全文获取类型
收费全文 | 2526篇 |
免费 | 141篇 |
国内免费 | 13篇 |
专业分类
化学 | 2063篇 |
晶体学 | 27篇 |
力学 | 74篇 |
数学 | 111篇 |
物理学 | 405篇 |
出版年
2023年 | 19篇 |
2022年 | 28篇 |
2021年 | 56篇 |
2020年 | 63篇 |
2019年 | 55篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 93篇 |
2015年 | 84篇 |
2014年 | 110篇 |
2013年 | 187篇 |
2012年 | 226篇 |
2011年 | 253篇 |
2010年 | 144篇 |
2009年 | 109篇 |
2008年 | 200篇 |
2007年 | 162篇 |
2006年 | 141篇 |
2005年 | 144篇 |
2004年 | 125篇 |
2003年 | 112篇 |
2002年 | 122篇 |
2001年 | 40篇 |
2000年 | 31篇 |
1999年 | 21篇 |
1998年 | 26篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有2680条查询结果,搜索用时 15 毫秒
171.
Sung-Seen Choi Boyoung Chu Seung Goo Lee Sung Wook Lee Sung Soon Im Seong Hun Kim Jong Kyoo Park 《Journal of Sol-Gel Science and Technology》2004,30(3):215-221
Titania-doped silica fibers were prepared by electrospinning of the sol of silica containing titania. The electrospun fibers had ribbon type morphology. The fibers had significant quantities of hydroxyl groups of Si—OH and Ti—OH. The fibers did not have crystalline structure. Diameters of the fibers were reduced by solvent evaporation and calcination. The hydroxyl groups on the fibers disappeared by calcination. The hydroxyl groups, M—OH (MSi, Ti) were changed to M—O—M by intermolecular and intramolecular condensation reactions. 相似文献
172.
A high-density array of vertically aligned ZnGa(2)O(4) nanowires has been synthesized on Si substrates via CVD of ZnO-Ga at 1000 degrees C consisting of a single-crystalline cubic spinel structure grown in a [111] direction and exhibiting strong photoluminescence and cathodoluminescence in the blue wavelength region. 相似文献
173.
Growth of poly(pseudorotaxane) on gold using host-stabilized charge-transfer interaction 总被引:1,自引:0,他引:1
A novel supramolecular polymer (poly(pseudorotaxane)) in which the repeating units are linked by host-stabilized charge-transfer interaction between the guest molecules is grown on gold and characterized. 相似文献
174.
Heterobimetallic Ru/Co nanoparticles, immobilized on charcoal, were synthesized and used as catalysts in the Pauson-Khand-type reaction in the presence of pyridylmethyl formate instead of carbon monoxide; the catalysts were effective for intra- and intermolecular reactions and easily reused without loss of catalytic activity. 相似文献
175.
In the reaction of paraoxon with alkali metal ethoxides, ion-paired EtO-M+ species are more reactive than the dissociated EtO- with the reactivity order EtO-Li+ EtO-Na+ > EtO-K+ > EtO-, while in the reaction of parathion, the reactivity follows the order EtO-K+ > EtO- > EtO-Na+ > EtO-Li+. 相似文献
176.
177.
178.
Jong-Moo Lee Yong-Soon Baek Kwang-Ryong Oh Hyung-Jong Lee Yong-Seok Kim 《Optics Communications》2007,270(2):189-194
We investigate on the variation of loss and temperature dependence of a polymeric arrayed waveguide grating (AWG) depending on its substrate, by fabricating 16-channel polymeric AWGs with various substrate conditions. Insertion loss for a polymeric AWG on a silicon substrate is measured as low as 3.1 dB. The temperature-dependent wavelength shift for a polymeric AWG detached from the substrate is maintained within 0.1 nm from 20 to 80 °C. But we observe a degradation of insertion loss and a little instability in wavelength characteristics both for the detached polymeric AWG and for a polymeric AWG on a polymer substrate. We investigate on those optical properties of the polymeric AWGs based on measured thermal expansion properties of the polymers. 相似文献
179.
Seung U. Lee Mun Heum Park Jin Won Kim Hyeun Kyung Jo Won-Jeong Kim 《Applied Surface Science》2007,254(5):1493-1497
Ferroelectric BiFeO3 thin films with Nd-Cr (or Sm-Cr) co-substitution (denoted by BNdFCr and BSmFCr, respectively) were deposited on the Pt(2 0 0)/TiO2/SiO2/Si(1 0 0) substrates by a chemical solution deposition method. X-ray diffraction patterns revealed the formation of BNdFCr and BSmFCr thin films without any secondary phases. The co-substituted BNdFCr (or BSmFCr) thin films, which were annealed at 550 °C for 30 min in N2 atmosphere, exhibited enhanced electrical properties compared to BFO thin films with the remanent polarization (2Pr) and coercive electric field (2Ec) of 196, 188 μC/cm2 and 600, 570 kV/cm with the electric field of 800 kV/cm, respectively. The leakage current densities of BNdFCr and BSmFCr thin films measured at room temperature were approximately three orders of magnitude lower than that of BFO thin film, and the leakage current at room temperature of the thin films exhibited three distinctive conduction behaviors. Furthermore, the values of pulse polarizations [i.e., +(P*-P^) or −(P*-P^)] of BNdFCr and BSmFCr thin films were reasonably unchanged up to 1.4 × 1010 switching cycles. 相似文献
180.
Influence of pretreatment methods on adsorption and catalytic characteristics of toluene over heterogeneous palladium based catalysts 总被引:1,自引:0,他引:1
The adsorption and catalytic characteristics of heterogeneous palladium based catalyst and its modified catalysts with gases (air and hydrogen) and acidic aqueous solution (HCl) were studied for evaluating the influence of pretreatment methods for toluene. The structural and energetic adsorption properties of the parent and pretreated catalysts were analyzed by means of nitrogen adsorption isotherms and gravimetric methods. The light-off curve and the XPS investigation were used for analyzing the catalytic activity and the surface state of palladium. It was clearly shown from the experimental results that hydrogen pretreated catalysts having metallic surface state exhibited the highest adsorption capacity and catalytic activity compared to that of parent and modified catalysts. The adsorption equilibrium data for toluene were obtained at three different temperatures and correlated successfully with the two-site Langmuir molecular isotherm model (L2m). It was also found that the palladium phase has more adsorption affinity for toluene molecules than the alumina support. The isosteric heat of adsorption calculated by using the Clausius-Clapeyron equation significantly changed with the coverage and the lateral interactions between the adsorbate-adsorbate molecules control the system. Furthermore, comparative analysis of the adsorption energy distribution revealed that the parent and its modified catalysts have different types of surface energetic heterogeneities. 相似文献