全文获取类型
收费全文 | 11814篇 |
免费 | 1847篇 |
国内免费 | 1021篇 |
专业分类
化学 | 7391篇 |
晶体学 | 193篇 |
力学 | 197篇 |
综合类 | 72篇 |
数学 | 242篇 |
物理学 | 6587篇 |
出版年
2024年 | 24篇 |
2023年 | 94篇 |
2022年 | 258篇 |
2021年 | 317篇 |
2020年 | 334篇 |
2019年 | 296篇 |
2018年 | 311篇 |
2017年 | 397篇 |
2016年 | 431篇 |
2015年 | 412篇 |
2014年 | 526篇 |
2013年 | 963篇 |
2012年 | 829篇 |
2011年 | 699篇 |
2010年 | 541篇 |
2009年 | 712篇 |
2008年 | 691篇 |
2007年 | 879篇 |
2006年 | 715篇 |
2005年 | 661篇 |
2004年 | 607篇 |
2003年 | 540篇 |
2002年 | 452篇 |
2001年 | 402篇 |
2000年 | 355篇 |
1999年 | 360篇 |
1998年 | 293篇 |
1997年 | 270篇 |
1996年 | 235篇 |
1995年 | 179篇 |
1994年 | 165篇 |
1993年 | 154篇 |
1992年 | 122篇 |
1991年 | 107篇 |
1990年 | 66篇 |
1989年 | 65篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 21篇 |
1984年 | 27篇 |
1983年 | 6篇 |
1982年 | 18篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1974年 | 8篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
101.
The optical nonlinearities of Cu(mpo)2 [formula = C10H8N2CuO2S2] complex have firstly been investigated by using the Z-scan technique with a nanosecond-pulsed Nd:YAG laser at its second harmonic (532 nm) radiation. The nonlinear optical absorption and refraction coefficients of Cu(mpo)2 have been measured with the different on-axial peak irradiances I
0 at the waist ranging from 0.48 to 5.66 GW/cm2. The nonlinear transmittance characteristics exhibit the near resonant two-photon absorption (TPA) at 532 nm and are explained by a population redistribution model. The nonlinear absorption originates from the near resonant TPA while the mechanism of the nonlinear refraction is the near resonant TPA transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant TPA. 相似文献
102.
Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献
103.
J. J. Rehr 《Foundations of Physics》2003,33(12):1735-1742
The Golden rule expression for x-ray absorption spectra (XAS) is typically calculated within a one-particle (quasiparticle) approximation and generally leads to good agreement between theory and experiment. The fact that a quasiparticle approximation works fairly well is surprising, since it neglects satellite excitations and intrinsic losses due to a suddenly created core-hole. The resolution of this paradox requires physics beyond the independent particle approximation. This is discussed here using an effective Green's function formulation based on a quasi-boson model that takes interference between inelastic losses into account. This approach shows that inelastic excitations such as multi-electron excitations tend to be suppressed, and that the XAS is given by a broadened quasiparticle particle approximation, together with weak satellite structure and edge singularity effects. 相似文献
104.
综述了暗中空光束自旋与轨道角动量的一些性质及其与中性原子之间的相互作用,并简单介绍了暗中空光束及其角动量在原子光学和玻色_爱因斯坦凝聚(BEC)以及各种原子光学器件研制方面的应用. 相似文献
105.
Phenethylammonium-based perovskites, which can be regarded as a semiconductor/insulator multiple quantum well consisting of lead halide semiconductor layers sandwiched between phenethylammonium insulator layers were prepared. To investigate the effects of the electronic state and the orientation of organic insulator layers on the optical properties of layered perovskites, fluorine substituted analogues were also prepared. The structure and optical properties were investigated by the XRD, UV–Vis absorption, and fluorescence measurements. The exciton absorption peak was shifted by the substitution of fluorine atoms in organic ammonium compounds. It became clear that the optical properties of two-dimensional perovskite compounds were controlled by the substitution of fluorine atoms. 相似文献
106.
Molar extinction coefficients of aqueous solutions of some organic compounds, viz. formamide (CH3NO),N-methylformamide (C2H5NO),NN-dimethylformamide (C3H7NO),NN-dimethylacetamide (C4H9NO), 1,4-dioxane (C4H8O24), succinimide (C4H5NO2) and solutions of acetamide (C2H5NO) and benzoic acid (C7H6O2) in 1,4-dioxane (C4H8O2) have been determined by narrow beam γ-ray transmission method at 81, 356, 511, 662, 1173 and 1332 keV. The experimental
values of mass attenuation coefficients of these compounds have been used to calculate effective atomic numbers and electron
densities. The additivity rule earlier used for aqueous solution has been extended to non-aqueous (1,4-dioxane) solutions. 相似文献
107.
Mohamed Haouas Amine Harrane Mohamed Belbachir Francis Taulelle 《Journal of Polymer Science.Polymer Physics》2007,45(22):3060-3068
Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. 1H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. 27Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the 29Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007 相似文献
108.
109.
Yu. M. Smirnov 《Journal of Russian Laser Research》2003,24(2):121-128
Excitation of rhenium atoms by electron impact is investigated by the method of extended crossing beams. At electron energies of 50 eV, the excitation cross sections of 36 resonance and competing transitions in ReI are measured. Within the energy range from the threshold value to 250 eV, six optical excitation functions are detected. The reliability of data on transition probabilities in ReI has been analyzed. 相似文献
110.
J. L. Gardea-Torresdey K. J. Tiemann J. R. Peralta-Videa J. G. Parsons M. Delgado 《Microchemical Journal》2004,76(1-2):65
Traditional treatment methods used to clean-up heavy metal contamination of soils and waters are cost intensive whereas more cost effective methods need to be developed. The use of plant materials to remediate heavy contamination has been studied for the past two decades. This technique has shown much promise for many of the common heavy metal contaminants, but few studies have focused on the lanthanide series elements. By investigating the binding and interactions of the lanthanide elements to alfalfa biomass, a more complete understanding of the binding mechanisms and the interactions of heavy metals with biomaterials can be obtained. Different chemical functional groups on the alfalfa biomass, carboxyl, amino, sulfur, and ester groups, were modified to investigate the binding mechanisms of erbium(III) and holmium(III). Batch experiments were performed with native and chemically modified alfalfa biomass suggesting that the carboxyl groups play a major role in the binding of erbium(III) and holmium(III) to the alfalfa biomass. In addition, X-ray absorption spectroscopy (XAS) studies corroborated the data obtained from the batch experiments. 相似文献