全文获取类型
收费全文 | 5631篇 |
免费 | 1030篇 |
国内免费 | 585篇 |
专业分类
化学 | 3687篇 |
晶体学 | 51篇 |
力学 | 252篇 |
综合类 | 33篇 |
数学 | 758篇 |
物理学 | 2465篇 |
出版年
2024年 | 3篇 |
2023年 | 128篇 |
2022年 | 111篇 |
2021年 | 186篇 |
2020年 | 236篇 |
2019年 | 201篇 |
2018年 | 188篇 |
2017年 | 172篇 |
2016年 | 293篇 |
2015年 | 242篇 |
2014年 | 308篇 |
2013年 | 379篇 |
2012年 | 482篇 |
2011年 | 554篇 |
2010年 | 339篇 |
2009年 | 333篇 |
2008年 | 360篇 |
2007年 | 332篇 |
2006年 | 321篇 |
2005年 | 266篇 |
2004年 | 196篇 |
2003年 | 174篇 |
2002年 | 195篇 |
2001年 | 150篇 |
2000年 | 127篇 |
1999年 | 157篇 |
1998年 | 130篇 |
1997年 | 110篇 |
1996年 | 109篇 |
1995年 | 75篇 |
1994年 | 52篇 |
1993年 | 52篇 |
1992年 | 48篇 |
1991年 | 59篇 |
1990年 | 31篇 |
1989年 | 31篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 22篇 |
1985年 | 19篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有7246条查询结果,搜索用时 15 毫秒
991.
992.
A. Greiner H. Hou A. Reuning A. Thomas J.H. Wendorff S. Zimmermann 《Cellulose (London, England)》2003,10(1):37-52
Cholesteric materials display unique optical properties which can be exploited in opto-electronic applications such as light emitting diodes. The key feature is the position of the wavelength of the emitted light relative to the one of the selective reflection band. We have synthesized a set of cellulose derivatives displaying the cholesteric phase with the aim to investigate the correlation between chemical structure and properties. Phase transition temperatures, the chain packing, the wavelength of selective reflection but also absorption and fluorescence spectra were investigated as a function of the degree of substitution (DS), the nature of lateral substituents, the composition of doped systems and blends of different cellulose derivatives. Investigated were furthermore the degree of circular polarization of the emitted light for guest–host systems and for cellulose systems with chromophores linked by covalent bonds to the cellulose backbone as well as their performance in light emitting diodes. The conclusion is that the optical properties can be accounted for on the basis of the model of a one-dimensional photonic crystal. The limiting factor with respect to opto-electronic applications is the poor control of the uniformity of the helix formation and orientation. 相似文献
993.
Liu J Hu X Hou S Wen T Liu W Zhu X Wu X 《Chemical communications (Cambridge, England)》2011,47(39):10981-10983
Nanostructured materials are a new class of enzyme mimics, the inhibitors of which have not been studied. Herein, we demonstrate the screening of inhibitors for Au@Pt nanorod (NR) oxidase mimics. In addition, based on the enzyme inhibition reaction, determination of "poisoning" inhibitors is demonstrated. 相似文献
994.
Ye Xu Dr. Huifeng Yao Lijiao Ma Ling Hong Jiayao Li Qing Liao Yunfei Zu Jingwen Wang Mengyuan Gao Prof. Long Ye Prof. Jianhui Hou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9089-9095
Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non-radiative energy loss ( ) is the dominant factor that hinders further improvements in state-of-the-art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed . Herein, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge-transfer (CT) state ratio in its hybridization with the local exciton state to facilitate charge generation, but simultaneously result in a larger . These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells. 相似文献
995.
996.
Hou R Huang TH Wang XJ Jiang XF Ni QL Gui LC Fan YJ Tan YL 《Dalton transactions (Cambridge, England : 2003)》2011,40(29):7551-7558
A series of Cu(I) complexes with a [Cu(NN)(PP)](+) moiety, [Cu(phen)(pba)](BF(4)) (1a), [Cu(2)(phen)(2)(pbaa)](BF(4))(2) (2a), [Cu(2)(phen)(2)(pnaa)](BF(4))(2) (3a), [Cu(2)(phen)(2)(pbbaa)](BF(4))(2) (4a), [Cu(dmp)(pba)](BF(4)) (1b), [Cu(2)(dmp)(2)(pbaa)](BF(4))(2) (2b), [Cu(2)(dmp)(2)(pnaa)](BF(4))(2) (3b) and [Cu(2)(dmp)(2)(pbbaa)](BF(4))(2) (4b) (phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, pba = N,N-bis((diphenylphosphino)methyl)benzenamine, pbaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)benzene-1,4-diamine, pnaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)naphthalene-1,5-diamine and pbbaa = N,N,N',N'-tetrakis((diphenylphosphino)methyl)biphenyl-4,4'-diamine), were rationally designed and synthesized. These complexes were characterized by (1)H and (31)P NMR, electrospray mass spectrometry, elemental analysis and X-ray crystal structure analysis. Introduction of different central arene spacers (phenyl, naphthyl, biphenyl) into ligands, resulting in the size variation of these complexes, aims to tune the photophysical properties of the complexes. Each Cu(I) ion in these complexes adopts a distorted tetrahedral geometry constructed by the chelating diimine and phosphine groups. Intermolecular C-H···π and/or π···π interactions are involved in the solid states. The dmp-containing complex exhibits better emission relative to the corresponding phen complex due to the steric encumbrance of bulky alkyl groups. Furthermore, for complexes with identical diimine but different phosphine ligands, the tendency of increased emission lifetime as well as blue-shifted emission in the solid state follows with the decrease in size of complexes. Intermolecular C-H···π interactions have an influence on the final solid state photophysical properties through vibrationally relaxed non-radiative energy transfer in the excited state. Smaller-sized complexes show better photophysical properties due to less vibrationally relaxed behavior related to flexible C-H···π bonds. Nevertheless, the tendency for increased quantum yield and emission lifetime, as well as blue-shifted emission in dilute solution goes with the increase in size of complexes. The central arene ring (phenyl, naphthyl or biphenyl) has an influence on the final photophysical properties. The larger the π-conjugated extension of central arene ring is, the better the photophysical properties of complex are. The rigid and large-sized complex 3b, with a high quantum yield and long lifetime, is the best luminophore among these complexes. 相似文献
997.
110例脑卒中患者血清中铁,锌,铜,锰,硒,铬,钴,镍的含量水平与对照组比较,结果显示:1.血清的,铜和铬的含量升高,锌,钴和镍的含量降低,两者之间的差异均有高度显著性,P〈0.01;2.血清锰和硒的含量与对照组差异无显著性,P〉0.05;3.在临床上述元素含量变化可用于脑座中的辅助诊断和治疗。 相似文献
998.
In this study, the root powder of Stellera chamaejasme was extracted with chloroform. The crude extract thus obtained was chromatographed several times with silica gel columns and finally one pure natural product was obtained. This product was identified as 2-isopropyl-5-methylphenol (thymol), which was separated for the first time from S. chamaejasme root. The results of a laboratorial bioassay showed that it had good insecticidal activity against Aphis craccivora and Pieris rapae. Its median lethal concentrations (LC50) (24 h after treatment) were 14.81 and 47.68 mg L(-1), respectively. This is the first time that the insecticidal activity of thymol against A. craccivora and P. rapae has been reported. 相似文献
999.
Qian S Joo SW Hou WS Zhao X 《Langmuir : the ACS journal of surfaces and colloids》2008,24(10):5332-5340
The electrophoretic motion of a spherical nanoparticle, subject to an axial electric field in a nanotube filled with an electrolyte solution, has been investigated using a continuum theory, which consists of the Nernst-Planck equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the Stokes equation for the hydrodynamic field. In particular, the effects of nonuniform surface charge distributions around the nanoparticle on its axial electrophoretic motion are examined with changes in the bulk electrolyte concentration and the surface charge of the tube's wall. A particle with a nonuniform charge distribution is shown to induce a corresponding complex ionic concentration field, which in turn influences the electric field and the fluid motion surrounding the particle and thus its electrophoretic velocity. As a result, contrary to the relatively simple dynamics of a particle with a uniform surface charge, dominated by the irradiating electrostatic force, that with a nonuniform surface charge distribution shows various intriguing behaviors due to the additional interplay of the nonuniform electro-osmotic effects. 相似文献
1000.
Lewis acid/base addition between Ln(NO3)3 · 6H2O (Ln = Pr, Nd, Sm, Eu, Tb and Lu) and H2salen [H2salen = N,N′-ethylenebis(salicylideneimine)] gives rise to an array of coordination polymeric structures. Crystal structural analysis reveals that Salen effectively functions as a bridging ligand in these compounds. The size of the lanthanide ions controls the structures of these Salen lanthanide complexes. Two representative structures with one dimensional and two dimensional topologies, viz. [Pr(H2salen)(NO3)3(CH3OH)2]n (1) and [Ln(H2salen)1.5(NO3)3]n [Ln = Pr (2), Nd (3), Sm (4), Eu (5), Tb (6) and Lu (7)] are reported. Luminescent spectra of complexes 4 and 5 exhibit characteristic metal-centered emission lines. However, the characteristic luminescence of the terbium(III) ion is not observed either in solution or in the solid state of complex 6. 相似文献