全文获取类型
收费全文 | 1498篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
化学 | 937篇 |
晶体学 | 10篇 |
力学 | 16篇 |
数学 | 241篇 |
物理学 | 329篇 |
出版年
2023年 | 13篇 |
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 20篇 |
2019年 | 25篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 22篇 |
2014年 | 32篇 |
2013年 | 80篇 |
2012年 | 71篇 |
2011年 | 92篇 |
2010年 | 47篇 |
2009年 | 39篇 |
2008年 | 89篇 |
2007年 | 72篇 |
2006年 | 78篇 |
2005年 | 62篇 |
2004年 | 50篇 |
2003年 | 35篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 20篇 |
1999年 | 28篇 |
1998年 | 18篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1994年 | 19篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 18篇 |
1989年 | 21篇 |
1988年 | 9篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 23篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1973年 | 12篇 |
排序方式: 共有1533条查询结果,搜索用时 0 毫秒
1.
2.
V. Katchkanov J.F.W. Mosselmans S. Dalmasso K.P. ODonnell S. Hernandez K. Wang R.W. Martin O. Briot N. Rousseau G. Halambalakis K. Lorenz E. Alves 《Superlattices and Microstructures》2004,36(4-6):729
The local structure of Tm3+ ions incorporated into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure. The samples were doped either in situ during growth by Molecular Beam Epitaxy or by ion implantation of layers grown by Metal Organic Chemical Vapour Deposition. The implantation was done at ion energy of 300 keV and different nominal fluences of 3×1015, 4×1015 cm−2 and 5×1015 cm−2. The concentration of Tm in the samples studied was measured by Wavelength Dispersive X-ray analysis. For the in situ doped sample with concentration of 0.5%, and for all of the implanted samples, Tm was found on the Ga site in GaN. The ion implanted sample and an in situ doped sample with a similar concentration of Tm showed the same local structure, which suggests that the lattice site occupied by Tm does not depend on the doping method. When the average Tm concentration for in situ doped samples is increased to 1.2% and 2.0%, Tm is found to occupy the Ga substitutional site and the presence of a substantial number of Tm ions in the second coordination sphere indicates dopant clustering in the films. The formation of pure TmN clusters was found in an in situ doped sample with a dopant concentration of 3.4%. 相似文献
3.
Hans-Peter Gittel 《Mathematische Nachrichten》1991,154(1):117-127
The transonic potential flow problem is handled as a variational problem over a closed convex set which is given by a bound for the gas velocity and by a local entropy condition. It can be shown that the minimum problem has a solution though the functional need not be convex and the given set is not compact. Furthermore, the convergence of an approximation method (KATCHANOV'S method) for the solution to the corresponding variational inequality is proved. 相似文献
4.
5.
The subject of the investigations are precipitation zones, which grew as a result of chemical diffusion in AgPd30/CuSn6 bimetals. These precipitation zones have been characterized by metallography, electron probe microanalysis and x-ray diffraction. The growth of precipitation zones in the plating layer and in the substrate layer in dependence on time have been determined. The use of x-ray diffraction alone for the identification of the precipitates could not supply satisfying results in every case. This problem was solved by the application of electron probe microanalysis using a correction method, which allows the estimation of the chemical composition of small particles.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
6.
The thermal decomposition of a chloride and water-containing basic cobalt carbonate was studied. As a first step, crystal water is lost without change of structure. The following decomposition steps overlap and proceed in different ways, depending on the atmosphere over the sample: under nitrogen, chloride volatilizes as HCl and CoCl2; in air, oxidation occurs. CoO and Co3O4, respectively, are the final solid products at 700–800°. 相似文献
7.
Brack HP Padeste C Slaski M Alkan S Solak HH 《Journal of the American Chemical Society》2004,126(4):1004-1005
In this work a simple novel method for preparing micro- and nanoscale patterns of polymer chains grafted onto flexible polymer substrates is described. A combination of the two techniques of radiation grafting and "grafting-from" has been made. This combination makes it possible to prepare grafted structures having micro- or nanoscale lateral dimensions that are determined by the electron beam or X-ray irradiation patterns used. The height of the grafted features can be controlled by the irradiation dose or such grafting reaction conditions as time, temperature, or monomer concentration. Our first results for nanopatterned samples demonstrate resolution comparable to those of other polymer-based lithography processes. 相似文献
8.
We present a unified approach for linear and nonlinear sensitivity analysis for models of reaction kinetics that are stated in terms of systems of ordinary differential equations (ODEs). The approach is based on the reformulation of the ODE problem as a density transport problem described by a Fokker-Planck equation. The resulting multidimensional partial differential equation is herein solved by extending the TRAIL algorithm originally introduced by Horenko and Weiser in the context of molecular dynamics (J. Comp. Chem. 2003, 24, 1921) and discussed it in comparison with Monte Carlo techniques. The extended TRAIL approach is fully adaptive and easily allows to study the influence of nonlinear dynamical effects. We illustrate the scheme in application to an enzyme-substrate model problem for sensitivity analysis w.r.t. to initial concentrations and parameter values. 相似文献
9.
B. W. Wenclawiak Torsten Hees Corinna E. Z?ller Hans-Peter Kabus 《Fresenius' Journal of Analytical Chemistry》1997,358(4):471-474
An on-line system of supercritical fluid extraction (SFE) and high performance liquid chromatography (HPLC) via solid phase
extraction (SPE) is described for the determination of palladium and rhodium 2,2,6,6-tetramethyl-3,5-heptanedione-(thd) as
well as rhodium-acetylacetonate-(acac) and benzylacetonate-(bzac) chelates. The chelates were extracted with supercritical
CO2 from sand and humic acid, concentrated on SPE cartridges and analysed with HPLC. Two cartridge materials were tested and
compared to off-line trapping. The percentage of the breakthrough and cartridge retained material were measured in liquid
dichloromethane. The SFE conditions could be optimized to separate metal chelates during the extraction. The supercritical
fluid (SF) behaviour of different ligands on rhodium were investigated.
Received: 19 July 1996/Revised: 11 December 1996/Accepted: 14 December 1996 相似文献
10.
The advantages of microelectrodes such as the improvement of signal-to-noise ratio, the ability to perform electrochemical measurements in high resistive solutions and small RC-time constants give the possibility of an extended use for voltammetric and chronoamperometric techniques in analytical chemistry. In this comparative study, the microelectrode properties of three selected electrodes were examined. The characterization of a RAM-microarray electrode, an epoxy-impregnated carbon electrode and a conventional glassy carbon macroelectrode was performed by cyclic voltammetry at different scan rates, by DP-voltammetric measurements using different concentrations of supporting electrolyte and by transient measurements. It could be shown, that in comparison to the microarray electrode and to the glassy carbon macroelectrode, respectively, the results obtained by using the epoxy-impregnated carbon electrode are caused by its semimicroelectrode character. 相似文献