全文获取类型
收费全文 | 3976篇 |
免费 | 53篇 |
国内免费 | 138篇 |
专业分类
化学 | 2820篇 |
晶体学 | 2篇 |
力学 | 58篇 |
综合类 | 27篇 |
数学 | 501篇 |
物理学 | 759篇 |
出版年
2024年 | 3篇 |
2023年 | 154篇 |
2022年 | 226篇 |
2021年 | 239篇 |
2020年 | 294篇 |
2019年 | 238篇 |
2018年 | 184篇 |
2017年 | 193篇 |
2016年 | 231篇 |
2015年 | 192篇 |
2014年 | 171篇 |
2013年 | 161篇 |
2012年 | 196篇 |
2011年 | 192篇 |
2010年 | 130篇 |
2009年 | 137篇 |
2008年 | 134篇 |
2007年 | 194篇 |
2006年 | 140篇 |
2005年 | 136篇 |
2004年 | 130篇 |
2003年 | 78篇 |
2002年 | 83篇 |
2001年 | 59篇 |
2000年 | 37篇 |
1999年 | 43篇 |
1998年 | 39篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 16篇 |
1994年 | 16篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 31篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 11篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有4167条查询结果,搜索用时 31 毫秒
961.
D. Ranchet J. B. Tommasino O. Vittori P. L. Fabre 《Journal of solution chemistry》1998,27(11):979-991
Electrochemical reduction of FeIIILCl where L is a Schiff base has been investigated in various aprotic solvents. From a plot of the half wave potential E
1/2 for the reduction of these complexes vs. E
1/2 for the oxidation of ferrocene, the solvent–solute interactions were studied: the E
1/2 variation is found to be a function of Lewis-type acceptor–donor interactions. The diffusion coefficients D in the different solvents were also been determined by linear sweep voltammetry. The variation of D is discussed in terms of viscosity and dielectric constant. 相似文献
962.
Sandeep Ghumaan Biprajit Sarkar Mahendra P. Patil Jan Fiedler Raghavan B. Sunoj Wolfgang Kaim Goutam Kumar Lahiri 《Polyhedron》2007
The complexes (μ3-L1/L2)[Ru(acac)2]3, acac− = 2,4-pentanedionato, L1 = 2,3,8,9,14,15-hexachlorodiquinoxalino[2,3-a:2′,3′-c]phenazine and L2 = 2,3,8,9,14,15- hexamethyldiquinoxalino[2,3-a:2′,3′-c]phenazine, undergo stepwise one-electron oxidation involving a total of three electrons and stepwise one-electron reduction with three (L2) or four electrons (L1). All reversibly accessible states were characterized by UV–Vis–NIR spectroelectrochemistry. Oxidation leads to mixed-valent intermediates {(μ3-L)[Ru(acac)2]3}+ and {(μ3-L)[Ru(acac)2]3}2+ of which the RuIIIRuIIRuII combinations exhibit higher comproportionation constants Kc than the RuIIIRuIIIRuII states – in contrast to a previous report for the unsubstituted parent systems {(μ3-L3)[Ru(acac)2]3}+/2+, L3 = diquinoxalino[2,3-a:2′,3′-c]phenazine. No conspicuous inter-valence charge transfer absorptions were observed for the mixed-valent intermediates in the visible to near-infrared regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic ruthenium(III) type signals for the former. Electron addition produces ruthenium(II) complexes of the reduced forms of the ligands L, a high resolution EPR spectrum with 14N and 35,37Cl hyperfine coupling and negligible g anisotropy was found for {(μ3-L1)[Ru(acac)2]3}−. DFT calculations of (μ3-L1)[Ru(acac)2]3 confirm several ligand-centered low-lying unoccupied MOs for reduction and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions. 相似文献
963.
According to the latest requirements of engineering education professional certification of chemical engineering and technology specialty on organic chemistry laboratory, current situation and problems of organic chemistry laboratory in Jianghan University are discussed from the perspective of teaching mode, teaching content, teachers and students. This paper has explored the blended teaching mode combining the online teaching with the traditional teaching. This teaching mode is successfully applied to the course of organic chemistry laboratory. It has been proved that this teaching mode improved the teaching quality, enhanced the classroom efficiency, achieved the teaching objectives, as well as met the requirements in the engineering education professional certification. 相似文献
964.
We are reporting on the hydroxyalkyl appended arene ruthenium half sandwich complexes [{η6‐C6H5(CH2)nOH}RuCl2] (n = 2, 3) and the methyl ether of the hydroxypropyl derivative. Most significantly, a structural comparison between the hydroxypropyl complex 1a and its methyl ether 2a reveals, that the latter adopts the conventional dichloro bridged dimeric structure while 1a is a monomer. Coordinative saturation of the ruthenium centre is achieved by intramolecular coordination of the appended hydroxy function, thus rendering the functionalized arene an eight electron donor chelate ligand. The structure is further stabilized by intermolecular OH···Cl hydrogen bridges between a terminal chloride ligand of one and the coordinated hydroxy group of a neighbour molecule, resulting in a sheet structure. These intermolecular interactions appear to be even stronger in the hydroxyethyl analogue. Several phosphine adducts have been prepared from the hydroxy or alkoxy functionalized [(η6‐arene)RuCl2]n precursors, including water soluble P(CH2OH)3 adducts. Electrochemical properties of the phosphine adducts and of the dichloro bridged aryl ether complex 2a are also discussed. 相似文献
965.
现代分析仪器的一个重要发展趋势是仪器的小型化(miniaturization)、微型化(microminiaturiza.ion),甚至于芯片实验室(lab-on-a-chip;或称微全分析系统,micro total analysis system,μ-TAS)。因此,许多科学工作者在提高光谱分析仪器的基本部件——辐射源、样品室、分光元件和检测器的性能和减小其体积方面做了大量的研究工作。半导体检测器在光谱分析中的应用越来越广泛,在实验室和实际工作中常常会接触到摄谱仪、光电倍增管(photomultiplier tube,PMT)和电荷耦合器件(charge coupled device,CCD)等,本文介绍微型CCD光谱仪在本科教学中的一些应用。 相似文献
966.
967.
Lubov’ V. Snegur Alexander A. Simenel Elena A. Morozova Svetlana M. Peregudova Valery N. Babin Natalia V. Bluchterova 《Journal of organometallic chemistry》2004,689(15):2473-2479
The syntheses, structures, electrochemical properties of the series of ferrocenylalkyl azoles, FcAlkAz, as well as the antitumor activity of ferrocenylmethyl benzimidazole (8) have been studied. Above mentioned compounds were investigated by the method of cyclic voltametry. All of them exhibited a reversible one-electron oxidation-reduction wave owing to the ferrocene-ferrocenium redox couple with a positive shift (0.50-0.65 V) compared with that of ferrocene (0.42 V). The X-ray determination of molecular structures of 1-(ferrocenylmethyl)imidazole (4), 1-(ferrocenylbenzyl)imidazole (7) and 1-(ferrocenylmethyl)bezimidazole (8) was carried out. Compound 4 with imidazolyl substituent was found to be present in N-protonated form. Antitumor activity of 1-(ferrocenylmethyl)benzimidazole (8) against some solid tumor models such as adenocarcinoma 755 (Ca755), melanoma B16 (B16) and Lewis lung carcinoma was studied. The antitumor activity of compound 8 was compared with cisplatin effectiveness against some experimental tumor systems. 相似文献
968.
The use of a carbon-nanotube paste (CNTP) electrode provides an effective means for the determination of homocysteine. A decrease of ca. 120 mV in the overpotential for the oxidation of homocysteine compared to a traditional carbon paste electrode, is reported along with greatly enhanced signal-to-noise characteristics. The analytical parameters have been assessed with a linear range from 5 to 200 μM and a detection limit of 4.6 μM. Furthermore, the generic nature of this increased reactivity of the CNTP surface towards thiol moieties has been demonstrated with cysteine, glutathione and n-acetylcysteine, providing a greatly enhanced electrochemical response compared to the carbon paste electrode. 相似文献
969.
This paper introduces our initial attempt and practice to carry out online teaching during the period of prevention and control of the new type coronavirus (COVID-19). Online teaching in our college generally adopts three means:MOOC network platform, QQ group and Tencent classroom live broadcast platform. This paper introduces in detail the online teaching, guiding students to participate in discussions, and the effective control of online teaching and effective combination of expertise and epidemic knowledge. The achievements were satisfied. 相似文献
970.