全文获取类型
收费全文 | 4373篇 |
免费 | 659篇 |
国内免费 | 347篇 |
专业分类
化学 | 1550篇 |
晶体学 | 82篇 |
力学 | 1584篇 |
综合类 | 31篇 |
数学 | 639篇 |
物理学 | 1493篇 |
出版年
2024年 | 4篇 |
2023年 | 38篇 |
2022年 | 99篇 |
2021年 | 72篇 |
2020年 | 152篇 |
2019年 | 114篇 |
2018年 | 142篇 |
2017年 | 149篇 |
2016年 | 202篇 |
2015年 | 135篇 |
2014年 | 212篇 |
2013年 | 304篇 |
2012年 | 230篇 |
2011年 | 236篇 |
2010年 | 200篇 |
2009年 | 239篇 |
2008年 | 247篇 |
2007年 | 282篇 |
2006年 | 268篇 |
2005年 | 246篇 |
2004年 | 222篇 |
2003年 | 204篇 |
2002年 | 181篇 |
2001年 | 146篇 |
2000年 | 139篇 |
1999年 | 130篇 |
1998年 | 123篇 |
1997年 | 117篇 |
1996年 | 67篇 |
1995年 | 78篇 |
1994年 | 63篇 |
1993年 | 38篇 |
1992年 | 59篇 |
1991年 | 43篇 |
1990年 | 36篇 |
1989年 | 23篇 |
1988年 | 17篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有5379条查询结果,搜索用时 15 毫秒
131.
132.
A novel core–shell TiO2@ZnIn2S4composite has been synthesized successfully by a simple and flexible hydrothermal route using TiO2as precursors.The as-synthesized samples were characterized by X-ray diffraction,UV–vis diffuse reflectance spectra and transmission electron microscopy.The photocatalytic properties of samples were tested by degradation of aqueous methylene blue(MB)under visible light irradiation.It was found that the as-synthesized TiO2@ZnIn2S4photocatalyst was more effcient than TiO2and ZnIn2S4in the photocatalytic degradation of MB.Moreover,TEM images confrmed the TiO2@ZnIn2S4nanoparticles possessed a well-proportioned core–shell morphology. 相似文献
133.
A solvothermal post‐treatment method was developed to synthesize Fe3O4@mesosilica core–shell nanospheres (CSNs) with a well‐preserved morphology, mesoporous structure, and tunable large pore diameters (2.5–17.6 nm) for the first time. N,N‐Dimethylhexadecylamine (DMHA), which was generated in situ during the heat‐treatment process, was mainly responsible for this pore‐size enlargement, as characterized by NMR spectroscopy. This pore‐size expansion can be strengthened with the aid of hexamethyldisilazane (HMDS), whilst the nature of the surface of the Fe3O4@mesosilica CSNs can be easily modified with trimethylsilyl groups during the pore‐size‐expansion process. The hydrophobicity of the Fe3O4@mesosilica CSNs increased for the enlarged mesopores and the adsorption capacity of these CSNs for benzene (up to 1.5 g g?1) is the highest ever reported for Fe3O4@mesosilica CSNs. The resultant Fe3O4@mesosilica CSNs (pore size: 10 nm) showed a 3.6‐times higher adsorption capacity of lysozyme than those without the pore expansion (pore size: 2.5 nm), thus making them a good candidate for loading large molecules. 相似文献
134.
Xiang Wang Dr. Qian Xu Dr. Fengtao Fan Dr. Xiuli Wang Dr. Mingrun Li Prof. Zhaochi Feng Prof. Can Li 《化学:亚洲杂志》2013,8(9):2189-2195
By taking advantage of UV‐Raman spectroscopy and high‐resolution TEM (HRTEM), combined with the focused ion beam (FIB) technique, the transformation from GaOOH into α‐Ga2O3 and then into β‐Ga2O3 was followed. We found that the stepwise transformations took place from the surface region before developing into the bulk of single particles without particle agglomeration and growth. During the transformation from GaOOH into α‐Ga2O3, the elimination of water vapor through the dehydroxylation of GaOOH resulted in the formation of micropores in the single particles, whilst maintaining their particle size. For the phase transformation from α‐Ga2O3 into β‐Ga2O3, the nucleation of β‐Ga2O3 was found to occur at the surface defects and this process could be retarded by occupying these defects with a small amount of La2O3. By finely controlling the process of the phase transformation, the β‐Ga2O3 domains gradually developed from the surface into the bulk of the single particles without particle agglomeration. Therefore, the surface structure of the α‐Ga2O3 single particles can be easily tuned and a particle with an α@β core–shell phase structure has been obtained. 相似文献
135.
The traditional method for opening the electron shells of noble gas atoms involves a strong electronegative atom or group. However, this approach is limited to only heavy noble‐gas atoms, such as Kr and Xe. In this paper, we performed accurate calculations of He@C8H8 and He@C10H16 and showed the possibility of opening the electron shell of a light noble‐gas atom. © 2012 Wiley Periodicals, Inc. 相似文献
136.
This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers. 相似文献
137.
The performance of a range density functional theory functionals combined in a quantum mechanical (QM)/molecular mechanical (MM) approach was investigated in their ability to reliably provide geometries, electronic distributions, and relative energies of a multicentered open‐shell mechanistic intermediate in the mechanism 8R–Lipoxygenase. With the use of large QM/MM active site chemical models, the smallest average differences in geometries between the catalytically relevant quartet and sextet complexes were obtained with the B3LYP* functional. Moreover, in the case of the relative energies between 4II and 6II , the use of the B3LYP* functional provided a difference of 0.0 kcal mol–1. However, B3LYP± and B3LYP also predicted differences in energies of less than 1 kcal mol–1. In the case of describing the electronic distribution (i.e., spin density), the B3LYP*, B3LYP, or M06‐L functionals appeared to be the most suitable. Overall, the results obtained suggest that for systems with multiple centers having unpaired electrons, the B3LYP* appears most well rounded to provide reliable geometries, electronic structures, and relative energies. © 2012 Wiley Periodicals, Inc. 相似文献
138.
139.
Phase change material (PCM, octadecane) nanocapsules were successfully prepared by resin fortified emulsion (RFE) polymerization using the alkali soluble resin (ASR) of poly(ethylene‐co‐acrylic acid) (EAA) and poly(styrene‐co‐acrylic acid) (SAA). Stable PCM nanocapsules were obtained by resin fortified emulsion polymerization, which could be attributed to the prevention of Ostwald ripening due to PCM being hydrophobic. Analysis of online FTIR measurements throughout the reaction confirmed that the nanocapsules contained octadecane as a PCM. TEM imaging of the PCM nanocapsules showed spherical and core/shell morphology. The characteristics of PCM nanocapsules can be controlled by process parameters. As a result, the particle size and particle size distribution (i.e., polydispersity index (Dw/Dn)) of the PCM nanocapsules were created by adjusting manufacturing conditions. The PCM nanocapsules exhibited thermal energy storage (~49.8 J/g) and release (~47.9 J/g) behavior. 相似文献
140.
Vera Homem Arminda Alves 《International journal of environmental analytical chemistry》2013,93(14-15):1063-1084
The adsorption of the antibiotic amoxicillin at low concentration levels (µg?L?1 order) from aqueous solution on almond shell ashes has been investigated, either by kinetic or equilibrium assays. The effect of the adsorbent amount, initial concentration of the antibiotic, particle diameter (dp) and temperature were considered to evaluate the adsorption capacity of the adsorbent. The results showed that amoxicillin sorption is dependent on these four factors. The adsorption process was relatively fast and equilibrium was established in about 12 hours. The optimum parameters for an initial concentration of 450?µg?L?1 were 50?mg of adsorbent, 303?K and dp?<?600?µm. A comparison of kinetic models showed that pseudo-second order kinetics provides the best correlation of the experimental data. Isotherm data adjusted better to Langmuir equation, with an adsorption capacity of 2.5?±?0.1?mg?g?1 at 303?K. The desorption process was also evaluated (maximum efficiency of 5%). Thermodynamic parameters were calculated and the negative value of ΔH0 and ΔG0 showed that adsorption was exothermic and a spontaneous process. 相似文献