全文获取类型
| 收费全文 | 2775篇 |
| 免费 | 267篇 |
| 国内免费 | 384篇 |
专业分类
| 化学 | 2044篇 |
| 晶体学 | 102篇 |
| 力学 | 27篇 |
| 综合类 | 16篇 |
| 数学 | 4篇 |
| 物理学 | 1233篇 |
出版年
| 2025年 | 5篇 |
| 2024年 | 26篇 |
| 2023年 | 45篇 |
| 2022年 | 89篇 |
| 2021年 | 79篇 |
| 2020年 | 152篇 |
| 2019年 | 153篇 |
| 2018年 | 122篇 |
| 2017年 | 122篇 |
| 2016年 | 113篇 |
| 2015年 | 99篇 |
| 2014年 | 103篇 |
| 2013年 | 152篇 |
| 2012年 | 165篇 |
| 2011年 | 160篇 |
| 2010年 | 113篇 |
| 2009年 | 165篇 |
| 2008年 | 160篇 |
| 2007年 | 196篇 |
| 2006年 | 151篇 |
| 2005年 | 116篇 |
| 2004年 | 113篇 |
| 2003年 | 107篇 |
| 2002年 | 133篇 |
| 2001年 | 102篇 |
| 2000年 | 79篇 |
| 1999年 | 57篇 |
| 1998年 | 63篇 |
| 1997年 | 54篇 |
| 1996年 | 47篇 |
| 1995年 | 50篇 |
| 1994年 | 25篇 |
| 1993年 | 16篇 |
| 1992年 | 19篇 |
| 1991年 | 16篇 |
| 1990年 | 13篇 |
| 1989年 | 6篇 |
| 1988年 | 10篇 |
| 1987年 | 2篇 |
| 1986年 | 5篇 |
| 1984年 | 2篇 |
| 1981年 | 2篇 |
| 1980年 | 2篇 |
| 1979年 | 1篇 |
| 1978年 | 5篇 |
| 1977年 | 1篇 |
| 1976年 | 2篇 |
| 1974年 | 2篇 |
| 1973年 | 3篇 |
| 1972年 | 1篇 |
排序方式： 共有3426条查询结果，搜索用时 15 毫秒
991.
992.
Chao Xu Zhaopeng Xu Yexia Fan Lei Xu Chunhui Yang Yuheng Xu 《Crystal Research and Technology》2012,47(8):863-867
Mg:Ru:Fe:LiNbO3 crystals with various doping concentration of MgO have been grown by Czochralski method. The type of charge carriers and photorefractive properties in Mg:Ru:Fe:LiNbO3 crystals were measured by two‐wave coupling method using Kr+ laser (476 nm) and He‐Ne laser (633 nm) as light sources. We found that holes were the dominant charge carriers under blue light irradiation while electrons were the dominant charge carriers under red light irradiation. Mg2+ ions behaved no longer as damage resistant, but promoter to the photorefractive properties at 476 nm wavelength. The photorefractive properties under blue light improved with the increase concentration of Mg2+ ions. The enhancement mechanisms of the blue photorefractive were suggested. Experimental results definitely showed that Mg‐doped two‐centre Ru:Fe:LiNbO3 was a promising blue photorefraction material for holographic volume storage. 相似文献
993.
A. Bloise E. Belluso E. Barrese D. Miriello C. Apollaro 《Crystal Research and Technology》2009,44(6):590-596
This study describes the formation of Fe‐doped chrysotile fibers with partial and total substitution of Mg by Fe. Syntheses were carried out with various starting mixtures (oxides, pure synthetic forsterite) in an externally heated pressure vessel in controlled hydrothermal conditions: temperature, 270 – 400 °C; pressure, 0.5 – 2 kbar; duration of treatment 160 – 480 hours. Pure synthetic forsterite was prepared by the flux growth technique. The starting material and run products were characterized by X‐ray powder diffraction (XRPD), scanning and transmission electron microscopies combined with energy‐dispersive spectrometry (SEM‐EDS and TEM‐EDS), differential scanning calorimetry (DSC) and thermogravimetry (TG). Variations observed in abundance and size of Fe‐doped chrysotile fibers were attributed to different experimental conditions for their synthesis. However, morphological shape turned out to depend on the starting mixtures used. Since natural samples are often difficult to obtain in a sufficiently pure state, these synthetic and well‐characterized Fe‐doped chrysotile fibers can be used for better understanding of the mechanisms involved in asbestos toxicity, as well as of the role of Fe in diseases induced by asbestos phases. These synthetic Fe‐doped chrysotile fibers, together with non‐toxicity testing, may also have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
Zhaopeng Xu Weihong Bi Binliang Jiao Yongzhi Ben Qizhu Lu Huihui Tang 《Crystal Research and Technology》2010,45(1):85-88
Mg:Ce:Fe:LiNbO3 crystals were prepared with fixed concentrations of Fe2O3 and CeO2, and differing concentrations of MgO by the Czochralski technique. Their infrared transmission spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the photoinduced birefringence change and transmission facula distortion method. The optical damage resistance of Mg:Ce:Fe:LiNbO3 crystals increases remarkably when the concentration of MgO exceeds a threshold concentration. The dependence of the optical damage resistance on the defect structure of Mg:Ce:Fe:LiNbO3 crystals is discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
995.
Xiudong Sun Hongxin Shi Suhua Luo Yongyuan Jiang Qingxin Meng 《Crystal Research and Technology》2010,45(3):249-253
Hf:Fe:LiNbO3 crystals were grown in air by the Czochralski technique with various ratios of [Li]/[Nb]=0.94, 1.05, 1.20 in melt. The defect structure and location of doped ions were analyzed by the UV‐visible and infrared spectroscopy. The optical damage resistance ability of Hf:Fe:LiNbO3 crystals was measured by the photo‐induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO3 crystals is enhanced with the increase of the [Li]/[Nb] ratio. The dependence of the optical damage resistance of Hf:Fe:LiNbO3 crystals on the defect structure is discussed in detail. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
996.
Liu Bo Li Chunliang Bi Jiancong Sun Liang Xu Yuheng 《Crystal Research and Technology》2008,43(3):260-265
Hf(2mol%):Fe(0.05wt%):LiNbO3 crystals with various [Li]/[Nb] ratios of 0.94, 1.05, 1.2 and 1.38 have been grown. The photorefractive resistant ability increases with the accretion of [Li]/[Nb] ratio. When the ratio of [Li]/[Nb] is 1.20 or 1.38, the OH‐ absorption band shifts to about 3477cm‐1. The mechanisms of the photorefractive resistant ability increase and the absorption band shift have been discussed. The exponential gain coefficient (Γ) of the crystals was measured with two‐beam coupling method and the effective charge carrier concentration (Neff) was calculated. The results show that Γ and Neff increase with the accretion of [Li]/[Nb] ratio. The temperature effect of codoped Hf:Fe:LiNbO3 crystals was also studied, it was found that the exponential gain coefficient increase dramatically at about 55°C, 70°C and 110°C, this is due to the inner electric field which is resulted from structure phase change. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
997.
Danielle J. Crouthers Shengda Ding Jason A. Denny Ryan D. Bethel Chung‐Hung Hsieh Michael B. Hall Marcetta Y. Darensbourg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(38):11254-11258
The Ph3PAu+ cation, renowned as an isolobal analogue of H+, was found to serve as a proton surrogate and form a stable Au2Fe2 complex, [(μ‐SAuPPh3)2{Fe(CO)3}2], analogous to the highly reactive dihydrosulfide [(μ‐SH)2{Fe(CO)3}2]. Solid‐state X‐ray diffraction analysis found the two SAuPPh3 and SH bridges in anti configurations. VT NMR studies, supported by DFT computations, confirmed substantial barriers of approximately 25 kcal mol−1 to intramolecular interconversion between the three stereoisomers of [(μ‐SH)2{Fe(CO)3}2]. In contrast, the largely dative S Au bond in μ‐SAuPPh3 facilitates inversion at S and accounts for the facile equilibration of the SAuPPh3 units, with an energy barrier half that of the SH analogue. The reactivity of the gold‐protected sulfur atoms of [(μ‐SAuPPh3)2{Fe(CO)3}2] was accessed by release of the gold ligand with a strong acid to generate the [(μ‐SH)2{Fe(CO)3}2] precursor of the [FeFe]H2ase‐active‐site biomimetic [(μ2‐SCH2(NR)CH2S){Fe(CO)3}2]. 相似文献
998.
A novel and efficient sample preconcentration technique based on the Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) coated with silica (SiO2) has been developed for extraction and determination of sulpiride. The functionalized MNPs showed excellent dispersibility in aqueous solution and were applied to magnetic solid‐phase extraction of sulpiride from human urine and blood prior to high‐performance liquid chromatography analysis. The separation, preconcentration and desorption procedure was completed in 10 min. Optimal experimental conditions, including sample pH, the amount of the MNPs, eluent type and volume, and the ultrasonication time were studied and established. The method showed good linearity for the determination of sulpiride in the concentration range of 10–1000 ng/mL in urine and blood. The recovery of the method was in the range between 91.2 and 97.5%, and the limit of detection was 2 ng/mL for sulpiride in human blood and urine. The results indicated that the present procedure is a suitable pretreatment method for biological samples. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
999.
Jin-Xiao Mi Cheng-Xin Wang Rong Li Yuanming Pan 《Journal of solid state chemistry》2010,183(12):2763-2769
A new iron phosphate (NH4)4Fe3(OH)2F2[H3(PO4)4] has been synthesized hydrothermally at HF concentrations from 0.5 to 1.2 mL. Single-crystal X-ray diffraction analysis reveals its three-dimensional open-framework structure (monoclinic, space group P21/n (No. 14), a=6.2614(13) Å, b=9.844(2) Å, c=14.271(3) Å, β=92.11(1)°, V=879.0(3) Å3). This structure is built from isolated linear trimers of corner-sharing Fe(III) octahedra, which are linked by (PO4) groups to form ten-membered-ring channels along [1 0 0]. This isolated, linear trimer of corner-sharing Fe(III) octahedra, [(FeO4)3(OH)2F2], is new and adds to the diverse linkages of Fe polyhedra as secondary building units in iron phosphates. The trivalent iron at octahedral sites for the title compound has been confirmed by synchrotron Fe K-edge XANES spectra and magnetic measurements. Magnetic measurements also show that this compound exhibit a strong antiferromagnetic exchange below TN=17 K, consistent with superexchange interactions expected for the linear trimer of ferric octahedra with the Fe-F-Fe angle of 132.5°. 相似文献
1000.
Pazderski L Pawlak T Sitkowski J Kozerski L Szlyk E 《Magnetic resonance in chemistry : MRC》2011,49(5):237-241
(1)H, (13)C and (15)N NMR studies of iron(II), ruthenium(II) and osmium(II) bis-chelated cationic complexes with 2,2':6',2″-terpyridine ([M(terpy)(2) ](2+) ; M = Fe, Ru, Os) were performed. Significant shielding of nitrogen-adjacent H(6) and deshielding of H(3'), H(4') protons were observed, both effects being mostly expressed for Fe(II) compounds. The metal-bonded nitrogens were shielded, this effect being much larger for the outer N(1), N(1″) than the inner N(1') atoms, and enhanced in the Fe(II) → Ru(II) → Os(II) series. 相似文献