全文获取类型
收费全文 | 5398篇 |
免费 | 36篇 |
国内免费 | 15篇 |
专业分类
化学 | 2300篇 |
晶体学 | 72篇 |
力学 | 250篇 |
数学 | 697篇 |
物理学 | 2130篇 |
出版年
2022年 | 50篇 |
2021年 | 80篇 |
2020年 | 86篇 |
2019年 | 103篇 |
2018年 | 131篇 |
2017年 | 127篇 |
2016年 | 160篇 |
2015年 | 58篇 |
2014年 | 123篇 |
2013年 | 238篇 |
2012年 | 203篇 |
2011年 | 192篇 |
2010年 | 208篇 |
2009年 | 194篇 |
2008年 | 225篇 |
2007年 | 185篇 |
2006年 | 212篇 |
2005年 | 171篇 |
2004年 | 149篇 |
2003年 | 126篇 |
2002年 | 141篇 |
2001年 | 141篇 |
2000年 | 129篇 |
1999年 | 81篇 |
1998年 | 98篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 53篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 67篇 |
1991年 | 56篇 |
1990年 | 85篇 |
1989年 | 53篇 |
1988年 | 55篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 58篇 |
1984年 | 67篇 |
1983年 | 55篇 |
1982年 | 68篇 |
1980年 | 55篇 |
1979年 | 48篇 |
1978年 | 49篇 |
1977年 | 60篇 |
1976年 | 60篇 |
1975年 | 57篇 |
1974年 | 61篇 |
1973年 | 73篇 |
1969年 | 45篇 |
排序方式: 共有5449条查询结果,搜索用时 15 毫秒
931.
A model of influence of non-heme Fe2+ ion on kinetics of electron transfer between quinone anion-radicals QA− and QB− in bacterial reaction centres is proposed and investigated. Physical mechanism of the influence is associated with singlet-triplet
transitions in QA−QB− Pair caused by interactions with paramagnetic Fe2+. The model incorporates exchange couplings between the particles and zero-field splittings in high-spin Fe2+. These interactions are shown to catalyze electron transfer in triplet pairs and alter the reaction yield significantly. 相似文献
932.
The lateral shift of a light beam reflected from the interface between an optically transparent dielectric and a medium for which the frequency dependences of the real and imaginary parts of the permittivity have a resonant form is investigated. At certain radiation frequencies and angles of incidence, a negative displacement of the reflected beam along the interface takes place. 相似文献
933.
934.
Olga V. Alekseeva Valeriya D. Shibaeva Andrew V. Noskov Vladimir K. Ivanov Alexander V. Agafonov 《Molecules (Basel, Switzerland)》2021,26(20)
In this study, an ionic liquid (IL), 1-butyl-3-methylimidazolium acetate, was used to prepare ionogels with microcrystalline cellulose (MCC) and halloysite (Hal). SEM, XRD, TG, DSC, FTIR spectroscopy, conductometry and mechanical tests were used to study the morphology, structure, thermal behaviour and electrophysical and mechanical characteristics of synthesised ionogels. XRD analysis showed a slight decrease in the interlayer space of halloysite in ionogels containing MCC, which may have been associated with the removal of residual water molecules resulting from hydrophilic IL anions and polymer macromolecules. A change in conductivity and glass-transition temperature of the ionic liquid was revealed due to intercalation into halloysite (a confinement effect) and modification with cellulose. For triple IL/Hal/MCC ionogels, the characteristic thermal degradation temperatures were higher than the corresponding values for IL/Hal composites. This indicates that the synthesised IL/Hal/MCC ionogels are characterised by a greater thermal stability than those of IL/Hal systems. 相似文献
935.
A new approach for photoregulation of supramolecular structure and optical properties of polyacrylic copolymers bearing azobenzene and cyanobiphenyl mesogenic groups is presented. The detailed study of photooptical behaviour, kinetics of photoinduced optical birefringence and mechanism of structural transformations taking place during a laser illumination are discussed. 相似文献
936.
Tatiana A. Vovk Semyon S. Rudyi Andrei V. Ivanov Evgeniy Y. Perlin Yuri V. Rozhdestvensky 《Physics letters. A》2019,383(9):923-928
One of the most interesting problems of modern physics is the realization of nanoparticles in macroscopic quantum states, in which they behave as a quantum objects. These states can only be implemented at ultra-low translational temperatures that have not been achieved so far. Here we develop a novel method for optical cooling of CaF2:Yb3+ nanocrystals, which is based on the coherent population transfer induced in the impurity ions by ultraviolet Raman pulses. A doped nanocrystal localized in a radio-frequency trap is cooled due to the photon recoil from the pulses of varied intensity. The proposed method allows to obtain nanocrystals with translational temperatures of the order of 10?9 K, which indicates that the nanocrystal approaches a macroscopic quantum state. 相似文献
937.
V. A. Ivanov Yu. V. Manilyuk V. F. Sannikov 《Journal of Applied Mechanics and Technical Physics》2018,59(4):594-600
Two-dimensional seiche oscillations in a rectangular basin of constant depth with an open entrance are considered within the framework of the linear theory of long waves. An analytical solution is obtained for the case where a nodal level line is located at the entrance to the basin. It is shown that transverse seiches in a basin with an open entrance are two-dimensional in contrast to similar modes in a completely closed basin, which are one-dimensional. Seiche parameters are calculated for model basins with dimensions and depth characteristic of a number of Sevastopol bays. Comparison of the calculation results with observations data shows that they are in satisfactory agreement. 相似文献
938.
Yu. F. Ivanov V. E. Kormyshev V. E. Gromov S. V. Konovalov A. D. Teresov A. P. Semin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2017,11(5):933-939
Structural phase states and tribological properties of the coating surfaced onto Hardox 450 martensite low-carbon steel with powder wire Fe?C?Cr?Nb?W and modified by subsequent electron-beam processing are studied by methods of modern physical material science. It is shown that irradiation of ~5 thick surfaced layer with high intensity pulsed electron beams results in the formation of ~20 μm thick surface layer with the master phases of α-Fe and NbC, Fe3C and M6C(Fe3W3C) carbides. The main difference of the surface layer modified with electron-beam processing from the unmodified volume of the surfacing is the morphology and dimensions of the second phase inclusions. In the modified layer of the surfacing the inclusions have smaller dimensions and are located in the form of interlayers along the grain boundaries. In unmodified surfacing the particles of the faceted shape located chaotically in the grain volume are the basic morphological type of the inclusions. It is noted that the small value of crystal lattice Nb parameter observed in the experiment may be caused by the high level of vacant interstitial sites having the smaller size in comparison with the occupied interstitial sites. It is established that wear resistance of the surfaced layer after electron-beam processing increases more than 70-fold relative to wear resistance of Hardox 450 steel and friction coefficient decreases significantly (~3-fold). 相似文献
939.
A. A. Rusinkevich A. S. Ivanov G. V. Belov M. V. Skupov 《Physics of Atomic Nuclei》2017,80(8):1470-1475
Calculation studies on the effect of carbon and oxygen impurities on the chemical and phase compositions of nitride uranium–plutonium fuel in the course of burnup are performed using the IVTANTHERMO code. It is shown that the number of moles of UN decreases with increasing burnup level, whereas UN1.466, UN1.54, and UN1.73 exhibit a considerable increase. The presence of oxygen and carbon impurities causes an increase in the content of the UN1.466, UN1.54 and UN1.73 phases in the initial fuel by several orders of magnitude, in particular, at a relatively low temperature. At the same time, the presence of impurities abruptly reduces the content of free uranium in unburned fuel. Plutonium in the considered system is contained in form of Pu, PuC, PuC2, Pu2C3, and PuN. Plutonium carbides, as well as uranium carbides, are formed in small amounts. Most of the plutonium remains in the form of nitride PuN, whereas unbound Pu is present only in the areas with a low burnup level and high temperatures. 相似文献
940.
S. N. Bagayev V. V. Osipov M. G. Ivanov V. V. Platonov A. N. Orlov A. V. Spirina S. M. Vatnik A. S. Kaygorodov 《Laser Physics》2009,19(5):1165-1168
About new technology of production of transparent ceramics including laser synthesis of nanopowders, their magnetic pulsed compaction and vacuum sintering is reported. The results of investigations of the synthesized samples of transparent ceramics made from neodymium-activated yttrium oxide are presented. It has been shown that in a 1.1 mm thickness sample with optical loss coefficient α1.07μm = 0.03 cm?1 laser generation at λ g ~ 1.08 μm with a slope efficiency of 15% at laser diode pumping at a wavelength of 807 nm has been obtained. 相似文献