全文获取类型
收费全文 | 285篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 139篇 |
晶体学 | 10篇 |
力学 | 21篇 |
综合类 | 1篇 |
数学 | 40篇 |
物理学 | 84篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 5篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 35篇 |
2012年 | 24篇 |
2011年 | 25篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有295条查询结果,搜索用时 15 毫秒
261.
The curing of epoxidized natural rubber with p-phenylenediamine catalyzed by bisphenol A was investigated. The curing reaction was found to be first order with respect to the amine and to have an activation energy of 67.5 kJ/mol. Vulcanizates of tensile strength 12.5–16.0 MPa were obtained at cure times of 30–75 min at 180°C. The amine-cured vulcanizate was observed to be more rigid than the sulfur-cured one at room temperature consistent with its relatively high Tg. Stress-strain analysis and dynamic mechanical properties indicated that the high Tg of the amine-cured vulcanizate could be attributed to the bulky amine crosslinks and hydrogen bonding effect of bisphenol A. © 1994 John Wiley & Sons, Inc. 相似文献
262.
Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites 总被引:1,自引:0,他引:1
Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks. 相似文献
263.
Unsteady flow in a semi-infinite contracting or expanding pipeis reinvestigated using long series analysis. The proposed seriesmethod is useful in analysing the problem for a moderately largeconstant ( = aa/, where a = a(t), the radius of the pipe isa function of time, a(t) is the velocity of the wall, and iskinematic viscosity). For positive values of (expansion ofthe pipe) accuracy of the series representing shear stress andpressure gradient is increased from = 2.89 to = 6.0 by extractingthe singularity followed by completion of the series. For negativevalues of (contraction of the pipe), we revert the series whichresults into the increase of the region of validity of the transposedseries from = -25.0 to = -2.89. Later we use Padé approximantsfor summing them. Also, the asymptotic solution for large valuesof is obtained and it agrees closely with pure numerical valuesof shear stress at the wall and pressure gradient. 相似文献
264.
A polyvinyl alcohol (PVA) cellulose electrolyte was prepared by casting a solution of PVA and H3PO4 on both sides of a cellulose membrane (filter paper). The ionic species H+ are caused by the H3PO4 acid which is entrapped inside the PVA and in the pores of the filter paper. The electrolyte was sandwiched between two carbon
electrodes to form an electric double layer capacitor (EDLC). The EDLC exhibits a good charge and discharge characteristics
with a capacitance value of 30 Fg−1.
Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 –
8, 2005. 相似文献
265.
266.
O. Abdulaziz N.F.M. Noor I. Hashim M.S.M. Noorani 《Chaos, solitons, and fractals》2008,36(5):1405-1411
The Adomian decomposition method (ADM) is treated as an algorithm for approximating the solutions of the Lorenz and Chen systems in a sequence of time intervals, i.e. the classical ADM is converted into a hybrid analytical–numerical method. Comparisons with the seventh- and eighth-order Runge–Kutta method (RK78) reconfirm the very high accuracy of the hybrid analytical–numerical ADM. 相似文献
267.
Effect of substrate temperature on the morphological,structural,and optical properties of RF sputtered Ge_(1-x)Sn_x films on Si substrate
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this study, Ge_(1-x)Sn_x alloy films are co-sputtered on Si(100) substrates using RF magnetron sputtering at different substrate temperatures. Scanning electron micrographs, atomic force microscopy(AFM), Raman spectroscopy, and x-ray photoemission spectroscopy(XPS) are conducted to investigate the effect of substrate temperature on the structural and optical properties of grown Ge Sn alloy films. AFM results show that RMS surface roughness of the films increases from 1.02 to 2.30 nm when raising the substrate temperature. This increase could be due to Sn surface segregation that occurs when raising the substrate temperature. Raman spectra exhibits the lowest FWHM value and highest phonon intensity for a film sputtered at 140?C. The spectra show that decreasing the deposition temperature to 140?C improves the crystalline quality of the alloy films and increases nanocrystalline phase formation. The results of Raman spectra and XPS confirm Ge–Sn bond formation. The optoelectronic characteristics of fabricated metal-semiconductor-metal photodetectors on sputtered samples at room temperature(RT) and 140?C are studied in the dark and under illumination. The sample sputtered at 140?C performs better than the RT sputtered sample. 相似文献
268.
H. Saleh & I. Hashim 《advances in applied mathematics and mechanics.》2016,8(2):279-292
Magnetohydrodynamic natural convection heat transfer in a rotating, differentially
heated enclosure is studied numerically in this article. The governing equations
are in velocity, pressure and temperature formulation and solved using the
staggered grid arrangement together with MAC method. The governing parameters
considered are the Hartmann number, 0≤$Ha$≤70, the inclination angle of the magnetic
field, 0$^◦$≤$θ$≤90$^◦$, the Taylor number, 8.9×10$^4$≤$Ta$≤1.1×10$^6$ and the centrifugal force
is smaller than the Coriolis force and the both forces were kept below the buoyancy
force. It is found that a sufficiently large Lorentz force neutralizes the effect of buoyancy,
inertial and Coriolis forces. Horizontal or vertical direction of the magnetic field
is the most effective in reducing the global heat transfer. 相似文献
269.
首先包含Higgs粒子的六维算符用物理场来表示,然后给出包含HHV和HVV相互作用顶点的有效拉氏量,其中V=A,Z,W^±。最后,推导出每个六维算符和有效拉氏量的费曼规则。 相似文献
270.
Plasma waves are oscillations of electron density in time and space, and in deep submicron field effect transistors, typical plasma frequencies, ωp, lie in the terahertz (THz) range and do not involve any quantum transitions. Hence, using plasma wave excitation for detection and/or generation of THz oscillations is a very promising approach. In this paper, the investigation of plasma wave interaction between the plasma waves propagating in a short-channel High-Electron-Mobility Transistor (HEMT) and the radiated electromagnetic waves was carried out. Experimentally, we have demonstrated the detection of the terahertz (THz) radiation by an AlGaAs/GaAs HEMT up to third harmonic at room temperature and their resonant responses show very good agreement with the calculated results. 相似文献