全文获取类型
收费全文 | 1191篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
化学 | 724篇 |
晶体学 | 22篇 |
力学 | 69篇 |
数学 | 77篇 |
物理学 | 318篇 |
出版年
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 21篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 24篇 |
2016年 | 37篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 100篇 |
2012年 | 72篇 |
2011年 | 55篇 |
2010年 | 56篇 |
2009年 | 48篇 |
2008年 | 64篇 |
2007年 | 51篇 |
2006年 | 48篇 |
2005年 | 38篇 |
2004年 | 37篇 |
2003年 | 11篇 |
2002年 | 19篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 23篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1971年 | 6篇 |
排序方式: 共有1210条查询结果,搜索用时 15 毫秒
11.
The stability constants of the Cu2+, Zn2+, Ni2+ and Mu2+ complexes of N-phenyl-o-methoxybenzohydroxamic acid at 30° in 50% v/v aqueous dioxan are: log K1 10·45, 8·16, 7·52, 6·33; log K2 8·90, 6·70, 6·01, 5·59 (for the ions in the order given). 相似文献
12.
A sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic method of analysis of nevirapine both as a bulk drug and in formulations was developed and validated. The solvent system consisted of toluene-carbon tetrachloride-methanol-acetone-ammonia (3.5:3.5:2.0:1.0:0.05, v/v/v/v/v). Densitometric analysis of nevirapine was carried out in the absorbance mode at 289nm. This system was found to give compact spots for nevirapine (R(f) value of 0.44+/-0.02). Nevirapine was subjected to acid and alkali hydrolysis, oxidation, dry heat and wet heat treatment and photodegradation. The drug undergoes degradation under acidic, basic conditions and oxidation. Also the degraded products were well resolved from the pure drug with significantly different R(f) values. Linearity was found to be in the range of 30-1000ng/spot with significantly high value of correlation coefficient. The linear regression analysis data for the calibration plots showed good linear relationship with r(2)=0.998+/-0.002 in the working concentration range of 300ng/spot to 1000ng/spot. The mean value of slope and intercept were 0.073+/-0.005 and 36.78+/-1.50, respectively. The method was validated for precision, robustness and recovery. The limit of detection and quantitation were 5 and 10ng/spot, respectively. As the method could effectively separate the drug from its degradation products, it can be employed as a stability indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of acid degradation process. Arrhenius plot was constructed and activation energy was calculated. 相似文献
13.
K. K. Verma Seema Shashi Chhabra 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):3037-3045
The synthesis and structural features of some newly synthesized 1,10-phenanthroline complexes of p-hydroxyphenyl-and 3-methyl-4-hydroxyphenyltellurium trihalides (chlorides, bromides, and iodides) are reported. The resulting complexes have been subjected to elemental analyses, conductance and cryoscopic measurements, infra-red and proton magnetic resonance spectral studies. Solution studies reveal the weak to 1:1 electrolyte type behavior of these complexes in solution. Spectral studies indicate the linkage of phenanthroline to the tellurium atom through the nitrogen atoms. Central tellurium atom in these complexes is hexa-coordinated in an octahedral way. 相似文献
14.
Viscous potential flow analysis of Kelvin-Helmholtz instability with heat and mass transfer has been studied. A dispersion relation has been obtained. Stability criterion is given by a critical value of relative velocity. It has been found that heat and mass transfer has destabilizing effect on relative velocity when lower fluid viscosity is low while it has stabilizing effect when lower fluid viscosity is high. Various graphs have been plotted for relative velocity and growth rate. In statically unstable situation viscosity has stabilizing effect while in statically stable situation it has destabilizing effect. 相似文献
15.
Magnesium aluminate doped with Tb3+ (MgAl2O4:Tb3+) was prepared by combustion synthesis. Three thermoluminsence (TL) peaks at 120, 220 and 340 °C were observed. PL and TL emission spectrum shows that Tb3+ acts as the luminescent centre. Optically stimulated luminescence (OSL) was observed when stimulated by 470 nm blue light.Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the TL and OSL processes in MgAl2O4:Tb3+. Two defect centres were identified in irradiated MgAl2O4:Tb3+ phosphor by ESR measurements which was carried out at room temperature and these were assigned to V and F+ centres. V centre (hole centre) is correlated to 120 and 220 °C TL peaks and F+ centre (electron centre), which acts as a recombination centre is correlated to 120, 220 and 340 °C. 相似文献
16.
17.
Experimental measurements of power spectra of a single longitudinal and transverse mode ring dye laser are presented that reveal the critical slowing down of the laser near threshold. External pump noise serves as a probe of the frequency response of the dye laser. Detailed comparisons of the spectral characteristics with computer simulations and an approximate analytic theory are given. The dynamics of spatial pattern formation in a multimode dye laser is examined through measurements of first-passage-time distributions. A comparison of the experiments with computer simulations based on a simple theoretical model of the two-mode laser shows qualitative agreement. These measurements indicate that there are a variety of complex phenomena associated with the transverse mode pattern formation dynamics that need to be addressed theoretically and studied further experimentally. 相似文献
18.
Sami I. Muslih Om P. Agrawal Dumitru Baleanu 《International Journal of Theoretical Physics》2010,49(8):1746-1752
This paper presents a fractional Schrödinger equation and its solution. The fractional Schrödinger equation may be obtained using a fractional variational principle and a fractional Klein-Gordon equation; both methods are considered here. We extend the variational formulations for fractional discrete systems to fractional field systems defined in terms of Caputo derivatives to obtain the fractional Euler-Lagrange equations of motion. We present the Lagrangian for the fractional Schrödinger equation of order α. We also use a fractional Klein-Gordon equation to obtain the fractional Schrödinger equation which is the same as that obtained using the fractional variational principle. As an example, we consider the eigensolutions of a particle in an infinite potential well. The solutions are obtained in terms of the sines of the Mittag-Leffler function. 相似文献
19.
20.
The electronic polarizabilities of ions in alkaline earth chalcogenides are estimated by taking account of the effect of the
crystalline potential. The polarizabilities thus obtained are found to present a good agreement with experimental data. It
has been shown that the polarizabilities and radii of alkaline earth and chalcogenide ions follow the polarizability-radius
cube relation approximately well. 相似文献