全文获取类型
收费全文 | 2303篇 |
免费 | 405篇 |
国内免费 | 596篇 |
专业分类
化学 | 1541篇 |
晶体学 | 100篇 |
力学 | 103篇 |
综合类 | 24篇 |
数学 | 9篇 |
物理学 | 872篇 |
无线电 | 655篇 |
出版年
2024年 | 6篇 |
2023年 | 31篇 |
2022年 | 41篇 |
2021年 | 40篇 |
2020年 | 44篇 |
2019年 | 57篇 |
2018年 | 55篇 |
2017年 | 80篇 |
2016年 | 81篇 |
2015年 | 101篇 |
2014年 | 104篇 |
2013年 | 190篇 |
2012年 | 149篇 |
2011年 | 156篇 |
2010年 | 126篇 |
2009年 | 139篇 |
2008年 | 147篇 |
2007年 | 202篇 |
2006年 | 178篇 |
2005年 | 158篇 |
2004年 | 160篇 |
2003年 | 159篇 |
2002年 | 189篇 |
2001年 | 140篇 |
2000年 | 99篇 |
1999年 | 109篇 |
1998年 | 84篇 |
1997年 | 70篇 |
1996年 | 50篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有3304条查询结果,搜索用时 15 毫秒
21.
由Q-Nd:YAG脉冲激光(波长1.06μm,脉宽10 ns)烧蚀Al靶产生等离子体.观测了在低气压和直流电场条件下的Al等离子体发射光谱.研究了激光功率密度和直流电场对各谱线强度的影响,分析了谱线半高全宽与外加电压,等离子体电子温度与激光能量的变化规律.结果表明,直流电场对铝原子谱线强度有显著的增强,铝原子谱线的半高全宽与直流电场的外加电压基本上呈线性关系. 相似文献
22.
E. V. Voronina E. P. Yelsukov A. V. Korolyov A. E. Yelsukova 《Hyperfine Interactions》2006,168(1-3):1079-1083
The experimental data from Mössbauer spectroscopy and magnetic measurements are presented as functions of the temperature and external magnetic field for a B2-type ordered Fe 66 Al 34 alloy. 相似文献
23.
G. Coudenys I. Moeeman G. Vermeire F. Vermaerke Y. Zhu P. Van Daele P. Demeester E. Maayan B. Elsner J. Salzman E. Finkman 《Journal of Electronic Materials》1994,23(2):225-232
The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate
during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of
photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate.
Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials.
Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked
channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor
pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow
mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore,
we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible
for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth. 相似文献
24.
25.
František Toman Ludvík Beneš 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):231-236
Differential molar adsorption enthalpies (DMAE) were determined by gas chromatographic measurements of specific retention
volume of vapors on the surface of two forms of Mg–Al hydrotalcite. A linear dependence of the DMAE on the number of the carbon
atoms in hydrocarbons was observed for both form of hydrotalcite. The dependence of the differential molar adsorption enthalpies
on the number of chlorine atoms in organic molecules is discussed. A linear dependence of DMAE on the molecular weight of
chloroderivatives of methane and ethylene on the basic form in an order monochloromethane < dichloromethane < trichloromethane
or vinylidene chloride < 1,1-dichloroethylene < trichloroethylene was found. 相似文献
26.
Haihong Fang Binyuan Hu Lingshen Wang Rongli Lu Cui Yang 《Frontiers of Chemistry in China》2008,3(2):193-197
Nanometer MgO was prepared via a sol-gel auto-combustion technique using magnesium nitrate as raw material and citric acid
as chelating agent. IR spectra of the dried gel were used to investigate the structure of the precursors. By studying the
different TG curves of magnesium citrate gel prepared by different methods, we found that a combustion process occurred and
the nitrate ions acted as an oxidant in the combustion process. TEM photographs of synthesized powders from the sol-gel auto-combustion
showed that the crystallites were uniform in size. In addition, the XRD pattern of this sample showed that the particle size
was 8.9 nm. The BET curves, in turn, showed that the specific surface of the sample was 26.34 m2/g. The mechanism of the frothing process in restraining agglomeration is discussed.
__________
Translated from Journal of East China Normal University (Natural Science), 2007, (2): 52–57 [译自: 华东师范大学学报(自然科学版)] 相似文献
27.
本文从速率方程出发,讨论了类锂铝复合等离子体的激发态结构,衰减常数,反转率和小信号增益等表征介质增益特性的物理量以及它们随电子温度,电子密度和光子逃逸几率的变化。找到了进行类锂铝离子通过复合机制产生X光激光设计应创造的等离子体状态目标区域。还讨论了这些物理量随原子序数变化的定标律。 相似文献
28.
In this Letter, structural properties of liquid Ni20Al80 have been studied through molecular dynamics (MD) simulations, and results agree well with X-ray experiments. The prepeak in the structure factor manifests the existence of medium-range structural order (MRSO) in liquid Ni20Al80. Analyses in MRSO reveal the dominance of ideal icosahedra and defective icosahedra which, furthermore, form clusters and share common atoms. 相似文献
29.
A 27Al nuclear magnetic resonance (NMR) investigation at room temperature of the Pb1 − xAlxF2 + x (0 ≤ x ≤ 0.12) solid solution and of the ordered Pb9Al2F24 phase is carried out. Two different types of aluminium ions are identified and their ratio is determined as a function of x. A clustering process based on the formation of column clusters, more and more extended when x increases, is proposed on the basis of results issued from the 19F (Part I) and 27Al NMR investigations. 相似文献
30.
Spin-lattice relaxation mechanisms in kaolinite have been reinvestigated by magic-angle spinning (MAS) of the sample. MAS is useful to distinguish between relaxation mechanisms: the direct relaxation rate caused by the dipole-dipole interaction with electron spins is not affected by spinning while the spin diffusion-assisted relaxation rate is. Spin diffusion plays a dominant role in 1H relaxation. MAS causes only a slight change in the relaxation behavior, because the dipolar coupling between 1H spins is strong. 29Si relaxes directly through the dipole-dipole interaction with electron spins under spinning conditions higher than 2 kHz. A spin diffusion effect has been clearly observed in the 29Si relaxation of relatively pure samples under static and slow-spinning conditions. 27Al relaxes through three mechanisms: phonon-coupled quadrupole interaction, spin diffusion and dipole-dipole interaction with electron spins. The first mechanism is dominant, while the last is negligibly small. Spin diffusion between 27Al spins is suppressed completely at a spinning rate of 2.5 kHz. We have analyzed the relaxation behavior theoretically and discussed quantitatively. Concentrations of paramagnetic impurities, electron spin-lattice relaxation times and spin diffusion rates have been estimated. 相似文献