全文获取类型
收费全文 | 38479篇 |
免费 | 1403篇 |
国内免费 | 160篇 |
专业分类
化学 | 24142篇 |
晶体学 | 244篇 |
力学 | 658篇 |
综合类 | 4篇 |
数学 | 5909篇 |
物理学 | 9085篇 |
出版年
2023年 | 262篇 |
2022年 | 357篇 |
2021年 | 596篇 |
2020年 | 565篇 |
2019年 | 559篇 |
2018年 | 571篇 |
2017年 | 565篇 |
2016年 | 1151篇 |
2015年 | 1023篇 |
2014年 | 1068篇 |
2013年 | 2023篇 |
2012年 | 2081篇 |
2011年 | 2488篇 |
2010年 | 1387篇 |
2009年 | 1307篇 |
2008年 | 2183篇 |
2007年 | 2082篇 |
2006年 | 1960篇 |
2005年 | 1743篇 |
2004年 | 1380篇 |
2003年 | 1222篇 |
2002年 | 1063篇 |
2001年 | 840篇 |
2000年 | 712篇 |
1999年 | 585篇 |
1998年 | 465篇 |
1997年 | 477篇 |
1996年 | 536篇 |
1995年 | 432篇 |
1994年 | 425篇 |
1993年 | 437篇 |
1992年 | 424篇 |
1991年 | 341篇 |
1990年 | 312篇 |
1989年 | 260篇 |
1988年 | 245篇 |
1987年 | 275篇 |
1986年 | 276篇 |
1985年 | 312篇 |
1984年 | 353篇 |
1983年 | 274篇 |
1982年 | 302篇 |
1981年 | 292篇 |
1980年 | 273篇 |
1979年 | 236篇 |
1978年 | 241篇 |
1977年 | 233篇 |
1976年 | 203篇 |
1975年 | 180篇 |
1973年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
J. Carlos Díaz-Ramos Ramón Vázquez-Lorenzo 《Differential Geometry and its Applications》2006,24(4):433-442
Explicit examples of Osserman 4-manifolds with exactly two distinct eigenvalues of the Jacobi operators, α and β=4α≠0, are given. The former has multiplicity two and is a double root of the minimal polynomial of the Jacobi operators. 相似文献
42.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
43.
44.
45.
46.
A. Guzmn E. Luna J. Miguel-Snchez E. Calleja E. Muoz 《Infrared Physics & Technology》2003,44(5-6):377-382
In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed. 相似文献
47.
48.
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
49.
The rational and sustainable exploitation of nature resources is one of the priority objectives of our society. In this article a method is proposed to evaluate and exploit the energetic resources contained in different forest formations. This method is based on the use of a combustion bomb calorimeter to determine the calorific values of the different samples studied. These results were complemented with chemical analysis of the samples and with environmental and geomorphological studies of the zones were samples were taken. The results obtained during the last 3 years for the residual biomass originated from the forest formations existing in Galicia ensure the reliability and usefulness of the method that can be extended to any forest formation all over the world. 相似文献
50.