全文获取类型
收费全文 | 407547篇 |
免费 | 2290篇 |
国内免费 | 1047篇 |
专业分类
化学 | 188853篇 |
晶体学 | 5868篇 |
力学 | 24386篇 |
综合类 | 16篇 |
数学 | 71457篇 |
物理学 | 120304篇 |
出版年
2020年 | 3253篇 |
2019年 | 4081篇 |
2018年 | 16013篇 |
2017年 | 15812篇 |
2016年 | 13460篇 |
2015年 | 4437篇 |
2014年 | 7022篇 |
2013年 | 14018篇 |
2012年 | 14400篇 |
2011年 | 22899篇 |
2010年 | 15817篇 |
2009年 | 16469篇 |
2008年 | 18545篇 |
2007年 | 20470篇 |
2006年 | 10946篇 |
2005年 | 10762篇 |
2004年 | 10553篇 |
2003年 | 10175篇 |
2002年 | 9392篇 |
2001年 | 9601篇 |
2000年 | 7217篇 |
1999年 | 5429篇 |
1998年 | 4873篇 |
1997年 | 4771篇 |
1996年 | 4445篇 |
1995年 | 3883篇 |
1994年 | 3908篇 |
1993年 | 3887篇 |
1992年 | 4107篇 |
1991年 | 4463篇 |
1990年 | 4336篇 |
1989年 | 4408篇 |
1988年 | 4208篇 |
1987年 | 4217篇 |
1986年 | 3957篇 |
1985年 | 5032篇 |
1984年 | 5079篇 |
1983年 | 4314篇 |
1982年 | 4392篇 |
1981年 | 4241篇 |
1980年 | 3927篇 |
1979年 | 4498篇 |
1978年 | 4607篇 |
1977年 | 4777篇 |
1976年 | 4848篇 |
1975年 | 4526篇 |
1974年 | 4393篇 |
1973年 | 4654篇 |
1972年 | 3658篇 |
1971年 | 3389篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
We investigate theoretically the effects of optical absorption and saturation of the non-linear index of refraction on the
bistability of non-linear distributed feedback structures (NLDFBs). By assuming that the Kerr non-linearity saturates in an
exponential fashion, we obtain for the first time closed-form expressions for the so-called self-phase and cross-phase modulation
terms. Our investigation shows that both absorption and, in particular, saturation significantly affect the bistable properties
of this structure and in many cases eliminate this response completely. In some cases, however, saturation alters the NLDFB's
transfer characteristics in a potentially useful manner. We find that weak levels of saturation may increase the contrast
ratio between the intensities of the high and low bistable states. At increasing levels of saturation, where bistability is
no longer observed, we find regimes where the NLDFB structure could possibly be used for optical amplification.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
5.
E. Jackiewicz M. Lukasiak M. Kopcewicz K. Szpila N. Bakun-Czubarow 《Hyperfine Interactions》1992,70(1-4):993-996
Terrestrial basalt rocks considered to be a good analogues of the Martian regolith were studied by using the Mössbauer spectroscopy and X-ray diffraction. The weathering of basalts was followed by the changes of the Fe2+/Fe3+ ratio. The basalt rock undergoes alteration from primary mineral composition (olivine+pyroxene+plagioclase) through smectite to kaolinite clay with oxides and hydroxides with the increase of the Fe2+/Fe3+ ratio. 相似文献
6.
Ya. V. Fattakhov M. F. Galyautdinov T. N. L’vova I. B. Khaibullin 《Technical Physics》1997,42(12):1457-1459
The first results regarding the formation of a two-dimensional periodic structure of local melting regions on a silicon surface
upon pulsed light irradiation are presented. The conditions are established, and the mechanism of the formation of such structures
is discussed.
Zh. Tekh. Fiz. 67, 97–99 (December 1997) 相似文献
7.
A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons
coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a
high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either
absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally
quantized levels can be up to 66%.
Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997) 相似文献
8.
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
9.
10.