全文获取类型
收费全文 | 651篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
化学 | 430篇 |
晶体学 | 2篇 |
力学 | 18篇 |
数学 | 120篇 |
物理学 | 115篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 5篇 |
2017年 | 12篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 32篇 |
2013年 | 35篇 |
2012年 | 51篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 36篇 |
2008年 | 32篇 |
2007年 | 19篇 |
2006年 | 30篇 |
2005年 | 25篇 |
2004年 | 27篇 |
2003年 | 19篇 |
2002年 | 24篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有685条查询结果,搜索用时 0 毫秒
131.
Lung Kwang Pan Che Chung Wang Ying Ching Hsiao Kye Chyn Ho 《Optics & Laser Technology》2005,37(1):33-42
The use of an Nd:YAG laser for thin plate magnesium alloy butt welding was optimized using the Taguchi analytical methodology. The welding parameters governing the laser beam in thin plate butt welding were evaluated by measuring of the ultimate tension stress. The effectiveness of the Taguchi method lies in clarifying the factor that dominates complex interactions in laser welding. The factors can be the shielding gas, laser energy, convey speed of workpiece, point at which the laser is focused, pulse frequency, and pulse shape. Furthermore, 18 combinations of these six essential welding parameters were set and Taguchi's method followed exactly. The optimal result was confirmed with a superior ultimate tension stress of 169 MPa, 2.5 times larger to that from original set for laser welding. 相似文献
132.
133.
Bruce X.Fu Benjamin S.Hsiao Gavin Chen Jack Zhou Susan Lin Jenny Yuan Ilya Koyfman Dennis D Jamiolkowski Edward Dormier 《高分子科学》2003,(2):159-167
Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-raydiffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGAfibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similarconditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain morecrystallinity and higher T_g than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate ofdegradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretchingstages was released in the post-annealing stage for a1l PGA and PGA-co-PLA samples. During earlier stages of in vitrodegradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. Theheat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLAsamples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, mostlikely due to relaxation of the cleaved chains. 相似文献
134.
Guey‐Sheng Liou Sheng‐Huei Hsiao Mina Ishida Masaaki Kakimoto Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》2002,40(16):2810-2818
A new triphenylamine‐containing aromatic diamine, N, N′‐bis(4‐aminophenyl)‐N, N′‐diphenyl‐1,4‐phenylenediamine, was prepared by the condensation of N,N′‐diphenyl‐1,4‐phenylenediamine with 4‐fluoronitrobenzene, followed by catalytic reduction. A series of novel aromatic polyamides with triphenylamine units were prepared from the diamine and various aromatic dicarboxylic acids or their diacid chlorides via the direct phosphorylation polycondensation or low‐temperature solution polycondensation. All the polyamides were amorphous and readily soluble in many organic solvents such as N, N‐dimethylacetamide and N‐methyl‐2‐pyrrolidone. These polymers could be solution cast into transparent, tough, and flexible films with good mechanical properties. They had useful levels of thermal stability associated with relatively high glass‐transition temperatures (257–287 °C), 10% weight‐loss temperatures in excess of 550 °C, and char yields at 800 °C in nitrogen higher than 72%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2810–2818, 2002 相似文献
135.
Shaofeng Ran Christian Burger Igors Sics Kyunghwan Yoon Dufei Fang Kwangsok Kim Carlos Avila-Orta Jongkahk Keum Benjamin Chu Benjamin S. Hsiao David Cookson Dave Shultz Myungae Lee Jim Viccaro Yasuo Ohta 《Colloid and polymer science》2004,282(8):802-809
The structural development of a nanocomposite, containing 95 wt% isotactic polypropylene (iPP) and 5 wt% modified carbon nanofiber (MCNF), during fiber spinning was investigated by in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. The modification of carbon nanofibers (CNFs) was accomplished by a chemical surface treatment using in situ polymerization of olefin segments to enhance its compatibility with iPP, where the iPP/MCNF nanocomposite was prepared by twostep blending to ensure the dispersion of MCNF. X-ray results showed that at low spin-draw ratios, the iPP/MCNF nanocomposite fiber exhibited much higher iPP crystalline orientation than the control iPP fiber. At higher spin-draw ratios, the crystalline orientation of the nanocomposite fiber and that of the pure iPP fiber was about the same. The crystallinity of the composite fiber was higher than that of the control iPP fiber, indicating the nucleating effect of the modified carbon nanofibers. The nanocomposite fiber also showed larger long periods at low spin-draw ratios. Measurements of mechanical properties indicated that the nanocomposite fiber with 5 wt% MCNF had much higher tensile strength, modulus and longer elongation to break. The mechanical enhancement can be attributed to the dispersion of MCNF in the matrix, which was confirmed by SEM results.Dedicated to Prof. E D. Fischer on his 75th birthday. 相似文献
136.
Consider a cylindrical pipe twisted by terminal couples. For a large twist θ, the elastic-plastic stress function, Ψ (·,θ), is shown to be the positive in the interior of the pipe, an increasing function of θ and converging to the completely plastic stress function, $ \bar \Psi \left(\cdot \right) $ (·), as θ→∞. A geometric procedure for constructing Ψ(·) has been developed to provide qualitative information. The main result states that $ \psi \left({\cdot,\theta} \right) = \bar \Psi \left(\cdot \right) $ on the cross-sectional boundary of the pipe, if θ is greater than or equal to a certain critical value, In addition, an example has been constructed to give additional insights. 相似文献
137.
Let F(θ k, α) be the far field pattern arising from the scattering of a time harmonic plane acoustic wave of wave number k and direction a by a sound-soft cylinder of cross section D. Suppose F has the Fourier expansion where an = an(k, . Then if ?2 is a Dirichlet eigenvalue for D, sufficient conditions are given on D for the existence of a nontrivial sequence |bn| where the bn are independent of such that for all directions Domains for which this is true are called generalized Herglotz domains. The conditions for a domain to be a generalized Herglotz domain are given either in terms of the Schwarz function for the analytic boundary ?D or in terms of the Rayleigh hypothesis in acoustic scattering theory and examples are given showing the applicability of these conditions. 相似文献
138.
Size Effect of Colloidal Selenium Particles on the Inhibition of LPS‐Induced Nitric Oxide Production
We have studied the size‐dependent inhibition capabilities of colloidal selenium (Se) particles on lipopolysaccharide (LPS)‐induced nitric oxide (NO) production in RAW 264.7 cells. Four particle sizes of the nano‐Se, ranging from 45 ? 220 nm in diameter, were examined. All of them, unlike their bulk material, show clear capabilities of inhibition and a trend dependent on the particles size. The inhibition becomes more potent as the particle size increases. It indicates that pursuing the reduction of colloidal sizes into nanoscale is not favoured in this biological system. 相似文献
139.
1-Benzenesulfonyl-2-trimethylsilylethane and 1-benzenesulfonyl-1-chloro-2-trimethylsilylethane are convertable to 1-benzenesulfonyl-1-chloro-1-substituted-2-trimethylsilylethanes which undergo elimination by fluoride ion to give phenyl -substituted-vinyl sulfones. 相似文献
140.
Horng Y. Tang Hsiao Y. Lin Ming Y. Liao Jean L. Liu Hwo S. Sheu 《Journal of solid state chemistry》2006,179(8):2728-2731
Bilayer hydrated Na0.35CoO2·1.3H2O structure has re-directed superconductivity research in recent years. Here, we develop a low temperature synthesis method to prepare a novel hydrous Cs0.2CoO2·0.63H2O compound in one step. The bilayer-hydrate of Cs0.2CoO2·0.63H2O with a greatest interlayer spacing d=10.0(2) Å among alkali cobalt oxides has been grown in crystal form. Magnetic susceptibility measurement of Cs0.2CoO2·0.63H2O displays a paramagnetic behavior down to 1.9 K. With the assistance of low temperature molten CsOH solvent, crystals of Rb0.30CoO2·0.36H2O and K0.35CoO2·0.4H2O can be grown. The results provide the capability for preparing a novel hydrous structure and the systematic investigation of interlayer coupling effect of alkali ion insertion compounds. 相似文献