全文获取类型
收费全文 | 55226篇 |
免费 | 6689篇 |
国内免费 | 8471篇 |
专业分类
化学 | 25126篇 |
晶体学 | 1364篇 |
力学 | 10205篇 |
综合类 | 711篇 |
数学 | 16589篇 |
物理学 | 16391篇 |
出版年
2024年 | 124篇 |
2023年 | 585篇 |
2022年 | 1137篇 |
2021年 | 1272篇 |
2020年 | 1567篇 |
2019年 | 1352篇 |
2018年 | 1401篇 |
2017年 | 1896篇 |
2016年 | 2131篇 |
2015年 | 1706篇 |
2014年 | 2760篇 |
2013年 | 4060篇 |
2012年 | 3931篇 |
2011年 | 3668篇 |
2010年 | 3090篇 |
2009年 | 3591篇 |
2008年 | 3608篇 |
2007年 | 3665篇 |
2006年 | 3378篇 |
2005年 | 3200篇 |
2004年 | 2776篇 |
2003年 | 2456篇 |
2002年 | 2184篇 |
2001年 | 1808篇 |
2000年 | 1734篇 |
1999年 | 1579篇 |
1998年 | 1403篇 |
1997年 | 1232篇 |
1996年 | 1068篇 |
1995年 | 946篇 |
1994年 | 854篇 |
1993年 | 674篇 |
1992年 | 738篇 |
1991年 | 565篇 |
1990年 | 454篇 |
1989年 | 341篇 |
1988年 | 276篇 |
1987年 | 210篇 |
1986年 | 159篇 |
1985年 | 169篇 |
1984年 | 148篇 |
1983年 | 75篇 |
1982年 | 96篇 |
1981年 | 66篇 |
1980年 | 39篇 |
1979年 | 53篇 |
1978年 | 41篇 |
1977年 | 43篇 |
1976年 | 16篇 |
1957年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Intramolecular alkene-carbonyl coupling reaction of N-benzyl-N-(o-alkenylaryl)carbamate derivative derived from o-aminostyrene, o-(aminomethyl)styrene and o-aminoallylbenzene smoothly proceeded by treating with zirconocene-butene complex to give the corresponding lactam derivative. 相似文献
952.
953.
Z. A. Starikova A. I. Yanovsky Yu. T. Struchkov S. V. Zubkov I. I. Seifullina 《Russian Chemical Bulletin》1996,45(9):2157-2162
The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template, K[Ni(C15H10N5O4)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]– anions and solvated [K+ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996. 相似文献
954.
955.
本文发现6~40号元素对能量为20keV的X_射线的质量吸收系数和质量相干散射系数之间呈二次幂函数关系,并据此提出了X_射线荧光定量分析校正基体效应的新方法——RhKa相干散射平方法.用国家标准物质GBW对该原理进行了验证.本法用于硅酸盐地质样品中微量元素的测定取得令人满意的结果. 相似文献
956.
The apparent molal volumes and compressibilities of NaCl, KCl, and CsCl in mixtures of 18-Crown-6 and water have been calculated from density and speed-of-sound measurements at 25°C. The partial molal volumes and compressibilities of the salts when all cations have formed complexes with 18-Crown-6 molecules have been evaluated. The sign and magnitude of the volume and compressibility changes of complex formation strongly suggest that the charge of the cation becomes very effectively screened by the crown ether. 相似文献
957.
The nano-ZnFe2O4/TiO2 films possess the functions of desulfurization and degradation for organic pollutants. The sols of ZnFe2O4/TiO2 were prepared by sol-gel method and coated on glass and porous ceramic by vertical coating and dipping-lift processes, respectively, and the samples were obtained after drying and sintering. The composition, appearance, absorption spectrum of the films, and the influence of the film on porous ceramic performances were analyzed using SEM, AFM, UV-Vis spectrometer, and mercury porosimeter, respectively, to determine the operation parameters of the multifunction porous ceramic elements for gas-purification. 相似文献
958.
0IntroductionCobaltcomplexeswithnonmacrocyclicchelatingligandscontainingtheamidefunctionalityhavere鄄ceivedmuchattentioninpastyears[1~3].Somestudieshaverevealedthatdeprotonatednitrogensoforganicamides,beinganionicinnature,arecapableofstabi鄄lizingthetriva… 相似文献
959.
Schiff碱双核Mn配合物的合成、结构和性能研究 总被引:3,自引:0,他引:3
Five manganese complexes of Schiff base were synthesized: [MnⅣ,Ⅳ(μ-O)(Salen)]2·DMF·H2O (1), [MnⅣ,Ⅳ(μ-O)(5-BrSalen)]2·DMF·0.5H2O (2), {MnⅣ,Ⅳ(μ-O)[Sal(1,2-pn)]}2·H2O (3), {MnⅣ,Ⅳ(μ-O)[5-Br-Sal(1,2-pn)]}2·H2O (4), {MnⅣ,Ⅳ(μ-O)[5-CH3-Sal(1,2-pn)]}2·2H2O (5), and were characterized by element analysis, IR and UV-Vis spectra. The results of cyclic voltammogram show that Schiff base ligands can drop the potential of manganese and steady high oxide state of manganese. The magnetic properties of 1 and 3 have also been studied. The results show that there is a weak ferromagnetically coupling of MnⅣ2 pair at room and low temperature, and the interactions of complex 3 are weaker than complex 1. 相似文献
960.