全文获取类型
收费全文 | 20357篇 |
免费 | 767篇 |
国内免费 | 378篇 |
专业分类
化学 | 11735篇 |
晶体学 | 118篇 |
力学 | 483篇 |
综合类 | 30篇 |
数学 | 2377篇 |
物理学 | 4200篇 |
无线电 | 2559篇 |
出版年
2022年 | 170篇 |
2021年 | 300篇 |
2020年 | 281篇 |
2019年 | 283篇 |
2018年 | 274篇 |
2017年 | 227篇 |
2016年 | 503篇 |
2015年 | 451篇 |
2014年 | 567篇 |
2013年 | 1049篇 |
2012年 | 964篇 |
2011年 | 1106篇 |
2010年 | 762篇 |
2009年 | 737篇 |
2008年 | 997篇 |
2007年 | 1052篇 |
2006年 | 866篇 |
2005年 | 866篇 |
2004年 | 851篇 |
2003年 | 851篇 |
2002年 | 880篇 |
2001年 | 644篇 |
2000年 | 549篇 |
1999年 | 448篇 |
1998年 | 342篇 |
1997年 | 293篇 |
1996年 | 297篇 |
1995年 | 314篇 |
1994年 | 281篇 |
1993年 | 236篇 |
1992年 | 226篇 |
1991年 | 209篇 |
1990年 | 224篇 |
1989年 | 186篇 |
1988年 | 184篇 |
1987年 | 158篇 |
1986年 | 148篇 |
1985年 | 252篇 |
1984年 | 256篇 |
1983年 | 182篇 |
1982年 | 204篇 |
1981年 | 166篇 |
1980年 | 166篇 |
1979年 | 158篇 |
1978年 | 125篇 |
1977年 | 180篇 |
1976年 | 153篇 |
1975年 | 129篇 |
1974年 | 114篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
151.
Fabiana Quaglia Giuseppe Fusco Giuseppe De Rosa Francesca Ungaro Agnese Miro Maria Immacolata La Rotonda 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):669-674
The aim of this work was to produce lycopene-containing powders from tomato products by a solvent-free method making use of
β-cyclodextrin (βCD). Powders were prepared by spray-drying a tomato concentrate (TC), one of the most bioavailable form of
lycopene, after mechanical treatment with βCD in different weight ratios. The obtained product was centrifuged to eliminate
partly food matrix and characterized for the amount of lycopene hydrodispersed/hydrosolubilized in the aqueous fraction. The
chemical antioxidant activity of sera was evaluated too. Powders obtained by spray-drying sera exhibited good flow properties,
a lycopene content between 0.4 and 1.09 mg/g and excellent water dispersability. The process developed, which makes use of
βCD for the treatment of tomato products, turns to be of great interest to obtain a bulk material for nutraceuticals displaying
superior biovailability of lycopene. 相似文献
152.
G. De Marzi H.J. TrodahlJ. Bok A. CantareroF. Sapiña 《Solid State Communications》2003,127(4):259-264
We report on the first Raman data of Cu substituted La1−ySryMn1−xCuxO3 (0≤x≤0.10 and 0.17≤y≤0.3, accordingly in order to have the same Mn4+/[Mn4++Mn3+] ratio), collected in the frequency range 100-900 cm−1 and at room temperature, with parallel (ei∥es) and crossed (ei⊥es) polarizations of the incident (ei) and scattered (es) light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm−1, together with two broad structures centered at near 500 and 670 cm−1, have been found. We also have observed that the A1g mode is substantially shifted with increasing Cu substitution. The A1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle αr, thus following the structural changes of the MnO6 octahedra in the system. 相似文献
153.
154.
The reaction pathway for the Ca3Al2O6 formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO3, was studied in situ by differential thermal analysis, constant heating rate dilatometry and time-resolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca3Al2O6 stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al2O3, crystalline CaO, CaAl2O4 and Ca12Al14O33 as transitory phases. Finally the nucleation and growth of the single phase Ca3Al2O6 took place at 1300°C and exhibited porous structure due to CO2 and H2O release. 相似文献
155.
Theoretical models for Monte Carlo simulation of radiative processes, i.e. bremsstrahlung and characteristic x-ray emission, are presented. Possible strategies for simulating electron transport are briefly described. For mechanisms involving energy loss and angular deflections, difficulties for strict implementation of accurate numerical differential cross sections still remain due to the strong correlations between these variables. Practical solutions for the case of inelastic collisions and bremsstrahlung emission are described. Comparisons of simulation results with experimental data for several problems of interest in electron probe microanalysis are presented. 相似文献
156.
Dielectric studies are presented of a banana-shaped compound that exhibits the antiferroelectric B2 phase. Upon application and subsequent removal of strong electric fields the textures and dielectric properties of the phase drastically change. Most notable is the huge increase of the low frequency permittivity. This behaviour would suggest the induction of ferroelectricity by the electric field. 相似文献
157.
Valerio De Angelis 《Journal of Mathematical Analysis and Applications》2004,294(1):288-293
We prove that the solutions of the non-autonomous Lyness equation xn+1=(xn+bn)/xn−1, bn>0, x0>0, x1>0, are bounded away from zero and infinity if the sequence bn is monotonic. We also give an example to show that the solutions need not be bounded even when the sequence bn attains only two values. 相似文献
158.
This study presents a method of adaptive identification of parameters describing Sugeno fuzzy inference system in presence of bounded disturbances while maintaining the readability and interpretability of the fuzzy model during and after identification. This method do not require any a priori knowledge of a bound on the disturbance and noise and of a bound on the unknown parameters values. The method can be used for the robust and adaptive identification of slowly time varying nonlinear systems using fuzzy inference systems. The suggested method was used to build a fuzzy expert system that approximates the functional relationship between physical fitness and some of the measurable physiological parameters by their real measurements and opinion (human-experiences) of a medical expert. 相似文献
159.
Sebastiaan van Dijken Xavier Fain Steven M. Watts Kentaro Nakajima J. M. D. Coey 《Journal of magnetism and magnetic materials》2004,280(2-3):322-326
A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe3O4 electrodes is presented. Fe3O4/Au/Fe3O4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe3O4 layers. By contrast, a negative GMR effect is measured on Fe3O4/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe3O4/Au interface or an induced spin scattering asymmetry in the Au interfacial layers. 相似文献
160.