全文获取类型
收费全文 | 5411篇 |
免费 | 673篇 |
国内免费 | 573篇 |
专业分类
化学 | 3339篇 |
晶体学 | 157篇 |
力学 | 520篇 |
综合类 | 37篇 |
数学 | 416篇 |
物理学 | 2188篇 |
出版年
2024年 | 13篇 |
2023年 | 54篇 |
2022年 | 122篇 |
2021年 | 160篇 |
2020年 | 189篇 |
2019年 | 139篇 |
2018年 | 151篇 |
2017年 | 184篇 |
2016年 | 208篇 |
2015年 | 183篇 |
2014年 | 251篇 |
2013年 | 534篇 |
2012年 | 316篇 |
2011年 | 386篇 |
2010年 | 222篇 |
2009年 | 361篇 |
2008年 | 341篇 |
2007年 | 343篇 |
2006年 | 298篇 |
2005年 | 250篇 |
2004年 | 266篇 |
2003年 | 205篇 |
2002年 | 238篇 |
2001年 | 142篇 |
2000年 | 148篇 |
1999年 | 109篇 |
1998年 | 118篇 |
1997年 | 90篇 |
1996年 | 116篇 |
1995年 | 76篇 |
1994年 | 80篇 |
1993年 | 64篇 |
1992年 | 49篇 |
1991年 | 41篇 |
1990年 | 28篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有6657条查询结果,搜索用时 187 毫秒
91.
J. Popplewell A. Al-Qenaie S. W. Charles R. Moskowitz K. Raj 《Colloid and polymer science》1982,260(3):333-338
The thermal conductivity of a number of ferrofluids consisting of colloidally dispersed Fe3O4 particles in diester, hydrocarbon, water and fluorcarbon carriers have been measured at 38°C. The variation in thermal conductivity with particle concentration is well described by Tareef's equation (1940). This has enabled the ratio of the physical to magnetic size to be determined and compared with estimates of the ratio obtained from electron micrographs and magnetic measurements.The fit between theory and experiment is particularly good for hydrocarbon carrier fluids giving the ratio of solid to magnetic radiusR
i/R
m=1.24±0.03 compared with the value obtained from magnetic data and electron micrographs of 1.19±0.07. The corresponding value from the fluids with a diester carrier ranges between 1.1<R
d/R
m<1.3 which is again consistent with microscopy and magnetic data.The application of a magnetic field of 0.1 T had no noticeable effect on the thermal conductivities of ferrofluids. 相似文献
92.
An anomaly is found in the vicinity of Tmax 560$ K on electric resistance versus temperature curves for yttrium hightemperature superconductors of the 123 phase. Xray phase analysis suggests a structural phase transition in the vicinity of Tmax due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band. 相似文献
93.
由聚苯胺粒子组成的电流变液的研究 总被引:6,自引:1,他引:6
由经碱处理的掺杂态聚苯胺(PAn)制得高介电常数的半导体PAn粒子,将其悬浮于电绝缘油可组成电流变液,讨论了电流变(ER)液的静态屈服应力(τ_s),电流密度等性能与PAn的介电常数(ε_p),导电率(σ),体积分数和应用电场强度的关系。对导电率相同的PAn粒子,用氨水处理的PAn粒子ε_p较用NaOH液处理的高,前者在σ足够低如σ≤1.0×10 ̄(-7)/cm时,ER液的τ_s随偶极系数的平方(β ̄2)的增大而呈现非线性增加;后者ER液的τ_s随β ̄2的增大出现一最大值.结果表明:由聚苯胺粒子可组成高电流变活性的无水ER液. 相似文献
94.
Laurence E. Strong Thomas G. Copeland Margaret Darragh Carter Van Waes 《Journal of solution chemistry》1980,9(2):109-128
Conductivities of aqueous solutions ofortho-, meta-, andpara-toluic acids have been measured for the concentration range 0.1–2 millimolar and at 5° intervals from 5 to 100°C. At each temperature pK
a(m) andA
0 have been calculated using the paired ion model recently described by Fuoss. Thermodynamic parameters have been calculated for the ionization of each acid, and Walden products for the anions. Results are discussed in terms of contributions to acidity by enthalpy and entropy changes as well as by hydration of the various solute species. 相似文献
95.
A copolymer of poly(acrylonitrile-co-styrene) (SAN) was synthesized via an emulsion polymerization method. Novel polymer electrolyte membranes cast from the blends of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), SAN and fumed silica (SiO2) are microporous and can be used in polymer lithium-ion batteries. The membrane shows excellent characteristics such as high ionic conductivity and good mechanical strength when the mass ratio between SAN and PVDF-HFP and SiO2 is 3.5/31.5/5. The ionic conductivity of the membrane soaked in a liquid electrolyte of 1 mol/L LiPF6/EC/DMC/DEC is 4.9×10-3 S cm-1 at 25℃. The membrane is electrochemical stable up to 5.5 V versus Li /Li in the liquid electrolyte. The influences of SiO2 content on the porosity and mechanical strength of the membranes were studied. Polymer lithium-ion batteries based on the membranes were assembled and their performances were also studied. 相似文献
96.
Dr. Dingfeng Yang Junzhu Yang Xuejun Quan Bin Zhang Guoyu Wang Xu Lu Xiaoyuan Zhou 《Chemphyschem》2021,22(24):2579-2584
Understanding the correlation between crystal structure and thermal conductivity in semiconductors is very important for designing heat-transport-related devices, such as high-performance thermoelectric materials and heat dissipation in micro-nano-scale devices. In this work, the lattice thermal conductivity ( ) of the cage-like compounds Cu3VSe4 and Cu3NbSe4 was investigated by experimental measurements and first-principles calculations. The experimental of Cu3NbSe4 is approximately 25 % lower than that of Cu3VSe4 at 300 K. The relevant important physical parameters, including the sound velocity, heat capacity, weighted phonon phase space (W), and third-order force constants along with atomic mass were theoretically analyzed. It is found that W is the dominant parameter in determining the , and the other factors only play a minor role. The physical origin is the relatively “soft” lattice of Cu3NbSe4 with heavier atomic mass. This research provides deep insight into the correlation between the thermal conductivity and crystal structure and paves the way for discovering high-performance thermal management device and thermoelectric materials with intrinsically low . 相似文献
97.
Structure, thermal elongation coefficient, and conductivity of Y1 ? x Ca x Cr1 ? y Me y O3 (Me = Mg, Cu) in air are studied at 100–1000°C. Electrochemical activity of electrodes made of most conducting compositions Y1 ? x Ca x Cr1 ? y Me y O3 (Me = Mg, Cu), contacting solid electrolyte 0.9ZrO2 + 0.1Y2O3, is studied over a wide range of polarizations, in air, at 700–900°C. 相似文献
98.
W/O型微乳液活化能和导电机理研究 总被引:15,自引:0,他引:15
电导行为是微乳液的重要性质之一。自Lagourette和Lagues发现了W/O型微乳液电导渗透(Percolation)现象后,人们开始了微乳液导电机理的研究。较流行的观点认为,界面层中表面活性剂分子的阴离子在微乳颗粒碰撞时发生跃迁而使W/O型微乳液具有导电性。 相似文献
99.
B. Sourd P. André J. Aubreton M.-F. Elchinger 《Plasma Chemistry and Plasma Processing》2007,27(2):225-240
In this paper, the calculated values of the viscosity and thermal conductivity of nitrogen plasma are presented taking into
account five (e, N, N+, N2 and N2+) or eight (e, N(4S), N(2P), N(2D), N(R), N+, N2 and N2+) species. The calculations are based on the supposition that the temperature dependent probability of occupation of the states
is given by the Boltzmann factor. The domain for which the calculations are performed, is for p = 1 and 10 atm in the temperature range from 5,000 K to 15,000 K. Classical collision integrals are used in calculating the
transport coefficients and we have introduced new averaged collision integrals where the weight associated at each interacting
species pair is the probable collision frequency. The influence of the collision integral values and energy transfer between
two different species is studied. These results are compared which those of published theoretical studies. 相似文献
100.
S. N. Shkerin D. I. Bronin S. A. Kovyazina V. P. Gorelov A. V. Kuz'min Z. S. Martem'yanova S. M. Beresnev 《Journal of Structural Chemistry》2003,44(2):216-221
Electric conductivity, Raman spectra, and thermal expansion of La0.88Sr0.12Ga0.82Mg0.18O2.85 solid solution (LSGM1218) based on lanthanum gallate were studied at various temperatures, and Xray phase analysis was performed at room temperature. Dilatometric measurements showed that secondorder phase transitions occur at 775±10$ and 880± 20 K. The transition around 880 K is confirmed by Raman spectra and by a change in the conductivity activation energy in this temperature range. This transition is associated with a symmetry change in the oxygen sublattice. 相似文献