全文获取类型
收费全文 | 13691篇 |
免费 | 375篇 |
国内免费 | 1157篇 |
专业分类
化学 | 11551篇 |
晶体学 | 675篇 |
力学 | 440篇 |
综合类 | 8篇 |
数学 | 111篇 |
物理学 | 2438篇 |
出版年
2023年 | 130篇 |
2022年 | 103篇 |
2021年 | 80篇 |
2020年 | 158篇 |
2019年 | 178篇 |
2018年 | 163篇 |
2017年 | 237篇 |
2016年 | 396篇 |
2015年 | 333篇 |
2014年 | 419篇 |
2013年 | 557篇 |
2012年 | 1765篇 |
2011年 | 882篇 |
2010年 | 735篇 |
2009年 | 973篇 |
2008年 | 1047篇 |
2007年 | 1225篇 |
2006年 | 846篇 |
2005年 | 733篇 |
2004年 | 722篇 |
2003年 | 528篇 |
2002年 | 293篇 |
2001年 | 228篇 |
2000年 | 178篇 |
1999年 | 180篇 |
1998年 | 196篇 |
1997年 | 178篇 |
1996年 | 197篇 |
1995年 | 188篇 |
1994年 | 181篇 |
1993年 | 151篇 |
1992年 | 118篇 |
1991年 | 126篇 |
1990年 | 88篇 |
1989年 | 64篇 |
1988年 | 86篇 |
1987年 | 63篇 |
1986年 | 60篇 |
1985年 | 66篇 |
1984年 | 64篇 |
1983年 | 40篇 |
1982年 | 76篇 |
1981年 | 45篇 |
1980年 | 43篇 |
1979年 | 46篇 |
1978年 | 15篇 |
1976年 | 8篇 |
1973年 | 8篇 |
1969年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Si-Yang Feng Tao Zheng Ai-Jing Sun Zuo-Xiang Wang 《Molecular Crystals and Liquid Crystals》2019,692(1):43-52
AbstractComplexes of [CdL2(NO3)2]·1.5H2O and [Ag2(μ-L)2(NO3)2] were synthesized by the reactions of 2-p-methylphenyl-5-(2-pyridyl)-1,3,4-thiadiazole (L) with Cd(NO3)2·4H2O and AgNO3, respectively. Their structures were determined by single crystal X-ray diffraction. The photophysical property and thermal stability were characterized by FT???IR, UV???Vis absorption, fluorescence, and thermogravimetric analysis (TGA). Both complexes belong to the triclinic system with space group p???1. The central metal of [CdL2(NO3)2]·1.5H2O has a distorted octahedral geometry [CdN4O2], while two central Ag(I) atoms of [Ag2(μ-L)2(NO3)2] exhibit distorted tetrahedral geometries [AgN3O]. 相似文献
2.
Mohammad Azam Saud I. Al-Resayes Agata Trzesowska-Kruszynska Rafal Kruszynski S.F. Adil N.K. Lokanath 《Journal of Saudi Chemical Society》2019,23(5):636-641
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded. 相似文献
3.
The bond ionicity in seventy two ANB8−N compounds is investigated according to the recently introduced first-principles ionicity scale, based on the centers of the maximally localized Wannier functions, which has several interesting features. The obtained bond ionicities (qi) are found to exhibit the expected trends, according to electronegativity arguments. In particular, the bond ionicity in the alkaline-earth oxides increases by going from MgO to BaO. A strong crystal structure dependence of qi is observed. A critical value of qi (of 0.91) that separates between the tetrahedrally and octahedrally coordinated systems is inferred directly from the calculated values of qi. The volume dependence of qi is investigated for all the considered compounds and found to reduce by volume decrease for most of the studied systems. The adopted ionicity scale is established as a very strong competitor to the most widely accepted Phillips and Pauling ionicity measures. 相似文献
4.
The dependence of the EPR g-factors on the local structural parameter for a 4f11 configuration ion Er3+ in a trigonal crystal-field has been studied by diagonalizing the 364×364 complete energy matrices. Our studies indicate that the EPR spectra of the trigonal Er3+–VK centers in KMgF3 and KZnF3 may be attributed to the translation of the cubic Kramers doublet Γ7. Furthermore, the EPR g-factors of the trigonal Er3+–VK centers may be interpreted reasonably by the shifts ΔZ≈0.340 Å and ΔZ≈0.303 Å of the Er3+ ions toward the charge compensator VK along the C3 axis for the KMgF3:Er3+ and the KZnF3:Er3+ systems respectively. 相似文献
5.
《Comptes Rendus Chimie》2015,18(6):619-625
A new terdentate acyclic pincer ligand, 2,6-bis(tert-butylthiomethyl)pyridine (tbtmp), was synthesized and reacted with several complexes of iron, zinc, nickel, cobalt, and copper. The ligand and its coordination compounds were characterized using elemental analysis, infrared, 1H- and 13C-NMR-spectroscopy, thermal analyses, plus—for the Zn complex—single-crystal X-ray diffractometry. The structure of [Zn(L)Br2] was solved in the tetragonal crystal system, chiral space groups P41212 and P43212 (No. 92 and No. 96, a = 947.2(1) pm, c = 2265.2(5) pm), revealing five-fold coordination of the metal atoms. According to spectroscopy, all complexes share the same coordination environment around the metal atoms, consisting of two halide anions and a sulfur-methylene-pyridine-methylene-sulfur entity; tbtmp acts as a tridentate ligand with the pyridine N atom and both tert-butylthio S atoms coordinating to the metal ions (NS2). The analysis results indicate that the metal ions are coordinated as distorted pseudo-bipyramids, LMX2, with the chelate ligand meridionally arranged. One of the complexes contains ethanol as an additional ligand, resulting in a pseudo-octahedral coordination sphere [Ni(L)Cl2EtOH]. The latter was obtained in the form of green crystals, which turn into a red powder with loss of the ethanol molecule. Fe (III), Co(II), Ni(II) and Cu(II) metal complexes [M(L)Cl2] were screened for their antibacterial activity against B. subtilis G(+) and Escherichia coli G(−) bacteria, and fungus (Candida albicans and Aspergillus flavus). 相似文献
6.
We report on the realization and characterization of electro-responsive and pressure sensitive polydimethylsiloxane (PDMS) conductive photonic structures combined with the reconfigurable properties of short pitch cholesteric liquid crystals (aligned in Grandjean configuration). By combining ion-implantation process and surface chemistry functionalization, we have overcome the insulating properties of PDMS and induced long range organization of cholesteric liquid crystals, thus controlling both diffraction and selective Bragg reflection of light by means of external perturbations (electric field, pressure). We have characterized our devices in terms of morphological, optical and electro-optical properties. 相似文献
7.
Bi-injection moulding is a widely used process to manufacture engineering products and consumer goods. Typically, a thermoplastic is combined with rubber or another thermoplastic to create colour differences or hard and soft areas, respectively. The aim of this study was to optimise the injection parameters and processing conditions for the moulding of two-component standard peel test specimens with suitable functional properties. In this work, all parameters of thermo-rheo-kinetic behaviour were identified to predict the entire filling stage and the effect of a liquid silicone rubber cross-linking reaction during the injection moulding process. The models of Carreau-Yasuda and Isayev-Deng regarding the thermal dependence assumed by Arrhenius’ law were used. In our study, over-injection moulding is simulated and examined using finite element software (Cadmould 3D) to investigate the thermo-rheo-kinetic behaviour and the adhesion of liquid silicone rubber during the filling mould process in over-moulding. Numerical simulation results were then compared with the experimental results, and good agreement was obtained. 相似文献
8.
4,4′-bipyridine bridged two Cu (II) complexes, [Cu2L12(4,4′-bipy)(H2O)2](ClO4)2 ( 1 ) and [Cu2L22(4,4′-bipy)]n·(2H2O)n ( 2 ) (where, HL1 = 2-[(3-methylamino-propylimino)-methyl]-phenol, H2L2 = 3-[(2-hydroxy-3-methoxy-benzylidene)-amino]-propionic acid, and 4,4′-bipy = 4,4′-bipyridine) have been synthesized and characterized by single crystal structure determination, mass spectrometry, FT-IR, electronic absorption, and emission spectroscopy. Complex 1 is dinuclear cationic compound and counter balanced by perchlorate anion, whereas complex 2 possesses 1D poly-nuclear structure. Both the complexes crystallize in monoclinic system with P21/c space group and the copper centers possess square pyramidal geometry. H-bonding, C-H···π, π···π interactions results the formation of two dimentional supramolecular structure for both the complexes. Interactions of complexes with bovine serum albumins (BSA) and human serum albumins (HSA) have been studied by using electronic absorption and emission spectroscopic technique. The calculated values of binding constants (Kb) are (9.22 ± 0.26) × 105 L mol−1 ( 1 -BSA), (7.19 ± 0.16) × 105 L mol−1 ( 1 -HSA), (5.05 ± 0.20) × 105 L mol−1 ( 2 -BSA) and (3.56 ± 0.25) × 105 L mol−1 ( 2 -HSA). The mechanism of serum albumins-complex interactions have been investigated by fluorescence lifetime measurement. Fluorescence spectroscopic studies indicate that both the complexes interact with calf thymas-DNA. Catecholase activity of the complexes has been studied in methanol using 3,5-di-tert-butylcatechol (3,5-DTBC) as substrate and the result show that both the complexes are active for catalytic oxidation of 3,5-DTBC to 3,5-di-tert-butylquinone (3,5-DTBQ) in presence of molecular oxygen. Calculated values of turnover numbers are 71.81 ± 1.04 h−1 and 69.45 ± 0.74 h−1 for 1 and 2 , respectively. 相似文献
9.
上海市力学学会成立于1959年9月20日,到今年正好是一个甲子.60个春秋真实写照了上海市力学学会的建立、成长、发展与壮大的过程.60年来,在上海市科协的领导和中国力学学会的指导下,在各团体成员单位的大力支持下,上海市力学学会一代代力学工作者薪火相传、开拓耕耘,历届理事会及下属工作委员会和专业委员会团结奋进、不断创新,广大会员踊跃参与,为上海力学大力发展、力学人才精心培养、力学知识科学普及、力学服务国家发展战略和区域经济建设中做出了重要贡献,学会持续发展壮大.在庆祝力学学会成立六十周年之际,让我们共同抒怀上海力学六十年薪火相传、回顾近10年重要发展,展望上海力学新时代. 相似文献
10.
Jan-Christoph Eichler Robert A. Skutnik Anupam Sengupta Marco G. Mazza Martin Schoen 《Molecular physics》2019,117(23-24):3715-3733
Anisotropic fluids (e.g. liquid crystals) offer a remarkable promise as optofluidic materials owing to the directional, tunable, and coupled interactions between the material, flow, and the optical fields. Here we present a comprehensive in silico treatment of this anisotropic interaction by performing nonequilibrium molecular dynamics simulations. We quantify the response of a nematic liquid crystal (NLC) undergoing a Poiseuille flow in the Stokes regime, while being illuminated by a laser beam incident perpendicular to the flow direction. We adopt a minimalistic model to capture the interactions, accounting for two features: first, the laser heats up the NLC locally; and second, the laser polarises the NLC and exerts an optical torque that tends to reorient molecules of the nematic phase. Because of this reorientation the liquid crystal exhibits small regions of biaxiality, where the nematic director is one symmetry axis and the axis of rotation for the reorientation of the molecules is the other one. We find that the relative strength of the viscous and the optical torques mediates the flow-induced response of the biaxial regions, thereby tuning the emergence, shape and location of the regions of enhanced biaxiality. The mechanistic framework presented here promises experimentally tractable routes toward novel optofluidic applications based on material-flow-light interactions. 相似文献