全文获取类型
收费全文 | 1982篇 |
免费 | 115篇 |
国内免费 | 23篇 |
专业分类
化学 | 1552篇 |
晶体学 | 23篇 |
力学 | 41篇 |
数学 | 148篇 |
物理学 | 356篇 |
出版年
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 49篇 |
2020年 | 46篇 |
2019年 | 47篇 |
2018年 | 27篇 |
2017年 | 38篇 |
2016年 | 74篇 |
2015年 | 59篇 |
2014年 | 89篇 |
2013年 | 129篇 |
2012年 | 194篇 |
2011年 | 177篇 |
2010年 | 115篇 |
2009年 | 82篇 |
2008年 | 128篇 |
2007年 | 122篇 |
2006年 | 109篇 |
2005年 | 89篇 |
2004年 | 82篇 |
2003年 | 66篇 |
2002年 | 61篇 |
2001年 | 42篇 |
2000年 | 49篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1933年 | 2篇 |
排序方式: 共有2120条查询结果,搜索用时 15 毫秒
131.
Kim MR Moon HI Chung JH Moon YH Hahm KS Woo ER 《Chemical & pharmaceutical bulletin》2004,52(12):1466-1469
A bioassay-guided fractionation of the ethyl acetate soluble fraction from the stem bark of Styrax japonica S. et Z. (Styracaceae) yielded two new lignan compounds, styraxjaponoside A (1) and styraxjaponoside B (2), along with three known compounds, matairesinoside (3), egonol glucoside (4), and dihydrodehydrodiconiferyl alcohol 9'-O-glucoside (5). The structures of compounds 1-5 were determined by spectroscopic method, as well as 1D- and 2D-NMR (HSQC, 1H-1H COSY, and HMBC) spectroscopy. Among them, compound 2 exhibited potent inhibitory activity against matrix metalloproteinase (MMP)-1, and prevented the UV-induced changes in the MMP-1 expression. In addition, compounds 3 and 5 were isolated from this plant for the first time. 相似文献
132.
The mobility of self-interstitials in α-zirconium (α-Zr) is studied with molecular dynamic (MD) and molecular static (MS)
simulations, using Ackland’s many-body inter-atomic potential. The basal crowdion configuration is found to be the ground
state. Four types of diffusion jumps can be identified via MS, in-plane in-line, in-plane off-line, out-of-plane in-line and
out-of-plane off-line. The in-plane migration is dominated by one-dimensional crowdion motion along the [110] directions, interrupted from time to time by off-line or out-of-plane jumps. Based on the MS results, the activation energies
and pre-exponentials for the diffusion processes are determined by fits to the Arrhenius plots of Dc and Da. The diffusional anisotropy factor Dc/Da is also obtained, and compares well with experimental results. The mean frequency of each type of jumps is then found using
Monte Carlo simulation, and is reported as a function of temperature. The mean lifetime and mean free path of the one-dimensional
mobility are then obtained. The 1-D mean free path is found to be unimportant for sink separations involved under the usual
irradiation damage conditions.
Received: 4 March 2002 / Accepted: 4 April 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. E-mail: Chung.Woo@polyu.edu.hk 相似文献
133.
Neuhauser RG Shimizu KT Woo WK Empedocles SA Bawendi MG 《Physical review letters》2000,85(15):3301-3304
We find a correlation between the dynamics of fluorescence intermittency and spectral diffusion in the spectroscopy of single CdSe nanocrystal quantum dots (QD). A statistical analysis of the data suggests two populations of blinking events: blinking followed by large spectral diffusion shifts and blinking with small or no spectral shifts. Although unexpected from earlier studies, the correlation between blinking and spectral shifting is consistent with a model of QD ionization as the mechanism for the blinking event, followed by a redistribution of local electric fields that results in spectral shifting. 相似文献
134.
Recently electron cyclotron resonance (ECR) plasma have been explored for wafer cleaning applications, since it is known to do less damage to silicon surface than conventional plasma. Organic contaminants removal efficiency and plasma radiation damage of the ECR plasma cleaning have been investigated. In oxygen ECR plasma cleaning, the plasma exposure time needed to remove the organic contaminants on the silicon surface down to the detection limit is 40 s, but the one to reach the lowest surface roughness is 10 s. The leakage current level of the MOS capacitor made using the Si substrate exposed to oxygen ECR plasma for 40 s is 8 × 10−9 A. The optimum exposure time determined by considering the contaminants removal efficiency and the plasma radiation damage (or the leakage current level) is 40 s. Organic contaminants seem to be removed through both sputter-off mechanism by oxygen ion bombardment and evaporation mechanism by chemical reactions with excited oxygen atoms. 相似文献
135.
Yttrium aluminum garnet (YAG) particles doped with Tb3+ or double doped with Tb3+ and Ce3+ were prepared by spray pyrolysis and characterized by photo- and cathode-luminescence. It was tried to incorporate a broad band of Ce3+ activator into the line peaks of Tb3+ in YAG host without the reduction of emission intensity. Ce-codoped YAG:Tb particles showed a broad band emission due to the d-f transition of Ce3+ and a reduction in the intensity of emission peaks due to 5D3-7Fj (j=3, 4, 5, 6) transition of Tb3+ when they were excited by the ultraviolet light of 270 nm. These results supported that an effective energy transfer occurs from Tb3+ to Ce3+ in YAG host. Codoping Ce3+ ions greatly intensified the excitation peak at 270 nm for the emission at 540 nm of Tb3+, which means that more lattice defects, involving in the energy absorption and transfer to Tb3+, are formed by the Ce3+ codoping. The finding gives a promising approach for enhancing the luminescence efficiency. 相似文献
136.
Jung-Kyen Moon Jung-Won Park Woo Song Lee Young-Jin Kang Hyun-A Chung Mi-Seon Shin Yong-Jin Yoon Ki Hun Park 《Journal of heterocyclic chemistry》1999,36(3):793-798
This paper presents the synthesis of 2-amino-, 2-acetamido- and 2-benzamidothioxanthones and their 10,10-dioxides. 相似文献
137.
Various phenomenon-mimicking algorithms, such as genetic algorithm, simulated annealing, tabu search, ant colony optimization, and particle swarm optimization, have their own algorithm parameters. These parameters need to be skillfully assigned in order to obtain good results. It is burdensome, especially to novice users, to assign these parameters. The same is true for the harmony search algorithm which was inspired by music performance. Thus, this study proposes a novel technique to eliminate tedious and experience-requiring parameter assigning efforts. The new parameter-setting-free (PSF) technique which this study suggests contains one additional matrix which contains an operation type (random selection, memory consideration, or pitch adjustment) for every variable in harmony memory. Three examples illustrate that the PSF technique can find good solutions robustly. 相似文献
138.
The interposition of surfactants between polymer and liquid crystal (LC) droplets was theoretically predicted by the positive spreading coefficient (0 < λ31) and utilized to interpret the morphology, grating formation kinetics, diffraction efficiency, and switching of the holographic polymer dispersed liquid crystal (HPDLC), prepared from various types (octanoic acid, poly oxyethylene octyl phenyl ether, and perfluoro‐1‐butanesulfonyl fluoride) and amounts (0–9 wt%) of surfactant and molecular weights of polyol (PPG). Regardless of the surfactant type, diffraction efficiency increased with the addition and increasing amount of surfactant, a tendency consistent with increasing value of spreading coefficient, which is determined by the formulations of grating formation. In contrast, diffraction efficiency showed a maximum with the polypropylene glycol (PPG) molecular weight. Surfactant effectively reduced the anchoring energy and electrically drove the film which otherwise was not driven. Overall, surfactant with greater λ31 gave smaller droplet, greater diffraction efficiency, driving voltage, contrast ratio, and smaller response time. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
139.
Hye Seok Park Dong Wan Seo Seung Woo Choi Young Gi Jeong Ju Ho Lee Dong Il Kim Whan‐Gi Kim 《Journal of polymer science. Part A, Polymer chemistry》2008,46(5):1792-1799
Branched sulfonated poly(ether ketone sulfone)s (Br‐SPEKS) were prepared with bisphenol A, bis(4‐fluorophenyl)sulfone, 3,3′‐disodiumsulfonyl‐4,4′‐difluorobenzophenone, and THPE (1,1,1‐tris‐p‐hydroxyphenylethane), respectively, at 180 °C using potassium carbonate in NMP (N‐methylpyrrolidinone). THPE, as a branching agent, was used with 0.4 mol % of bisphenol A to synthesize branched copolymers. Copolymers containing 10–50 mol % disulfonated units were cast from dimethylsulfoxide solutions to form films. Linear sulfonated poly(ether ketone sulfone)s (SPEKS) were also synthesized without THPE. The films were converted from the salt to acid forms with dilute hydrochloric acid. A series of copolymers were studied by Fourier transform infrared, 1H‐NMR spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. The ion‐exchange capacity (IEC), a measure of proton conductivity, was evaluated. The synthesized Br‐SPEKS and SPEKS membranes exhibit conductivities (25 °C) from 1.04 × 10?3 to 4.32 × 10?3 S/cm, water swell from 20.18 to 62.35%, IEC from 0.24 to 0.83 mequiv/g, and methanol diffusion coefficients from 3.2 × 10?7 to 4.7 × 10?7 cm2/S at 25 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1792–1799, 2008 相似文献
140.