全文获取类型
收费全文 | 2242篇 |
免费 | 537篇 |
国内免费 | 432篇 |
专业分类
化学 | 1802篇 |
晶体学 | 51篇 |
力学 | 53篇 |
综合类 | 18篇 |
数学 | 45篇 |
物理学 | 1242篇 |
出版年
2024年 | 19篇 |
2023年 | 49篇 |
2022年 | 151篇 |
2021年 | 123篇 |
2020年 | 176篇 |
2019年 | 119篇 |
2018年 | 114篇 |
2017年 | 125篇 |
2016年 | 139篇 |
2015年 | 117篇 |
2014年 | 180篇 |
2013年 | 187篇 |
2012年 | 141篇 |
2011年 | 141篇 |
2010年 | 106篇 |
2009年 | 117篇 |
2008年 | 139篇 |
2007年 | 121篇 |
2006年 | 93篇 |
2005年 | 94篇 |
2004年 | 76篇 |
2003年 | 82篇 |
2002年 | 83篇 |
2001年 | 78篇 |
2000年 | 101篇 |
1999年 | 57篇 |
1998年 | 39篇 |
1997年 | 35篇 |
1996年 | 31篇 |
1995年 | 31篇 |
1994年 | 23篇 |
1993年 | 17篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有3211条查询结果,搜索用时 15 毫秒
1.
Vishal Sipani Ann Kirsch Alec B. Scranton 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4409-4416
The effective propagation rate constant (kp; averaged over all the propagating active centers) was characterized for solvent‐free cationic photopolymerizations of phenyl glycidyl ether over the entire range of conversions, including the high conversion regime in which mass transfer limitations become important. The profile for the kp as a function of conversion was found to exhibit a constant plateau value at low to intermediate conversions, followed by a monotonic increase above a threshold value of conversion. To explain this trend, it is proposed that at high conversion the diffusional mobility of the photoinitiator counterion is reduced whereas the mobility of the cationic active center remains high because of reactive diffusion. Therefore, with increasing conversion, the average distance between the active centers and counterions may increase, resulting in an increase in the propagation rate constant. The profiles for the kp values were investigated as a function of the temperature, photoinitiator anion, and photoinitiator concentration. As the photoinitiator concentration was increased, the plateau value of the effective propagation rate constant decreased whereas the threshold conversion increased. All of the experimental trends are consistent with the proposed increase in ion separation at high conversions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4409–4416, 2004 相似文献
2.
Michael Stoukides 《Research on Chemical Intermediates》2006,32(3):187-204
Solid electrolyte membrane reactors (SEMRs) have been used to both study and influence catalytic reaction rates. Methane coupling
is the reaction most thoroughly and intensively studied in these membrane reactors. In the last 20 years, oxygen ion (O2−), proton (H+) and mixed (O2−-e−, H+-e−) conducting membranes have been tested in order to maximize the conversion of methane to C2 compounds. The present review contains the fundamental operating principles of the various SEMR types and their applications
in this reaction. The difficulties that should be overcome in order to promote this SEMR process to an industrial scale are
discussed. 相似文献
3.
作为一种洁净能源,硅锗合金的热电转换性能的研究越来越受到人们的重视.本文重点研究了不同Ge浓度的硅锗合金以及Si、Ge单晶在300~1100K温度范围内,Seebeck系数随温度的变化.并对组分相同导电类型不同、晶向不同以及结晶状态不同的样品的Seebeck系数进行了比较.在研究温度区间,Seebeck系数的绝对值大小一般在200~600μV/K之间,随温度不同连续变化.通过对比发现SiGe合金的Seebeck系数大小不仅与Ge的浓度和温度有关,其他因素对其绝对值也有影响,其中晶向最为明显,表现出了明显的各向异性.此外,材料本身的电阻率除了作为一个热电参数影响最优值外,其大小还对Seebeck系数的绝对值有影响,即掺杂济浓度对Seebeck系数的影响. 相似文献
4.
M. Sadiq M. Bensitel K. Nohair J. Leglise C. Lamonier 《Journal of Saudi Chemical Society》2012,16(4):445-449
The synthesis of vanadyl phosphate by reaction of an alcoholic solution of V2O5 and o-H3PO4 has been studied. The solids obtained were investigated by various physico-chemical techniques as in situ X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) under inert atmosphere. The compounds have been further characterized by infrared and UV–Visible spectroscopies. The isopropanol conversion is carried out to evaluate the catalytic activity of the samples. The isopropanol conversion increases with the reaction temperature from 433 to 503 K for vanadyl phosphorus oxides calcined at a different temperature. However, the conversion attains 100% at 503 K, and the solid calcined at 973 K exhibits high selectivity towards propene (100% at 503 K). 相似文献
5.
A new thin-film electro-optic switch employing two stable states of polarization is proposed and investigated. The design can be further employed to realize a TE-TM polarization converter by constructing a Mach-Zehnder type interferometer integrated optical switch. The limitations and design procedures for electro-optic devices are also discussed. 相似文献
6.
在把离子伯恩斯坦波处理成对快阿尔芬波的响应下,导出了点火托卡马克等离子体的离子回旋共振加热的二阶模转换方程。这个二阶方程的数值积分表明,结果与由高阶方程的计算很好地一致。只有在弱阻尼的情况下,α粒子吸收的功率才是重要的。 相似文献
7.
Drevensek Olenik I Kocevar K Musevic I Rasing T 《The European physical journal. E, Soft matter》2003,11(2):169-175
Brewster-angle reflection ellipsometry and surface optical
second harmonic generation were used to study the growth of
4'-n-octyl-4-cyanobiphenyl
(8CB) films evaporated in air onto polymeric and quartz glass
substrates. The layer-by-layer growth of the films terminates
after formation of two distinctive interfacial layers. Both of
these two layers are polar and tilted. In the first layer the
molecules lie nearly flat on the surface, while in the second
layer they point on average about 50° toward the surface normal.
The dipole moment of the second layer has a lower magnitude and
an opposite direction with respect to the dipole moment of the
first layer. 相似文献
8.
R.-D. Herzberg N. Amzal J.E. Bastin F. Becker P.M.T. Brew P.A. Butler A.J.C. Chewter J.F.C. Cocks O. Dorvaux K. Eskola J. Gerl P.T. Greenlees N.J. Hammond K. Hauschild K. Helariutta F. Heßberger M. Houry A. Hürstel R.D. Humphreys G.D. Jones P.M. Jones R. Julin S. Juutinen H. Kankaanpää H. Kettunen T.L. Khoo W. Korten P. Kuusiniemi Y. Le Coz M. Leino A.P. Leppänen C.J. Lister R. Lucas M. Muikku P. Nieminen R.D. Page T. Page P. Rahkila P. Reiter Ch. Schlegel C. Scholey G. Sletten O. Stezowski Ch. Theisen W.H. Trzaska J. Uusitalo H.J. Wollersheim 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):205-208
In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei 253, 254No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator
RITU at the University of Jyv?skyl?. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations.
The implications for the ground-state configuration of 253No are discussed.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: rdh@ns.ph.liv.ac.uk
RID="b"
ID="b"Present address: GANIL, F-14021 Caen, France.
RID="c"
ID="c"Permanent address: IReS Strasbourg, IN2P3-CNRS, F-67037-Strasbourg, France.
RID="d"
ID="d"Present address: CEA/DIF DCRE/SDE/LDN F-91680 Bruyeres-le-Chatel.
RID="e"
ID="e"Present address: Daresbury Laboratory, Daresbury WA4 4AD, UK.
RID="f"
ID="f"Permanent address: IPN Lyon, IN2P3-CNRS, F-69037 Lyon, France. 相似文献
9.
Kadyrzhanov K. K. Rusakov V. S. Turkebaev T. E. Vereschak M. F. Kerimov E. A. Plaksin D. A. 《Hyperfine Interactions》2002,141(1-4):453-457
Beryllium coating of the iron foil is made by means of magnetron sputtering. Mössbauer studies are performed by means of two registration techniques: conversion electron Mössbauer spectroscopy (CEMS) and the γ-ray technique in absorption geometry. Performed investigations confirm the original thermodynamic approach to creation of thermally stable multi-layer materials.
相似文献10.