全文获取类型
收费全文 | 548篇 |
免费 | 6篇 |
国内免费 | 71篇 |
专业分类
化学 | 340篇 |
晶体学 | 2篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 24篇 |
物理学 | 255篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 9篇 |
2021年 | 3篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 71篇 |
2012年 | 50篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 38篇 |
2007年 | 72篇 |
2006年 | 21篇 |
2005年 | 25篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 33篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有625条查询结果,搜索用时 15 毫秒
91.
92.
The equations of state and phase stability of calcium chalcogenides, CaS, CaSe and CaTe are investigated via first principles theoretical calculations. We report results of the structural properties of these compounds in the B1(NaCl) and the B2(CsCl) phases, the theoretical transition pressure and the volumes compression ratio. For CaTe we investigate the possible existence of an intermediate phase between the B1 and the B2 structure. 相似文献
93.
The observation of optical second harmonic generation (SHG) from wetspun films of Na-DNA is reported. The SHG signal is stronger at a relative humidity of 92% (corresponding to the B conformation of Na-DNA) than at low humidity of -33% (corresponding to a disordered conformation of Na-DNA). The strength of the SHG signal is also dependent on the orientation of the incident laser beam polarization with respect to the DNA helical axes. 相似文献
94.
The spicy taste is stimulated by sanshool when eating Sichuan pepper. α-Hydroxy sanshool is one of the main components of the sanshool derivatives. In this paper, in form of a short story, we introduced the basic properties, physiological functions and synthetic method of α-hydroxy sanshool and the mechanism of spicy taste which is stimulated by α-hydroxy sanshool. 相似文献
95.
The fractional Fourier transform (FRT) of an elliptical dark-hollow beam (EDHB) is studied in detail. Based on the definition of FRT in the rectangular coordinate system, analytical formulae are derived for the FRT of an EDHB with the help of a tensor method. The properties of an EDHB in the FRT plane are illustrated numerically by use of the derived formulae. The results show that the properties of the EDHB in the FRT plane are closely related to the parameters of the beam and to the fractional order. The derived formula provides a convenient way for analyzing and calculating the FRT of an EDHB. 相似文献
96.
《Journal of Saudi Chemical Society》2014,18(1):69-76
Pure and Li-doped NiO/Al2O3 and CuO/Al2O3 catalysts were prepared to contain 2, 4 and 8 wt.% of Ni and Cu, respectively. The structural properties were determined using DTA, XRD and FTIR techniques, and the textural properties of the catalysts were determined from their adsorption–desorption isotherms of nitrogen at 77 K. The chemisorption of hydrogen at 473–823 K with the pre-reduced catalysts was measured. The data obtained allowed the determination of the metal surface area, S (m2/g); the percentage of metal distribution, R; and the diameter of metal crystallite, d (nm). The amount of surface acidity, measured in mmol/g, was determined from the amount of chemisorbed pyridine necessary to completely inhibit the catalytic dehydration (DHD) of isopropanol. The conversion of isopropanol at 533–623 K was investigated using the micro-catalytic pulse technique. DTA, XRD and FTIR indicated that NiO and CuO exist as separate phases with crystallite sizes too small to be detected. No evidence has been gathered to indicate the existence of an aluminate phase.With the increase of metal loading, the surface area decreased whereas the total pore volume and the mean pore radius increased. Conversion of iso-propanol to propene proceeded via (DHD) on surface acid sites, and conversion of isopropanol to acetone proceeded via dehydrogenation (DHG) on redox sites. DHD and DHG exhibited first-order kinetics, and the rates of both reactions increased with temperature, with the latter being more temperature-dependent. 相似文献
97.
Formulated products represent a particular class of complex chemical products, and their design is typically based on experience and extensive experimentation. Although still at an early stage, and despite that their potential is not fully accessed and not fully used by the industry, computer-aided design (CAD) methods and tools offer many possibilities in the design of formulated products. The CAD methodology based on computerized models enables the formulation chemists to speed up the design process, without completely replacing experiments.In this work, we summarize previous studies in the field and present important elements of the CAD framework, emphasizing estimation methods for key target properties, link to specifications, and finally, some case studies will illustrate how the CAD framework can be used in practice for formulated products. 相似文献
98.
以噻吩-2,5-二羧酸为主要配体,借助第二配体----4,4-联吡啶或者邻菲罗啉通过水热法合成了三种MOFs材料,分别是[Cd (tdc) (bpy)]n、[Zn (tdc) (bpy)]n、[Co (tdc) (phen)]n。利用X射线单晶衍射仪、红外光谱仪对三种MOFs材料进行了结构表征与分析,同时利用荧光光谱仪、热重分析仪和电化学工作站测定了三种MOFs材料的荧光性质、热稳定性和MOFs材料修饰玻碳电极的电化学行为,结果表明,三种MOFs材料比配体更好的荧光强度和热稳定性,制备的[Co (tdc) (phen)]n修饰玻碳电极,对铁氰化钾溶液和含1.0mmol/L NaNO2的pH = 5 PBS溶液,均比裸玻碳电极表现出更强的循环伏安响应,有望作为修饰剂应用于修饰玻碳电极中。 相似文献
99.
Preparation of polypropylene (PP)/waste tyre dust (WTD) blends with addition of dicumyl peroxide (DCP) and N,N′-m-phenylenebismaleimide (HVA-2) (PP/WTDP-HVA2) was described. The blends were characterized based on their tensile properties, swelling resistance and morphology, as well as thermal properties. The results reveal that the presence of both chemicals in PP/WTDP-HVA2 blends brought about noticeable improvements in tensile properties, swelling resistance and interfacial adhesion. The thermal stability was also improved, indicating existence of some chemical interaction between WTD and the PP matrix in the presence of both DCP and HVA-2 during processing. The results imply that both chemicals had great influences on WTD destabilization, leading to the enlargement and intensification of the copolymer formation and, hence, improved the interfacial adhesion between WTD and the PP matrix. A competing reaction mechanism that may contribute to the property enhancement of PP/WTDP-HVA2 blends was proposed. 相似文献
100.
Éadaoin McCourt Dr. Kane Esien Li Zhenyu Dr. Solveig Felton Dr. Peter Nockemann 《Angewandte Chemie (International ed. in English)》2023,62(7):e201809334
Herein, we report on the preparation of liquid dimeric lanthanide(III)-containing compounds. Starting from the design of dimeric solids, we demonstrate that by tuning of anion and cation structures we can lower the melting points below room temperature, whilst maintaining the dimeric structure. Magnetic measurements could establish the spin-spin interactions of the neighboring lanthanide(III) ions in the liquid state at low temperatures, and matched the interactions of the analogous crystalline solid compounds. 相似文献