全文获取类型
收费全文 | 453164篇 |
免费 | 5714篇 |
国内免费 | 2408篇 |
专业分类
化学 | 250978篇 |
晶体学 | 6575篇 |
力学 | 18213篇 |
综合类 | 64篇 |
数学 | 54807篇 |
物理学 | 130649篇 |
出版年
2020年 | 3764篇 |
2019年 | 4156篇 |
2018年 | 4880篇 |
2017年 | 4890篇 |
2016年 | 7701篇 |
2015年 | 5360篇 |
2014年 | 7700篇 |
2013年 | 20018篇 |
2012年 | 16211篇 |
2011年 | 19647篇 |
2010年 | 13246篇 |
2009年 | 12867篇 |
2008年 | 17976篇 |
2007年 | 18145篇 |
2006年 | 16894篇 |
2005年 | 15652篇 |
2004年 | 13913篇 |
2003年 | 12258篇 |
2002年 | 12099篇 |
2001年 | 12763篇 |
2000年 | 9717篇 |
1999年 | 7527篇 |
1998年 | 6333篇 |
1997年 | 6325篇 |
1996年 | 6131篇 |
1995年 | 5546篇 |
1994年 | 5486篇 |
1993年 | 5411篇 |
1992年 | 5843篇 |
1991年 | 5889篇 |
1990年 | 5532篇 |
1989年 | 5441篇 |
1988年 | 5431篇 |
1987年 | 5294篇 |
1986年 | 5133篇 |
1985年 | 7035篇 |
1984年 | 7213篇 |
1983年 | 5951篇 |
1982年 | 6533篇 |
1981年 | 6136篇 |
1980年 | 5917篇 |
1979年 | 6050篇 |
1978年 | 6395篇 |
1977年 | 6305篇 |
1976年 | 6491篇 |
1975年 | 5868篇 |
1974年 | 6025篇 |
1973年 | 6302篇 |
1972年 | 4377篇 |
1971年 | 3459篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
L. K. Aminov I. N. Kurkin D. A. Lukoyanov K. P. Chernov 《Physics of the Solid State》1997,39(8):1184-1186
Results are reported for measurements of the spin-lattice relaxation times of E′1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz
over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of
the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency
dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation
of irradiation centers in crystalline quartz and quartz glass.
Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997) 相似文献
12.
The effect of iodine sorption on the free volume of polycarbonate is investigated by Positron Annihilation Lifetime method.
The observed results are interpreted in terms of the Charge Transfer Complex formation and precipitation of iodine at the
initial and final stages of sorption, respectively. At higher levels of sorption, changes in the second lifetime and its intensity
seem to suggest a conformational transformation, probably due to the net change in the amorphous-crystalline boundary regions
of the polymer matrix. The free volume cavities have been predominantly occupied by I-
3 species and the diffusion process obeys Fick’s law. An exponential type correlation has been observed between fractional
free volume and the diffusion coefficient.
Received: 13 June 1996/Accepted: 20 September 1996 相似文献
13.
Daniel L. Feldheim Del R. Lawson Charles R. Martin 《Journal of Polymer Science.Polymer Physics》1993,31(8):953-957
We report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation-exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-coun-terion interaction. © 1993 John Wiley & Sons, Inc. 相似文献
14.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
15.
Using an integral theory of grating diffraction we calculate efficiencies greater than 100% if a coating with gain is taken into account. A connection with guided modes is conjectured. The application in optical computing seems to be possible. 相似文献
16.
17.
L. A. Khalfin 《Journal of Mathematical Sciences》1987,36(5):616-626
The article surveys the main results of the statistical approach to the solution of ill-posed problems of mathematical physics, in application to specific ill-posed inverse problems in geophysics.Invited paper presented at the International Seminar on Mathematical Foundations of the Interpretation of Geophysical Fields, Moscow, May–June 1972.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 79, pp. 67–81, 1978. 相似文献
18.
19.