全文获取类型
收费全文 | 2493篇 |
免费 | 91篇 |
国内免费 | 22篇 |
专业分类
化学 | 1835篇 |
晶体学 | 14篇 |
力学 | 86篇 |
综合类 | 1篇 |
数学 | 347篇 |
物理学 | 323篇 |
出版年
2024年 | 15篇 |
2023年 | 35篇 |
2022年 | 269篇 |
2021年 | 176篇 |
2020年 | 108篇 |
2019年 | 91篇 |
2018年 | 90篇 |
2017年 | 76篇 |
2016年 | 124篇 |
2015年 | 72篇 |
2014年 | 88篇 |
2013年 | 201篇 |
2012年 | 139篇 |
2011年 | 154篇 |
2010年 | 89篇 |
2009年 | 81篇 |
2008年 | 105篇 |
2007年 | 100篇 |
2006年 | 82篇 |
2005年 | 83篇 |
2004年 | 61篇 |
2003年 | 61篇 |
2002年 | 42篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 20篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 18篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有2606条查询结果,搜索用时 15 毫秒
21.
Mohammed Ejaz 《Mikrochimica acta》1976,65(6):643-650
Summary Radiochemical procedures have been worked out to prepare234Th(UX1) with and without carrier from uranium using N-oxide of 4-(5-nonyl)pyridine in sulphuric acid media. This reagent has also been employed in the development of a combined solvent extraction-ion exchange-spectrophotometric method for the determination of thorium in various samples.
Zusammenfassung Radiochemische Methoden zur Herstellung von234Th(UX1) aus Uran mit und ohne Träger und unter Verwendung von 4-(5-Nonyl)pyridin-N-oxid in schwefelsaurer Lösung wurden ausgearbeitet. Dieses Reagens wurde auch für die Ausarbeitung einer Thoriumbestimmung in verschiedenartigen Proben auf der Grundlage von Extraktion, Ionenaustausch und Spektro-photometrie verwendet.相似文献
22.
Kamel Guedri Tahmoor Bashir A. Abbasi Waseh Farooq Sami Ullah Khan M. Ijaz Khan Mohammed Jameel Ahmed M. Galal 《印度化学会志》2022,99(9):100614
The electroosmotic peristaltic flow of modified hybrid nanofluid in presence of entropy generation has been presented in this thermal model. The Hall impact and thermal radiation with help of nonlinear relations has also been used to modify the analysis. The assumed flow is considered due to a non-uniform trapped channel. The properties of modified hybrid nanofluid model are focused with interaction of three distinct types of nanoparticles namely copper (, silver () and aluminum oxide ( The mathematical modeling and significances of entropy generation and Bejan number are identified. With certain flow assumptions, the governing equations are attained for optimized peristaltic electroosmotic problem. Widely used assumptions of long wave length and low Reynolds number reduced the governing equations in ordinary differential equations. The ND solver is flowed for the solution process. The physical significant of results is observed by assigning the numerical values to parameters. 相似文献
23.
Saify ZS Mushtaq N Khan KM Perveen S Shah ST Abdel-Jalil RJ Fecker M Voelter W 《Chemical & pharmaceutical bulletin》2005,53(1):64-66
A new series of 4-(4'-chlorophenyl)-4-hydroxypiperidine derivatives (2-5), substituted at nitrogen, were synthesized and tested as potential analgesic compounds as well as evaluated for their effect on hypotensive activity. Results showed that all the derivatives exhibit significant analgesic activity in male Wistar rats at a dose of 50 mg/kg of body weight after intramuscular injection, when tested by thermal stimuli (tail flick test). Pethidine was used as reference drug. Compounds 2, 3 and 5 produced reduction in blood pressure in normotensive rat. 相似文献
24.
A. M. El-Kot S. Abd El Haleem S. Mohammed 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):965-975
Summary The potentiodynamic polarization of the iron electrode in sulphuric acid solutions was studied. The formation of a passivating film on the electrode upon anodic oxidation in sulphuric acid solution depends on the concentration of the acid. Addition of Cl– ions to sulphuric acid solutions raises the current densities along both the active and passive regions. The difference between the dissolution current in halogen-containing media and solutions devoid of these ions, i. e., the enhancing effect of Cl– ions, i, varies with the aggressive ions concentration according to log i=a
5+b
5 logC
agg. Organic carboxylates enhance the active dissolution of iron through their participation in the dissolution mechanism, while they inhibit pitting corrosion through competitive adsorption with Cl– ions for adsorption sites on the metal surface.
Elektrochemische Polarisation und Passivierung von Eisen in sauren Lösungen
Zusammenfassung Es wurde die potentiodynamische Polarisierung der Eisenelektrode in schwefelsauren Lösungen untersucht. Die Ausbildung eines passivierenden Films auf der Eisenelektrode nach der anodischen Oxidation hängt von der Säurekonzentration ab. Zugabe von Cl–-Ionen zur Schwefelsäurelösung erhöht die Stromdichten sowohl in den aktiven als auch den passiven Bereichen. Der entsprechende Lösungsstrom mit bzw. ohne diese Ionen, also der verstärkende Effekt der Cl–-Ionen variiert mit der Konzentration der aggressiven Ionen: log i=a 5+b 5 logc agg. Organische Carboxylate verstärken die aktive Lösung von Eisen durch ihre Teilnahme am Lösungsmechanismus, andererseits inhibieren sie Narben-Korrosion, da sie mit den Cl–-Ionen bezüglich möglicher Adsorptionsstellen an der Metalloberfläche konkurrieren.相似文献
25.
26.
The new unsymmetrical N‐bridgehead, apo (zeromethine), mono‐methine, dimethine, meso substituted tetramethine and styryl cyanine dyes incorporating pyrazolo (4,5‐b) indolizine (benzoindolizine) nuclei were prepared. Structural confirmation was carried out by elemental analyses, IR, H‐NMR, mass spectra and 13C‐NMR with the aid of carbon DEPT spectral data. The visible absorption spectra for the newly synthesized cyanines were examined in 95% ethanol. 相似文献
27.
Mohammed A. Suliman Mohammed A. Gondal Mohamed A. Dastageer Gaik‐Khuan Chuah Chanbasha Basheer 《Photochemistry and photobiology》2019,95(6):1485-1494
An efficient method of photocatalytic degradation of methylparaben in water using Ag nanoparticles (NPs) loaded AgBr‐mesoporous‐WO3 composite photocatalyst (Ag/AgBr@m‐WO3), under visible light is presented. In this process, quantification of methylparaben in water was carried out by high‐performance liquid chromatography (HPLC) and the HPLC results showed a significant reduction of methylparaben in water due to the enhanced of photocatalytic degradation efficiency of Ag/AgBr@m‐WO3. For the material synthesis, highly ordered mesoporous‐WO3 (m‐WO3) was initially synthesized by sol–gel method and AgBr nanoparticles (NPs) were subsequently introduced in the pores of m‐WO3, and finally, the Ag nanoparticles were introduced by light irradiation. The enhanced photocatalytic degradation of methylparaben in water is attributed to the formation of surface plasmonic resonance (SPR) due to the introduction of Ag NPs on the surface of the catalyst. Also, the formation of heterojunction between AgBr and mesoporous‐WO3 in Ag/AgBr@m‐WO3 significantly inhibited the recombination of light‐induced electron‐hole pairs in the semiconductor composite. The morphological and optical characterizations of the synthesized photocatalysts (Ag/AgBr@m‐WO3) were carried out using SEM, TEM, XDR, N2 adsorption–desorption, UV‐VIS diffuse reflectance spectroscopy (DRS). Also, the photocatalytic studies using radical scavengers were carried out and the results indicated that is the main reactive species. 相似文献
28.
Subhi A. Al-Jibori Afra S. S. Al-Zaubai Modher Y. Mohammed Talal A. K. Al-Allaf 《Transition Metal Chemistry》2007,32(3):281-286
Palladium(II) and platinum(II) complexes containing the mixed ligands tertiary diphosphines Ph2P(CH2)
n
PPh2, (n = 1–4) and benz-1,3-imidazoline-2-thione, benz-1,3-oxazoline-2-thione or benz-1,3-thiazoline-2-thione have been prepared
and characterized by elemental analysis, magnetic susceptibility, molar conductance and i.r. spectral data. 31P–{1H}-n.m.r. data have been applied to characterize the produced linkage isomers. 相似文献
29.
Mohammed R. Arshadi 《Journal of mass spectrometry : JMS》1978,13(7):379-381
The 70 eV positive and negative ion mass spectra of the oxygen, sulphur and selenium 2,1,3-benzodiazoles have been studied. The influence of hetero atom on the fragmentation modes of the benzodiazole molecular ions has been discussed. 相似文献
30.
Fettouhi M Ouahab L Boukhari A Cador O Mathonière C Kahn O 《Inorganic chemistry》1996,35(17):4932-4937
The goal of this work was to synthesize new molecular bricks which could be used as precursors of heterobimetallic low-dimensional compounds. Along this line, four compounds have been synthesized and structurally characterized, namely (NBu(4))(2)[Ni(Cl(2)opba)] (1), (NBu(4))(2)[Cu(Cl(2)opba)] (2), (NBu(4))(5)[Mn(Cl(2)opba)(DMSO)(2)](4) (3), and Cu(en)(2)[Mn(Cl(2)opba)(H(2)O)(2)](2).2DMSO (4), with Cl(2)opba = (4,5-dichloro-o-phenylene)bis(oxamato), NBu(4) = tetra-n-butylammonium, en = ethylenediamine, and DMSO = dimethyl sulfoxide. Compounds 1 and 2 are isostructural; they crystallize in the monoclinic system, space group C2/c, Z = 4, with a = 18.708(2) ?, b = 17.525(2) ?, c = 14.763(9) ?, and beta = 92.03(4) degrees for 1 and a = 18.928(2) ?, b = 17.634(2) ?, c = 14.704(9) ?, and beta = 92.38(3) degrees for 2. 3 crystallizes in the tetragonal system, space group P&fourmacr;2(1)c, Z = 2, with a = 26.295(10) ? and c = 12.342(7) ?. The structure shows a random occupation of the metal site by Mn(III) and Mn(II) ions in 3/4 and 1/4 ratios, respectively. 4 crystallizes in the triclinic system, space group P&onemacr;, Z = 1, with a = 7.066(7) ?, b = 11.844(1) ?, c = 14.292(5) ?, alpha = 105.64(2) degrees, beta = 97.67(5) degrees, and gamma = 102.13(3) degrees. The structure consists of Mn(III)Cu(II)Mn(III) trinuclear species, with Cu-O-Mn bridges involving oxygen atoms of the oxamato groups already linked to the metal atom. The magnetic properties of compounds 1-4 have been investigated and quantitatively interpreted. For 3, this magnetic investigation has been performed on a single crystal, which allows us to determine unambiguously the sign of the axial zero-field splitting parameter for the Mn(III) ion. The potentialities of these new molecular bricks have been discussed. 相似文献