全文获取类型
收费全文 | 2259篇 |
免费 | 447篇 |
国内免费 | 1128篇 |
专业分类
化学 | 1873篇 |
晶体学 | 111篇 |
力学 | 248篇 |
综合类 | 71篇 |
数学 | 421篇 |
物理学 | 1110篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 97篇 |
2021年 | 91篇 |
2020年 | 87篇 |
2019年 | 68篇 |
2018年 | 79篇 |
2017年 | 120篇 |
2016年 | 88篇 |
2015年 | 115篇 |
2014年 | 163篇 |
2013年 | 218篇 |
2012年 | 194篇 |
2011年 | 230篇 |
2010年 | 195篇 |
2009年 | 237篇 |
2008年 | 224篇 |
2007年 | 220篇 |
2006年 | 224篇 |
2005年 | 205篇 |
2004年 | 147篇 |
2003年 | 98篇 |
2002年 | 125篇 |
2001年 | 111篇 |
2000年 | 110篇 |
1999年 | 53篇 |
1998年 | 32篇 |
1997年 | 27篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 21篇 |
1993年 | 32篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 2篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1971年 | 1篇 |
排序方式: 共有3834条查询结果,搜索用时 46 毫秒
991.
制造和提纯了单壁碳纳米管 (SWCNTs) ,用水溶胶体将其竖直地组装在Au薄膜表面 .用此组装技术制造了扫描隧道显微镜 (STM)的针尖 ,成功地观测到了Au晶粒的形貌像和高定向石墨 (HOPG)的原子像 .将单根SWCNT组装在W尖前端 ,置于场发射显微镜 (FEM)系统中 ,观察到了SWCNT开口端的碳原子电子发射像 .测量了站立在Au表面SWCNT的电学特性 .其电子态分布 ,有的呈现半导体特性 ,有的为金属特性 .这种组装技术可用于制造高亮度相干电子源、高分辨场发射显示器、高性能的扫描探针显微镜 (SPM)针尖和组装纳米电子器件等 . 相似文献
992.
XUE Zengquan LIU Weimin HOU Shimin SHI Zujin GU Zhennan LIU Hongwen ZHAO Xingyu ZHANG Zhaoxiang WU Mianlei PENG Lianmao WU Quande 《中国科学A辑(英文版)》2000,43(11):1182-1188
Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble
SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces.
Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented
pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold
film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties
of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel
display, tips for scanning probe microscopes, new nanoelectronic devices, etc. 相似文献
993.
对硝基苯酚丙酸酯水解反应的CTAB胶团催化作用研究 总被引:1,自引:0,他引:1
在Na2CO3-NaHCO3缓冲溶液中,测定了对硝基苯酚丙酸酯(NPP)的十六烷基三甲基溴化铵(CTAB)胶团催化反应的表观活化能和活化参数; 考察了无机盐(NaCl, NaBr, Na2SO4)对该催化反应的影响. 结果表明: 无机盐的加入,主要产生压缩CTAB胶团双电层、降低OH-离子的胶团表面浓度以及减小NPP的加溶程度的双重减速效应. 反离子浓度(或活度)愈高及水合反离子半径愈小,则减速效应愈明显. 相似文献
994.
995.
聚乙酰亚胺涂敷单晶硅表面上全氟亏酸单层膜 总被引:8,自引:1,他引:7
Ultra-thin film of perfluorodecanoic acid expected to be excellent lubricant for micro-machines was prepared successfully on single crystal silicon substrate.The film was characterized by means of X-ray photoelectron spectroscopy (XPS) and contact-angle meter.The chemical reaction involved in the preparation of the ultra-thin film was discussed as well.After being immersed in a dilute aqueous solution of polyethyleneimine (PEI) for 15 minutes and rinsed with distilled water,the silicon substrate was coated with a thin film of PEI,which was then put into a dilute solution (1× 10- 3 mol· L- 1) of perfluorodecanoic acid in hexadecane.Subsequently the steady perfluorodecanoic acid ultra-thin film was developed on PEI coating in the presence of a covalent amide bond between carboxylic group and the primary or secondary amine groups of PEI.This process was accompanied by the contact angle changes of water droplet on the Si surface (see Table 1).Moreover,the reaction between perfluorodecanoic acid and PEI was significantly influenced by N,N′ -dicyclohexylcarbodiimide (DCCD).The contact angle on the ultra-thin film of perfluorodecanoic acid is only 66.3° in the absence of DCCD in the reacting solution; it rises to 89.4° in the presence of DCCD.This indicates that the reaction between perfluorodecanoic acid and PEI was accelerated by DCCD,and the quality of perfluorodecanoic acid ultra-thin film thus improved.XPS analysis of the ultra-thin film indicates that the derivatization of PEI with perfluorodecanoic acid was accompanied by several changes.First,a large and highly symmetrical F 1s peak appeared at 688.3 eV (C- F*).Secondly,a new peak of N 1s appeared at 400.7 eV (chemical shift 1.4 eV),which was attributed to the N atom attached to the carbonyl group (O=C- N*).Thirdly,three new peaks of C 1s appeared at 286.1 eV (chemical shift 1.5 eV),288.1 eV (chemical shift 3.5 eV),and 291.0 eV (chemical shift 5.4 eV),respectively.These C 1s peaks were attributed to the C atom attached to the O=C- N group (O=C- N- C*),the carboxyl C atom (O=C*- N),and the C atom in - CF3 group (C*- F),respectively.Therefore it can be concluded that perfluorodecanoic acid has been chemically adsorbed onto the surface of PEI and perfluorodecanoic acid ultra-thin film prepared successfully. 相似文献
996.
两步法制备多孔硅及其表征II:脉冲电流法 总被引:1,自引:1,他引:0
采用脉冲阳极/阴极电流和化学氧化两步法分别在1:1的氢氟酸和乙醇溶液中及20%硝酸溶液中制备出孔径约为0.5-3μm,厚度大约为10-20μm的多孔硅样品,将获得的多孔硅结构再进一步用扫描电子显微镜和拉曼光谱仪进行表面形貌和光学性质的考察,与恒电流-化学氧化两步法制得的多孔硅相比,用脉冲电流法得到的多孔硅的孔径范围较大,且多孔层较厚,制备时加紫外光照显著提高了多孔硅的,并发生“蓝移”现象,用脉冲电流法制得的多孔硅在老化后(在干燥器放置一年)同样观察到光致发光明显增强。 相似文献
997.
Synthesis of Nanometer-sized Mesoporous Oxide Spheres 总被引:1,自引:0,他引:1
IntroductionMesoporous materials have been used as versatile catalysts, catalyst supports, host forclusters, and applied to normal phase chromatography, and they are potentially applicable for...sensor arrays, m1nlaturized electronic and magnetic device.[l--6]. More recently the meso-porous silicas with morphologies including thin films, monoliths and hexagonal prisms,toroidal, disk-like, spiral and hollow tubular shapes have been synthesized['--1'1. In addition,mesoporous silica spheres of de… 相似文献
998.
999.
The authors consider the irreducibility of the Cowen-Douglas
operator $T$. It is proved that $T$ is irreducible iff the unital $C^*$-algebra
generated by some non-zero blocks in the decomposition of $T$ with respect to
$\bigoplus^\infty_{n=0}\limits(\Ker T^{n+1}\ominus\Ker T^n)$ is
$\text{M}_n(\Bbb C).$ 相似文献
1000.