全文获取类型
收费全文 | 51648篇 |
免费 | 8127篇 |
国内免费 | 6421篇 |
专业分类
化学 | 37051篇 |
晶体学 | 717篇 |
力学 | 2950篇 |
综合类 | 448篇 |
数学 | 6021篇 |
物理学 | 19009篇 |
出版年
2024年 | 126篇 |
2023年 | 825篇 |
2022年 | 1612篇 |
2021年 | 1668篇 |
2020年 | 1794篇 |
2019年 | 1867篇 |
2018年 | 1597篇 |
2017年 | 1624篇 |
2016年 | 2216篇 |
2015年 | 2412篇 |
2014年 | 2922篇 |
2013年 | 3839篇 |
2012年 | 4550篇 |
2011年 | 4748篇 |
2010年 | 3359篇 |
2009年 | 3443篇 |
2008年 | 3839篇 |
2007年 | 3311篇 |
2006年 | 3058篇 |
2005年 | 2519篇 |
2004年 | 2028篇 |
2003年 | 1704篇 |
2002年 | 1636篇 |
2001年 | 1326篇 |
2000年 | 1103篇 |
1999年 | 868篇 |
1998年 | 659篇 |
1997年 | 571篇 |
1996年 | 598篇 |
1995年 | 467篇 |
1994年 | 488篇 |
1993年 | 391篇 |
1992年 | 335篇 |
1991年 | 272篇 |
1990年 | 272篇 |
1989年 | 192篇 |
1988年 | 196篇 |
1987年 | 146篇 |
1986年 | 158篇 |
1985年 | 189篇 |
1984年 | 121篇 |
1983年 | 125篇 |
1982年 | 85篇 |
1981年 | 97篇 |
1980年 | 84篇 |
1979年 | 78篇 |
1978年 | 69篇 |
1977年 | 74篇 |
1974年 | 90篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We investigate the origin of ultraviolet (UV) emission from Mg0.12 Zn0.88 O alloy thin films with a wurtzite structure fabricated on c-plane Al2O3 substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg0.12Zn0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region. 相似文献
82.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
83.
家用吊扇的核心部分是单相异步电动机,此绕组如图1,有一主绕组(工作绕组)与一串联电容器C的副绕组(启动绕组)相并联.这样做可使二绕组的电流在相位上相差90°,从而形成旋转磁场.转子的转动过程与三相异步电动机相似. 相似文献
84.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献
85.
The title compound (C2H7NO·C7H4N2O6) has been obtained by the reaction of etha- nolamine with 3,5-dinitrobenzoic acid in deionized water at room temperature. The crystal crystal- lizes in orthorhombic, space group P212121 with a = 6.048(2), b = 9.146(3), c = 21.955(7)(A), C9H11N3O7, Mr = 273.21, Z = 4, V = 1214.3(7)(A)3, Dc = 1.494 g/cm3, F(000) = 568, μ(MoKα) = 0.131 mm-1, R1 = 0.0338 and wR2 = 0.0497. The new organic adduct is composed of one ethanolamine and one 3,5-dinitrobenzoic acid, which are linked up by O-H…O and N-H…O types of hydrogen bonds to form a nine-membered ring and an eleven-membered ring, extending into a one-dimensional network structure. 相似文献
86.
Donghyun Cho Taihyun Chang Apostolos Avgeropoulos Nikos Hadjichristidis 《European Polymer Journal》2003,39(11):2155-2160
Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species. 相似文献
87.
双氯芬酸钠与牛血清白蛋白结合反应的特征 总被引:2,自引:0,他引:2
在模拟人体生理条件下,采用荧光光谱和紫外 可见吸收光谱法研究了双氯芬酸钠与牛血清白蛋白的结合反应.实验结果显示,双氯芬酸钠对牛血清白蛋白有较强的荧光猝灭作用,该猝灭过程主要为静态荧光猝灭过程;二者结合常数KLB=2.167×105mol·L-1;二者的结合位置距212位色氨酸2.13nm;同时,由结合反应的热力学参数得出二者作用力主要是氢键或VanderWall's力. 相似文献
88.
89.
90.