全文获取类型
收费全文 | 239984篇 |
免费 | 2531篇 |
国内免费 | 1159篇 |
专业分类
化学 | 121237篇 |
晶体学 | 4051篇 |
力学 | 11102篇 |
综合类 | 41篇 |
数学 | 26502篇 |
物理学 | 80741篇 |
出版年
2020年 | 2080篇 |
2019年 | 2297篇 |
2018年 | 2924篇 |
2017年 | 2840篇 |
2016年 | 4227篇 |
2015年 | 2698篇 |
2014年 | 4247篇 |
2013年 | 10548篇 |
2012年 | 8027篇 |
2011年 | 9953篇 |
2010年 | 7034篇 |
2009年 | 6958篇 |
2008年 | 9111篇 |
2007年 | 9125篇 |
2006年 | 8633篇 |
2005年 | 7794篇 |
2004年 | 7157篇 |
2003年 | 6327篇 |
2002年 | 6229篇 |
2001年 | 7209篇 |
2000年 | 5451篇 |
1999年 | 4322篇 |
1998年 | 3617篇 |
1997年 | 3515篇 |
1996年 | 3354篇 |
1995年 | 3054篇 |
1994年 | 3006篇 |
1993年 | 3090篇 |
1992年 | 3195篇 |
1991年 | 3361篇 |
1990年 | 3119篇 |
1989年 | 3054篇 |
1988年 | 3087篇 |
1987年 | 2975篇 |
1986年 | 2814篇 |
1985年 | 3837篇 |
1984年 | 4039篇 |
1983年 | 3209篇 |
1982年 | 3436篇 |
1981年 | 3350篇 |
1980年 | 3244篇 |
1979年 | 3362篇 |
1978年 | 3440篇 |
1977年 | 3362篇 |
1976年 | 3465篇 |
1975年 | 3151篇 |
1974年 | 3167篇 |
1973年 | 3206篇 |
1972年 | 2242篇 |
1971年 | 1851篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
22.
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
23.
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
24.
25.
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
26.
27.
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
28.
A. P. Voronov G. N. Babenko V. M. Puzikov A. D. Roshal’ V. I. Salo 《Crystallography Reports》2008,53(4):708-712
The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λmax= 350 nm. 相似文献
29.
K. Morigaki K. Takeda H. Hikita C. Ogihara P. Roca i Cabarrocas 《Journal of Non》2008,354(19-25):2131-2134
Our model for light-induced defect creation in hydrogenated amorphous silicon is applied to its kinetics, i.e., the growing curve of light-induced dangling bond density as a function of illumination time, which is fitted to a stretched exponential function. Two parameters β and τ involved in the function are estimated as functions of saturated dangling bond density in terms of our model. These are compared with two experimental results, i.e., our results obtained from ESR measurements and Shimakawa et al.’s results obtained from photoconductivity measurements. The saturated dangling bond density is also measured as a function of the generation rate of free carriers. The experimental results are compared with calculated results and discussed. 相似文献
30.