全文获取类型
收费全文 | 1019篇 |
免费 | 75篇 |
国内免费 | 94篇 |
专业分类
化学 | 400篇 |
晶体学 | 11篇 |
力学 | 85篇 |
数学 | 58篇 |
物理学 | 634篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 18篇 |
2021年 | 28篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 26篇 |
2017年 | 49篇 |
2016年 | 44篇 |
2015年 | 61篇 |
2014年 | 48篇 |
2013年 | 62篇 |
2012年 | 41篇 |
2011年 | 101篇 |
2010年 | 45篇 |
2009年 | 63篇 |
2008年 | 73篇 |
2007年 | 77篇 |
2006年 | 67篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 34篇 |
2002年 | 18篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 33篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1948年 | 1篇 |
排序方式: 共有1188条查询结果,搜索用时 8 毫秒
141.
Arshak L. Vartanian Mkrtich A. Yeranosyan Albert A. Kirakosyan 《Physica E: Low-dimensional Systems and Nanostructures》2005,27(4):447-456
Using a variational technique, the effect of electron-longitudinal optical (LO) phonon interaction on the ground and the first few excited states of a hydrogenic impurity in a semiconductor quantum wire of rectangular cross section under an external electric field is studied theoretically for the impurity atom doped at various positions. The results for the binding energy as well as polaronic correction are obtained as a function of the size of the wire, the applied uniform electric field and the position of the impurity. It is found that the presence of optical phonons changes significantly the values of the impurity binding energies of the system. Taking into account the electron–LO phonon interaction the 1s→2py and 1s→2pz transition energies are calculated as a function of applied electric field for different impurity positions. 相似文献
142.
Summary The excitation of metastable states in an atomic beam apparatus by means of electron collision is a widespread technique.
We have observed a large bistable behaviour in our apparatus designed to provide an intense and collimated beam of metastable
helium by excitation with orthogonally impinging electrons. This bistable behaviour largely affects the efficiency of the
apparatus and is therefore worth of being carefully investigated. The apparatus has an electrode configuration equivalent
to that of a tetrode valve with large intergrid distances. The bistability consists in a hysteresis cycle in the curve of
the anode currentvs. grid voltage. Experimental measurements, supported by a simple theoretical model and by numerical simulation, stress out
the crucial role played by space charge effects for the onset of bistability. A comparison with previous observation of this
phenomenon is given. Spontaneous current oscillations with various shapes have been recorded in one of the two curves of the
hysteresis cycle. 相似文献
143.
电场驱动的高分子凝胶 总被引:1,自引:0,他引:1
本文较系统地阐述了电场驱动的高分子水凝胶、有机凝胶的响应机理,并扼要介绍了此类凝胶应用的最新进展。 相似文献
144.
电弧-AES法测定金属硅中12个杂质元素 总被引:2,自引:0,他引:2
用直流电弧粉末法在氩气气氛中摄谱,消除硅带干扰,采用铍为内标,直接测定金属硅中12个杂质元素,此法较化学光谱法具有操作简便、快速,试剂耗量少;较化学法和分光光度法更加优越,能同时测定12个元素,更能反映金属硅的真实含量。 相似文献
145.
This paper presents detailed numerical calculations of the dielectrophoretic force in traps designed for single-cell trapping. A trap with eight planar electrodes is studied for spherical and ellipsoidal particles using the boundary element method (BEM). Multipolar approximations of orders one to three are compared with the full Maxwell stress tensor (MST) calculation of the electrical force on spherical particles. Ellipsoidal particles are also studied, but in their case only the dipolar approximation is available for comparison with the MST solution. The results show that a small number of multipolar terms need to be considered in order to obtain accurate results for spheres, even in the proximity of the electrodes, and that the full MST calculation is only required in the study of non-spherical particles. 相似文献
146.
Zhi-Hai Zhang Kang-Xian GuoBin Chen Rui-Zhen WangMin-Wu Kang Shuai Shao 《Superlattices and Microstructures》2010
The optical absorption coefficients and the changes in the refractive index in GaAs/AlGaAs parabolic quantum dots(QDs) with applied electric and magnetic fields are studied in detail. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using a compact density matrix approach and an iterative procedure. Finally, the calculated results show the incident optical intensity, the frequencies of the confined potential of the QDs and the applied electric and magnetic fields have a great influence on the optical absorption coefficients and refractive index changes in this system. 相似文献
147.
László Janovák 《Applied Surface Science》2010,256(9):2809-1312
Poly(acrylamide) [poly(AAm)] and poly(N-isopropyl-acrylamide) [poly(NIPAAm)] based gel films containing Au nanoparticles (d = 14 ± 2.5 nm) were synthesized. Monomers and cross-linker were added to a gold nanodispersion, and after the addition of the initiator, polymer films were prepared on the surface of an interdigital microelectrode by photopolymerization. In the course of the syntheses the gold concentration of the films was constant (10.8 μg/cm2) and the volume fraction of Au nanoparticles (?Au) in the polymer gel films varied in the range of 0.58-85.3%. Poly(AAm)-based films swell when the temperature increases: due to a temperature shift of 15 °C the Au plasmon absorption maximum at λ = ∼532 nm was shifted towards shorter wavelengths by 16.6 nm (blue shift) through the swelling of the polymer gel film. In the case of poly(NIPAAm) the temperature-induced shrinking resulted in a red shift, namely the maximum was shifted by 18.07 nm by a temperature shift of 15 °C. In the case of both composites, the electric conductivity of the samples was shown to increase with increasing Au particle concentration. In the case of the poly(AAm)-based composite containing ?Au = 0.85 gold the resistance of the film spread on the surface of the electrode was 0.16 MΩ at 25 °C and 0.66 MΩ at 50 °C, i.e. the conductivity of the sample decreased with increasing temperature. The opposite effect is observed in the case of the poly(NIPAAm)-based composite: as temperature is raised, the resistance of the composite abruptly drops at the point of collapse of the NIPAAm gel (it is 0.28 MΩ at 32 °C and only 0.021 MΩ at 35 °C). This thermosensitive effect was detectable only at sufficiently high Au contents (?Au = 0.85) in both gels. 相似文献
148.
In the work, short multi-walled carbon nanotubes (S-CNTs) were synthesized by chopping conventional μm-long multi-walled carbon nanotubes (L-CNTs) under ultrasonication in H2SO4/HNO3 mixed acids. A comparative electrochemical investigation performed in 6 M KOH solution demonstrated that a specific capacitance (SC) of ca. 14.6 μF cm−2 was delivered by the S-CNTs with the specific surface area (SSA) of 207 m2 g−1, much larger than that of ca. 10.1 μF cm−2 for the L-CNTs with the SSA of 223 m2 g−1, the reason for which was that S-CNTs with two open ends, due to good ion penetrability, provided more entrances for electrolyte ions to access the inner surface easily through their shorter inner pathway so as to enhance their SSA utilization and geometric SC. The surface structure disruption of S-CNTs, owing to ultrasonication and oxidation during chopping process, deteriorated their electronic conductivity and resulted in an inferior power property in contrast to L-CNTs. 相似文献
149.
Abstract The photovoltaic effect in Cu2s-CdS heterojunction has been the subject of study by a large number of investigators. Proper heat treatment of the junction plays crucial role in optimizing the performance of the heterojunction. In this paper, after a brief review of the work on Cu2S-CdS heterojunctions, the profile of copper in CdS as a function of heat treatment will be discussed. The diffusion of copper from Cu2S into CdS has been studied at various temperatures, by radioactive tracer methods. This has a bearing on the spectral response of the Cu2S-CdS cells as a function of heat treatment. 相似文献
150.
Jin Ming Luo Jing Qiang Xing-Yong Zhang Jun Tang 《Communications in Nonlinear Science & Numerical Simulation》2013,18(11):3219-3225
The dynamical behavior of spiral waves in a period-2 oscillatory medium is investigated under the influence of an external applied alternating current field. Open and closed transversal line defects which wiggle along the direction parallel to the wave fronts, are generated in the spiral-wave patterns when the stimulus frequency of the electric field is equal to one, three or five times of the local oscillatory frequency in the period-2 state. Their generations are directly related with the change in the spatial wavelength induced by the electric field. These wigglings proliferate along the transverse direction parallel to the wave fronts as the stimulus strength increases, and become denser when the stimulus frequency increases by multiples of the period-2 oscillatory frequency. 相似文献