全文获取类型
收费全文 | 1455篇 |
免费 | 66篇 |
国内免费 | 2篇 |
专业分类
化学 | 1059篇 |
晶体学 | 27篇 |
力学 | 41篇 |
数学 | 86篇 |
物理学 | 310篇 |
出版年
2023年 | 11篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 42篇 |
2019年 | 33篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 73篇 |
2015年 | 45篇 |
2014年 | 65篇 |
2013年 | 119篇 |
2012年 | 116篇 |
2011年 | 103篇 |
2010年 | 56篇 |
2009年 | 52篇 |
2008年 | 111篇 |
2007年 | 81篇 |
2006年 | 62篇 |
2005年 | 51篇 |
2004年 | 41篇 |
2003年 | 30篇 |
2002年 | 42篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1974年 | 5篇 |
1971年 | 4篇 |
1969年 | 6篇 |
1968年 | 6篇 |
1964年 | 4篇 |
1963年 | 6篇 |
1962年 | 6篇 |
1961年 | 12篇 |
1958年 | 7篇 |
1955年 | 5篇 |
排序方式: 共有1523条查询结果,搜索用时 15 毫秒
41.
The orientational order parameters fot two liquid crystal materials, 4-cyanophenyl 4-butylbenzoate and 4-cyanophenyl 4-pentylbenzoate, have been derived by measuring the change in the refractive index as function of temperature. The order parameters are compared with MaierSaupe theory, and the sharpness of the transitions has been shown using the Haller's plot. 相似文献
42.
T. Arun Kumar V.S.S. Sastry Ken Ishikawa Hideo Takezoe N.V. Madhusudana 《Liquid crystals》2013,40(8):971-979
We report experimental studies on defects in a nematic liquid crystal with negative dielectric anisotropy mounted in a cell with perfluoropolymer-coated surfaces. The sample exhibits a discontinuous anchoring transition from planar to homeotropic on cooling at zero or a small electric field, and above a cross-over voltage a continuous ‘inverse Freedericksz transition’, at which the director starts tilting in opposite directions at the two surfaces. Defects of strength ±1/2 are either annihilated or expelled when the director tilts. On the other hand, disclination lines of ±1 which end in partial point defects (boojums) at the surfaces in the planar alignment regime acquire point defects of strength ±1 at the midplane of the cell when the director tilts. At a low enough temperature, the homeotropic anchoring becomes strong, and an electric field above the Freedericksz threshold generates the usual umbilic defects, which follow the dynamic scaling laws found in earlier studies. 相似文献
43.
Parthiban A. Lingam K. Arun Prasath Mangalaraj S. Muthukrishnan P. Surendiran M. 《Journal of Cluster Science》2021,32(5):1401-1409
Journal of Cluster Science - Single crystal electron paramagnetic resonance (EPR), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) and UV–Visible (UV–Vis)... 相似文献
44.
Pyrazolopyrimidine and pyrimidopyrimidine derivatives have shown a wide range of biological activities such as acting as A1 adenosine receptors, kinase insert domain receptor (KDR), Rous sarcoma oncogene (Src), epidermal growth factor receptor (EGFR), antiproliferative, dihydrofolate reductase (DHFR), antimicrobial, antifungal, and lipid peroxidation. Because of this wide range of activities, we have synthesized pyrazolo[3,4‐d]pyrimidines and pyrimido[4,5‐d]pyrimidin‐4‐one derivatives. 相似文献
45.
46.
Swadesh Kumar Gupta Dharmendra Pratap Singh Pankaj Kumar Tripathi Mahesh Varia Laxmi K. Sagar 《Liquid crystals》2013,40(4):528-533
Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system. 相似文献
47.
48.
Chemoselective esterification of phenolic acids with dialkyl sulphates or alkyl halides in the presence of sodium bicarbonate in 1,3‐dialkylimidazolium ionic liquids is reported in excellent yields and less reaction time as compared to organic solvents. 相似文献
49.
50.