全文获取类型
收费全文 | 696篇 |
免费 | 139篇 |
国内免费 | 104篇 |
专业分类
化学 | 504篇 |
晶体学 | 17篇 |
力学 | 34篇 |
综合类 | 16篇 |
数学 | 65篇 |
物理学 | 303篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 24篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 23篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 52篇 |
2012年 | 65篇 |
2011年 | 62篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 60篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 31篇 |
2004年 | 28篇 |
2003年 | 47篇 |
2002年 | 56篇 |
2001年 | 51篇 |
2000年 | 33篇 |
1999年 | 30篇 |
1998年 | 16篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有939条查询结果,搜索用时 437 毫秒
931.
932.
The study of bending of cracked circular cylinders is of more significance. The bending of cylinders containing radical crack
or cracks was discussed by refs. [1]–[4] and that of concentrically craked circular cylinders was studied by [5]. Continuing
[6] and using complex variable methods in elasticity, this paper deals with the bending problems of a circular cylinder, containing
an internal linear crack at any position under an acting force perpendicular to the crack. The general forms of displacements,
stresses, and stressintensity factors, expressed in terms of series, are obtained and to this bending problems with small
Ah are presented good approximate formulas for the stress-intensity factors whose variations with the center of the crack
are analysed. Finally, the twist angle per unit length and the center of bending for the radically cracked circular cylinder,
one of whose crack-tips is located at the origin, have been computed and the results are almost the same as that calculated
in [1]. 相似文献
933.
Cycloaddition of nitrile oxides to substituted vinylphosphonates was performed. A series of 4,5‐dihydroisoxazoles containing phosphonyl group were synthesized under very mild condition in excellent regiospecificity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:309–311, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10149 相似文献
934.
Sheng‐Li Li Anwar Usman Ibrahim A. Razak Hoong‐Kun Fun Jie‐Ying Wu Yu‐Peng Tian Min‐Hua Jiang Zu‐Yao Chen 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(5):m181-m183
In the title compound, [Ni(CH5N3S)2(H2O)2](C4H3O4)2·2H2O, the Ni atom lies on a center of symmetry and is coordinated by N and S atoms from two thiosemicarbazide ligands and the O atoms of two water molecules in a distorted octahedral geometry. In the asymmetric unit, the three components are linked together by one O—H⋯O and two N—H⋯O hydrogen bonds. The packing is built from molecular ribbons parallel to the b direction, stabilized by intramolecular hydrogen bonds, and by one N—H⋯S and two N—H⋯O intermolecular hydrogen bonds. The ribbons are further connected into columns by N—H⋯O interactions and then into a three‐dimensional network by three O—H⋯O hydrogen bonds. 相似文献
935.
Zu‐Sheng Xu Vah Drnoyan Almeria Natansohn Paul Rochon 《Journal of polymer science. Part A, Polymer chemistry》2000,38(12):2245-2253
The synthesis and optical properties of a series of amorphous polyesters with amino‐sulfone azobenzene chromophores in the main chain are presented. The condensation of alkyl diacid chlorides with 4‐[(2‐hydroxyethyl)ethylamino]‐4′‐(2‐hydroxyethylsulfonyl)azobenzene (7) gave polymers that showed low and unstable photoinduced birefringence because of their low glass‐transition temperature. The condensation of 7 with mixtures of adipoyl chloride and terephthaloyl chloride gave a polymer with a higher glass‐transition temperature and a stable reversible photoinduced birefringence. A photostationary birefringence of 0.07 was observed. Surface profile gratings were optically inscribed and produced diffraction efficiencies less than or equal to 19%. Photostationary, long‐term stable birefringence and surface‐grating efficiency increased with polymer rigidity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2245–2253, 2000 相似文献
936.
In accord with the Hurd‐Mori reaction conditions, 1‐ or 2‐phosphonyl hydrazones reacted with thionyl chloride to afford 4‐ or 5‐phosphonyl 1,2,3‐thiadiazoles in good yields and purity. A synthesis of 1‐ or 2‐phosphonyl hydrazones using two methods is described. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 16:413–416, 2000 相似文献
937.
938.
Bioreduction of 3‐substituted‐2‐oxoal‐kanephosphonates by baker's yeast afforded 3‐substituted‐2‐hydroxy‐alkanephosphonates in moderate to good yields and ee value. These compounds could serve as useful chirons for the stereoselective synthesis of phosphorus analogs of biologically active molecules including R‐(—)‐3‐trimethylammonium‐2‐hydroxypropanoic acid and R‐(—)‐3‐ trimethylammonium‐2‐hydroxypropanoic acid. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:551–556, 2001 相似文献
939.
近年来,银卤化物双钙钛矿作为铅基杂化卤化物钙钛矿的潜在环保替代品得到了广泛的研究。最近实验上合成的新型无铅双钙钛矿单晶材料Cs2AgFeCl6是一种立方结构半导体,吸收光谱可拓宽至800 nm。本论文采用密度泛函理论的第一性原理方法,对Cs2AgFeX6(X = Cl,Br,I)的电子结构和光学性质进行研究,讨论了二者之间的内在关联,并分析了X位元素的改变对材料性质的影响。电荷密度计算结果显示,由Cl到I,Fe-X键逐渐减弱,即原子对电荷的束缚能力减弱。另一方面,三种材料的带隙宽度是逐渐减小的,Cs2AgFeCl6和Cs2AgFeBr6带隙分别为1.40 eV和0.91 eV,而Cs2AgFeI6则呈现金属性质。Cs2AgFeX6双钙钛矿的光谱特征峰随 X 位原子序数的增加明显红移,且在可见至红外光波段均有明显的光吸收:Cs2AgFeCl6在534 nm处的吸收系数达到21.28×104 cm-1,Cs2AgFeBr6在712 nm处的吸收系数为20.54×104 cm-1,而Cs2AgFeI6在1200 nm后的红外波段有一极宽的吸收峰,吸收系数可以达到10×104 cm-1。本论文为Cs2AgFeX6(X = Cl,Br,I)在光电子器件领域的广泛应用提供了理论指导。 相似文献