全文获取类型
收费全文 | 606967篇 |
免费 | 30234篇 |
国内免费 | 18695篇 |
专业分类
化学 | 333909篇 |
晶体学 | 8673篇 |
力学 | 28897篇 |
综合类 | 38篇 |
数学 | 73184篇 |
物理学 | 211195篇 |
出版年
2021年 | 4956篇 |
2020年 | 5723篇 |
2019年 | 6617篇 |
2018年 | 7943篇 |
2017年 | 8472篇 |
2016年 | 12403篇 |
2015年 | 9121篇 |
2014年 | 12278篇 |
2013年 | 29399篇 |
2012年 | 23538篇 |
2011年 | 29411篇 |
2010年 | 23815篇 |
2009年 | 23820篇 |
2008年 | 25242篇 |
2007年 | 24709篇 |
2006年 | 23041篇 |
2005年 | 21339篇 |
2004年 | 20767篇 |
2003年 | 17910篇 |
2002年 | 17541篇 |
2001年 | 19554篇 |
2000年 | 14752篇 |
1999年 | 12139篇 |
1998年 | 9996篇 |
1997年 | 9617篇 |
1996年 | 9711篇 |
1995年 | 9139篇 |
1994年 | 9067篇 |
1993年 | 8896篇 |
1992年 | 9256篇 |
1991年 | 9054篇 |
1990年 | 8371篇 |
1989年 | 8316篇 |
1988年 | 8278篇 |
1987年 | 7560篇 |
1986年 | 7240篇 |
1985年 | 9094篇 |
1984年 | 9332篇 |
1983年 | 7203篇 |
1982年 | 7789篇 |
1981年 | 7574篇 |
1980年 | 7121篇 |
1979年 | 7362篇 |
1978年 | 7519篇 |
1977年 | 7462篇 |
1976年 | 7686篇 |
1975年 | 6695篇 |
1974年 | 6617篇 |
1973年 | 6824篇 |
1972年 | 4743篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
992.
使用结构简单的单温炉设备,通过三步升温热解二茂铁、三聚氰氨混合物方法,在二氧化硅、多晶陶瓷基底上分别合成了碳纳米管阵列、碳纳米管捆束.使用扫描电子显微镜、透射电子显微镜、电子能量损失谱和x射线光电子能谱对合成样品进行了结构和成分分析.结果显示:两种基底上合成的纳米管均为多壁纯碳管;生长于光滑二氧化硅表面的碳纳米管具有高度取向性和一致的外径,长度为10—40μm.碳纳米管采取催化剂顶端生长模式并展示出类杯状形貌;生长于粗糙多晶陶瓷表面的碳纳米管捆束随机取向,碳纳米管直径为15—80nm,长度在几百微米,展示
关键词:
碳纳米管
热解法
三步升温工艺 相似文献
993.
E. Rebollar M. Oujja M. Castillejo S. Georgiou 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1357-1360
Optical emission and laser-induced fluorescence spectroscopies (OES and LIF) are employed to examine the plume ejected into vacuum upon UV pulsed laser ablation (248 nm, 20 ns, and 266 nm, 5 ns) of poly(methyl methacrylate) PMMA films doped with photostable compounds naphthalene (NapH) and phenanthrene (PhenH), and their photolabile iodide derivatives iodonaphthalene (NapI) and iodophenanthrene (PhenI). Spontaneous emissions observed in the irradiation of NapI and PhenI sensitised films can be assigned to excited products resulting from photodissociation of the dopants and to excited C2, CH, and CN radicals. The presence in the plume of ground state products is revealed by LIF upon excitation at 266 nm. Measurements of the dependence of the spontaneous and LIF emissions on distance to the surface, ablation fluence, and flight velocities of species are discussed with reference to the mechanistic implications derived from the measurements. PACS 52.38.Mf; 61.82.Pv; 82.50 相似文献
994.
Vytautas Getautis Maryte Daskeviciene Tadas Malinauskas Vygintas Jankauskas 《Monatshefte für Chemie / Chemical Monthly》2007,28(5):277-283
Synthesis of a new monomer and polymer containing both ferrocene and hydrazone moieties are reported. The obtained materials
were examined by various techniques including differential scanning calorimetry, UV, IR, NMR spectroscopy, and time of flight
method. These materials may be of particular interest for the development of future electrophotographic photoreceptors as
electron photoemission spectra of the layers showed ionization potentials of 5.35–5.41 eV. The hole drift mobility values
in compositions of the designed structures with bisphenol Z polycarbonate exceeded 10−8 cm2/Vs at strong electric fields. 相似文献
995.
Azizollah Habibi Leyla Mousavifar Issa Yavari Mohammad R. Yazdanbakhsh 《Monatshefte für Chemie / Chemical Monthly》2007,4(8):603-606
Alkyl isocyanides undergo a smooth reaction with alkylidene Meldrum’s acids in the presence of arylhydroxylamines to produce N
1-alkyl-2-(3,5-dioxo-2-aryltetrahydro-4-isoxazolyl)alkanamides in high yields. 相似文献
996.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
997.
N. Wright und W. C. Lee 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):39-40
Ohne Zusammenfassung 相似文献
998.
W. A. Simpson und J. C. Olsen 《Fresenius' Journal of Analytical Chemistry》1940,119(5-6):231-233
Ohne Zusammenfassung 相似文献
999.
C. Foces‐Foces M. Lpez‐Rodríguez C. Prez 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(2):o95-o97
The title compound, C12H21NO3, crystallizes in two polymorphic forms, viz. the tetragonal form described here and the monoclinic form described previously [Foces‐Foces, López‐Rodríguez, Pérez, Martín & Pérez‐Hernández (2007). Cryst. Growth Des. 7 , 905–911]. The differences in the conformations of the hydroxymethyl and methylaminocarbonyl substituents have important consequences in the hydrogen‐bond interaction motifs and, therefore, in the packing arrangements. These forms are concomitant polymorphs with melting points differing by 3 K. 相似文献
1000.
Gujie Qian S. Baccaro M. Falconieri Jiafang Bei A. Cecilia Guorong Chen 《Journal of Non》2008,354(40-41):4626-4629
Glasses in SiO2–ZnO–BaO system with the different ZnO/BaO ratio were studied. In some cases, BaF2 was introduced to substitute for BaO on the equal base. Photoluminescent spectra showed that ZnO in glass matrices behaved somewhat differently from ZnO crystals. Especially, the introduction of fluorine ions led to dramatic shift of UV emission band of glasses closer to that of ZnO crystals. Raman spectral analysis provided consistent results. In particular, Raman bands in the high frequency region are sensitive to effects of different ZnO/BaO or BaF2/BaO ratio on structure of glasses. 相似文献