全文获取类型
收费全文 | 397377篇 |
免费 | 10624篇 |
国内免费 | 3180篇 |
专业分类
化学 | 216599篇 |
晶体学 | 5323篇 |
力学 | 18487篇 |
综合类 | 14篇 |
数学 | 56193篇 |
物理学 | 114565篇 |
出版年
2021年 | 4181篇 |
2020年 | 5565篇 |
2019年 | 7649篇 |
2018年 | 8461篇 |
2017年 | 8231篇 |
2016年 | 13257篇 |
2015年 | 8505篇 |
2014年 | 11868篇 |
2013年 | 20142篇 |
2012年 | 17048篇 |
2011年 | 18095篇 |
2010年 | 15233篇 |
2009年 | 15308篇 |
2008年 | 17248篇 |
2007年 | 16248篇 |
2006年 | 14395篇 |
2005年 | 13147篇 |
2004年 | 12676篇 |
2003年 | 11300篇 |
2002年 | 11985篇 |
2001年 | 10316篇 |
2000年 | 8545篇 |
1999年 | 5759篇 |
1998年 | 5056篇 |
1997年 | 4780篇 |
1996年 | 4562篇 |
1995年 | 3902篇 |
1994年 | 3997篇 |
1993年 | 4010篇 |
1992年 | 3988篇 |
1991年 | 4253篇 |
1990年 | 4295篇 |
1989年 | 4218篇 |
1988年 | 3956篇 |
1987年 | 4002篇 |
1986年 | 3689篇 |
1985年 | 4371篇 |
1984年 | 4579篇 |
1983年 | 3871篇 |
1982年 | 4052篇 |
1981年 | 3743篇 |
1980年 | 3450篇 |
1979年 | 3911篇 |
1978年 | 3975篇 |
1977年 | 4141篇 |
1976年 | 4203篇 |
1975年 | 3908篇 |
1974年 | 3777篇 |
1973年 | 3957篇 |
1972年 | 3330篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
202.
C. Czeranowsky V. M. Baev G. Huber P. A. Khandokhin Ya. I. Khanin I. V. Koryukin E. Yu. Shirokov 《Radiophysics and Quantum Electronics》2004,47(10-11):723-728
Experimental study of low-frequency dynamics of an intracavity frequency-doubled Nd:YAG laser demonstrates the influence of the interaction of orthogonally polarized modes, participating in frequency doubling (type II phase matching), on the stability of the laser output. At a sufficiently low pump rate and low conversion efficiency, the laser shows stable operation with a low noise level at the frequencies of relaxation oscillations. At a high pump power and/or a high conversion efficiency, the laser emission becomes unstable as a result of Hopf bifurcation at the frequencies of relaxation oscillations that are responsible for the anti-phase polarization dynamics of the laser. 相似文献
203.
Dedushenko S. K. Makhina I. B. Mar'in A. A. Mukhanov V. A. Perfiliev Yu. D. 《Hyperfine Interactions》2004,158(1-4):417-421
A colourless quartz crystal doped with 57Fe3+ was obtained by hydrothermal synthesis in an NH4F solution. The crystal was transformed into violet amethyst by gamma-irradiation. The change in colour was accompanied by changes in the Mössbauer spectrum that can be interpreted as the conversion of trivalent iron into the tetravalent state: Fe3+→Fe4+.
相似文献204.
Porous silicon (PS) exhibits several photoluminescence (PL) bands, whose spectral position and intensity depend strongly on the actual conditions of preparation of PS, its treatment, and subsequent use. The PS PL band peaking at about 1.8 eV and usually assigned to the intrinsic emission of silicon nanocrystals was studied. It was shown that the temperature-induced variation of the PL kinetics in the 80 to 300-K interval follows a complex pattern and depends noticeably on the actual point on the band profile. The temperature behavior of PL decay in the 1.8-eV band is determined by the electron-hole recombination rate within a nanocrystal and the cascade carrier transitions from small to large nanocrystals, with an attendant decrease in energy. 相似文献
205.
J. M. Martínez‐Burgos R. Benavente E. Prez M. L. Cerrada 《Journal of Polymer Science.Polymer Physics》2003,41(11):1244-1255
Several composites were prepared on the basis of an ethylene homopolymer and different copolymers of ethylene and 1‐hexene, synthesized with a metallocene catalyst, as matrices and a content of a 5 wt % of short glass fiber. The effect of the fiber incorporation on the structure and mechanical and viscoelastic behaviors was analyzed for the different samples. The glass fibers induced a slightly higher crystallinity, and the crystallite morphology significantly changed (long spacings and crystal orientation). The incorporation of fibers did not reinforce the different matrices under study at this low content; consequently, the mechanical parameters, such as Young's modulus, yielding stress, and microhardness, were lower in the composites as compared with those values found in the neat polyolefins. The location and apparent activation energies of distinct relaxation processes are also discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1244–1255, 2003 相似文献
206.
For the decay of two identical particles with close momenta, the angular correlations between the directions of emission of decay products are considered on the basis of the model of independent single-particle sources emitting unstable unpolarized particles of nonzero spin. These correlations reflect spin correlations that are caused by quantum-statistics and final-state-interaction effects. A general theory of angular correlations in the decays of two arbitrarily polarized particles (resonances) is constructed. 相似文献
207.
208.
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002. 相似文献
209.
Monika Goikoetxea María J. Barandiaran José M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5838-5846
The mechanisms involved in the formation of n‐butanol during the synthesis of butyl acrylate containing latices were investigated. The experimental results showed that neither the hydrolysis of butyl acrylate nor of the ester bond in the butyl acrylate segments of the polymer played a major role in the formation of n‐butanol, which was mainly generated from the polymer backbone, by transfer reactions to polymer chain followed by cyclization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5838–5846, 2007 相似文献
210.
Hana Macková Daniela Králová Daniel Horák 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):5884-5898
The aim of this study was to develop novel thermally responsive polymer microspheres with magnetic properties. Dispersion and inverse emulsion copolymerization of N‐isopropylacrylamide (NIPAAm) and N,N′‐methylenebisacrylamide (MBAAm) was investigated in the presence of γ‐Fe2O3 nanoparticles. The resulting microspheres were characterized in terms of morphology, size, polydispersity, iron content, and temperature‐dependent swelling using optical microscopy, transmission electron microscopy, scanning electron microscopy, QELS, and AAS. The effects of several variables, such as the concentration of γ‐Fe2O3, MBAAm crosslinking agent, Span 80 surfactant, 2,2′‐azobis(2‐methyloctanenitrile) (AMON) initiator, and polymerization temperature on the properties of the microspheres were studied. Swelling and thermoresponsive behavior of the microspheres containing γ‐Fe2O3 nanoparticles were also investigated. The microspheres contained about 8 wt % of iron. The presence of magnetic nanoparticles and their concentration changes did not have any significant effect on the temperature sensitivity of the composites. The particles gradually shrink into an increasingly collapsed state when the temperature is raised to 40 °C since the increase in temperature weakens the hydration and PNIPAAm chains gradually become more hydrophobic, which leads to the collapse of the particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5884–5898, 2007 相似文献