全文获取类型
收费全文 | 124580篇 |
免费 | 20584篇 |
国内免费 | 13296篇 |
专业分类
化学 | 84511篇 |
晶体学 | 1488篇 |
力学 | 8141篇 |
综合类 | 872篇 |
数学 | 14585篇 |
物理学 | 48863篇 |
出版年
2024年 | 412篇 |
2023年 | 2378篇 |
2022年 | 4202篇 |
2021年 | 4601篇 |
2020年 | 4903篇 |
2019年 | 4786篇 |
2018年 | 4147篇 |
2017年 | 3916篇 |
2016年 | 5936篇 |
2015年 | 5786篇 |
2014年 | 7065篇 |
2013年 | 9134篇 |
2012年 | 10972篇 |
2011年 | 11409篇 |
2010年 | 7701篇 |
2009年 | 7452篇 |
2008年 | 7928篇 |
2007年 | 7186篇 |
2006年 | 6616篇 |
2005年 | 5618篇 |
2004年 | 4283篇 |
2003年 | 3368篇 |
2002年 | 3205篇 |
2001年 | 2648篇 |
2000年 | 2276篇 |
1999年 | 2495篇 |
1998年 | 2171篇 |
1997年 | 2023篇 |
1996年 | 2164篇 |
1995年 | 1730篇 |
1994年 | 1670篇 |
1993年 | 1321篇 |
1992年 | 1192篇 |
1991年 | 1121篇 |
1990年 | 890篇 |
1989年 | 647篇 |
1988年 | 562篇 |
1987年 | 450篇 |
1986年 | 426篇 |
1985年 | 355篇 |
1984年 | 273篇 |
1983年 | 183篇 |
1982年 | 169篇 |
1981年 | 121篇 |
1980年 | 91篇 |
1979年 | 52篇 |
1978年 | 35篇 |
1976年 | 42篇 |
1975年 | 41篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Perovskite-type lithium fast ion conductors of Li3xLa0.67−xScyTi1−2yNbyO3 system were prepared by solid state reaction. X-Ray powder diffraction shows that perovskite solid solution form in the ranges
of x=0.10, y≤0.10. AC impedance measurements indicate that the bulk conductivities and the total conductivities are of the
order of 10−4 S·cm−1 and 10−5 S·cm−1 at 25 °C respectively. The compositions have low bulk activation energies of about 17 kJ/mol in the temperature ranges of
298 – 523 K and total activation energies of about 37 kJ/mol in the temperature ranges of 298 – 523 K. 相似文献
103.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
104.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献
105.
The theory of Ribaucour transformations for hypersurfaces in space forms is established. For any such hypersurface M, that admits orthonormal principal vector fields, it was shown the existence of a totally umbilic hypersurface locally associated to M by a Ribaucour transformation. A method of obtaining linear Weingarten surfaces in a three-dimensional space form is provided. By applying the theory, a new one-parameter family of complete constant mean curvature (cmc) surfaces in the unit sphere, locally associated to the flat torus, is obtained. The family contains a class of complete cmc cylinders in the sphere. In particular, one gets a family of complete minimal surfaces and minimal cylinders, locally associated to the Clifford torus.Mathematics Subject Classifications (2000): 53C20. 相似文献
106.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
107.
108.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
109.
The three dimensional problem of steady fluid deposition on an inclined rotating disk is solved by similarity transform. For a given spraying rate there may be one, two or no steady state solution. The inclination causes a downward draining flow and a lateral flow. Perturbation solutions compare well with exact similarity solutions when the fluid film is thin. 相似文献
110.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献