全文获取类型
收费全文 | 4490篇 |
免费 | 652篇 |
国内免费 | 903篇 |
专业分类
化学 | 4333篇 |
晶体学 | 54篇 |
力学 | 76篇 |
综合类 | 24篇 |
数学 | 42篇 |
物理学 | 1516篇 |
出版年
2024年 | 9篇 |
2023年 | 54篇 |
2022年 | 94篇 |
2021年 | 102篇 |
2020年 | 185篇 |
2019年 | 142篇 |
2018年 | 105篇 |
2017年 | 118篇 |
2016年 | 203篇 |
2015年 | 178篇 |
2014年 | 215篇 |
2013年 | 447篇 |
2012年 | 308篇 |
2011年 | 272篇 |
2010年 | 221篇 |
2009年 | 242篇 |
2008年 | 275篇 |
2007年 | 339篇 |
2006年 | 292篇 |
2005年 | 212篇 |
2004年 | 229篇 |
2003年 | 280篇 |
2002年 | 212篇 |
2001年 | 241篇 |
2000年 | 177篇 |
1999年 | 138篇 |
1998年 | 117篇 |
1997年 | 129篇 |
1996年 | 90篇 |
1995年 | 92篇 |
1994年 | 73篇 |
1993年 | 48篇 |
1992年 | 43篇 |
1991年 | 33篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有6045条查询结果,搜索用时 15 毫秒
991.
992.
The reductive coupling of 1,3-dimethyluracil with benzophenone by Zn-TiCl4 in THF gave unusual two-to-one adduct and its further reduced product. The reductive coupling of 1,3-dimethyl-5-fluorouracil with benzophenone by Zn-TiCl4 also gave two-to-one adduct. 1,3-Dimethylthymine was, however, completely inert under the same conditions. 相似文献
993.
Osamu Matsumoto Eiji Hayami Mamoru Samejima Yasushi Kanzaki 《Plasma Chemistry and Plasma Processing》1984,4(1):33-42
The nitriding of titanium with argon-nitrogen (3%) and argon-nitrogen (3%)-hydrogen (2%) plasma jets at pressures of 190 torr was studied. The reaction kinetics obeyed mainly a parabolic law. The parabolic kinetic constants were 10–10–10–8 g2 cm–4 s–1, which were 2–3 orders of magnitude larger than those in R.F. discharges. From emission spectroscopy, nitrogen atoms in the excited states were observed. The nitrogen atoms can promote the nitriding reaction. The effect of the addition of hydrogen to nitrogen is also briefly discussed. 相似文献
994.
A series of Cp2Ti(SB)Cl complexes, whereSB is the anion of bidentate Schiff bases derived from salicylaldehyde and different primary aminesviz o-anisidine,m-anisidine,o-phenetidine,o-chloroaniline,m-chloroaniline,m-nitroaniline, α-naphthylamine and benzylamine, have been synthesised by the reaction of dichloro-bis(cyclopentadienyl) titanium(IV),
Cp2TiCl2, and bidentate Schiff base (sbh) in a 1:1 molar ratio in refluxingthf in the presence of triethylamine. The new derivatives have been characterised on the basis of their elemental analyses, conductance
measurements and spectral (IR,1Hnmr and electronic) studies 相似文献
995.
采用密度泛函理论中的广义梯度近似(DFT-GGA)对(CoO)_n(n≤6)合金团簇进行了系统的几何、电子结构和磁性质研究.研究结果表明(CoO)n(n≤6)团簇最稳定结构除(CoO)6团簇为三维立体结构外,其余团簇均呈二维平面结构,且(CoO)_n(n=1,2,3,4和6)结构均表现明显的钴氧分离特征,而(CoO)5团簇表现明显的Co—Co聚合和O—O分离特征.团簇的总磁矩在n=1,3,4时,以3μB为单元成倍增长,(CoO)5团簇显著降低,减小至1μB,(CoO)6团簇又有所增加,增大至6μB.(CoO)n(n≤6)团簇磁性变化的起因也从电荷转移、磁性耦合、电子差分密度和态密度进行了详细阐释. 相似文献
996.
Synchrotron X‐ray CT characterization of titanium parts fabricated by additive manufacturing. Part I. Morphology 下载免费PDF全文
Nicola Vivienne Yorke Scarlett Peter Tyson Darren Fraser Sheridan Mayo Anton Maksimenko 《Journal of synchrotron radiation》2016,23(4):1006-1014
Synchrotron X‐ray tomography has been applied to the study of titanium parts fabricated by additive manufacturing (AM). The AM method employed here was the Arcam EBM® (electron beam melting) process which uses powdered titanium alloy, Ti64 (Ti alloy with approximately 6%Al and 4%V), as the feed and an electron beam for the sintering/welding. The experiment was conducted on the Imaging and Medical Beamline of the Australian Synchrotron. Samples were chosen to examine the effect of build direction and complexity of design on the surface morphology and final dimensions of the piece. 相似文献
997.
在相对论有效原子实势近似下,用密度泛函理论方法,对Pdn(n=2,3,4),Yn(n=2,3,4),PdnY(n=1,2,3,4),PdYn(n=2,3,4),Pd2 Yn(n=2,3,4)团簇的各种可能的几何构型进行全优化计算,得到它们的基态结构和 光谱性质.结果表明,由于 Jahn-Teller效应, Pd4和Y4的基态结 构为Cs构型,P d3和Y3为C2v 构型;混合微团簇Pd3Y,Pd 4Y,PdY3,PdY4 和 Pd2Y4基态为Cs构型.最后计算了团簇的能级分布和最 高占据轨道与最低空轨道之间的能级间隙,分析了团簇的化学活性.
关键词:
Pd-Y团簇
有效原子实势
密度泛函 相似文献
998.
Liang CHEN 《Frontiers of Physics》2009,4(3):356
In this review, we present our recent first principles studies on the sequential H2 dissociative chemisorption and H desorption on the Ptn and Pdn clusters (n =2-9, 13). Upon full saturation by H atoms, the calculated H2 dissociative chemisorption energy and H desorption energy on Pt13 and Pd13 clusters are similar to the corresponding values on smaller close-packed clusters. Indeed, the catalytic performances of these subnano clusters do not vary significantly with the particle sizes or shapes. Instead, they are dependent on the surface metal atoms which can be accessed by H atoms. In addition to the coverage dependency of the H2dissociative chemisorption and H sequential desorption energies, the phase transition of both Pt13 and Pd13from the icosahedral to fcc -like structures at certain H coverage was also investigated. 相似文献
999.
Guanglong Chen Cheng Wang Haiyang Lu Jiansheng Liu Ruxin Li Guoquan Ni Zhizhan Xu 《中国光学快报(英文版)》2008,6(6)
We use an electrostatic model to study the average kinetic energy of ions ejected from the pure Coulomb explosions of methane clusters (CA4)n (light atom A=H and D). It is found that the ratio of the average kinetic energy of the ions to their initial average electrostatic potential energy is irrelevant to the cluster size. This finding implies that as long as the ratio is given, the average kinetic energies of the ions can be simply estimated from their initial average electrostatic potential energies, rather than from the time- consuming simulations. The ratios for the different charge states of carbon ions are presented. 相似文献
1000.
A. N. Murashkevich A. S. Lavitskaya T. I. Barannikova I. M. Zharskii 《Journal of Applied Spectroscopy》2008,75(5):730-734
The composites xTiO2-(1−x)SiO2 (x = 0.1, 0.5, 0.9) were obtained by coprecipitation from solutions of alkoxides: tetraethoxysilane (TEOS) and titanium tetraisopropoxide
(TIPT). Intermolecular interaction of the components of the composite is apparent in the IR absorption spectra in the 928–952
cm−1 region, and is connected with bending vibrations of the Si-O-Ti bond.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 724–728, September–October, 2008. 相似文献