全文获取类型
收费全文 | 272165篇 |
免费 | 2675篇 |
国内免费 | 912篇 |
专业分类
化学 | 121433篇 |
晶体学 | 4037篇 |
力学 | 10826篇 |
综合类 | 1篇 |
数学 | 26192篇 |
物理学 | 79537篇 |
无线电 | 33726篇 |
出版年
2020年 | 2245篇 |
2019年 | 2476篇 |
2018年 | 3109篇 |
2017年 | 3026篇 |
2016年 | 4568篇 |
2015年 | 2776篇 |
2014年 | 4659篇 |
2013年 | 11060篇 |
2012年 | 8426篇 |
2011年 | 10406篇 |
2010年 | 7523篇 |
2009年 | 7809篇 |
2008年 | 10282篇 |
2007年 | 10622篇 |
2006年 | 10047篇 |
2005年 | 9177篇 |
2004年 | 8583篇 |
2003年 | 7603篇 |
2002年 | 7485篇 |
2001年 | 8495篇 |
2000年 | 6762篇 |
1999年 | 5491篇 |
1998年 | 4798篇 |
1997年 | 4656篇 |
1996年 | 4343篇 |
1995年 | 4064篇 |
1994年 | 3978篇 |
1993年 | 4027篇 |
1992年 | 4046篇 |
1991年 | 4216篇 |
1990年 | 3943篇 |
1989年 | 3797篇 |
1988年 | 3741篇 |
1987年 | 3330篇 |
1986年 | 3202篇 |
1985年 | 4168篇 |
1984年 | 4390篇 |
1983年 | 3540篇 |
1982年 | 3666篇 |
1981年 | 3616篇 |
1980年 | 3498篇 |
1979年 | 3531篇 |
1978年 | 3628篇 |
1977年 | 3568篇 |
1976年 | 3633篇 |
1975年 | 3322篇 |
1974年 | 3314篇 |
1973年 | 3369篇 |
1972年 | 2374篇 |
1971年 | 1967篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
V. N. Jmerik A. M. Mizerov T. V. Shubina A. V. Sakharov A. A. Sitnikova P. S. Kop’ev S. V. Ivanov E. V. Lutsenko A. V. Danilchyk N. V. Rzheutskii G. P. Yablonskii 《Semiconductors》2008,42(12):1420-1426
Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells. Structural and optical properties of the Al x Ga1 ? x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm. 相似文献
42.
The optical properties of bismuth telluride crystals doped with donor-and acceptor-type impurities are studied. The fact that energy corresponding to the resonance frequency of plasma oscillations of free charge carriers (plasmons) approaches the band-gap energy is detected in the infrared spectral region, where the main elementary excitations in the electronic system of these materials are observed. The mentioned approach of energies varies the intensity of electron-plasmon interaction, which affects the recombination processes in the materials widely used for the fabrication of thermoelectric energy converters. 相似文献
43.
M. M. Zverev N. A. Gamov D. V. Peregoudov V. B. Studionov E. V. Zdanova I. V. Sedova S. V. Gronin S. V. Sorokin S. V. Ivanov P. S. Kop’ev 《Semiconductors》2008,42(12):1440-1444
Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ~0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ~8.5% are attained for the electron-beam energy of 23 keV. 相似文献
44.
A fine-grained reconfigurable architecture based on double gate technology is proposed and analyzed. The logic function operating on the first gate of a double-gate (DG) transistor is reconfigured by altering the charge on its second gate. Each cell in the array can act as logic or interconnect, or both, contrasting with current field-programmable gate array structures in which logic and interconnect are built and configured separately. Simulation results are presented for a fully depleted SOI DG-MOSFET implementation and contrasted with two other proposals from the literature based on directed self-assembly. 相似文献
45.
R. Hefelmann P. Mann A. Aignan F. Filsinger und H. Amsel 《Fresenius' Journal of Analytical Chemistry》1902,41(1):66-68
Ohne Zusammenfassung 相似文献
46.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous. 相似文献
47.
48.
Silica@copper (SiO2@Cu) core–shell nanoparticles were synthesized and well characterized by XRD, TEM, AFM, XPS, UV/Vis, TGA–MS, and ICP–AES techniques. The synthesized SiO2@Cu core–shell nanoparticles were employed as catalysts for the conjugate addition of amines to α,β‐unsaturated compounds in water to obtain β‐amino carbonyl compounds in excellent yields in shorter reaction times. Furthermore, the catalyst works well for hetero‐Michael addition reactions of heteroatom nucleophiles such as thiols to α,β‐unsaturated compounds. As the reaction is performed in water, it allows for easy recycling of the catalyst with consistent activity. 相似文献
49.
50.
V. P. Ershov D. A. Kas’yanov V. I. Rodchenkov D. A. Sergeev 《Crystallography Reports》2008,53(2):339-343
The growth of the isolated (100) face of a KDP crystal at exposure of the phase boundary to the initial ultrasound field and a standing acoustic wave has been investigated. A significant growth response of this face, exposed to sound normally along the acoustic axis in the near zone of a piston-like half-wave vibrator with f = 20 kHz and tangentially in the pulsed two-frequency (f = 600 and 900 kHz) standing-wave mode, has been revealed. It is shown that the mechanisms of mass exchange enhancement in these acoustic modes are different. The results obtained show a fundamental possibility of controlling crystal growth and dissolution by varying the parameters of inhomogeneous acoustic field. 相似文献