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991.
992.
Ying Wan Prof. Dr. Dieqing Zhang Yunpu Zhai Cuimiao Feng Jia Chen Hexing Li Prof. Dr. 《化学:亚洲杂志》2007,2(7):875-881
Hybrid mesoporous periodic organosilicas (Ph‐PMOs) with phenylene moieties embedded inside the silica matrix were used as a heterogeneous catalyst for the Ullmann coupling reaction in water. XRD, N2 sorption, TEM, and solid‐state NMR spectroscopy reveal that mesoporous Ph‐PMO supports and Pd/Ph‐PMO catalysts have highly ordered 2D hexagonal mesostructures and covalently bonded organic–inorganic (all Si atoms bonded with carbon) hybrid frameworks. In the Ullmann coupling reaction of iodobenzene in water, the yield of biphenyl was 94 %, 34 %, 74 % and for palladium‐supported Ph‐PMO, pure silica (MCM‐41), and phenyl‐group‐modified Ph‐MCM‐41 catalysts, respectively. The selectivity toward biphenyl reached 91 % for the coupling of boromobenzene on the Pd/Ph‐PMO catalyst. This value is much higher than that for Pd/Ph‐MCM‐41 (19 %) and Pd/MCM‐41 (0 %), although the conversion of bromobenzene for these two catalysts is similar to that for Pd/Ph‐PMO. The large difference in selectivity can be attributed to surface hydrophobicity, which was evaluated by the adsorption isotherms of water and toluene. Ph‐PMO has the most hydrophobic surface, and in turn selectively adsorbs the reactant haloaryls from aqueous solution. Water transfer inside the mesochannels is thus restricted, and the coupling reaction of bromobenzene is improved. 相似文献
993.
针对背景为固定场所的数字视频监控系统,提出了一种通过比较图像彩色直方图距离实现视频监视系统自动控制的方法.通过在线动态更换参考图像,消除了时间变化引起的阳光、天气等因素对背景图像的影响.采用均匀压缩的方法,将真彩色颜色空间压缩到16色的索引色空间,降低了计算复杂度,滤掉了背景的微小变化引入的噪声,实现了10 ms内完成对一幅图像的处理.准确的自动控制在保证监视系统正常工作的同时,极大地减小了所需的存储空间.
关键词:
视频监视系统
彩色直方图
直方图距离 相似文献
994.
L.N. Tong M.H. Pan J. Wu X.S. Wu J. Du M. Lu D. Feng H.R. Zhai H. Xia 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):61-66
The structural, magnetic and transport properties of sputtered Fe/Si multilayers were studied. The analyses of the data of
the X-ray diffraction, resistance and magnetic measurements show that heavy atomic interdiffusion between Fe and Si occurs,
resulting in multilayers of different complicated structures according to different sublayer thicknesses. The nominal Fe layers
in the multilayers generally consist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si
silicide interface layers, while the nominal Si spacers turn out to be Fe-Si compound layers with additional amorphous Si
sublayers only under the condition either for the series or for the series multilayers. A strong antiferromagnetic (AFM) coupling and negative magnetoresistance (MR) effect, about 1%, were observed
only in multilayers with iron silicide spacers and disappeared when -Si layers appear in the spacers. The dependences of MR on and on bilayer numbers N resemble the dependence of AFM coupling. The increase of MR ratio with increasing N is mainly attributed to the improvement of AFM coupling for multilayers with N. The dependence of MR ratio is similar to that in metal/metal system with predominant bulk spin dependent scattering and is fitted
by a phenomenological formula for GMR. At 77 K both the MR effect and saturation field increase. All these facts suggest that the mechanisms of the AFM coupling and MR effect in sputtered Fe/Si multilayers are
similar to those in metal/metal system.
Received: 11 February 1998 / Revised: 9 March 1998 /
Accepted: 9 March 1998 相似文献
995.
Fabao Zhao Zhilei Liu Liang Feng Jianping Sun Jiwen Hu 《Journal of Polymer Science.Polymer Physics》2009,47(14):1345-1355
Optically active poly(ethylene glycol) monomethyl ether‐b‐poly(methacryloyl‐L ‐leucine methyl ester) (denoted as MPEG‐b‐PMALM) copolymers were prepared via atom transfer radical polymerization (ATRP), using bromine (Br) end‐capped poly(ethylene glycol) monomethyl ether (denoted as MPEG‐Br) as macroinitiator in the presence of CuBr/tris(2‐dimethylaminoethy1)amine (Me6TREN) as catalytic system. Broad range of morphologies, such as spherical, cylindrical, and vesicular micelles, which were prepared by initially dissolving prepared polymer in organic solvent at different concentration followed by addition various amount of water before dialysis against water to remove any added solvent, was observed by transmission electron microscope (TEM). More detailed chiroptical properties of the micelles/aggregates in aqueous solution were evaluated by circular dichroism (CD) spectroscopy as a function of micelles morphologies, polymer concentration, solvents employed, temperature, etc. The micellar solutions exhibit almost the same CD spectra regardless of its morphologies. The intensity of the CD spectra of the cylindrical micelles decreased in the molar ellipticities as the micellar concentration in water was increased. The Cotton effect was markedly changed when the solvent hydrophobicity was changed by addition of trifluoromethyl ethanol (TFME) to water. The intensity of the CD spectra decreased not too much within the temperature range from 20 °C to 90 °C, indicating good stability of the micelles upon temperature variation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1345–1355, 2009 相似文献
996.
Non-constant stable solutions to Landau-Lifshitz equation 总被引:3,自引:0,他引:3
Jian Zhai 《Calculus of Variations and Partial Differential Equations》1998,7(2):159-171
We prove the existence of solutions to the static Landau-Lifshitz equation corresponding to the homotopy classes of continuous
functions from . Here is a non-simply connected bounded domain in . The stability of the solutions to the time-dependent Landau-Lifshitz equation is also obtained.
Received June 29, 1996 / in revised form June 18, 1997 / Accepted July 13, 1997 相似文献
997.
A static physical model of the larynx (model M5) was used to obtain a large set of volume flows as a function of symmetric glottal geometry and transglottal pressure. The measurements cover ranges of these variables relevant to human phonation. A generalized equation was created to accurately estimate the glottal volume flow given specific glottal geometries and transglottal pressures. Both the data and the generalized formula give insights into the flow behavior for different glottal geometries, especially the contrast between convergent and divergent glottal angles at different glottal diameters. The generalized equation produced a fit to the entire M5 dataset (267 points) with an average accuracy of 3.4%. The accuracy was about seven times better than that of the Ishizaka-Flanagan approach to glottal flow and about four times better than that of a pressure coefficient approach. Thus, for synthesis purposes, the generalized equation presented here should provide more realistic glottal flows (based on steady flow conditions) as suitable inputs to the vocal tract, for given values of transglottal pressure and glottal geometry. Applications of the generalized formula to pulses generated by vocal fold motions typical of those produced by the Ishizaka-Flanagan coupled-oscillator model and the more recent body-cover model of Story and Titze are also included. 相似文献
998.
假设G是一个1-可扩图.G的1-因子覆盖是G的某些1-因子的集合M使得∪M∈M M=F(G).1-因子数目最小的1.因子覆盖称为excessive factorization.一个excessive factorization中的1.因子数目称为图G的excessive index,记为x:(G).本文我们基于G的耳朵分解和E(C)的依赖关系给出了X'e(G)的上界.对任意正整数k≥3,我们构造出一个图G使得A(G)=3而X'e(G)=k.进而,我们考虑了乘积图的excessive index. 相似文献
999.
Borromean链环分子是指具有"任意两个分支环都不互相锁套,但所有的分支环却是锁套在一起而不可分开"结构的链环分子分子.设计合成Borromean链环分子已成为化学拓扑学的目标之一.本文介绍了已合成的Borromean链环分子、DNA Borromean链环以及以Borromean环方式连接的配合物的新颖结构及其实验事实. 相似文献
1000.