全文获取类型
收费全文 | 787篇 |
免费 | 19篇 |
国内免费 | 4篇 |
专业分类
化学 | 469篇 |
晶体学 | 16篇 |
力学 | 35篇 |
数学 | 108篇 |
物理学 | 182篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 19篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 42篇 |
2015年 | 24篇 |
2014年 | 33篇 |
2013年 | 54篇 |
2012年 | 54篇 |
2011年 | 65篇 |
2010年 | 42篇 |
2009年 | 21篇 |
2008年 | 38篇 |
2007年 | 40篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1926年 | 2篇 |
排序方式: 共有810条查询结果,搜索用时 15 毫秒
61.
Trinh An Huy Rameshwar Adhikari Thomas Lüpke Sven Henning Goerg H. Michler 《Journal of Polymer Science.Polymer Physics》2004,42(24):4478-4488
The orientation behavior of isotactic polypropylene (iPP) in α‐ and β‐crystal form was investigated by rheo‐optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by α‐PP, whereas β‐PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478–4488, 2004 相似文献
62.
Failure of paper oil insulation due to formation of copper sulphide in transformer windings is a serious issue affecting the performance and life of large transformers. Though chemical effects leading to corrosion are well understood, quantification of electric stress and its correlation to formation and migration of copper sulphide has not been reported in literature. Hence electric stress distribution under copper corrosion using FEM simulation has been studied and discussed in this paper. The simulation results are compared and correlated to experimental findings. The study clearly points towards increase in electric stress in unaffected paper and non-uniform electric stress distribution in paper–oil insulation system. Implications of using enamel coating on copper conductor as a mitigation technique to combat copper corrosion is also discussed. 相似文献
63.
Yeasudhasan Christu Rajan 《Tetrahedron letters》2008,49(18):3023-3026
Enantiopure bis-chromanones were prepared from (S)-Binol and bromo esters via a Baylis-Hillman approach. Chiroptical studies indicate that the two-naphthyl units of the chromanone system are non-coplanar. 相似文献
64.
Anwar Usman Ibrahim Abdul Razak Suchada Chantrapromma Hoong-Kun Fun Jayanta Kumar Ray Sujit Das Adhikari Bishnu Pada Datta 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(12):1441-1442
In the title compound, C20H20FNO5S, the pyrrolidine ring adopts an envelope conformation. The fluorophenyl and thiophene rings are individually planar. The molecular and crystal structures are stabilized by intra- and intermolecular C—H⋯O interactions. 相似文献
65.
Medha Rele B. S. Patro S. Adhikari G. P. Kalena S. Chattopadhyay T. Mukherjee 《Journal of Chemical Sciences》2002,114(6):739-747
The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported.
Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl3O2
•, N3
• and•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled
rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient
absorption peak was shifted in the case of CCl3OO• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption
band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with•OH and•N3 radicals. In a biological system also, 1 showed significant inhibitory activity against Fe2+-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed. 相似文献
66.
67.
68.
Copper crystals have been grown by Czochralski technique in a 6-bar argon gas environment. X-ray analysis shows that these
are single crystals and are strain-free. A slight pressure environment that is truly hydrostatic seems to improve the quality
of the crystals. Thermal profile estimation results show that the values of temperature which decrease upto the neck region
are same in magnitude as those measured during the experiments and that necking improves the thermal profile and, consequently,
the crystal quality. No facet formation has been observed in these crystals. 相似文献
69.
70.
A calix[5]arene-based solvent extraction reagent displaying very high selectivity for lead has been prepared, one molecule of which extracts two lead ions in a stepwise manner. The first Pb2+ ion is bound to five phenoxy oxygen atoms inside the calixarene cavity due to which the ligand undergoes conformational freezing in stable cone conformer. This causes positive allosteric effect for co-extraction of the second lead ion due to the aggregation of functional groups. 相似文献