全文获取类型
收费全文 | 723635篇 |
免费 | 6333篇 |
国内免费 | 2065篇 |
专业分类
化学 | 365527篇 |
晶体学 | 10678篇 |
力学 | 36166篇 |
综合类 | 20篇 |
数学 | 96439篇 |
物理学 | 223203篇 |
出版年
2021年 | 6536篇 |
2020年 | 7008篇 |
2019年 | 7914篇 |
2018年 | 10609篇 |
2017年 | 10876篇 |
2016年 | 15143篇 |
2015年 | 8547篇 |
2014年 | 14184篇 |
2013年 | 33117篇 |
2012年 | 25478篇 |
2011年 | 30464篇 |
2010年 | 22592篇 |
2009年 | 22537篇 |
2008年 | 28418篇 |
2007年 | 28103篇 |
2006年 | 25762篇 |
2005年 | 22947篇 |
2004年 | 21302篇 |
2003年 | 19110篇 |
2002年 | 18979篇 |
2001年 | 20984篇 |
2000年 | 16021篇 |
1999年 | 12482篇 |
1998年 | 10637篇 |
1997年 | 10404篇 |
1996年 | 9744篇 |
1995年 | 8705篇 |
1994年 | 8651篇 |
1993年 | 8345篇 |
1992年 | 8954篇 |
1991年 | 9500篇 |
1990年 | 9063篇 |
1989年 | 8935篇 |
1988年 | 8554篇 |
1987年 | 8509篇 |
1986年 | 8117篇 |
1985年 | 10362篇 |
1984年 | 10784篇 |
1983年 | 9021篇 |
1982年 | 9311篇 |
1981年 | 8734篇 |
1980年 | 8425篇 |
1979年 | 9038篇 |
1978年 | 9276篇 |
1977年 | 9116篇 |
1976年 | 9041篇 |
1975年 | 8675篇 |
1974年 | 8511篇 |
1973年 | 8808篇 |
1972年 | 6321篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
53.
54.
The finite-size corrections, central chargesc, and scaling dimensionsx of tricritical hard squares and critical hard hexagons are calculated analytically. This is achieved by solving the special functional equation or inversion identity satisfied by the commuting row transfer matrices of these lattice models at criticality. The results are expressed in terms of Rogers dilogarithms. For tricritical hard squares we obtainc=7/10,x=3/40, 1/5, 7/8, 6/5 and for hard hexagons we obtainc=4/5,x=2/15, 4/5, 17/15, 4/3, 9/5, in accord with the predictions of conformal and modular invariance. 相似文献
55.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
56.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection. 相似文献
57.
A. A. Slavnov 《Theoretical and Mathematical Physics》1989,79(3):579-587
V. A. Steklov Mathematics Institute, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 347–358, June, 1989. 相似文献
58.
59.
H.S RagabA Shehap M.S Abo EllilW.H Osman F.H Abd El-Kader 《Journal of Physics and Chemistry of Solids》2002,63(10):1839-1847
Ternary-phase ceramic system of Li2O Al2O3 4SiO2 doped with CuO, FeO and TiO2 has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively. 相似文献
60.
The sound field in the region of a deep shadow behind an impedance cylinder is analyzed for the case of plane wave diffraction by the cylinder surface. The main part of the field is represented by a cylindrical wave that has a complex index determined from the boundary conditions and decays with the angular coordinate. An expression for the amplitude of this wave is determined by extracting it from the total field formed in the shadow region. It is demonstrated that this wave approximates more closely the total field behind the cylinder, as compared to the least damped wave in the field representation obtained on the basis of the Watson transform. A way to improve the sound barriers is indicated. 相似文献