全文获取类型
| 收费全文 | 5671篇 |
| 免费 | 76篇 |
| 国内免费 | 1篇 |
专业分类
| 5748篇 |
出版年
| 2024年 | 54篇 |
| 2023年 | 61篇 |
| 2022年 | 89篇 |
| 2021年 | 104篇 |
| 2020年 | 145篇 |
| 2019年 | 135篇 |
| 2018年 | 264篇 |
| 2017年 | 253篇 |
| 2016年 | 234篇 |
| 2015年 | 149篇 |
| 2014年 | 171篇 |
| 2013年 | 713篇 |
| 2012年 | 410篇 |
| 2011年 | 416篇 |
| 2010年 | 257篇 |
| 2009年 | 173篇 |
| 2008年 | 323篇 |
| 2007年 | 259篇 |
| 2006年 | 234篇 |
| 2005年 | 218篇 |
| 2004年 | 126篇 |
| 2003年 | 137篇 |
| 2002年 | 132篇 |
| 2001年 | 58篇 |
| 2000年 | 78篇 |
| 1999年 | 45篇 |
| 1998年 | 29篇 |
| 1997年 | 20篇 |
| 1996年 | 29篇 |
| 1995年 | 19篇 |
| 1994年 | 14篇 |
| 1993年 | 16篇 |
| 1992年 | 31篇 |
| 1991年 | 21篇 |
| 1990年 | 25篇 |
| 1989年 | 23篇 |
| 1988年 | 26篇 |
| 1987年 | 18篇 |
| 1986年 | 11篇 |
| 1985年 | 12篇 |
| 1984年 | 16篇 |
| 1983年 | 15篇 |
| 1979年 | 16篇 |
| 1978年 | 12篇 |
| 1976年 | 14篇 |
| 1974年 | 10篇 |
| 1971年 | 10篇 |
| 1970年 | 10篇 |
| 1968年 | 11篇 |
| 1965年 | 10篇 |
排序方式： 共有5748条查询结果，搜索用时 15 毫秒
861.
Jan Zirk‐Sadowski Charlotte Lamptey Amy Devine Mark Haggard Dénes Szűcs 《Developmental science》2014,17(3):366-375
We studied whether the origins of math anxiety can be related to a biologically supported framework of stress induction: (un)controllability perception, here indicated by self‐reported independent efforts in mathematics. Math anxiety was tested in 182 children (8‐ to 11‐year‐olds). Latent factor modeling was used to test hypotheses on plausible causal processes and mediations within competing models in quasi‐experimental contrasts. Uncontrollability perception in mathematics, or (in)dependence of efforts, best fit the data as an antecedent of math anxiety. In addition, the relationship of math anxiety with gender was fully mediated by adaptive perception of control (i.e. controllability). That is, young boys differ from girls in terms of their experience of control in mathematics learning. These differences influence math anxiety. Our findings are consistent with recent suggestions in clinical literature according to which uncontrollability makes women more susceptible to fear and anxiety disorders. A video abstract of this article can be viewed at http://www.youtube.com/watch?v=I4b_47Y-e_U 相似文献
862.
863.
864.
Alejandrina Cristia Yasuyo Minagawa‐Kawai Natalia Egorova Judit Gervain Luca Filippin Dominique Cabrol Emmanuel Dupoux 《Developmental science》2014,17(4):628-635
The present study investigated the neural correlates of infant discrimination of very similar linguistic varieties (Quebecois and Parisian French) using functional Near InfraRed Spectroscopy. In line with previous behavioral and electrophysiological data, there was no evidence that 3‐month‐olds discriminated the two regional accents, whereas 5‐month‐olds did, with the locus of discrimination in left anterior perisylvian regions. These neuroimaging results suggest that a developing language network relying crucially on left perisylvian cortices sustains infants’ discrimination of similar linguistic varieties within this early period of infancy. 相似文献
865.
It is shown that initially sharp interface in AB diffusion couple, above the ordering temperature, can shift with anomalous kinetics, i.e. deviations from the parabolic growth kinetics are possible. The initial slopes of the shift versus time functions can be even unity for large diffusion asymmetry (the ratio of diffusion coefficients of the parent materials in orders of magnitude) and gradually decrease to 0.5 at larger distances (longer times). This is in accordance with earlier results obtained in phase separating systems. It is shown that from the results of simulations the crossover thickness, X*, between the linear and parabolic regimes can also be calculated, and the applicability of the linear–parabolic law is confirmed. Furthermore, it is illustrated that the crossover thickness depends exponentially on the diffusion asymmetry parameter, with the exponent close to the value obtained from analytical estimations. 相似文献
866.
Julien Favre Damien Fabrègue Akihiko Chiba Yves Bréchet 《Philosophical Magazine Letters》2013,93(11):631-639
AbstractA new criterion for nucleation in the case of dynamic recrystallization is proposed in order to include the contribution of the grain boundary energy stored in the microstructure in the energy balance. Due to the nucleation events, the total surface area of pre-existing grain boundaries decreases, leading to a nucleus size smaller than expected by conventional nucleation criteria. The new model provides a better prediction of the nucleus size during recrystallization of pure copper compared with the conventional nucleation criterion. 相似文献
867.
An enhancement of the UV-visible optical absorption spectra of Ag nanoparticles (NPs) deposited on indium tin oxide (ITO) surfaces of different resistance by a seed-mediated growth technique is presented. A bicolour coherent beam, obtained from a pulsed Nd:YAG laser providing a 1060-nm fundamental wavelength and a double-frequency one at 530?nm, was used. A significant change in the optical density is observed for Ag NPs on low-resistance ITO surfaces (≈4?Ω/square), while almost nothing occurs with high-resistance (≈50?Ω/square surfaces). The spectral position of the maximal absorption at 440?nm is almost preserved in both cases. This result is explained in terms of a local photoinduced static field and surface-plasmon polaritons interacting with photoexcited phonons. A grating effect, arising from the coherent bicolour light forming a superstructure as for quantum crystals, could be another contribution. 相似文献
868.
A. Concustell F.O. Méar S. Suriñach M.D. Baró A.L. Greer 《Philosophical Magazine Letters》2013,93(12):831-840
The metallic glass Pd40Cu30Ni10P20 in as-cast or pre-annealed states was shot-peened successively at room temperature or at 77 K. The structural state of the glass was characterized by the relaxation spectrum measured in a differential scanning calorimeter. Mechanically induced relaxation of the as-cast glass and mechanically induced rejuvenation of pre-annealed samples are both more evident at 77 K than at 298 K, enabling deductions about the underlying mechanisms. The relaxation spectrum of the glass as a function of temperature displays two broad maxima, which occurring at the higher temperature is attributed to the part of the free-volume distribution associated with flow defects. In samples shot-peened at 77 K, the stored energy after deformation can be as high as 20% of the cold work. Shot-peening simultaneously generates flow defects within shear bands and destroys them in the matrix between bands: whose effect dominates is principally dependent on the initial state of relaxation of the glass. Shot-peening of partially crystallized samples appears capable of breaking up and dispersing crystallites without inducing any further significant crystallization. 相似文献
869.
S. Miro J.-M. Costantini S. Sorieul L. Gosmain L. Thomé 《Philosophical Magazine Letters》2013,93(11):633-639
Single crystals of 6H–SiC were implanted at room temperature with 4-MeV Au ions to a fluence of 1015?cm?2. Raman spectra showed that full amorphization was achieved. The recrystallization process was studied by micro-Raman spectrometry after isochronal thermal annealing between 700 and 1500°C. The spectra permitted the evolution upon annealing of Si–C bonds, and also of Si–Si and C–C bonds, to be followed. Amorphous phase relaxation takes place below 700°C; then recrystallization of the 6H polytype sets in at 700°C. At 900°C crystallites with different crystalline states are formed. Moreover, Raman spectra provide evidence of graphitic nanocluster formation at 1500°C. 相似文献
870.
Sébastien Allain Frédéric Danoix Mohamed Goune Khalid Hoummada Dominique Mangelinck 《Philosophical Magazine Letters》2013,93(2):68-76
The work-hardening behaviour of virgin martensitic steel has been investigated in a strictly un-aged state and after various ageing conditions. At room temperature (RT), the un-aged alloy shows astonishing tensile performances (ultimate tensile stress?=?1600?MPa/uniform elongation?=?15%) but unexpected serrations. These serrations can be suppressed by static ageing (at RT or higher) while maintaining the initial work-hardening rate (ageing at RT). Parallel investigations using atom probe tomography reveal that the distribution of carbon at the atomic scale evolves from purely homogeneous for virgin martensite to partly segregated at a very fine scale (5–10?nm) after static ageing. This particular mechanical behaviour can therefore be associated with a very local decrease in available carbon in solid solution due to redistribution and segregations on defects (nanotwins) that occurs rapidly, even after few days at RT. 相似文献