全文获取类型
收费全文 | 8028篇 |
免费 | 1245篇 |
国内免费 | 3299篇 |
专业分类
化学 | 6506篇 |
晶体学 | 459篇 |
力学 | 440篇 |
综合类 | 111篇 |
数学 | 2381篇 |
物理学 | 2675篇 |
出版年
2024年 | 31篇 |
2023年 | 80篇 |
2022年 | 215篇 |
2021年 | 259篇 |
2020年 | 286篇 |
2019年 | 269篇 |
2018年 | 260篇 |
2017年 | 420篇 |
2016年 | 553篇 |
2015年 | 369篇 |
2014年 | 544篇 |
2013年 | 947篇 |
2012年 | 842篇 |
2011年 | 809篇 |
2010年 | 672篇 |
2009年 | 695篇 |
2008年 | 691篇 |
2007年 | 670篇 |
2006年 | 546篇 |
2005年 | 477篇 |
2004年 | 401篇 |
2003年 | 334篇 |
2002年 | 336篇 |
2001年 | 289篇 |
2000年 | 239篇 |
1999年 | 216篇 |
1998年 | 183篇 |
1997年 | 150篇 |
1996年 | 146篇 |
1995年 | 129篇 |
1994年 | 119篇 |
1993年 | 85篇 |
1992年 | 67篇 |
1991年 | 41篇 |
1990年 | 45篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
殖民地文物归还事件引发的争议揭示了去殖民化进程的困境。“归还”被期待生成新的关系伦理,但其认知与行动都基于以所有权为核心的物权伦理,未能关照殖民主义文物占有的神话学经验,遮蔽了物伦理的政治性与异质性;而将物权伦理作为“普世伦理”正是资本主义全球扩张的结果。维护物权伦理的物的知识巩固了对文物的祛魅与分裂,使文物即便归还,也仍需“神圣”博物馆赋能,有悖于“恢复原状”的假设。以物为主体/物质化的伦理考察有助于突破物权伦理的普世意识,建立起对普遍困境的反身性思考。作为争议性文化遗产的殖民地文物及其归还事件应作为生产性的实践,激发去殖民化的知识反思。 相似文献
22.
Tanmoy Dutta Yong Li Aaron L. Thornton Da‐Ming Zhu Zhonghua Peng 《Journal of polymer science. Part A, Polymer chemistry》2013,51(18):3818-3828
Donor‐acceptor conjugated polymers containing a new imide‐functionalized naphthodithiophene (INDT) as the acceptor unit and a 2,2'‐bithiophene with varied substituents as the donor unit have been synthesized. The bandgaps of these polymers depend strongly on the dihedral angle of the 2,2'‐bithiophene unit. The 3,3'‐dialkoxy substitution (polymers PDOR / PBOR ) leads to near planar bithiophene conformation due to the well‐known S–O short contact, while the 3,3'‐dialkyl substitution (polymer PDR ) results in significant twisting due to the steric effect. Consequently PDOR / PBOR shows the lowest bandgap of 1.82/1.85 eV while PDR has a bandgap of 2.38 eV. Bulk‐heterojunction solar cells of the polymer/fullerene blends have been fabricated. Preliminary results show that PBOR gives the best device performance with power conversion efficiencies as high as 2.45% in air without any thermal annealing treatment, indicating the promising potential of INDT‐containing conjugated polymers for efficient solar cells. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3818–3828 相似文献
23.
《Journal of Coordination Chemistry》2012,65(21):3473-3483
Two Co(II) coordination polymers, [CoL(npa)]·2H2O (1) and [CoL(Hnpa)2] (2) (L = 1,4-bis(5,6-dimethylbenzimidazole-1-yl)benzene, H2npa = 5-nitroisophthalic acid), have been synthesized in different solvent systems and characterized by Infrared (IR) spectroscopy, elemental analysis, and powder and single crystal X-ray diffraction. Compound 1 was synthesized under solvothermal conditions with DMF as solvent and had a pair of L ligands adopting a μ2-bridging mode and connecting two Co2+ cations to generate a 26-membered Co2L2 loop. The npa2? link adjacent Co2L2 loops via a bis(monodentate) bridging mode to create a 1-D channel-like chain structure. Compound 2 was obtained under hydrothermal conditions, and the carboxylate of the monodeprotonated Hnpa? adopt a μ1-η0?:?η1 coordination to connect adjacent Co2+ cations into a 2-D polymeric layer. The μ2-bridging L ligands connect adjacent 2-D [Co(Hnpa)]n polymeric layers into a 3-D NaCl-like framework. The Co2+ cations and the L ligands in compounds 1 and 2 exhibit different coordination geometries and conformations. Effects of solvents on the construction of Co(II) coordination polymers were investigated. In addition, the electrochemical behavior of carbon paste electrodes containing 1 and 2 and the thermal stabilities of 1 and 2 were investigated. 相似文献
24.
《Journal of Coordination Chemistry》2012,65(7):1212-1220
A tetranuclear Zn(ΙΙ) complex, [Zn4L2(OAc)2(CH3OH)2] with an unsymmetric Salen-type bisoxime (H3L?=?6-hydroxy-4′,6′-dibromo-2,2′-[ethylenediyldioxybis(nitrilomethylidyne)]diphenol), has been synthesized and structurally characterized. There are two kinds of coordination geometry (trigonal bipyramidal and square pyramidal) in the Zn(ΙΙ) complex. The molecule has serious distortion probably from the asymmetry. The complex exhibits blue emission with the maximum emission wavelength λ max?=?423?nm when excited with 340?nm. 相似文献
25.
Aishakhanam H. Pathan Ganesh N. Naik Raghavendra P. Bakale Shrinath S. Machakanur Kalagouda B. Gudasi 《应用有机金属化学》2012,26(3):148-155
A series of Co(II), Ni(II), Cu(II), and Zn(II) complexes of a tridentate hydrazone were prepared and characterized by various spectro‐analytical techniques and magnetic moment studies. The complexes were found to be monomeric and non‐electrolytes. The copper complex is electrochemically active in the applied potential range. The compounds synthesized in the present study have shown promising antiproliferative activity when screened using the in vitro method against two human cancer cell lines: HeLa and HepG2. The Escherichia coli DNA‐binding properties of all the compounds were investigated with UV–visible absorption spectrophotometric titrations, viscosity measurements, DNA melting experiments and gel electrophoreses measurements. The compounds were demonstrated to act as DNA intercalators with appreciable DNA‐binding constant values. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
26.
Silver nanoparticles have been prepared in a polyacrylamide (PA) matrix, as well as in the presence of a hyperbranched polyamine/polyacrylamide combined system (HB‐PA) by using a reductive technique. The stability of colloidal solution of silver nanoparticles is higher (5 months) in combined matrix compared to PA alone (4 months). The prepared silver nanoparticles were characterized by different spectroscopic and analytical techniques such as FTIR, UV‐visible, X‐ray diffraction, TEM etc. TEM and XRD studies confirmed the formation of well‐dispersed nanoparticles with an average size of 9.91 nm and 8.5 nm for PA and HB‐PA matrices, respectively. The antibacterial activity of silver nanoparticles in both the matrices was tested against Bacillus Subtilis bacteria by using the diffusion disc technique. The result shows that the antibacterial activity of the active agent, Ag(0) is a little higher in the case of HB‐PA system. The dielectric constant of the matrices decreases with an increase in frequency, but the values increase with an increase of concentration of silver nanoparticles in PA matrix. 相似文献
27.
Chao Sun 《化学物理学报(中文版)》2013,(6):617-626,I0003
This work presents a theoretical insight into the variation of the site-specific intermolecular hydrogen-bonding (HB), formed between C=O group of fluorenone (FN) and O-H groups of methanol (MeOL) molecules, induced by both the electronic excitation and the bulk solvent effect. Through the calculation of molecular ground- and excited-state properties, we not only demonstrate the characters of HB strengthening induced by electronic excitation and the bulk solvent effect but also reveal the underlying physical mechanism which leads to the HB variation. The strengthening of the intermolecular HB in electronically excited states and in liquid solution is characterized by the reduced HB bond-lengths and the red-shift IR spectra accompanied by the increasing intensities of IR absorption corresponding to the characteristic vibrational modes of the O-H and C--O stretching. The HB strengthening in the excited electronic states and in solution mainly arises from the charge redistribution of the FN molecule induced by the electronic excitation and bulk solvent instead of the intermolecular charge transfer. The charge redistribution of the solute molecule increases the partial dipole moment of FN molecule and the FN-MeOL intermolecular interaction, which subsequently leads to the HB strengthening. With the bulk solvent effect getting involved, the theoretical IR spectra of HBed FN-MeOL complexes agree much better with the experiments than those of gas-phase FN-MeOL dimer. All the calculations are carried out based on our developed analytical approaches for the first and second energy derivatives of excited electronic state within the time-dependent density functional theory. 相似文献
28.
《Green Chemistry Letters and Reviews》2013,6(1):13-17
Abstract Amberlyst-15® (H+) resin catalyzes efficient one-pot solvent free Prins cyclization of an aldehyde and a homoallylic alcohol to yield dihydropyrans and 4-hydroxytetrahydropyrans. The products, which display interesting olfactory property, are obtained under mild condition and by simple work up. The recovered resin can be used repeatedly . 相似文献
29.
Water‐soluble porphyrin‐porphyrin and porphyrin‐CdSe nanoparticle monolayer films were self‐assembled on different substrates. The influence of substrates, types of films, and heat treatment temperature on fluorescence of different kinds of porphyrin films was investigated. The SEM images showed the formation of monolayer films on porous alumina foil. The films assembled on porous alumina foil possessed higher fluorescence intensity and thermal stability. The result of conductance measurement indicated that the interaction of trimethylamidophenylporphyrin iodide (TAPPI) molecules with hydroxyl groups on porous alumina foil was weakened after CdSe nanoparticles assembled with TAPPI. 相似文献
30.