全文获取类型
收费全文 | 4064篇 |
免费 | 844篇 |
国内免费 | 447篇 |
专业分类
化学 | 1318篇 |
晶体学 | 58篇 |
力学 | 251篇 |
综合类 | 58篇 |
数学 | 1001篇 |
物理学 | 2669篇 |
出版年
2024年 | 10篇 |
2023年 | 54篇 |
2022年 | 197篇 |
2021年 | 138篇 |
2020年 | 141篇 |
2019年 | 119篇 |
2018年 | 130篇 |
2017年 | 203篇 |
2016年 | 202篇 |
2015年 | 191篇 |
2014年 | 327篇 |
2013年 | 340篇 |
2012年 | 265篇 |
2011年 | 332篇 |
2010年 | 250篇 |
2009年 | 290篇 |
2008年 | 258篇 |
2007年 | 230篇 |
2006年 | 184篇 |
2005年 | 205篇 |
2004年 | 169篇 |
2003年 | 145篇 |
2002年 | 132篇 |
2001年 | 105篇 |
2000年 | 102篇 |
1999年 | 89篇 |
1998年 | 74篇 |
1997年 | 65篇 |
1996年 | 72篇 |
1995年 | 62篇 |
1994年 | 35篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有5355条查询结果,搜索用时 0 毫秒
131.
High fidelity power measurements in free wheel devices require accurate inertia measurements. To evaluate the turbine efficiency,
a new experimental technique to measure the momentum of inertia has been developed at the von Karman Institute (VKI). This
experimental methodology allows the determination of the inertia of complex shape bodies without being dismounted from their
rotating housing. 相似文献
132.
133.
134.
A. Amari A. Walther M. Huang M. Afzelius B. Lauritzen H. de Riedmatten 《Journal of luminescence》2010,130(9):1579-1585
We present an efficient photon-echo experiment based on atomic frequency combs [Phys. Rev. A 79 (2009) 052329]. Echoes containing an energy of up to 35% of that of the input pulse are observed in a Pr3+-doped Y2SiO5 crystal. This material allows for the precise spectral holeburning needed to make a sharp and highly absorbing comb structure. We compare our results with a simple theoretical model with satisfactory agreement. Our results show that atomic frequency combs has the potential for high-efficiency storage of single photons as required in future long-distance communication based on quantum repeaters. 相似文献
135.
We comment on the paper [Song et al., J. Comput. Chem. 2009, 30, 399]. and discuss the efficiency of the orbital optimization and gradient evaluation in the Valence Bond Self Consistent Field (VBSCF) method. We note that Song et al. neglect to properly reference Broer et al., who published an algorithm [Broer and Nieuwpoort, Theor. Chim. Acta 1988, 73, 405] to use a Fock matrix to compute a matrix element between two different determinants, which can be used for an orbital optimization. Further, Song et al. publish a misleading comparison with our VBSCF algorithm [Dijkstra and van Lenthe, J. Chem. Phys. 2000, 113, 2100; van Lenthe et al., Mol. Phys. 1991, 73, 1159] to enable them to favorably compare their algorithm with ours. We give detail timings in terms of different orbital types in the calculation and actual timings for the example cases. © 2012 Wiley Periodicals, Inc. 相似文献
136.
A mesh‐free particle method, based on the moving particle semi‐implicit (MPS) interaction model, has been developed for the simulation of two‐dimensional open‐boundary free‐surface flows. The incompressibility model in the original MPS has been replaced with a weakly incompressible model. The effect of this replacement on the efficiency and accuracy of the model has been investigated. The new inflow–outflow boundary conditions along with the particle recycling strategy proposed in this study extend the application of the model to open‐boundary problems. The final model is able to simulate open‐boundary free surface flow in cases of large deformation and fragmentation of free surface. The models and proposed algorithms have been validated and applied to sample problems. The results confirm the model's efficiency and accuracy. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
137.
One can construct photonic single quantum well structures by sandwiching a homogeneous medium slab as a defect between two symmetrical photonic crystals (PCs). It is shown that the number of observed resonant peaks increases with increasing slab thickness. It is found that while the slab is composed of alternatively stacked step-index films, the frequencies of these resonant peaks can be adjusted finely by changing the film thickness properly. In this case, the frequency and frequency interval of confined states can be tuned accurately, and the spectral efficiency can be greatly enhanced without increasing the volume of optical devices. Numerical simulation is based on the finite-difference time-domain (FDTD) method. 相似文献
138.
We revisited the vanadium oxide phosphors, AVO3 (A:K, Rb, and Cs) and M3V2O8 (A:Mg and Zn) for a revaluation of possibility of these compounds for lighting applications, and the internal quantum efficiency (η) and luminescent colour properties for AVO3 (A:K, Rb, and Cs) and M3V2O8 (A:Mg, and Zn) have been presented. The AVO3 showed the broadband emission from 380 to 800 nm, and the η for the KVO3, RbVO3 and CsVO3 were 4%, 79% and 87%, respectively. The CIE colour coordinates are located at white region on the chromaticity diagram. The M3V2O8 (A:Mg and Zn) also exhibited a quite broadband emission between 410 and 900 nm, indicating yellow luminescent colour. The Zn3V2O8 showed high η value, 52%, compared to that of the Mg3V2O8 (η=6%). This enhancement of η in the Zn3V2O8 could be due to the increasing exciton diffusion assisted by the hybridizations of Zn 3d and O 2p orbitals for the valence band, and Zn 4s and Ti 3d orbitals for the conduction band. 相似文献
139.
基于金属包覆磁性波导结构的磁光Bragg器件特性分析 总被引:1,自引:0,他引:1
使用金属包覆磁性波导中的磁光耦合理论分析了静磁表面波与导波光在金属/电介质/钇铁石榴石/钆镓石榴石结构中的磁光共线作用,讨论了金属覆层和斜向场对磁光模式转换效率的影响。计算表明,金属包覆波导可以提高磁光作用,通过调节金属覆层与磁性薄膜间距得到了比空气/4a铁石榴石/钆镓石榴石的传统三明治波导情形高8.7dB的模式转换效率;而同时优化偏置磁场方向和金属包覆波导参数,模式转换效率可以进一步提高5.25dB。因此,金属包覆波导可以用于提高磁光Bragg器件性能,在微波和光信息处理等方面具有广阔的应用前蒂。 相似文献
140.
A general version of the maximum pseudolikelihood estimate of parameters within the class of Gauss–Markov random fields is
stated in a rigorous way. Its asymptotic properties, namely the consistency, the asymptotic normality, and the relative asymptotic
efficiency are studied. Explicit formulas for the asymptotic covariance matrix are given, and a decrease of efficiency is
proved. A numerical example is added to show that the efficiency can be improved by enlarging the range of the conditional
distribution used in the estimator.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献