全文获取类型
收费全文 | 1359篇 |
免费 | 62篇 |
国内免费 | 5篇 |
专业分类
化学 | 902篇 |
晶体学 | 7篇 |
力学 | 17篇 |
数学 | 198篇 |
物理学 | 302篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 31篇 |
2020年 | 29篇 |
2019年 | 25篇 |
2018年 | 10篇 |
2017年 | 15篇 |
2016年 | 47篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 62篇 |
2012年 | 70篇 |
2011年 | 94篇 |
2010年 | 52篇 |
2009年 | 47篇 |
2008年 | 64篇 |
2007年 | 80篇 |
2006年 | 88篇 |
2005年 | 50篇 |
2004年 | 63篇 |
2003年 | 28篇 |
2002年 | 26篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 19篇 |
1998年 | 24篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 16篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1972年 | 9篇 |
排序方式: 共有1426条查询结果,搜索用时 15 毫秒
1.
Positivity - We prove new characterisations of exponential stability for positive linear discrete-time systems in ordered Banach spaces, in terms of small-gain conditions. Such conditions have... 相似文献
2.
3.
4.
Adam Kiersnowski Jochen S. Gutmann Jacek Pigłowski 《Journal of Polymer Science.Polymer Physics》2007,45(17):2350-2367
ε‐caprolactone was polymerized in the presence of neat montmorillonite or organomontmorillonites to obtain a variety of poly(ε‐caprolactone) (PCL)‐based systems loaded with 10 wt % of the silicates. The materials were thoroughly investigated by different X‐ray scattering techniques to determine factors affecting structure of the systems. For one of the nanocomposites it was found that varying the temperature in the range corresponding to crystallization of PCL causes reversible changes in the interlayer distance of the organoclay. Extensive experimental and literature studies on this phenomenon provided clues indicating that this effect might be a result of two‐dimensional ordering of PCL chains inside the galleries of the silicate. Small angle X‐ray scattering and wide angle X‐ray scattering investigation of filaments oriented above melting point of PCL revealed that polymer lamellae were oriented perpendicularly to particles of unmodified silicate, while in PCL/organoclay systems they were found parallel to clay tactoids. Calorimetric and microscopic studies shown that clay particles are effective nucleating agents. In the nanocomposites, PCL crystallized 20‐fold faster than in the neat polymer. The crystallization rate in nanocomposites was also significantly higher than in microcomposite. Further research provided an insight how the presence of the filler affects crystalline fraction and spherulitic structure of the polymer matrix in the investigated systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2350–2367, 2007 相似文献
5.
Upon irradiation, cyclic enol ethers such as 1-methoxy-cyclopentene (4) mainly add across the cyano group of benzonitrile (1), under formation of 2-azabutadienes of an imidoester type. This is in agreement with the so-called Δ G-correlation which was reported earlier (ref. 5 and 6). 4-Phenyloxazole (9) is formed from 1 and 1,3-dioxole (5) probably by a similar photochemical process followed by electrocyclic ring opening and hydrolysis. The low yield of the latter photoreaction and the almost exergonic electron transfer between 5 and 1 may point to back electron transfer as the main energy wasting process. From 1 and 2,3-dihydrido-furan (2) only the ortho cycloadduct 6 has been isolated in low yields. 相似文献
6.
7.
8.
Markus Hegland Jochen Garcke Vivien Challis 《Linear algebra and its applications》2007,420(2-3):249-275
The combination technique has repeatedly been shown to be an effective tool for the approximation with sparse grid spaces. Little is known about the reasons of this effectiveness and in some cases the combination technique can even break down. It is known, however, that the combination technique produces an exact result in the case of a projection into a sparse grid space if the involved partial projections commute.
The performance of the combination technique is analysed using a projection framework and the C/S decomposition. Error bounds are given in terms of angles between the spanning subspaces or the projections onto these subspaces. Based on this analysis modified combination coefficients are derived which are optimal in a certain sense and which can substantially extend the applicability and performance of the combination technique. 相似文献
9.
Michael Höft Jochen Weinzierl Rolf Judaschke 《International Journal of Infrared and Millimeter Waves》2002,23(7):1127-1146
Holography is a promising technique for power combining applications in the frequency range of short millimeter and submillimeter waves. In this paper, quasi-optical holographic power combining circuits are investigated. An equivalent network is utilized which rigorously models horn arrays and biperiodic dielectric structures in order to design computer-generated holograms. We apply the network model to a 5-element quasi-optical power combiner and demonstrate its capability. The hologram is designed for 150 GHz and has an efficiency of 92.5 % with a 90 % bandwidth of 5.3 %. With the aid of a broadband waveguide power divider and a vector field measurement system, the circuit is analyzed. 相似文献
10.