全文获取类型
收费全文 | 59567篇 |
免费 | 2199篇 |
国内免费 | 117篇 |
专业分类
化学 | 38023篇 |
晶体学 | 287篇 |
力学 | 1800篇 |
综合类 | 2篇 |
数学 | 10129篇 |
物理学 | 11642篇 |
出版年
2023年 | 418篇 |
2022年 | 458篇 |
2021年 | 788篇 |
2020年 | 876篇 |
2019年 | 838篇 |
2018年 | 1531篇 |
2017年 | 1169篇 |
2016年 | 1834篇 |
2015年 | 1613篇 |
2014年 | 1680篇 |
2013年 | 3406篇 |
2012年 | 3890篇 |
2011年 | 4076篇 |
2010年 | 2472篇 |
2009年 | 2152篇 |
2008年 | 3563篇 |
2007年 | 3527篇 |
2006年 | 3156篇 |
2005年 | 3035篇 |
2004年 | 2582篇 |
2003年 | 2152篇 |
2002年 | 1848篇 |
2001年 | 1099篇 |
2000年 | 995篇 |
1999年 | 698篇 |
1998年 | 527篇 |
1997年 | 497篇 |
1996年 | 598篇 |
1995年 | 391篇 |
1994年 | 458篇 |
1993年 | 438篇 |
1992年 | 462篇 |
1991年 | 404篇 |
1990年 | 402篇 |
1989年 | 377篇 |
1988年 | 307篇 |
1987年 | 316篇 |
1986年 | 281篇 |
1985年 | 448篇 |
1984年 | 431篇 |
1983年 | 294篇 |
1982年 | 402篇 |
1981年 | 377篇 |
1980年 | 325篇 |
1979年 | 312篇 |
1978年 | 319篇 |
1976年 | 314篇 |
1975年 | 280篇 |
1974年 | 269篇 |
1973年 | 269篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We present the design and study of waveguide structures based on porous silicon where the light confinement is not due to the usual total reflection effect but to the use of photonic crystals (PCs) as confining walls. These PC are omnidirectional mirrors (OMs), consisting of the periodic repetition of two porous silicon layers with different refractive indices and thicknesses. They reflect the radiation for all angles of incidence within a frequency range called the omnidirectional band gap (OBG). We have followed the PC formalism to investigate the properties of the OM as a multimode waveguide: the number of modes within the band gap, their field spatial distribution and their confinement as a function of the frequency and the core thickness. 相似文献
62.
63.
In this Note, we study a 2×2 system of evolution equations with some codimension 3 crossing. We derive two conditions of non-degeneracy. We focus on one of them and reduce our system to some Landau–Zener's type system. Using this reduction, we describe the energy transfer at the crossing by Landau–Zener formula for 2-scales semi-classical measures. To cite this article: C. Fermanian Kammerer, P. Gérard, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 915–920. 相似文献
64.
65.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
66.
Bajdik J. Pintye-Hódi K. Novák Cs. Kelemen A. Regdon G. Erős I. 《Journal of Thermal Analysis and Calorimetry》2002,68(2):613-627
The extents of the protective effects of coating films on the surface of crystals were determined. Three different samples
were made with different quantities of coating fluid (Sepifilm LP 010 in 10% aqueous solution). Since the atomizing rate was
constant, the coating time increased in parallel with the volume of coating fluid applied. The direct measurement of film
thickness and smoothness is very difficult, and therefore indirect methods were used. Dimenhydrinate was chosen as model drug;
this is a heat-sensitive antihistamine with a low melting point. This temperature can be reached during the tableting process.
The behaviour of samples on exposure to heat was examined by differential scanning calorimetry. The water uptakes of the samples
were determined with an Enslin apparatus. Plasticity was studied with an instrumented tablet machine. These indirect methods
(thermal conductivity, water uptake and plasticity measurements) revealed connections between the results of the various experiments.
An overlong coating time decreased the protective effect of the coating film.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
67.
Jesús Vázquez 《Tetrahedron letters》2006,47(10):1657-1661
Use of a semicarbazide resin for the solid-phase preparation of peptide ketones and aldehyde led to optimal results in terms of both purity of the final product and overall yield. This resin was prepared without complication by activation of the commercial available aminomethyl polystyrene with CDI at room temperature, followed by treatment with tert-butyl carbazate. Furthermore, the TNBSA colorimetric assay has been adapted for checking the incorporation of the carbonyl moiety onto hydrazine-based resins. 相似文献
68.
69.
I. M. Kolthoff S. R. Cooper V. J. Tulane F. Reimers H. A. J. Pieters K. Höppner V. H. Matula C. B. Macek W. N. Skworzow J. S. Schepelewa F. Čuta K. Kámen S. Cohen R. E. Oesper D. S. Narayanamurthi T. R. Seshadri H. M. State A. W. Kirssanow W. M. Tscherkassow D. M. Mukherjee T. Akiyama Y. Mine S. Yabe Y. Volmar M. Déribéré 《Analytical and bioanalytical chemistry》1937,111(5-6):192-197
70.
J.-C. Thomas L. Achouri J. Äystö R. Béraud B. Blank G. Canchel S. Czajkowski P. Dendooven A. Ensallem J. Giovinazzo N. Guillet J. Honkanen A. Jokinen A. Laird M. Lewitowicz C. Longour F. de Oliveira Santos K. Peräjärvi M. Stanoiu 《The European Physical Journal A - Hadrons and Nuclei》2004,21(3):419-435