全文获取类型
收费全文 | 22256篇 |
免费 | 2909篇 |
国内免费 | 2025篇 |
专业分类
化学 | 9068篇 |
晶体学 | 401篇 |
力学 | 866篇 |
综合类 | 123篇 |
数学 | 723篇 |
物理学 | 16009篇 |
出版年
2024年 | 38篇 |
2023年 | 189篇 |
2022年 | 336篇 |
2021年 | 401篇 |
2020年 | 527篇 |
2019年 | 497篇 |
2018年 | 543篇 |
2017年 | 627篇 |
2016年 | 829篇 |
2015年 | 711篇 |
2014年 | 1270篇 |
2013年 | 2394篇 |
2012年 | 1118篇 |
2011年 | 1726篇 |
2010年 | 1256篇 |
2009年 | 1546篇 |
2008年 | 1463篇 |
2007年 | 1477篇 |
2006年 | 1311篇 |
2005年 | 1122篇 |
2004年 | 977篇 |
2003年 | 913篇 |
2002年 | 848篇 |
2001年 | 660篇 |
2000年 | 650篇 |
1999年 | 562篇 |
1998年 | 503篇 |
1997年 | 364篇 |
1996年 | 361篇 |
1995年 | 250篇 |
1994年 | 262篇 |
1993年 | 244篇 |
1992年 | 200篇 |
1991年 | 166篇 |
1990年 | 137篇 |
1989年 | 108篇 |
1988年 | 82篇 |
1987年 | 75篇 |
1986年 | 72篇 |
1985年 | 66篇 |
1984年 | 69篇 |
1983年 | 24篇 |
1982年 | 42篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1974年 | 8篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Electron paramagnetic resonance (EPR) investigations has been carried out on the new family of molybdenum doped vanadium sesquioxides (V1−xMox)2−δO3. The oxidation effects were monitored from the rate of paramagnetic V4+ created when the sample is exposed to the air. The effects of the oxidation time, sample temperature, and annealing at 1000 °C under a diluted hydrogen atmosphere on the EPR signal features are analyzed. The V4+ concentration in the oxidized samples is determined and the relaxation effects driven by the conduction electrons are pointed out from the thermal behaviour of the EPR line features. EPR spectra of all the oxidized samples also reveal a small ferromagnetic contribution strongly correlated with the V4+ content. 相似文献
122.
U. Turgut 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,86(4):353-359
The Coster-Kronig transition, f23, was determined using differential fluorescence cross sections of Ll X-ray for Th and U. The targets were irradiated an Am-241 radioisotope at the different incident angle. The Ll X-rays were counted with a Si (Li) detector at the different scattering angle varying from 60° to 90° at 10° intervals. For each angle, the Coster-Kronig transition probability, f23, was found. An obtained Coster-Kronig transition probability value was fitted versus emission angle. According to present results we can say that the Coster-Kronig transition probability, f23, shows isotropic distribution. 相似文献
123.
P.S Erdman M Fajardo K.M Sando W.C Stwalley 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,88(4):447-481
Experimental results are reported for a unique spectroscopic device called the Plasma Spectroscopy Cell. Optical absorption of lithium metal vapor was observed at high density and temperature. Absorption spectra are analyzed using theoretical calculations of absorption cross sections for lithium-helium interactions, and singlet and triplet state transitions of diatomic lithium in the visible spectral range. This is believed to be the most complex example yet calculated in which absolute bound-bound, bound-free, free-bound, and free-free contributions for all possible optically allowed transitions are all included, in quite respectable agreement with experiment. 相似文献
124.
It is suggested that the question of existence of a jamming phase transition in a broad class of single-lane cellular-automaton traffic models may be studied using a correspondence to the asymmetric chipping model. In models where such correspondence is applicable, jamming phase transition does not take place. Rather, the system exhibits a smooth crossover between free-flow and jammed states, as the car density is increased. 相似文献
125.
The Hawking radiation of Dirac particles on the event horizon of a nonuniformly rectilinearly accelerating black hole is studied in this paper. First, we construct the symmetrized null tetrad from which the spin coefficients and Dirac equation are derived. Next, by proposing generalized tortoise coordinate transformation, the decoupling problem of the Dirac equation with nonzero rest mass is solved. Finally, by analytic continuation, the Hawking thermal spectrum formula of Dirac particle for nonuniformly rectilinearly accelerating black hole is obtained. 相似文献
126.
We study the elastic responses of double-(ds) and single-stranded (ss) DNA at external force fields. A double-strand-polymer
elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity,
cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that short-ranged
base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairpin-coil transition in
ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized
by base pairing and base-pair stacking, into random coils. This phase transition is predicted to be of first order for stacking
potential higher than some critical level, in accordance with experimental observations. 相似文献
127.
The crystal structure of [N(CH3)4]3[As2Cl9] is determined at 293 K. It crystallizes in trigonal space group P31c: a = 9.2199(8), c = 21.065(3)Å, Z = 2, R1 = 0.0505, wR2 = 0.1283. The crystal is built of the discrete bioctahedral [As2Cl9]3— anions and the deformed tetramethylammonium cations. A structural phase transition in [N(CH3)4]3[As2Cl9] is detected by the DSC and dilatometric techniques at 146/151 K (on cooling/heating). Dielectric relaxation studies in the frequency range 75 kHz — 5 MHz indicate reorientations of the tetramethylammonium cations within the high temperature phase. Optical observations show the existence of the ferroelastic domain structure below 146 K. The possible mechanism of phase transition is discussed on the basis of the presented results. 相似文献
128.
M. B. Litvinova 《Journal of Applied Spectroscopy》2004,71(1):143-146
It has been established that undoped gallium crystals exhibit anti-Stokes radiation with energy corresponding to the interband recombination of these crystals. Its appearance is most probably determined by EL2 defects, and its intensity depends on the product of the cross sections for photoionization of electrons and the holes from these defects. 相似文献
129.
130.
A new double pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated. The noise figure is improved by about 2.6 dB with the incorporation of broadband conventional-band fiber Bragg grating (FBG) in between the two segments of erbium-doped fiber. By incorporating both the pre-amplifier and the FBG, the noise figure is further improved, which varies from 4.0 to 5.0 dB in the flat gain region from 1570 to 1600 nm. The gain varies from 32.0 to 33.4 dB within this region. The new amplifier with high gain and low noise figure can be useful as an inline amplifier in a wavelength division multiplexing transmission system. 相似文献