全文获取类型
收费全文 | 1890篇 |
免费 | 318篇 |
国内免费 | 52篇 |
专业分类
化学 | 969篇 |
晶体学 | 206篇 |
力学 | 13篇 |
综合类 | 4篇 |
数学 | 8篇 |
物理学 | 1060篇 |
出版年
2024年 | 5篇 |
2023年 | 10篇 |
2022年 | 35篇 |
2021年 | 35篇 |
2020年 | 42篇 |
2019年 | 39篇 |
2018年 | 36篇 |
2017年 | 52篇 |
2016年 | 95篇 |
2015年 | 49篇 |
2014年 | 58篇 |
2013年 | 200篇 |
2012年 | 99篇 |
2011年 | 167篇 |
2010年 | 94篇 |
2009年 | 119篇 |
2008年 | 117篇 |
2007年 | 116篇 |
2006年 | 108篇 |
2005年 | 87篇 |
2004年 | 92篇 |
2003年 | 66篇 |
2002年 | 88篇 |
2001年 | 44篇 |
2000年 | 61篇 |
1999年 | 51篇 |
1998年 | 58篇 |
1997年 | 35篇 |
1996年 | 30篇 |
1995年 | 34篇 |
1994年 | 32篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有2260条查询结果,搜索用时 437 毫秒
51.
Since the physical properties of lithium borate glasses xLi2O-(1-x)B2O3 (0<x< 0.28) vary over a wide range with the composition, this binary system is particularly suitable for studying the relationship
between vibrational anharmonicity and fragility. The density, the linear expansion coefficient, the longitudinal and transverse
ultrasonic velocities and their respective temperature coefficients of the velocities are measured, from which the vibrational
anharmonicity in lithium borate glasses is evaluated with the help of the Grüneisen parameter at the Debye cut-off frequency
and the Anderson-Grüneisen parameter: these two parameters plotted vs. composition have the same characteristics with minima at x≈0.08. The fragility is evaluated from the temperature width of the glass transition; the fragility also shows a minimum at
x≈0.08. The presence of minima at x≈0.08 is ascribable to the fact that the crosslinking density between six-membered rings in the glass reaches a maximum at
this composition. We show that the anharmonic parameters strongly correlate with the fragility metrics.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
52.
Nithyanandhan J Jayaraman N Davis R Das S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(3):689-698
A series of azobenzene-functionalized poly(alkyl aryl ether) dendrimers have been synthesized and their photochemical and photophysical properties in solution and as thin films have been investigated. Although the photochemical behavior of the azodendrimers in solution indicated that the azobenzene units behave independently, very similar to the constituent monomer azobenzene unit, the properties of thin solid films of the dendrimers were distinctly different. The azodendrimers, AzoG1, AzoG2, and AzoG3 were observed to form stable supercooled glasses, which showed long-wavelength absorption and red emission characteristics of J-aggregates of the azobenzene chromophores. Reversible photoinduced isomerization of the azodendrimers in the glassy state is described. 相似文献
53.
Rouxel Tanguy Massouras Georges Sorarù Gian-Domenico 《Journal of Sol-Gel Science and Technology》1999,14(1):87-94
The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in-situ ultrasonic echography measurements. Temperature induced changes include structural relaxation and densification from 1000 to 1200°C, and crystallization to form a fine and homogeneous -SiC/glass-matrix nanocomposite with 2.5 nm large crystals above 1200°C. Young's modulus measurements clearly reveal a consolidation of the material upon annealing below 1200°C. Crystallization is almost complete after few hours at 1300°C and results in a significant increase in Young's modulus. The viscosity of the oxycarbide glass is much higher than that of fused silica, with two orders of magnitude difference at 1200°C, and the glass transition temperature ranges from 1320 to 1370°C. 相似文献
54.
选择水杨基荧光酮-乳化剂OP-盐酸为显色体系,应用双波长分光光度法扣除硫酸锌的基体干扰,不分离直接测定了湿法炼锌过程中硫酸锌净化液中的痕量锗。测定范围在0-40mg/L。本法应用于株洲冶炼厂锌净化液中锗的测定,结果与该厂长期的萃取-比色法结果相吻合,而测定速度较萃取-比色法至少提高了一倍。 相似文献
55.
P. Melnikov R. Rolim A. Delben J. R. Delben A. C. Souza A. E. Job 《Journal of Thermal Analysis and Calorimetry》2004,75(1):87-93
Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
56.
Takeuchi Y Nishikawa M Hachiya H Yamamoto H 《Magnetic resonance in chemistry : MRC》2005,43(8):662-664
High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium. 相似文献
57.
Min-zhi Chen Xiao-liang Wang Fang-fang Tao Qi Xue Ping-chuan 《高分子科学》2007,(1):107-111
The concept of entanglement provides the basis of our current understanding of the flow behavior of polymer melts, Current techniques developed to investigate the degree of interpenetration of polymer chains only provide indirectly the information of the degree of entanglement in a relatively large scale (several to tens of nanometer). In this article, we report ^1H-NMR spectroscopy with dipolar filters under fast magic angle spinning for probing chain interpenetration of polymer glasses at the molecular level. 相似文献
58.
A review of the synthesis and properties of ionenes is presented. Particular attention is paid to the electrical and related properties of conductive teteracyano-p-quinodimethane (TCNQ) complex salts of ionenes containing ammonium or sulfonium groups in the main chain and to their chemical stability. The recent work on preparation of such ionenes with inorganic and organic counterions which show interesting linear and nonlinear optical properties is also discussed. It is shown that in the solid state ionenes act as a kind of a matrix fixing, in a chemically controlled way, positions and distribution of different kinds of counterions. Because the reaction of counterion exchange is easy in the case of ionenes it provides a convenient way to prepare a broad class of polyelectrolytes with many different properties. 相似文献
59.
The heat capacity and the heat content of bismuth niobate BiNbO4 and bismuth tantalate BiTaO4 were measured by the relaxation method and Calvet-type heat flux calorimetry. The temperature dependencies of the heat capacities in the form Cpm=128.628+0.03340 T−1991055/T2+136273131/T3 (J K-1 mol-1) and 133.594+0.02539 T−2734386/T2+235597393/T3 (J K-1 mol-1) were derived for BiNbO4 and BiTaO4, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K Sm(BiNbO4)=147.86 J K-1 mol-1 and Sm(BiTaO4)=149.11 J K-1 mol-1 were assessed from the low temperature heat capacity measurements. To complete a set of thermodynamic data of these mixed oxides an attempt was made to estimate the values of the heat of formation from the constituent binary oxides. 相似文献
60.
A. V. Safronova L. N. Bochkarev N. E. Stolyarova I. K. Grigorieva I. P. Malysheva G. V. Basova G. K. Fukin E. V. Baranov Yu. A. Kurskii G. A. Abakumov 《Russian Chemical Bulletin》2006,55(2):218-221
New germanium-containing tungsten carbyne complexes Ph3GeC≡W(CH2R)3 (R = But or SiMe3) were synthesized by the reaction of the alkoxy derivative Ph3GeC≡W(OBut)3 with alkyllithium reagents RCH2Li. The new compounds were isolated in individual form as crystals in 95 and 90% yields, respectively, and were characterized
by elemental analysis, 1H and 13C NMR spectroscopy, and X-ray diffraction. X-ray diffraction study showed that the coordination environment of the W and Ge
atoms in the Ph3GeC≡ W(CH2But)3 and Ph3GeC≡W(CH2SiMe3)3 complexes can be described as a distorted tetrahedron.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 213—216, February, 2006. 相似文献