全文获取类型
收费全文 | 991篇 |
免费 | 83篇 |
国内免费 | 40篇 |
专业分类
化学 | 766篇 |
晶体学 | 9篇 |
力学 | 30篇 |
综合类 | 1篇 |
数学 | 104篇 |
物理学 | 204篇 |
出版年
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 25篇 |
2018年 | 20篇 |
2017年 | 11篇 |
2016年 | 38篇 |
2015年 | 45篇 |
2014年 | 40篇 |
2013年 | 70篇 |
2012年 | 70篇 |
2011年 | 75篇 |
2010年 | 62篇 |
2009年 | 44篇 |
2008年 | 77篇 |
2007年 | 55篇 |
2006年 | 52篇 |
2005年 | 48篇 |
2004年 | 31篇 |
2003年 | 22篇 |
2002年 | 29篇 |
2001年 | 15篇 |
2000年 | 23篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1985年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1967年 | 4篇 |
1964年 | 2篇 |
1934年 | 2篇 |
排序方式: 共有1114条查询结果,搜索用时 15 毫秒
71.
Kuo‐Chung Cheng Jiun‐Jeng Chen Wen‐Yen Chiu Lee Yih Wang Ping‐Chieh Wang 《Journal of polymer science. Part A, Polymer chemistry》2005,43(1):42-49
Dodecylbenzenesulfonic acid, DDBSA, was chosen as a new rate‐accelerating additive for 2,2,6,6,‐teramethyl‐1‐piperidinyloxy (TEMPO)‐mediated stable free radical polymerization of n‐butyl acrylate (n‐BA) monomers with 2,2′‐azobisisobutyronitrile (AIBN). It was found that the number‐average molecular weight of polymers could reach about ten thousand with a narrow polydispersity index (PDI) of 1.4 in a few minutes, which was faster than other systems reported previously. But, at higher conversion, the molecular weight distribution of polymers became broad, and a bimodal distribution occurred. The macro‐initiators isolated from the former polymers with narrow PDI could be extended by polymerization with monomers by the addition of DDBSA. Furthermore, a proposed kinetic model demonstrated that the decay of the concentration of DDBSA would reduce the living polymer concentration and retard the growth of the polymers, which could be further propagated by the supplement of DDBSA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 42–49, 2005 相似文献
72.
Y.-K. Kuo S.-H. Yen M.-W. Yao M.-C. Tsai M.-L. Chen B.-T. Liou 《Applied physics. B, Lasers and optics》2008,93(2-3):497-506
In this work, the multiple-quantum-well InGaAsN laser structures with indirect-GaAsP and direct-GaAsN barriers are investigated by using LASTIP simulation program. We vary the quantum-well number, from 1 to 5, to find appropriate barrier material for InGaAsN laser structures. The simulation results show that InGaAsN laser structure has higher characteristic temperature regardless of what quantum-well number is if the indirect-GaAsP barrier is utilized. Furthermore, for InGaAsN laser structure, the usage of indirect-GaAsP barrier is beneficial for reducing the threshold current when the quantum-well number is from 1 to 2 and the usage of direct-GaAsN barrier is beneficial for reducing the threshold current when the quantum-well number is from 3 to 5. 相似文献
73.
74.
C. Chan T. E. Drake R. Abegg D. Frekers O. H usser K. Hicks D. A. Hutcheon L. Lee C. A. Miller R. Schubank S. Yen 《Nuclear Physics A》1990,510(4):713-730
The complete set of Wolfenstein parameters, the polarization, the asymmetry of scattering and the unpolarized double-differential cross section are presented for inclusive quasielastic proton scattering from 12C at a central momentum transfer of q = 1.9 fm−1 and incident energies of 290 and 420 MeV. The spin observables D0, Dx, Dy and Dz as well as the longitudinal-to-transverse ratio of spin-flip probabilities are extracted from the data. Across the quasielastic continuum, the experimental data is compared to the variations expected from a single-scattering Fermi-gas approximation using the free NN amplitudes. Medium effects are evident in the pronounced quenching of the polarization parameter relative to the free value. 相似文献
75.
Different cellular accumulations with distinct fluorescence properties of BMVC in cancer cells from normal cells allow us to establish a simple and economic method for the diagnosis of cancer cells. With using a light emitting diode to excite the BMVC molecule, microarray fluorescence analysis of a cell‐based glass chip provides an easy method towards the detection of a limited number of cancer cells. 相似文献
76.
Sheng-Horng Yen 《Optics Communications》2008,281(18):4735-4740
The laser performance of violet InGaN laser diodes is investigated numerically. The polarization-dependent properties, including overlap of electron and hole wavefunctions, threshold current, and slope efficiency, are studied through the use of step-like quantum well structure. Furthermore, the electron and hole wavefunctions, band diagrams, and emission wavelength are compared and analyzed. The simulation results show that the lowest threshold current and the highest slope efficiency are obtained when the step-like quantum well structure is designed as In0.12Ga0.88N (2.5 nm)-In0.18Ga0.82N (1 nm) or In0.18Ga0.82N (2.5 nm)-In0.12Ga0.88N (1 nm) for violet laser diodes due to sufficiently enhanced overlap of electron and hole wavefunctions. 相似文献
77.
78.
Yun‐Sheng Ye Ying‐Chieh Yen Wen‐Yi Chen Chih‐Chia Cheng Feng‐Chih Chang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(18):6296-6304
This article describes a new and simple method for preparing polyimide nanocomposites that have very low dielectric constants and good thermal properties: simply through blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane derivative, octakis(dimethylsiloxyhexafluoropropyl) silsesquioxane (OF). The low polarizability of OF is compatible with polyimide matrices, such that it can improve the dispersion and free volume of the resulting composites. Together, the higher free volume and lower polarizability of OF are responsible for the lower dielectric constants of the PI‐OF nanocomposites. This simple method for enhancing the properties of polyimides might have potential applicability in the electronics industry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6296–6304, 2008 相似文献
79.
H. G. Miller Yiharn Tzeng G. D. Yen N. Canosa R. Rossignoli A. Plastino 《Zeitschrift für Physik A Hadrons and Nuclei》1986,356(2):141-144
Unphysical behavior in the QR algorithm based least squares determination of the expansion coefficients of the charge density obtained from limited information about the charge form factor occurs when the spread of the singular values in the matrix relating these quantities becomes too large. Setting the smallest singular values equal to zero in the singular value decomposition used in the minimum norm method yields a much more reasonable determination of the charge density. Increasing the size of the basis without increasing the range of the prior information about the charge form factor leads to ambiguities in the determination of the charge density. Numerical results in an analytic model are presented. 相似文献
80.
Ying‐Da Luo I‐Chen Chou Wen‐Yen Chiu Chia‐Fen Lee 《Journal of polymer science. Part A, Polymer chemistry》2009,47(17):4435-4445
In this research, poly(methyl methacrylate)‐b‐poly(butyl acrylate) (PMMA‐b‐PBA) block copolymers were prepared by 1,1‐diphenylethene (DPE) controlled radical polymerization in homogeneous and miniemulsion systems. First, monomer methyl methacrylate (MMA), initiator 2,2′‐azobisisobutyronitrile (AIBN) and a control agent DPE were bulk polymerized to form the DPE‐containing PMMA macroinitiator. Then the DPE‐containing PMMA was heated in the presence of a second monomer BA, the block copolymer was synthesized successfully. The effects of solvent and polymerization methods (homogeneous polymerization or miniemulsion polymerization) on the reaction rate, controlled living character, molecular weight (Mn) and molecular weight distribution (PDI) of polymers throughout the polymerization were studied and discussed. The results showed that, increasing the amounts of solvent reduced the reaction rate and viscosity of the polymerization system. It allowed more activation–deactivation cycles to occur at a given conversion thus better controlled living character and narrower molecular weight distribution of polymers were demonstrated throughout the polymerization. Furthermore, the polymerization carried out in miniemulsion system exhibited higher reaction rate and better controlled living character than those in homogeneous system. It was attributed to the compartmentalization of growing radicals and the enhanced deactivation reaction of DPE controlled radical polymerization in miniemulsified droplets. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4435–4445, 2009 相似文献