全文获取类型
收费全文 | 206375篇 |
免费 | 1571篇 |
国内免费 | 454篇 |
专业分类
化学 | 107089篇 |
晶体学 | 3425篇 |
力学 | 10359篇 |
综合类 | 10篇 |
数学 | 22522篇 |
物理学 | 64995篇 |
出版年
2021年 | 2011篇 |
2020年 | 2038篇 |
2019年 | 2607篇 |
2018年 | 3696篇 |
2017年 | 3698篇 |
2016年 | 4865篇 |
2015年 | 2417篇 |
2014年 | 4355篇 |
2013年 | 8762篇 |
2012年 | 6999篇 |
2011年 | 8295篇 |
2010年 | 6568篇 |
2009年 | 6745篇 |
2008年 | 7838篇 |
2007年 | 7799篇 |
2006年 | 6901篇 |
2005年 | 6093篇 |
2004年 | 5797篇 |
2003年 | 5304篇 |
2002年 | 5311篇 |
2001年 | 5659篇 |
2000年 | 4180篇 |
1999年 | 3207篇 |
1998年 | 2749篇 |
1997年 | 2811篇 |
1996年 | 2608篇 |
1995年 | 2244篇 |
1994年 | 2368篇 |
1993年 | 2277篇 |
1992年 | 2559篇 |
1991年 | 2685篇 |
1990年 | 2591篇 |
1989年 | 2655篇 |
1988年 | 2555篇 |
1987年 | 2581篇 |
1986年 | 2431篇 |
1985年 | 3068篇 |
1984年 | 3150篇 |
1983年 | 2629篇 |
1982年 | 2593篇 |
1981年 | 2569篇 |
1980年 | 2366篇 |
1979年 | 2737篇 |
1978年 | 2705篇 |
1977年 | 2900篇 |
1976年 | 2907篇 |
1975年 | 2689篇 |
1974年 | 2635篇 |
1973年 | 2728篇 |
1972年 | 2101篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
192.
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
193.
A. N. Troflmchuk 《Journal of Mathematical Sciences》1991,57(5):3407-3409
We develop a method of computing the nonsteady-state and free oscillations of a framed elastic structure situated on an elastic base and containing an ideal compressible fluid. The solution uses the method of integral transforms in conjunction with the method of orthogonal polynomials. In the transform space the problem reduces to systems of linear algebraic equations. The Fourier transform is applied to return to the original space. Examples of the computation are given.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 69–72. 相似文献
194.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
195.
The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate
only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the
carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in
the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are
obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities).
Variation of FCA is numerically studied with photon frequency and well width. 相似文献
196.
N. N. Manuylov 《Journal of Mathematical Sciences》2006,133(6):1686-1692
Renormalization formulas connecting the points of the orbits O
0
±
, i.e., the sequences generated by an irrational shift on the half-open interval [0, 1) or (0, 1], and the points of the orbits'
derivatives dmO
0
±
, i.e., the sequences obtained by restricting O
0
±
to half-open intervals of smaller length, are obtained. Bibliography: 5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 314, 2004, pp. 142–154. 相似文献
197.
S. N. Solov’ev K. A. Minasyan A. A. Korunov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):663-664
The enthalpies of reactions of La2CoO4(cr) and CoCl2(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La2CoO4(cr) at 298.15 K, Δf H o = ?2179 ± 7 kJ/mol. 相似文献
198.
N. Kiriushcheva 《Annals of Physics》2006,321(4):958-986
It is shown that the Lagrangian reduction, in which solutions of equations of motion that do not involve time derivatives are used to eliminate variables, leads to results quite different from the standard Dirac treatment of the first-order form of the Einstein-Hilbert action when the equations of motion correspond to the first class constraints. A form of the first-order formulation of the Einstein-Hilbert action which is more suitable for the Dirac approach to constrained systems is presented. The Dirac and reduced approaches are compared and contrasted. This general discussion is illustrated by a simple model in which all constraints and the gauge transformations which correspond to first class constraints are completely worked out using both methods to demonstrate explicitly their differences. These results show an inconsistency in the previous treatment of the first-order Einstein-Hilbert action which is likely responsible for problems with its canonical quantization. 相似文献
199.
Electron spin resonance spectra of Mn2+ in diluted solid solutions of MnO2 in Y2O3 have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn2+ ions in sites with two different symmetries were observed, as well as Mn2+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn2+ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn2+ ions of 0.53 nm, of the same order as that of Mn2+ ions in CaO. 相似文献
200.
A noiselike fine structure of ferromagnetic resonance spectra in magnetic powders was investigated after ultrasonic treatment. Magnetic interactions between particles are proved to have an influence upon the fine structure formation. After decreasing dipole-dipole magnetic interactions in dilute suspension a special order appears in fine-structure spectra, which is generally the same for different systems. 相似文献