全文获取类型
收费全文 | 297篇 |
免费 | 15篇 |
国内免费 | 27篇 |
专业分类
化学 | 114篇 |
晶体学 | 3篇 |
力学 | 2篇 |
综合类 | 4篇 |
数学 | 27篇 |
物理学 | 189篇 |
出版年
2023年 | 3篇 |
2022年 | 20篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 9篇 |
2011年 | 3篇 |
2010年 | 9篇 |
2009年 | 31篇 |
2008年 | 42篇 |
2007年 | 20篇 |
2006年 | 23篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
41.
以没食子酸为原料。经烷基化、肼解得3,4,5-三甲氧基苯甲酰肼(2),2与芳香醛进行缩合反应合成了9个新的酰腙化合物。其结构经元素分析。IR,1H NMR和MS表征。 相似文献
42.
B. Lobe W. Janke K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):283-291
We analyze recently extended high-temperature series expansions for the “Edwards-Anderson” spin-glass susceptibility of the
p-state Potts glass model on d-dimensional hypercubic lattices for the case of a symmetric bimodal distribution of ferro- and antiferromagnetic nearest-neighbor
couplings . In these star-graph expansions up to order 22 in the inverse temperature , the number of Potts states p and the dimension d are kept as free parameters which can take any value. By applying several series analysis techniques to the new series expansions,
this enabled us to determine the critical coupling Kc and the critical exponent of the spin-glass susceptibility in a large region of the two-dimensional (p,d)-parameter space. We discuss the thus obtained information with emphasis on the lower and upper critical dimensions of the
model and present a careful comparison with previous estimates for special values of p and d.
Received: 25 May 1998 / Revised and Accepted: 11 August 1998 相似文献
43.
A.K. Hartmann U. Nowak 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):105-109
We investigate the critical behavior of three-dimensional random-field Ising systems with both Gauss and bimodal distribution
of random fields and additional the three-dimensional diluted Ising antiferromagnet in an external field. These models are
expected to be in the same universality class. We use exact ground-state calculations with an integer optimization algorithm
and by a finite-size scaling analysis we calculate the critical exponents , , and . While the random-field model with Gauss distribution of random fields and the diluted antiferromagnet appear to be in same
universality class, the critical exponents of the random-field model with bimodal distribution of random fields seem to be
significantly different.
Received: 9 July 1998 / Received in final form: 15 July 1998 / Accepted: 20 July
1998 相似文献
44.
T.J. Rinke R.B. Bergmann J.H. Werner 《Applied Physics A: Materials Science & Processing》1999,68(6):705-707
Thermal crystallization of a double layer porous Si film creates a monocrystalline Si film with a thin separation layer between
the Si film and the reusable starting wafer. The process enables transfer of thin monocrystalline Si films to foreign substrates,
whereby devices may be formed before or after separation of the film. Sub-micrometer thick films are almost compact, while
films with a thickness of several μm contain voids, and are therefore termed “quasi-monocrystalline”. Internal voids strongly
enhance optical absorption by light scattering. The hole mobility is 78 cm2 V-1 s-1 at a p-type starting wafer resistivity of 0.05 Ω cm.
Received: 24 March 1999 / Accepted: 29 March 1999 / Published online: 5 May 1999 相似文献
45.
选取纯弯曲梁进行裂缝扩展研究,在理论上符合Ⅰ型断裂模式.因此,本文利用扩展有限元法(XFEM)模拟了混凝土纯弯曲梁裂缝发展的全过程,结合线性叠加渐进假定,得到了不同初始缝高比的P-δ曲线、P-CMOD曲线以及临界有效裂缝扩展长度(ac-a0)/h与裂缝发展路经.对比试验数据和模拟结果表明:随着初始缝高比的增大,起裂荷载Pini、最大荷载Pmax、离散弗雷歇距离δdF与δd F′,以及临界有效裂缝长度(ac-a0)/h均逐渐减小;试验与模拟的裂纹发展路径存在一定偏差,可知试验数据与模拟结果存在规律性差异. 相似文献
46.
Hanene Zemmouri Sonda Ammar Amel Boumendjel Mahfoud Messarah Abdelfattah El Feki Mohamed Bouaziz 《Arabian Journal of Chemistry》2019,12(8):1954-1963
The aqueous and hydroalcoholic extracts of borage (Borago officinalis) leaves from Annaba region (Algeria) were preliminary analyzed for their phenolic profile (total phenolics, total flavonoids, total flavonols, total tannins and total anthocyanins). These extracts were evaluated for their antioxidant properties by different methods such as DPPH radical scavenging, test NBT and total antioxidant activity. The two extracts have exhibited a high antiradical capacity. Indeed, the ethanolic extract showed the lower IC50 values and the highest amount of phenolics (94.09 ± 1.72 mg gallic acid/g dry extract). Using LC-MS/MS analysis, it was possible to identify phenolic acids, flavonoids, sterol and for the first time oleuropein was identified in the aqueous extract of the plant. The obtained results have demonstrated that phenolic compounds are the major contributor to the antioxidant activity of plants. 相似文献
47.
S. Berkebile G. Koller P. Puschnig C. Ambrosch-Draxl F. P. Netzer M. G. Ramsey 《Applied Physics A: Materials Science & Processing》2009,95(1):101-105
Here we report the electronic π-band structure of sexithiophene obtained from 6T(010) oriented films. The angle-resolved valence band photoemission results
taken parallel and perpendicular to the molecular axis are compared to those of sexiphenyl and interpreted in terms of intra-
and inter-molecular band dispersion. We show that the strong photoemission intensity variations with emission angle parallel
to the molecular axis are well reproduced by the Fourier transforms of the molecular orbitals of the isolated molecules. These
results imply that ARUPS can yield quite detailed information about molecular geometry, both in terms of molecular orientation
and internal structure. 相似文献
48.
The visual quality of human eyes is much restricted by high-order aberrations as well as low-order aberrations (defocus and astigmatism), but each term of high-order aberrations contributes differently. The visual acuity and contrast of the image on the retina can be gained by inducing aberrations to each term of high orders. Based on an adaptive optics system, the visual acuity of four subjects is tested by inducing aberrations to each Zernike term after correcting all the aberrations of the subjects. Zernike terms near the center of the Zernike tree affect visual quality more than those near the edge both theoretically and experimentally, and 0.1μm aberration of these terms can clearly degrade the optical quality and vision. The results suggest that correcting the terms near the center of Zernike tree can improve the visual quality effectively in practice. 相似文献
49.
50.
利用映射的Fréchet可微的概念研究具约束的向量均衡问题的弱有效解,Henig有效解,超有效解以及全局有效解的最优性条件,在不具任何凸性条件下给出了的向量均衡问题的K-T必要性条件,在加上凸性条件下给出了向量均衡问题的K-T充分性条件。 相似文献