全文获取类型
收费全文 | 18228篇 |
免费 | 3337篇 |
国内免费 | 1671篇 |
专业分类
化学 | 12705篇 |
晶体学 | 174篇 |
力学 | 1022篇 |
综合类 | 68篇 |
数学 | 2039篇 |
物理学 | 7228篇 |
出版年
2024年 | 17篇 |
2023年 | 392篇 |
2022年 | 405篇 |
2021年 | 597篇 |
2020年 | 732篇 |
2019年 | 735篇 |
2018年 | 714篇 |
2017年 | 565篇 |
2016年 | 954篇 |
2015年 | 817篇 |
2014年 | 1042篇 |
2013年 | 1391篇 |
2012年 | 1708篇 |
2011年 | 1762篇 |
2010年 | 1172篇 |
2009年 | 1087篇 |
2008年 | 1209篇 |
2007年 | 1056篇 |
2006年 | 1019篇 |
2005年 | 807篇 |
2004年 | 610篇 |
2003年 | 420篇 |
2002年 | 405篇 |
2001年 | 328篇 |
2000年 | 266篇 |
1999年 | 371篇 |
1998年 | 264篇 |
1997年 | 285篇 |
1996年 | 276篇 |
1995年 | 241篇 |
1994年 | 207篇 |
1993年 | 213篇 |
1992年 | 144篇 |
1991年 | 157篇 |
1990年 | 129篇 |
1989年 | 99篇 |
1988年 | 88篇 |
1987年 | 69篇 |
1986年 | 68篇 |
1985年 | 54篇 |
1984年 | 57篇 |
1983年 | 30篇 |
1982年 | 32篇 |
1981年 | 24篇 |
1980年 | 26篇 |
1978年 | 13篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Zhang Menghua Zhang Yongfeng Ouyang Huimin Ma Changhui Cheng Xingong 《Nonlinear dynamics》2020,99(4):2727-2741
Nonlinear Dynamics - An adaptive integral sliding mode control (AISMC) method with payload sway reduction is presented for 4-DOF tower cranes in this paper. The designed controller consists of... 相似文献
92.
Nonlinear Dynamics - We show that planar continuous alternating systems, which can be used to model systems with seasonality, can exhibit a type of Parrondo’s dynamic paradox, in which the... 相似文献
93.
Kun Lu Ju Huang Li Ren Chao Li Yejun Guan Bingwen Hu Hao Xu Jingang Jiang Yanhang Ma Peng Wu 《Angewandte Chemie (International ed. in English)》2020,59(15):6258-6262
Precisely controlled crystal growth endows zeolites with special textural and catalytic properties. A nanosheet mordenite zeolite with a thickness of ca. 11 nm, named as MOR‐NS, has been prepared using a well‐designed gemini‐type amphiphilic surfactant as bifunctional structure‐directing agent (SDA). Its benzyl diquarternary ammonium cations structurally directed the formation of MOR topology, whereas the long and hydrophobic hexadecyl tailing group prevented the extensive crystal growth along b axis. This kind of orientated crystallization took place through the inorganic–organic interaction between silica species and SDA molecules present in the whole process. The thin MOR nanosheets, with highly exposed (010) planes and 8‐membered ring (MR) windows, exhibited a much improved ethylene selectivity (42.1 %) for methanol‐to‐olefin (MTO) reactions when compared with conventional bulk MOR crystals (3.3 %). 相似文献
94.
The landscape of organic molecule on Si(100) surface has a great significance for organic functionalisation of Si semiconductor. Several possible adsorption configurations for pyridazine on Si(100) surface have been forecasted by systemic comparison and investigation. The C1s XPS and NEXAFS spectra of these adsorption systems based on density functional theory and full core-hole potential approximation have been calculated. Although the sensibility of XPS to these adsorption configurations is not very strong, these configurations can be absolutely distinguished by NEXAFS spectra, which will bring tremendous reference to the future experimental study. Mode II, III, V and VI have a significantly higher adsorption energy, which are most likely to be present in experiment. In addition, we have made the research on specific sources of the peaks in spectra by analysing their decomposed NEXAFS spectra, the results show that the Carbon atoms which do not bond to surface atoms, make the most contribute to the intensity of characteristic peaks in spectra. 相似文献
95.
The polarization of a D-shaped fiber is modulated after immersing it in magnetic fluid(MF)and applying a magnetic field.Theoretical analysis predicts that magneto-optical dichroism of MF plays a key role in light polarization modulation.During light polarization modulation,the evanescent wave polarized parallel to the magnetic field has greater loss than its orthogonal component.Light polarization of a D-shaped fiber with a wide polished surface can be modulated easily.High concentration MF and a large magnetic field all have great ability to modulate light polarization. 相似文献
96.
本文研究了不同衬底温度对Ga液滴在Al_(0.4)Ga_(0.6)As表面形成纳米结构的影响,当300℃≤T≤380℃时,Ga液滴演化成纳米孔(Nanohole)和盘状结构(diffusion halo),纳米结构的尺寸随温度升高而增大.当T≥385℃时,盘状结构消失,形成一定平坦的Al_xGa_(1-x)As薄膜,Ga液滴在界面处继续向下刻蚀直至耗尽,形成平均直径为75 nm,平均孔深为5.52 nm的纳米孔.本文还通过盘状结构测出平均扩散长度△R,并拟合出Ga原子在Al_(0.4)Ga_(0.6)As表面的激活能E_A=0.78(±0.01) eV和扩散前因子D_0=0.15(×4.1~(±1))10~(-2 ) cm~2s~(-1). 相似文献
97.
Liu Xue Ma Hua Xu Heng Tan Ziqi Liu Qiongzhen Wang Yuedan Shu Hongbo Wang Dong 《Journal of Solid State Electrochemistry》2020,24(1):81-91
Journal of Solid State Electrochemistry - CoS2 nanooctahedrons homogeneously encapsulated by hierarchical porous-reduced graphene oxide and polypyrrole thin film are constructed via a simple... 相似文献
98.
Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction 下载免费PDF全文
Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications. 相似文献
99.
AbstractReactive oxygen species including free radicals are responsible for noxious changes in living organisms which can be associated with many diseases for e.g. cardiovascular, neurodegenerative, and inflammatory diseases or cancer. In the struggle against free radicals the organism is supported by antioxidants. As they are often provided by nature, they can be considered safe. 5-Caffeoylquinic acid is one of main chlorogenic acids found in vegetables and fruits. The main objective of the presented article was monitoring the changes of 5-caffeoylquinic acid during the reaction with colorful radicals. The experiments were conducted at different molar ratios of radicals to antioxidant using liquid chromatography–mass spectrometry. Irrespective of the applied molar ratios, the obtained results proved that the antioxidant takes part in the reaction for three days. Additionally, during the radical neutralization the formation of semiquinones and/or quinones, methoxy adduct of caffeoylquinic acid, and quinones adduct with methanol was observed. 相似文献
100.