全文获取类型
收费全文 | 725篇 |
免费 | 140篇 |
国内免费 | 98篇 |
专业分类
化学 | 696篇 |
晶体学 | 69篇 |
力学 | 3篇 |
综合类 | 5篇 |
数学 | 1篇 |
物理学 | 189篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 29篇 |
2021年 | 26篇 |
2020年 | 30篇 |
2019年 | 31篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 28篇 |
2015年 | 42篇 |
2014年 | 32篇 |
2013年 | 55篇 |
2012年 | 51篇 |
2011年 | 29篇 |
2010年 | 56篇 |
2009年 | 37篇 |
2008年 | 43篇 |
2007年 | 35篇 |
2006年 | 45篇 |
2005年 | 30篇 |
2004年 | 48篇 |
2003年 | 34篇 |
2002年 | 45篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 20篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有963条查询结果,搜索用时 15 毫秒
81.
Hairui Xia Jiyang Wang Lixia Li Zhigiang Zou 《Progress in Crystal Growth and Characterization of Materials》2000,40(1-4):253-261
A new series of non-ferroelectric crystals, the piezoelectric solid solution aluminium gallium orthophosphate Al1-xGaxPO4 (AGP, 0 < x < 1) system has been successfully developed by a hydrothermal method. The AGP crystal with X = 0.10 shows a phase transition temperature T−β = 587 ± 3 °C with a cell parameters A = b = 0.49386(3) and C = 1.09563(2) nm. Raman spectra including directional dispersion in AGP are similar to those from -AIPO4 and -quartz crystals, indicating all of them belong to an isomorphic family, the short-range interaction being dominant in AGP. Comparison with -AIPO4 crystals, there exists an apparent red shift of the mode frequency and a smaller TO/LO mode splitting of the E species in the AGP crystals. 相似文献
82.
Using cyclic voltammetric techniques the electrochemical behaviour of gallium in alkali media has been investigated. Three
anodic peaks, one cathodic peak, and a secondary anodic peak—an observation hitherto unreported—are obtained. Detailed analyses
of these various stages of oxidation and reduction based on their peak potential and peak current characteristics have revealed
the nature of the underlying electrochemical reactions. 相似文献
83.
N. D. Nguyen M. Germain M. Schmeits R. Evrard B. Schineller M. Heuken 《Journal of Crystal Growth》2001,230(3-4):596-601
The ac characteristics of GaN : Mg and undoped GaN layers, grown by MOVPE on sapphire substrates, are measured for a wide range of temperature and bias conditions, in order to investigate the effect of the magnesium-related level on the transport properties. Two peaks, whose height and position depend on the measurement temperature, are observed in the admittance curves (G/ω versus frequency) of the Mg-doped samples, whereas only one peak appears in undoped samples. The study of the frequency dependence of the impedance, with a model including the two metallic Au/GaN junctions, the GaN layer itself, shows that, besides the effect of the differential resistance of the layer which plays a role in both sample types, the presence of a Mg-related deep level contributes to the observed variations of the peaks in the admittance curves of the p-doped samples. Results of a theoretical steady-state and small-signal analysis based on numerical modelling of the Au/GaN/Au heterostructure complete our analysis. 相似文献
84.
85.
Series of compositions Bi2(M′xM1−x)4O9 with x=0.0, 0.1,…, 1.0 and M′/M=Ga/Al, Fe/Al and Fe/Ga were synthesized by dissolving appropriate amounts of corresponding metal nitrate hydrates in glycerine, followed by gelation, calcination and final heating at 800 °C for 24 h. The new compositions with M′/M=Ga/Al form solid-solution series, which are isotypes to the two other series M′/M=Fe/Al and Fe/Ga. The XRD data analysis yielded in all cases a linear dependence of the lattice parameters related on x. Rietveld structure refinements of the XRD patterns of the new compounds, Bi2(GaxAl1−x)4O9 reveal a preferential occupation of Ga in tetrahedral site (4 h). The IR absorption spectra measured between 50 and 4000 cm−1 of all systems show systematic shifts in peak positions related to the degree of substitution. Samples treated in 18O2 atmosphere (16 h at 800 °C, 200 mbar, 95% 18O2) for 18O/16O isotope exchange experiments show a well-separated IR absorption peak related to the M-18Oc-M vibration, where Oc denotes the common oxygen of two tetrahedral type MO4 units. The intensity ratio of M-18Oc/M-16Oc IR absorption peaks and the average crystal sizes were used to estimate the tracer diffusion coefficients of polycrystalline Bi2Al4O9 (D=2×10−22 m2s−1), Bi2Fe4O9 (D=5×10−21 m2s−1), Bi2(Ga/Al)4O9 (D=2×10−21 m2s−1) and Bi2Ga4O9 (D=2×10−20 m2s−1). 相似文献
86.
There has been an increasing interest in the use of gallium in anticancer activity. However, whether the uptakes of two species of transferrin, including digallium transferrin (Ga2‐Tf) and the C‐terminal monogallium transferrin (GaC‐Tf) by cells, are different is not well understood. In this work the mechanism of both species passing in and out K562 cells has been established by using 125I‐labeled transferrin. There were about (1.5±0.08)×105 binding sites per cell surface. Both Ga2‐Tf and GaC‐Tf were recycled to the cell exterior with a protracted endocytic cycle compared to apotransferrin (apoTf). The cycling time from the internalization to release was calculated about t1/2= (3.15±0.055) min for apoTf, t1/2= (4.69±0.09) min for Ga2‐Tf and t1/2= (4.78±0.15) min for GaC‐Tf. The result implies that metal dissociating from transferrin in acidic endosomes was likely to be the key step. Both Ga2‐Tf and GaC‐Tf into K562 cells are transferrin receptor‐mediated process with a similar rate of endocytosis and release. Our present observations provide useful information for better targeted drugs in specific therapy. 相似文献
87.
Kwangmin Park Eungjin Ahn Yu Jin Jeon Hyeonsik M. Cheong Jin Soak Kim Eun Kyu Kim Jungil Lee Young Ju Park Gun-Do Lee Euijoon Yoon 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):169
InAs quantum dots (QDs) were grown on InP substrates by metalorganic chemical vapor deposition. The width and height of the dots were 50 and 5.8 nm, respectively on the average and an areal density of 3.0×1010 cm−2 was observed by atomic force microscopy before the capping process. The influences of GaAs, In0.53Ga0.47As, and InP capping layers (5–10 ML thickness) on the InAs/InP QDs were studied. Insertion of a thin GaAs capping layer on the QDs led to a blue shift of up to 146 meV of the photoluminescence (PL) peak and an InGaAs capping layer on the QDs led to a red shift of 64 meV relative to the case when a conventional InP capping layer was used. We were able to tune the emission wavelength of the InAs QDs from 1.43 to 1.89 μm by using the GaAs and InGaAs capping layers. In addition, the full-width at half-maximum of the PL peak decreased from 79 to 26 meV by inserting a 7.5 ML GaAs layer. It is believed that this technique is useful in tailoring the optical properties of the InAs QDs at mid-infrared regime. 相似文献
88.
The present work deals with the electrochemical formation of superlattice structures on n-type (1 0 0) InP in HCl solutions. The superlattices consist of a stack of two layers with alternating high and low porosity on n-type material obtained by changing the anodizing current or the potential periodically in HCl solutions. The superlattice structures were characterized by scanning electron microscopy. The pore morphology and structure depend strongly on the electrochemical conditions. For anodization with low currents (e.g., 1 or 10 mA) or at low potentials (e.g., 1.5 VAg/AgCl), a porous layer with a facet-like structure was formed. For higher currents or potentials, such as 50 or 100 mA or 3 VAg/AgCl, respectively, a tree-like structure with random and/or tangled branches was observed. Finally, samples anodized at 5 VAg/AgCl, show a porous layer with a regular array of straight pores. The morphology and structure of the stacks of the porous layers can be controlled in the nanometer range, depending on the electrochemical conditions. 相似文献
89.
Cooperative Bond Activation and Catalytic Reduction of Carbon Dioxide at a Group 13 Metal Center 下载免费PDF全文
Joseph A. B. Abdalla Dr. Ian M. Riddlestone Rémi Tirfoin Prof. Simon Aldridge 《Angewandte Chemie (International ed. in English)》2015,54(17):5098-5102
A single‐component ambiphilic system capable of the cooperative activation of protic, hydridic and apolar H? X bonds across a Group 13 metal/activated β‐diketiminato (Nacnac) ligand framework is reported. The hydride complex derived from the activation of H2 is shown to be a competent catalyst for the highly selective reduction of CO2 to a methanol derivative. To our knowledge, this process represents the first example of a reduction process of this type catalyzed by a molecular gallium complex. 相似文献
90.
Revealing the Preferred Interlayer Orientations and Stackings of Two‐Dimensional Bilayer Gallium Selenide Crystals 下载免费PDF全文
Dr. Xufan Li Dr. Leonardo Basile Dr. Mina Yoon Dr. Cheng Ma Dr. Alexander A. Puretzky Dr. Jaekwang Lee Dr. Juan C. Idrobo Dr. Miaofang Chi Dr. Christopher M. Rouleau Dr. David B. Geohegan Dr. Kai Xiao 《Angewandte Chemie (International ed. in English)》2015,54(9):2712-2717
Characterizing and controlling the interlayer orientations and stacking orders of two‐dimensional (2D) bilayer crystals and van der Waals (vdW) heterostructures is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) crystals that result from different layer stackings provide an ideal platform to study the stacking configurations in 2D bilayer crystals. Through a controllable vapor‐phase deposition method, bilayer GaSe crystals were selectively grown and their two preferred 0° or 60° interlayer rotations were investigated. The commensurate stacking configurations (AA′ and AB stacking) in as‐grown bilayer GaSe crystals are clearly observed at the atomic scale, and the Ga‐terminated edge structure was identified using scanning transmission electron microscopy. Theoretical analysis reveals that the energies of the interlayer coupling are responsible for the preferred orientations among the bilayer GaSe crystals. 相似文献