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Roger H. Newman 《Cellulose (London, England)》2004,11(1):45-52
Solid-state 13C NMR spectroscopy was used to characterize a bleached softwood kraft pulp in the never-dried state and after cycles of drying and remoistening. Changes in NMR signal strengths indicated that growth of crystalline domains involved cocrystallization rather than accretion of cellulose from noncrystalline domains. A cluster of C-4 signals at 89.4 ppm, assigned to the interiors of crystalline domains, grew at the expense of C-4 signals at 84.0 and 84.9 ppm, assigned to the well-ordered surfaces of crystalline domains. Irreversible changes were not detected until the moisture content dropped below 18%. They were enhanced by a second drying/remoistening cycle, but showed little further change on subsequent cycles. The necessary conditions resembled those reported for hornification, suggesting that cocrystallization might provide a mechanism for hornification. 相似文献
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Ultraviolet and blue-green photoluminescence (PL) was investigated on multicrystalline silicon (mc-Si) samples chemically etched by Secco and Yang solutions. The samples were characterized by dislocation density (105-106 cm−2). The form of etched pits is triangular with Yang etch and like a honeycomb with Secco etch as observed with a scanning electron microscope (SEM). These textures of mc-Si wafers give a PL activity similar to that obtained with nanostructures of porous silicon (PS) as reported in the literature. The ultraviolet PL spectra observed with Yang etch shift to the blue-green spectrum range when applying Secco etch. In our experiments we have observed 3-5 μm diameter macro pores separated by a high density of nanowalls. These observations suggest that the origin of the PL activity are quantum dots resulting from the silicon nanocrystallites obtained after few minutes of chemical etching. 相似文献
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Jiaqiang Wang Hua Fang Ying Li Junjie Li Zhiying Yan 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):75-79
Cobalt-doped mesoporous titania with a crystalline framework synthesized by surfactant templating method presented highly selective (99%) and reasonable conversion rate (49%) of catalytic oxidation of para-chlorotoluene to para-chlorobenzaldehyde in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. By contrast, cobalt-doped mesoporous titania without a crystalline structure and cobalt doped the commercial titania, Degussa P25 prepared by impregnation method with the similar concentration of cobalt were found inactive. The effects of catalyst concentration, reaction time, reaction temperature, and solvents on the performance of the catalyst were also investigated. 相似文献
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文章合成了N,N'-二正丁基苝四羧酸二酰亚胺,并纯化、调晶,进行了IR、元素分析、X射线等测定.分析该化合物在DMF中的紫外光谱(最大吸收波长524.80 nm)、荧光光谱(最大发射波长539.0 nm)、Stokes位移(数值15 nm)等光谱性质.在400~700 nm范围内,α晶型薄膜紫外-可见吸收出现很强的吸收峰,且由β型变为α型,最大吸收波长有明显的红移(545 nm变为580 nm).X射线粉末衍射也反映出α晶型的2θ在26.0°处衍射峰CPS为2 508,β型在25.2°为1 891.α,β晶型作为电荷产生材料制得的功能分离型有机光导体,在光源滤波波长λ=532 nm曝光下,测得含α,β感光体达到饱和电位的时间分别为46,93.98 s,光衰电位(5.3千伏电压负充电电晕,1~2 s后的表面电位)分别为727和525 V,半衰曝光量分别为4.32,4.34μJ·cm-2,残余电位分别为30和45 V等光导性能数值. 相似文献
6.
Junsaku Nitta Yiping Lin Takaaki Koga Tatsushi Akazaki 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):429
We report on electron g-factor in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In0.53Ga0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor. 相似文献
7.
K. A. Vorotilov V. D. Zvorykin I. G. Lebo A. S. Sigov 《Journal of Russian Laser Research》2004,25(3):234-238
Preliminary experiments on laser annealing of ferroelectric samples by ultraviolet radiation of a KrF laser are carried out. In principle, laser annealing allows one to reduce appreciably the duration of thermal action, minimize the size of the samples treated, and control the crystallization processes in the samples. A special focussing system was employed to provide homogeneous irradiation of the spot with dimensions of ~1×1 cm2 within a broad energy range from 0.1 to 10~J per pulse. The range of energy densities leading to phase transitions in thin films is determined. 相似文献
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