全文获取类型
收费全文 | 2133篇 |
免费 | 52篇 |
国内免费 | 17篇 |
专业分类
化学 | 1592篇 |
晶体学 | 27篇 |
力学 | 13篇 |
数学 | 231篇 |
物理学 | 339篇 |
出版年
2023年 | 12篇 |
2021年 | 14篇 |
2020年 | 26篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 35篇 |
2014年 | 45篇 |
2013年 | 106篇 |
2012年 | 90篇 |
2011年 | 120篇 |
2010年 | 69篇 |
2009年 | 69篇 |
2008年 | 128篇 |
2007年 | 143篇 |
2006年 | 109篇 |
2005年 | 125篇 |
2004年 | 131篇 |
2003年 | 124篇 |
2002年 | 107篇 |
2001年 | 54篇 |
2000年 | 52篇 |
1999年 | 36篇 |
1998年 | 26篇 |
1997年 | 30篇 |
1996年 | 26篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 21篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1975年 | 13篇 |
1974年 | 28篇 |
1973年 | 13篇 |
1972年 | 9篇 |
排序方式: 共有2202条查询结果,搜索用时 15 毫秒
61.
Fujitani T Nakamura I Kobayashi Y Takahashi A Haneda M Hamada H 《The journal of physical chemistry. B》2005,109(37):17603-17607
Adsorption and reactions of NO on clean and CO-precovered Ir(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(111) surface at saturation coverage. NO adsorbed on hollow sites dissociated to Na and Oa at temperatures above 283 K. The dissociated Na desorbed to form N2 by recombination of Na at 574 K and by a disproportionation reaction between atop-NO and Na at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated Oa and desorbed as CO2 at 574 K. 相似文献
62.
Terutaka Watanabe Takeshi Wada Masaaki Takehisa Sueo Machi 《Journal of polymer science. Part A, Polymer chemistry》1974,12(8):1619-1628
The heterogeneous polymerization of ethylene initiated by radiation in tert-butyl alcohol was studied. The polymerization was carried out in a 100-ml reactor at 25–100°C and pressures of 200–300 kg/cm2 in the presence of 50 ml of tert-butyl alcohol containing 7 wt-% water. The amounts of polymerized monomer, the average molecular weight of polymer formed, and the molecular weight distribution of polymer were measured at various stages of reaction and at various temperatures. The molecular weight distribution was found to be very much dependent on the reaction time and temperature. For the polymer formed at 50–60°C in the very early stages of reaction, the molecular weight distribution is unimodal, and in the intermediate stage a shoulder appears at a molecular weight higher than the first peak which increases as the polymerization proceeds; eventually a bimodal curve is formed. The bimodal distribution curves were analyzed to determine the fractions and average molecular weights of the each peak. On the basis of these data for the molecular weight distribution and kinetic behavior, a new scheme for the heterogeneous polymerization is proposed which indicates that the polymerization proceeds via propagating radicals in two different physical states, namely, loose and rigid states. 相似文献
63.
Summary Atomic absorption spectrometry combined with extraction is described for the determination of tri- and hexavalent chromium. The chromium diethyldithiocarbamate chelate was used for chromium (VI), whereas hydroxyquinolate or thenoyltrifluoroacetonate chelate for chromium(III). The method is rapid and precise.
Zusammenfassung Extraktion und darauffolgende Messung der Atomarabsorption wurden zur Bestimmung von drei- und sechswertigem Chrom verwendet. Die Chelatverbindung mit Diäthyldithiocarbamat wurde für Chrom(VI), der Chelatkomplex mit Hydroxychinolin oder Thenoyltrifluoraceton für Chrom(III) verwendet. Das Verfahren ist rasch und genau.相似文献
64.
Masaaki?HanedaEmail author Isao?Nakamura Tadahiro?Fujitani Hideaki?Hamada 《Catalysis Surveys from Asia》2005,9(4):207-215
Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active
site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal
model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures,
the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder
Pd/Al2O3 catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the
step sites act as the catalytic active site for NO decomposition on Pd/Al2O3. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science
study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co3O4 serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed
in which the reaction is initiated by NO adsorption onto alkali metals to form NO2− species and then NO2− species react with the adsorbed NO species to form N2 over the interface between the alkali metal and Co3O4. 相似文献
65.
[reaction: see text] Catalytic Mannich reactions of 1,1-difluoro-2-trialkyl(aryl)silyl-2-trimethylsilyloxyethenes (3) with a variety of sulfonylimines were utilized for the preparation of alpha,alpha-difluoro-beta-amino acid derivatives (7). The influence of the Lewis acid on the reaction was examined. Methods for the conversion of alpha,alpha-difluoroacylsilanes to alpha,alpha-difluorocarboxylic acids were also explored. 相似文献
66.
Keiichi Kimura Masayuki Kaneshige Hideo Tokuhisa Masaaki Yokoyama 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2809-2813
Copolymers of bis[4-(N,N-dimethylamino)phenyl]-4-vinylphenylmethanenitrile (vinyl Malachite Green leuconitrile) with methyl methacrylate or ω-methoxyoligo(oxyethylene) methacrylate have been synthesized, aiming at designing one-component-type organic polymers for photoswitchable ion-conducting films. The triphenylmethanenitrile copolymers with ω-methoxyoligo(oxyethylene) methacrylate were found to undergo ionic-conductivity switching by turning on and off UV light at ambient temperature, owing to their low glass transition temperature. © 1993 John Wiley & Sons, Inc. 相似文献
67.
Six new furostanol-type steroid saponins called trigoneosides Xa, Xb, XIb, XIIa, XIIb, and XIIIa were isolated from the seeds of Egyptian Trigonella foenum-graecum L. (Leguminosae) together with six known furostanol-type steroid saponins: trigoneosides Ia, Ib, and Va, glycoside D, trigonelloside C, and compound C. The structures of trigoneosides Xa, Xb, Xlb, XIIa, Xllb, and XIIIa were determined on the basis of chemical and physicochemical evidence as 26-O-beta-D-glucopyranosyl-(25S)-5alpha-furostane-2alpha+ ++,3beta,22xi,26-tetraol 3-O-alpha-L-rhamnopyranosyl(1-->2)-,beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-5alpha-furostane-2 alpha,beta,22xi,26tetraol 3-O-alpha-L-rhamnopyranosyl(l -->2)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-5alpha-furostane2alpha++ +,beta,22xi,26-tetraol 3-O-beta-D-xylopyranosyl(l -->4)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25S)-furost-4-ene-3beta,22xi,26- triol 3-O-Ca-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-furost-4-ene-3beta,22xi+ ++,26-triol 3-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside, and 26-O-beta-D-glucopyranosyl(25S)-furost-5-ene-3beta,22xi,26-t riol 3-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranosyl (1-->3)-beta-D-glucopyranosyl(1--4)]-beta-D-glucopyranoside, respectively. 相似文献
68.
Emission spectroscopy is applied for characterization of reactions occurring in air—acetylene flames normally used for atomic absorption spectrometry. Inter-element effects on the emissions of chromium and iron are discussed. Two atomic emission lines with different upper energies and a molecular emission line of the diatomic oxide MO are compared for determination of the excitation temperature and the degree of atomization in fuel-rich and lean flames. The reductive power of the fuel-rich flame is essential for atomization of chromium salts. Inter-element effects by iron can be attributed to the formation of refractory oxides, and to mutual catalytic oxidation. 相似文献
69.
Hayami S Hashiguchi K Juhász G Ohba M Okawa H Maeda Y Kato K Osaka K Takata M Inoue K 《Inorganic chemistry》2004,43(14):4124-4126
Cobalt(II) compounds [Co(pyterpy)Cl(2)].MeOH (1.(MeOH)) and [Co(pyterpy)Cl(2)].2H(2)O (1.(2H(2)O)) were synthesized. The compound 1.(MeOH) forms the quasi 3-D networks by making pi-pi stacking between the 1-D chains. The methanol molecules from 1.(MeOH) can be removed by heating, and substituted by absorption of water molecules. The MeOH molecules in 1.(MeOH) are removed by heating at 410 K, and they are substituted by water molecules to form 1.(2H(2)O). 1.(2H(2)O) exhibits a S = (3)/(2) (HS) left arrow over right arrow S = (1)/(2) (LS) spin transition with a thermal hysteresis. We have succeeded in constructing a guest dependent 1-D spin-crossover cobalt(II) compound. 相似文献
70.
Kiuchi M Matsumoto T Yoshikawa T Goto S Ensinger W 《Colloids and surfaces. B, Biointerfaces》2000,19(3):269-273
To investigate crystallization in the ion beam deposition process, titanium ions were deposited on silicon wafers at 105 and 55 eV. As titanium is an active metal, titanium compounds are formed by absorbing backfilled or residual gas. At energy levels of 105 or 55 eV, titanium crystallizes in a NaCl-type titanium compound with the backfilling of air. In all samples, (110)-oriented crystals grew with a rectangular lattice arrangement of titanium atoms. The open channel <110> of preferentially oriented crystal growth was parallel to the direction of incident ions normal to the substrate surface. 相似文献