全文获取类型
收费全文 | 30036篇 |
免费 | 3742篇 |
国内免费 | 2836篇 |
专业分类
化学 | 14498篇 |
晶体学 | 208篇 |
力学 | 1526篇 |
综合类 | 196篇 |
数学 | 2320篇 |
物理学 | 7993篇 |
综合类 | 9873篇 |
出版年
2024年 | 145篇 |
2023年 | 530篇 |
2022年 | 860篇 |
2021年 | 1013篇 |
2020年 | 959篇 |
2019年 | 864篇 |
2018年 | 763篇 |
2017年 | 695篇 |
2016年 | 1082篇 |
2015年 | 1226篇 |
2014年 | 1454篇 |
2013年 | 1798篇 |
2012年 | 2062篇 |
2011年 | 2292篇 |
2010年 | 1569篇 |
2009年 | 1534篇 |
2008年 | 1604篇 |
2007年 | 1606篇 |
2006年 | 1464篇 |
2005年 | 1379篇 |
2004年 | 1118篇 |
2003年 | 832篇 |
2002年 | 826篇 |
2001年 | 779篇 |
2000年 | 718篇 |
1999年 | 887篇 |
1998年 | 809篇 |
1997年 | 783篇 |
1996年 | 739篇 |
1995年 | 637篇 |
1994年 | 592篇 |
1993年 | 490篇 |
1992年 | 510篇 |
1991年 | 415篇 |
1990年 | 388篇 |
1989年 | 333篇 |
1988年 | 227篇 |
1987年 | 195篇 |
1986年 | 133篇 |
1985年 | 84篇 |
1984年 | 43篇 |
1983年 | 44篇 |
1982年 | 37篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
Research on Chemical Intermediates - Defective TiO2 nanocrystals (D-TiO2) were synthesized by a simple, mild and green sol–gel hydrothermal method. The as-prepared sample possesses a high... 相似文献
992.
Long Chen Hanrui Zhang Shengnan Liu Chenghua Sun Xiujie Hu Shuyun Zhou 《Surface and interface analysis : SIA》2020,52(7):389-395
Designed growth of zinc oxide (ZnO)/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell hybrid nanotube arrays has been achieved by electropolymerization technique. The ZnO/PEDOT hybrid nanotubes electropolymerized for 2000-second display enhanced electrochromic properties of the contrast ratio up to 31.3%, a lot higher than those of the pure PEDOT and ZnO/PEDOT hybrid nanorods. Moreover, the coloring efficiency of the hybrid nanotubes increases from 105.2 cm2 C−1 of ZnO/PEDOT hybrid nantotube with the electrodeposition time of 1000 seconds to 122.2 cm2 C−1 of 2000 seconds at 520 nm. Therefore, the hybrid composite nanotubes fabricated by the in situ electrodeposition techniques may demonstrate huge potential applications in energy-saving technologies such as smart windows. 相似文献
993.
Chao Hu Tao Wang Matthias Rudolph Thomas Oeser Abdullah M. Asiri A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2020,59(22):8522-8526
A novel gold‐catalyzed cycloisomerization of 1,6‐diynes was achieved, providing an atom‐economic approach to a diverse set of bicyclo[2.2.1]hept‐5‐en‐2‐ones in moderate to good yields. With unsymmetrical starting materials with two different internal alkynyl substituents, to some extent, the regioselectivity could be controlled by both electronic and steric factors. This unprecedented reactivity pattern may inspire new and unconventional strategies for the preparation of bridged ring systems. 相似文献
994.
Li Gaoliang He Hui Zheng Weifang Tang Hongbin Li Huirong Lan Tian Liu Xiechun Zhang Hu Yang He Luo Fangxiang Xiao Songtao Ye Guoan 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):279-284
Oxidation of Pu(III) in 1 bp solution to Pu(IV) was studied using the salt-free oxidant N2O4. It was proved that the reductants N,N-dimethylhydroxylamine (DMHAN) and monomethyl-hydrazine (MMH) present in 1 bp solution of CIAE-APOR process can be oxidized and removed from the solutions also by N2O4 before the oxidation of Pu(III). The effects of the acidity, the temperature and the amount of N2O4 added on the oxidation of DMHAN and MMH were studied. 相似文献
995.
A new mono-nuclear Mn(Ⅱ) complex [Mn(MPT)2(NCS)(HOCH3)]ClO4(MPT = 2-methoxyl-1,10-phenanthroline) has been synthesized with 2-methoxyl-1,10-phenanthroline and thiocyanate anion as ligands,and its crystal structure was determined by X-ray crystallography.The crystal data:monoclinic system,space group P21/c with a = 12.8849(17),b = 15.684(2),c = 14.2703(19) ,β = 92.126(2)°,V = 2881.9(7) 3,Z = 4,C28H24ClMnN5O7S,Mr = 664.97,Dc = 1.533 g/cm3,F(000) = 1364 and μ = 0.679 mm-1.In the crystal,MPT functions as a bidentate ligand and Mn(Ⅱ) ion assumes a distorted octahedral geometry.In the crystal there are two types of π-π stacking interactions among the adjacent complexes,which involves 1,10-phenanthroline rings.The theoretical calculations reveal that the two types of π-π stacking resulted in a weak anti-ferromagnetic coupling with 2J =-14.68 cm-1 and a weak ferromagnetic coupling with 2J = 0.70 cm-1,respectively.The theoretical calculations also reveal that there are both spin polarization and spin delocalization in the two π-π stacking systems,and the magnetic coupling signs are unable to explain with McConnell I spin-polarization mechanism. 相似文献
996.
997.
The UV‐cured organic‐inorganic hybrid nanocomposite (nano‐Si‐m‐PI) was prepared through the photopolymerization of acrylic resin initiated by ethoxysilane‐modified multifunctional oligomeric photoinitiator (Si‐m‐PI). The esterification reaction of 2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone (Irgacure 2959) with thioglycolic acid, and the following addition reactions with dipentaerythritol hexaacrylate and then 3‐aminopropyltriethoxysilane were carried out for preparing the Si‐m‐PI. The Si‐m‐PI exhibits the similar UV absorption and molar extinction coefficient with Irgacure 2959. The photoinitiating activity study by photo‐DSC analysis showed that the Si‐m‐PI possesses high photopolymerization rate at the peak maximum (Rpmax) and final unsaturation conversion (Pf) in the cured hybrid films. From the scanning electron microscope (SEM) observation, the SiO2 nanoparticles dispersed uniformly in the formed nano‐Si‐m‐PI, whereas the aggregation of nanoparticals occurred in nano‐Irg, which was prepared through the photopolymerization of acrylic resin initiated by Irgacure 2959. Moreover, compared with the UV‐cured pure polymer and nano‐Irg, the nano‐Si‐m‐PI showed remarkably enhanced thermal stability and mechanical properties. 相似文献
998.
999.
1000.
脱铝丝光沸石的制备和结构特征 总被引:1,自引:0,他引:1
用高温水蒸气结合酸洗的方法制备了SiO_2/Al_2O_3为16~186的脱铝丝光沸石。用X光衍射和红外光谱法研究了它们的结构持征。随丝光沸石脱铝,晶格参数呈非线性和各向不同步收缩。由于α方向发生明显收缩,使椭园形主孔道的长轴方向缩小。其骨架振动频率自600~1300cm~(-1)随着脱铝明显向高频方向漂移。当Al/u.c.自4脱至3时,丝光沸石的结构特征发生了明显的变化,可能与骨架上2位铝的脱除有关。当Al/u.c.≤3时,有新的Si—O—Si骨架生成,同时晶体重排为均匀有序的结构。 相似文献