全文获取类型
收费全文 | 115篇 |
免费 | 2篇 |
国内免费 | 4篇 |
专业分类
化学 | 41篇 |
晶体学 | 4篇 |
力学 | 2篇 |
数学 | 39篇 |
物理学 | 35篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 8篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有121条查询结果,搜索用时 15 毫秒
1.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
2.
3.
Karla J. Moreno Antonio F. Fuentes Javier García-Barriocanal Jacobo Santamaría 《Journal of solid state chemistry》2006,179(3):928-934
Different compositions in a solid solution of general formula Dy2(Ti1−yZry)2O7, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y?0.4, which, as observed in the similar Y2(Ti1−yZry)2O7, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y>0.6, reaching a maximum value of ∼5×10−3 for Dy2Zr2O7 at 900 °C. 相似文献
4.
A versatile process for the preparation of composite films consisting of magnetite (Fe3O4) nanoparticles embedded in a polyaniline (PANI) matrix is reported. Spectroscopic properties of polyaniline matrix (PANI-EB), polyaniline protonated with camphor sulfonic acid (PANI-CSA0.5) PANI-ES and PANI/Fe3O4-CSA0.5 composites were studied, both in the state of the solutions of m-cresol and in thin films processed from the same solvents. The results of these studies indicate that m-cresol can be used for PANI/Fe3O4 composite preparation. Such films show both reasonably high electrical conductivity and magnetic permeability. A controlled application of a magnetic field during the casting process resulted in the formation of the materials with an unusual combination of magnetic and transport properties. The obtained films show the behavior that can be explained by the presence of both ferromagnetic and paramagnetic phases. The superparamagnetic contribution, if any, is very small. Application of the external magnetic field during fabrication of the composites stimulates creation of the aggregates of magnetic particles which, although keeps conductivity at a relatively high level, leads to a small decrease of the conductivity value. 相似文献
5.
Braverman Michael SH.; Stepanov Vladimir D. 《Bulletin London Mathematical Society》1994,26(3):283-287
Necessary and sufficient conditions for the boundedness of thediscrete Hardy operator of the form , from to when 0 < q < 1 <p , is given. 相似文献
6.
7.
8.
Karen Rodríguez-Villar Lilin Ypez-Mulia Miguel Corts-Gines Jacobo David Aguilera-Perdomo Edgar A. Quintana-Salazar Kevin Samael Olascoaga Del Angel Francisco Corts-Benítez Juan Francisco Palacios-Espinosa Olivia Soria-Arteche Jaime Prez-Villanueva 《Molecules (Basel, Switzerland)》2021,26(8)
Indazole is an important scaffold in medicinal chemistry. At present, the progress on synthetic methodologies has allowed the preparation of several new indazole derivatives with interesting pharmacological properties. Particularly, the antiprotozoal activity of indazole derivatives have been recently reported. Herein, a series of 22 indazole derivatives was synthesized and studied as antiprotozoals. The 2-phenyl-2H-indazole scaffold was accessed by a one-pot procedure, which includes a combination of ultrasound synthesis under neat conditions as well as Cadogan’s cyclization. Moreover, some compounds were derivatized to have an appropriate set to provide structure-activity relationships (SAR) information. Whereas the antiprotozoal activity of six of these compounds against E. histolytica, G. intestinalis, and T. vaginalis had been previously reported, the activity of the additional 16 compounds was evaluated against these same protozoa. The biological assays revealed structural features that favor the antiprotozoal activity against the three protozoans tested, e.g., electron withdrawing groups at the 2-phenyl ring. It is important to mention that the indazole derivatives possess strong antiprotozoal activity and are also characterized by a continuous SAR. 相似文献
9.
Ever since the pioneering works of Bekenstein and Hawking, black hole entropy has been known to have a quantum origin. Furthermore, it has long been argued by Bekenstein that entropy should be quantized in discrete (equidistant) steps given its identification with horizon area in (semi-)classical general relativity and the properties of area as an adiabatic invariant. This lead to the suggestion that the black hole area should also be quantized in equidistant steps to account for the discrete black hole entropy. Here we shall show that loop quantum gravity, in which area is not quantized in equidistant steps, can nevertheless be consistent with Bekenstein's equidistant entropy proposal in a subtle way. For that we perform a detailed analysis of the number of microstates compatible with a given area and show consistency with the Bekenstein framework when an oscillatory behavior in the entropy-area relation is properly interpreted. 相似文献
10.
Elena V. Basiuk Jacobo Gómez-Lara Vladimir A. Basiuk Rubén Alfredo Toscano 《Journal of chemical crystallography》2000,30(3):199-202
A complex of 5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (dioxocyclam) and 2,6-dihydoxyanthraquinone (anthraflavic acid) has been obtained. The complex (crystals grown from water-ethanol solution) has a stoichiometry dioxocyclam-anthraflavic acid 1:1:5. C31H32N4O8, chemical formula weight 588.61, triclinic, P – 1, a = 10.542(3) Å, b = 11.936(2) Å, c = 12.206(2) Å, = 104.00(1)°, = 92.68(2)°, = 103.64(2)°, V = 1439.4 (5) Å3, Z = 2, Dx = 1.358 g cm–3. Only one of the two amine N-atoms of the macrocycle is protonated due to very weak acidic properties of 2,6-dihydoxyanthraquinone. Due to the rather poor quality of the crystals and structure refinement, reliable determination of H-bonds is complicated. Nevertheless, several types of H-bonding responsible for the formation of a developed supramolecular network can be suggested: between the protonated amino groups and macrocycle's C=O moieties; between non-protonated amino groups and macrocycle's C=O moieties; between protonated and non-protonated amino groups; between the amide NH and C=O groups of anthraflavic acid; and between protonated and deprotonated hydroxy groups of the acid. Two types of anthraflavic components can be distinguished in the lattice: those having a parallel orientation with respect to the macrocyclic fragments and forming hydrogen bonds with the latter, and those lying in an approximately perpendicular plane and not involved in H-bonding with the macrocycles. 相似文献