全文获取类型
收费全文 | 26046篇 |
免费 | 2400篇 |
国内免费 | 6626篇 |
专业分类
化学 | 29551篇 |
晶体学 | 428篇 |
力学 | 348篇 |
综合类 | 218篇 |
数学 | 1588篇 |
物理学 | 2939篇 |
出版年
2024年 | 27篇 |
2023年 | 231篇 |
2022年 | 496篇 |
2021年 | 715篇 |
2020年 | 894篇 |
2019年 | 751篇 |
2018年 | 767篇 |
2017年 | 871篇 |
2016年 | 1179篇 |
2015年 | 1170篇 |
2014年 | 1454篇 |
2013年 | 2572篇 |
2012年 | 1697篇 |
2011年 | 1798篇 |
2010年 | 1494篇 |
2009年 | 1768篇 |
2008年 | 1830篇 |
2007年 | 1940篇 |
2006年 | 1922篇 |
2005年 | 1820篇 |
2004年 | 1739篇 |
2003年 | 1486篇 |
2002年 | 1014篇 |
2001年 | 704篇 |
2000年 | 610篇 |
1999年 | 651篇 |
1998年 | 598篇 |
1997年 | 522篇 |
1996年 | 386篇 |
1995年 | 369篇 |
1994年 | 326篇 |
1993年 | 300篇 |
1992年 | 294篇 |
1991年 | 157篇 |
1990年 | 102篇 |
1989年 | 102篇 |
1988年 | 84篇 |
1987年 | 49篇 |
1986年 | 32篇 |
1985年 | 40篇 |
1984年 | 36篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Eremenko L. T. Oreshko G. V. Nesterenko D. A. Lagodzinskaya G. V. Eremenko I. L. 《Russian Chemical Bulletin》2002,51(1):157-159
The reactions of ethylene glycol mononitrate and glycerol 1,3-dinitrate with methylphosphonic dichloride afforded new nitroxyalkyl methylphosphonates. 相似文献
82.
By an elementary calculation we obtain the exact mean values of Minkowksi functionals for a standard model of percolating sets. In particular, a recurrence theorem for the mean Euler characteristic recently put forward is shown to be incorrect. Related previous mathematical work is mentioned. We also conjecture bounds for the threshold density of continuum percolation, which are associated with the Euler characteristic. 相似文献
83.
84.
85.
Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L−1 cadmium chloride (CdCl2) and 16 mmol L−1 thioacetamide (CH3CSNH2) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λonset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent. 相似文献
86.
基于移动Agent技术的医学图像检索方法 总被引:1,自引:0,他引:1
针对现有医学图像检索方法中,检索算法速度较慢、准确性较低以及远程检索时占用大量带宽等问题,设计并实现了一种基于移动Agent技术的医学图像检索方法,重点讨论了该方法实现的关键技术,包括提升框架下的M带整数小波变换和提取多通道纹理特征的检索算法.模拟实验结果表明,该方法实时性较强,占用网络带宽较少,采用的算法运算速度提高近10倍、运算复杂度降低约50%,提取的纹理特征能充分表达图像内容,较好地满足了医学图像的检索要求,实现了对医学图像库快速较准确的检索. 相似文献
87.
A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose. 相似文献
88.
Yuri L. Sachkov 《Transactions of the American Mathematical Society》2004,356(2):457-494
Flat sub-Riemannian structures are local approximations -- nilpotentizations -- of sub-Riemannian structures at regular points. Lie algebras of symmetries of flat maximal growth distributions and sub-Riemannian structures of rank two are computed in dimensions 3, 4, and 5.
89.
N.M. Shash F.E. Salman M.G. El-Sharawy M.K. El-Mansy 《Journal of Physics and Chemistry of Solids》2004,65(5):881-889
Vitrification suppression in the (V2O5)1−x (P2O5)x glasses where x=0.10, 0.15, 0.20, and 0.25 was controlled by changing the rate of quenching glasses. The structure variations occurring in the glasses were detected by differential thermal analysis and optical microscope. The results implied the separation and growth of V2O5 orthorhombic microcrystal in the samples with x=0.10 and 0.15 whereas other samples did not illustrate remarkable changes in their microstructure. However, in temperature range between 300 and 473 K a semiconducting behavior for all samples appears during the study of electrical conductivity-temperature dependence. A decrease in conductivity values accompanied with some variations in activation energies by reducing quenching rate was observed. The conductivity results suggested that the conduction occurs by the phonon assisted hopping of a small polaron between V4+ and V5+ states at relatively higher temperature range above θD/2. Whereas at relatively low temperatures the conduction may occur by electron jumping between filled and empty states at Fermi level in the disordered matrix besides polaronic conduction. Reasonable values for the density of localized states, carrier concentration and carrier mobility were estimated and discussed. Also, dielectric constant and dielectric loss were studied as a function of frequency at different temperatures confirming the structure variations in the glass system. 相似文献
90.
Electron paramagnetic resonance (EPR) investigations has been carried out on the new family of molybdenum doped vanadium sesquioxides (V1−xMox)2−δO3. The oxidation effects were monitored from the rate of paramagnetic V4+ created when the sample is exposed to the air. The effects of the oxidation time, sample temperature, and annealing at 1000 °C under a diluted hydrogen atmosphere on the EPR signal features are analyzed. The V4+ concentration in the oxidized samples is determined and the relaxation effects driven by the conduction electrons are pointed out from the thermal behaviour of the EPR line features. EPR spectra of all the oxidized samples also reveal a small ferromagnetic contribution strongly correlated with the V4+ content. 相似文献