全文获取类型
收费全文 | 301篇 |
免费 | 30篇 |
国内免费 | 23篇 |
专业分类
化学 | 244篇 |
力学 | 8篇 |
综合类 | 1篇 |
数学 | 28篇 |
物理学 | 73篇 |
出版年
2024年 | 1篇 |
2023年 | 22篇 |
2022年 | 36篇 |
2021年 | 41篇 |
2020年 | 40篇 |
2019年 | 37篇 |
2018年 | 26篇 |
2017年 | 25篇 |
2016年 | 17篇 |
2015年 | 18篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有354条查询结果,搜索用时 11 毫秒
261.
S.C.?Lyu H.W.?Kim S.J.?Kim J.W.?Park C.J.?LeeEmail author 《Applied Physics A: Materials Science & Processing》2004,79(3):697-700
We have studied the effect of temperature on the growth and crystallinity of carbon nanotubes (CNTs), synthesized by a vapor-phase growth method using a catalytic reaction of iron pentacarbonyl (Fe(CO)5) and acetylene (C2H2) gas. By increasing the growth temperature from 750 °C to 950 °C, both the growth rate and the diameter of the CNTs increase. Moreover, the crystallinity of the graphite sheets improves progressively with increasing growth temperature. Adjustment of the growth temperature gives potential for controlled growth of CNTs in a large-scale synthesis of CNTs. PACS 61.46.+w; 68.37.-d; 81.07.De 相似文献
262.
Suping Lyu Xiaoguang Zhu Zongneng Qi 《Journal of Polymer Science.Polymer Physics》1994,32(13):2151-2154
A microcrack-shear band chain model for the fracture of ductile materials is proposed. The fractal dimension (D) of the fracture surfaces is derived and correlated with the fracture toughness (KIc) of ductile materials. The fractal dimension of the fracture surface is predicted to have an inverse trend with the fracture toughness. The theoretical results are consistent with the experimental results of some polymers and metals. © 1994 John Wiley & Sons, Inc. 相似文献
263.
H. M. Kim K. Kim S. J. Lee J. Joo H. S. Yoon S. J. Cho S. C. Lyu C. J. Lee 《Current Applied Physics》2004,4(6):577-580
We report charge transport properties such as d.c. conductivity (σDC) and its temperature dependence for composites of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs). The MWCNTs were synthesized through chemical vapor deposition with Fe or Co as catalyst. The MWCNTs were homogeneously dispersed in PMMA matrix through sonication to prepare MWCNT–PMMA composite films. We controlled mass concentration of MWCNTs in the composites, and the thickness of MWCNT–PMMA composite films was 20–400 μm. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy were used to study structure and homogeneity of the composites. The σDC at room temperature of MWCNT–PMMA composites increased as mass concentration of MWCNTs increased, which followed percolation theory. Electromagnetic interference (EMI) shielding efficiency (SE) of MWCNT–PMMA composites was measured in the frequency range of 50 MHz–3.5 GHz. We observed the increase of EMI SE of MWCNT–PMMA composites with increasing the concentration of MWCNTs. 相似文献
264.
Sh. T. Lyu I. D. Troshkina E. G. Rakov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(11):2275-2279
Magnetic composites based on graphene oxides and functionalized carbon nanotubes containing magnetite nanoparticles are synthesized. The dispersing ability of these composites in water at different pH values is studied. It is shown that the solubility of Fe3O4 composites is constant in the рН range of 3.5–10, though these composites are unstable at both lower and higher pH values. Magnetic sorbents for extracting Се(NO3)3 and La(NO3)3 from solutions are tested. Dependences of the volume on the sorbent’s composition, pH value, and salt concentration in the solution are found. Maximum sorption capacity in relation to Се3+ and La3+ at рН 7.5 and 8.5 are found to be 1040 and 920 mg/g respectively. 相似文献
265.
Sh. T. Lyu E. G. Rakov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(10):2011-2015
The ion-exchange sorption of La(III) and Ce(III) from nitrate solutions using oxidized carbon nanotubes with a solubility of 4.2 g/L is studied at metal concentration С = 5–160 mg/L, рН 2.5–6.0, ratio S: L = 0.002–0.06, and room temperature. At С = 35 mg/L, the equilibrium capacity is shown to grow dramatically with рН rising from 3.0 to 4.0–4.5 and reaching 840 mg/g in La and 950 mg/g in Се when S: L < 0.006 and рН > 4.0–4.5. The introduction of ionic salts is found to reduce the capacity (at рН > 4 and concentrations of 0.01 М and 0.1 М NaCl, the Се capacity is reduced to ~500 and ~200 mg/g). It is concluded that the sorption equilibrium is better described by the Langmuir equation, while the process kinetics, by pseudo-first and pseudo-second order equations. 相似文献
266.
豆纹动脉是大脑内部的重要动脉,其阻塞往往会导致腔隙性脑梗死.现在在临床上主要利用数字减影血管造影(Digital Subtraction Angiography,DSA)技术实现豆纹动脉成像,然而DSA的有创性是其重要的限制因素.有研究表明,在高场磁共振系统(7 T)下,时间飞跃法(Time-Of-Flight,TOF)已经能够得到较好的豆纹动脉影像,但是在临床使用的1.5 T或3 T磁共振系统下,由于豆纹动脉的管腔直径非常小(大约为0.3~0.7 mm)、血流速度比较慢,对其成像仍然是个挑战.该文主要研究了在3 T磁共振系统下使用流动敏感黑血(Flow-Sensitive Black-Blood,FSBB)序列对豆纹动脉进行成像的方法,并对该成像序列中流动敏感梯度的设计进行了优化,使其在扫描时间和图像分辨率、对比度、信噪比等方面都能够基本满足临床使用的要求. 相似文献
267.
(1R,2R)-N1-2-amyl-1,2-diaminocyclohexane, which has an amyl substituent as compared with 1,2-diaminocyclohexane, was used as the carrier group to construct three platinum(II) complexes. MTT assay revealed that the complexes showed decent cytotoxicity against all of the four tested tumor cell lines with the IC50 values ranging from 1.08 to 253.36 μM. Particularly, the IC50 values of 2 against A549 and HCT-116 reached 3.32 and 1.08 μM, respectively, which were much lower than those of cisplatin and oxaliplatin. Flow cytometry demonstrated that 2 inhibited HepG2 cells proliferation and caused cytotoxicity by inducing apoptosis and arresting cells in the G2 phase. Furthermore, agarose gel electrophoresis showed that 2 had the ability to interact with DNA in a manner different from cisplatin and oxaliplatin, indicating the carrier ligand with an alkyl moiety had an influence on the action mode of the complex. 相似文献
268.
Ir‐catalyzed cascade dehydrogenative CH/BH and BH/OH cross‐coupling of carboranyl carboxylic acid with readily available benzoic acid has been achieved, leading to the facile synthesis of previously unavailable carborano‐coumarin in a simple one‐pot process. Two cage B—H, one aryl C—H and one O—H bonds are activated to construct efficiently new B—C and B—O bonds. The cascade cyclization can stop at the first B—H/C—H cross‐coupling step by tuning the reaction conditions, resulting in a series of α‐carboranyl benzoic acid and aryl carborane derivatives. Control experiments indicate that B—H/C—H dehydrocoupling proceeds preferentially over B—H/O—H dehydrocoupling, and both directing groups and oxidants are crucial for this reaction. An iridium(V) intermediate is proposed to be involved in the catalytic cycle. 相似文献
269.
Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes. Extensive theoretical and experimental research, together with continuous development of nanotechnology, has significantly broadened the scope of SERS and made it a hot research field in chemistry, physics, materials, biomedicine, and so on. However, SERS has not been developed into a routine analytical technique, and continuous efforts have been made to address the problems preventing its real-world application. The present minireview focuses on analyzing current and potential strategies to tackle problems and realize the SERS performance necessary for translation to practical applications.Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes. 相似文献
270.
A. M. Turuta A. V. Kamernitskii Lyu Dyk Hu T. M. Fadeeva 《Russian Chemical Bulletin》1991,40(5):1059-1063
The HBF4·Et2O-catalyzed methanolysis reactions of the 16, 17-oxides of 17-ethy-nylandrost-4-en-3-one and its dicobalt hexacarbonyl complex were studied. It was shown that these reactions proceed with the same regiodirectivity of the oxide ring opening at the tertiary center but with a different mode of stabilization of the intermediates formed. The reaction of the free oxide proceeds without the inclusion of the external nucleophile and is concluded by the Wagner-Meerwein rearrangement; the C17-carbocation formed in the Co-coordinated oxide is stabilized by the addition of the methoxide ion and the elimination of a proton or of water. The opening of the oxide ring of dicobalt tetracarbonyl 16, 17-epoxy-17-ethynylandrost-4-en-3-one can be realized with decomplexation accompanied by carbonylation and heterocyclization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp.1180–1184, May, 1991. 相似文献