全文获取类型
收费全文 | 2287篇 |
免费 | 450篇 |
国内免费 | 1130篇 |
专业分类
化学 | 1891篇 |
晶体学 | 111篇 |
力学 | 253篇 |
综合类 | 71篇 |
数学 | 421篇 |
物理学 | 1120篇 |
出版年
2024年 | 1篇 |
2023年 | 22篇 |
2022年 | 97篇 |
2021年 | 91篇 |
2020年 | 88篇 |
2019年 | 70篇 |
2018年 | 81篇 |
2017年 | 120篇 |
2016年 | 90篇 |
2015年 | 119篇 |
2014年 | 166篇 |
2013年 | 221篇 |
2012年 | 195篇 |
2011年 | 230篇 |
2010年 | 195篇 |
2009年 | 239篇 |
2008年 | 224篇 |
2007年 | 223篇 |
2006年 | 225篇 |
2005年 | 208篇 |
2004年 | 149篇 |
2003年 | 98篇 |
2002年 | 125篇 |
2001年 | 111篇 |
2000年 | 110篇 |
1999年 | 54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 | 26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3867条查询结果,搜索用时 31 毫秒
991.
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
992.
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
993.
994.
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
995.
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
996.
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
997.
998.
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
999.
1000.
用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。 相似文献