelino Maneiro Manuel R. Bermejo M. Isabel Fernndez Ana M. Gonzlez‐Noya Alexei M. Tyryshkin Robin G. Pritchard 《无机化学与普通化学杂志》2003,629(2):285-290
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement. 相似文献
3.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
The linearized stability of charged thin shell wormholes under spherically symmetric perturbations is analyzed. It is shown that the presence of a large value of charge provides stabilization to the system, in the sense that the constraints onto the equation of state are less severe than for non-charged wormholes. 相似文献
5.
G. Romero L. Alvarez E. Alanís L. Nallim R. Grossi 《Optics and Lasers in Engineering》2003,40(1-2):81-90
Real-time electronic speckle pattern interferometry (ESPI) was used for tuning and visualization of natural frequencies of a trapezoidal plate. The plate was excited to resonant vibration by a sinusoidal acoustical source, which provided a continuous range of audio frequencies. Fringe patterns produced during the time-average recording of the vibrating plate—corresponding to several resonant frequencies—were registered. From these interferograms, calculations of vibrational amplitudes by means of zero-order Bessel functions were performed in some particular cases. The system was also studied analytically. The analytical approach developed is based on the Rayleigh–Ritz method and on the use of non-orthogonal right triangular co-ordinates. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated by using the Gram–Schmidt procedure. A high degree of correlation between computational analysis and experimental results was observed. 相似文献
6.
Joaquin Barbera Anne-Marie Levelut Mercedes Marcos Pilar Romero Jose Luis Serrano 《Liquid crystals》1991,10(1):119-126
We present a comparative study of various metallomesogenic complexes, using X-ray diffraction methods. For a given ligand linked to different metal atoms (Cu, Ni, VO), the nature of this central atom influences mainly the magnetic susceptibilities of the mesophases. With different ligands, which keep the close neighbourhood of the metal atom unchanged, the apparent length of the mesogenic unit is longer for short ligands than for longer ones. This unexpected behaviour is qualitatively well explained by taking into account the global shape of the different complexes. 相似文献
7.
8.
9.
Isabel Echeverria Ping-Chung Su Sindee L. Simon Donald J. Plazek 《Journal of Polymer Science.Polymer Physics》1995,33(17):2457-2468
Creep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short-time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc. 相似文献
10.