全文获取类型
收费全文 | 4520篇 |
免费 | 560篇 |
国内免费 | 140篇 |
专业分类
化学 | 2629篇 |
晶体学 | 415篇 |
力学 | 82篇 |
综合类 | 6篇 |
数学 | 64篇 |
物理学 | 2024篇 |
出版年
2024年 | 5篇 |
2023年 | 31篇 |
2022年 | 47篇 |
2021年 | 68篇 |
2020年 | 149篇 |
2019年 | 113篇 |
2018年 | 147篇 |
2017年 | 150篇 |
2016年 | 277篇 |
2015年 | 159篇 |
2014年 | 175篇 |
2013年 | 754篇 |
2012年 | 191篇 |
2011年 | 212篇 |
2010年 | 171篇 |
2009年 | 252篇 |
2008年 | 227篇 |
2007年 | 303篇 |
2006年 | 247篇 |
2005年 | 222篇 |
2004年 | 163篇 |
2003年 | 159篇 |
2002年 | 128篇 |
2001年 | 114篇 |
2000年 | 91篇 |
1999年 | 114篇 |
1998年 | 94篇 |
1997年 | 42篇 |
1996年 | 63篇 |
1995年 | 41篇 |
1994年 | 37篇 |
1993年 | 30篇 |
1992年 | 28篇 |
1991年 | 17篇 |
1990年 | 31篇 |
1989年 | 13篇 |
1988年 | 25篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 7篇 |
排序方式: 共有5220条查询结果,搜索用时 359 毫秒
131.
《Progress in Solid State Chemistry》2014,42(3):23-36
The series of compounds in the BaLn2O4 family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV2O4 structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe2O4 and BaYb2O4 display large crystal fields effects and suppression of magnetic ordering. All compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure. 相似文献
132.
We investigate wave mixing effects in a phononic crystal that couples the wave dynamics of two channels – primary and control ones – via a variable stiffness mechanism. We demonstrate analytically and numerically that the wave transmission in the primary channel can be manipulated by the control channel's signal. We show that the application of control waves allows the selection of a specific mode through the primary channel. We also demonstrate that the mixing of two wave modes is possible whereby a modulation effect is observed. A detailed study of the design parameters is also carried out to optimize the switching capabilities of the proposed system. Finally, we verify that the system can fulfill both switching and amplification functionalities, potentially enabling the realization of an acoustic transistor. 相似文献
133.
《中国化学会会志》2017,64(10):1235-1241
A novel colorimetric chemosensor with good sensitivity, specificity, and self‐reporting capability for chloramphenicol (CAP ) has been successfully constructed based on colloidal, magnetically assembled photonic crystals coupled with molecular imprinting. The colloidal, magnetically assembled, molecularly imprinted photonic crystals (CMA ‐MIPCs ) were prepared by assembling CAP in magnetic, molecularly imprinted nanohydrogels (MMIHs ) in a magnetic field. The magnetic assembly of photonic crystals and the sensing processes could be completed simultaneously when MMIHs were dispersed in CAP solutions and in a magnetic field, and the response time was less than 1 min. The CAP concentration could be visually determined from the color change of the CMA ‐MIPCs sensor. The diffraction color blue‐shifted from luminous yellow of the blank to purple in a 1.0 mg/mL CAP solution, with a determination limit of 1.0 × 10−3 mg/mL. It could provide a new strategy for qualitative or semiquantitative detection of CAP . 相似文献
134.
Dr. Nicole M. G. Franssen Dr. Bernd Ensing Maruti Hegde Prof. Dr. Theo J. Dingemans Ben Norder Prof. Dr. Stephen J. Picken Gert O. R. Alberda van Ekenstein Dr. Ernst R. H. van Eck Dr. Johannes A. A. W. Elemans Mark Vis Prof. Dr. Joost N. H. Reek Prof. Dr. Bas de Bruin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11457-11457
135.
Due to the anisotropy of the conductivity in AsF5-intercalated HOPG, eddy current methods have to be used for the measurement of transport effects. The measurements yield carrier concentration, mobility and charge transfer for C8nAsF5 with n=l-4 at temperatures between 4.2K and 300K. 相似文献
136.
Large-aperture liquid crystal (LALC) lens with hole-patterned electrodes possesses small lens power and high addressing voltage because of the thick dielectric layer inserted between the hole-patterned electrode and LC layer. With an embedded narrow floating ring electrode (FRE), the lens power and addressing voltage of the LALC lens could be effectively increased and decreased, respectively. In this study, we analyse the electro-optic performance of LALC lens upon variation of the diameter of the embedded FRE. Results reveal that the FRE diameter determines the electric-field distribution and hence the electro-optic behaviour of the LALC lens. The LALC lens with embedded 2-mm-diameter FRE has excellent lens properties, such as low aberration, high focal quality and modulation transfer function performance comparable with solid glass lens. 相似文献
137.
Julien Iehl Thi Le Anh Nguyen Stéphane Frein Uwe Hahn Joaquín Barberá Jean-François Nierengarten 《Liquid crystals》2017,44(12-13):1852-1860
ABSTRACTLiquid-crystalline [60]fullerodendrimers were constructed via click chemistry based on the reaction between hexa-adducts of [60]fullerene (C60) bearing 12 azide groups and alkyne-terminated cyanobiphenyl dendrons of first- and second-generation. The structure of all the new compounds was confirmed by IR, UV, 1H and 13C NMR spectroscopies and mass spectrometry. The mesomorphic properties were studied by polarised optical microscopy, differential scanning calorimetry and small-angle X-ray scattering. The hexa-adduct of C60 functionalised with the first-generation dendrons gave rise to the formation of a smectic A phase and a rectangular columnar phase (c2mm symmetry) while the hexa-adduct of C60 decorated with the second-generation dendrons displayed only a rectangular columnar phase (c2mm symmetry). Our results show that the hexa-adduct of C60 is a unique synthetic platform for the design of fullerodendrimers and dendronised materials. 相似文献
138.
Zourab Brodzeli Andrew Michie Qi Guo Evgeny P. Pozhidaev Vladimir Chigrinov 《Liquid crystals》2013,40(10):1427-1435
We present a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers. Using a model based on the effective dielectric tensor approximation, we derive simple analytical formulas to design a LC cell with maximum modulation depth and optimal linearity of the electro-optical response intensity versus the electric field. Our experimental results show that the cell works at frequencies up to 10 kHz and exhibits excellent linearity, with a total harmonic distortion as low as ?70 dB. These findings suggest that DHF-LCs can be exploited to develop simple and accurate optical sensors. 相似文献
139.
A new series of hydrogen bonded liquid crystal (HBLC) complexes, made up with substituted benzoic acids (BAs) and nonyloxy benzoic acid, viz., x-(p/m)BA:9OBAs are reported for x = F, Cl, Br and –CH3 substituted at para (p) or meta (m) positions of BA moiety. Proton nuclear magnetic resonance (1H-NMR) spectrum confirms the HBLC complex. Infra red (IR) spectrum confirms linear, double and complementary type of hydrogen bonding (HB) between x-(p/m)BAs and 9OBA. The liquid crystal (LC) phases are characterised by polarisation optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. x-(p/m)BA:9OBA exhibit N, C and G LC phase variance. HB induces tilted phases and enhances LC phase stability. The influence of configuration, size, electronegativity, electron directing capacity and inductive nature of substituent (x) is investigated for the stability of LC phases. An overview of the LC phase data indicates predominant ‘negative inductive effect’ in HBLCs with electron withdrawing substituents. Inductive effect operates effectively for para substitutions. Results are discussed in the wake of reports in other HBLCs. 相似文献
140.
Hong Sun Frederick Roussel Wing Shun Cheung B. M. Fung Sandy S. Keast Mark Lohman 《Liquid crystals》2013,40(10):1483-1486
Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region. 相似文献