全文获取类型
收费全文 | 1777篇 |
免费 | 240篇 |
国内免费 | 93篇 |
专业分类
化学 | 749篇 |
晶体学 | 61篇 |
力学 | 135篇 |
综合类 | 7篇 |
数学 | 12篇 |
物理学 | 1146篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 25篇 |
2021年 | 29篇 |
2020年 | 46篇 |
2019年 | 53篇 |
2018年 | 55篇 |
2017年 | 40篇 |
2016年 | 66篇 |
2015年 | 67篇 |
2014年 | 56篇 |
2013年 | 250篇 |
2012年 | 108篇 |
2011年 | 114篇 |
2010年 | 84篇 |
2009年 | 89篇 |
2008年 | 107篇 |
2007年 | 103篇 |
2006年 | 148篇 |
2005年 | 65篇 |
2004年 | 69篇 |
2003年 | 72篇 |
2002年 | 87篇 |
2001年 | 60篇 |
2000年 | 54篇 |
1999年 | 44篇 |
1998年 | 34篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有2110条查询结果,搜索用时 437 毫秒
61.
The new electrolytic dissolution in batch of aluminum alloys samples as grains or turns and the determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP OES was investigated. In on-line electrodissolution procedures described in the literature, samples were restricted to be in the form of solid blocks or plates with one polished flat face. Here, the sample was loaded in the barrel of a modified disposable syringe (the anodic semi-cell) and pressed with a modified plunger fitted with a platinum disk to establish electrical contact with the analyte. This arrangement was introduced in a beaker containing the electrolyte (1 mol L−1 HNO3) and a platinum wire as the cathode. The resulting solution from electrodissolution (0.6 A) was used for the ICP OES determinations. The influence of the aluminum concentration increase on the determination of the elements was evaluated. Electrodissolution of certified reference materials and commercial samples revealed relative errors lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti (when their content is above 0.1%). Higher inaccuracies (>10%) were observed for Mn and for Fe in B.C.S. 268/1 reference material certified. The proposed method presented a relative standard deviations (R.S.D.) lower or circa 10% to all of the elements (except Pb). In comparison with traditional acid dissolution, the proposed electrodissolution method is relatively fast (about 30 min), it is clean (there is no projection of solution) and simple (heating and fumes exhaust system were not necessaries). 相似文献
62.
A simple, sensitive and selective Spectrophotometric method has been developed for the determination of cobalt using indane 1,2,3-trionetrioxime (ITT): The method is based on the colour reaction between ITT and cobalt(II) in sodium acetate-acetic acid buffer (pH 4.5–7.5) medium. The calibration graph for measurement at 320 nm is linear in the range 1.18–23.60g of cobalt per 25 ml, with molar absorptivity of 5.32×1041mol–1 cm–1. The effect of interfering ions has been studied and the method was applied to the determination of cobalt in alloys, with good results. 相似文献
63.
Inductively coupled plasma optical emission spectrometry (ICP-OES) was applied to the analysis of major and minor elements of Ni-Nb alloys obtained by aluminothermic reduction process. Digestion of samples was made using a mixture of HF+HNO3. Minor and trace elements were determined without matrix separation. The precision for all constituents was <3%. Recoveries for the analyte-spiked samples were 95%. 相似文献
64.
本文用差热分析法系统地研究了La掺杂对Al-Si共晶合金、亚共晶、超共晶的动态凝固过程的影响。结果表明,La促使α(Al)成核,使体系中初晶α(Al)的析出温度比AJ-Si二元合金中Al初晶的实际析出温度明显提高;La对初晶Si的成核和长大起抑制作用,使超共晶中初晶Si相析出温度较二元合金中的Si初晶的实际析出温度明显降低。 相似文献
65.
采用多步电沉积法制备的三维多孔铜箔作为集流体、低温液相化学还原法制备的纳米Sn/SnSb 合金作为负极材料, 制备出一种新型三维多孔结构的纳米Sn/SnSb合金复合负极. 通过与普通负极电化学性能的对比实验发现, 这种新型三维复合负极具有如下优点: 三维多孔网络结构提高了负极活性材料与集流体之间的结合力, 使不含粘结剂电极的制备成为可能; 有效缓解了高容量负极活性材料在充放电过程中的体积膨胀, 提高了负极活性材料的循环性能, 当循环到第30周时, 普通负极剩余容量为初始容量的33%, 而三维复合负极剩余容量为初始容量的41%; 三维铜箔集流体的特殊结构为高容量负极活性材料提供了一个良好的导电环境, 使电极反应进行得更加完全, 从而获得了更高的电极比容量, 普通负极初始容量为480 mAh·g-1, 而三维复合负极达到了800 mAh·g-1. 纳米Sn/SnSb合金三维复合负极良好的电化学性能为锂离子电池负极结构的设计开发提供了新的思路. 相似文献
66.
F. H. B. Lima M. L. Calegaro E. A. Ticianelli 《Russian Journal of Electrochemistry》2006,42(12):1283-1290
This work reviews the studies conducted in this laboratory of the oxygen reduction reaction (ORR) on electrocatalysts formed
by Pt-M/C (M = V, Cr, Co) and Ag-Pt/C alloys and on different Mn oxides (MnO/C, Mn3O4/C, MnO2/C) in KOH electrolyte. The physical and electronic properties of the materials are investigated by in situ XAS (x-ray absorption
spectroscopy) in the XANES (x-ray absorption near edge structure) region. The electrocatalytic activity for the ORR on the
different catalysts is compared through mass-transport-corrected Tafel plots. The XANES results for the Pt-M/C and Ag-Pt/C
composites at high electrode potentials show lower vacancy of the Pt 5d band compared to pure Pt/C, while for the results indicate a chance of the Mn oxidation state as a function of the electrode
potential. The electrochemical measurements evidence increased electrocatalytic activity of the Pt alloys compared to pure
Pt and this is attributed to a lowering of the adsorption strength of adsorbed oxygen species caused by the reduced Pt reactivity.
An activity enhancement of the Ag atoms on the Ag-Pt/C alloys compared to pure Ag is ascribed to an electronic effect induced
by the presence of Pt, increasing the Ag-O adsorption strength. In the case of the MnyOx/C materials, the electrochemical results show low activity for MnO/C and higher activity for MnO2/C and Mn3O4/C. This is explained based on the activation for the ORR, which is higher for the material with higher MnO2 contents and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron
transfer of Mn(III) to oxygen.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1417–1426.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
67.
Single crystals of the first anhydrous thallium nickel phosphates were prepared by reaction of heterogeneous Tl/Ni/P alloys with oxygen. TlNi4(PO4)3 (pale‐yellow, orthorhombic, space group Cmc21, a = 6.441(2)Å, b = 16.410(4)Å, c = 9.624(2)Å, Z = 4) crystallizes with a structure closely related to that of NaNi4(PO4)3. Tl4Ni7(PO4)6 (yellow‐brown, monoclinic, space group Cm, a = 10.711(1)Å, b = 14.275(2)Å, c = 6.688(2)Å, β = 103.50(2)°, Z = 8) is isotypic with Na4Ni7(PO4)6, and Tl2Ni4(P2O7)(PO4)2 (brown, monoclinic, space group C2/c, a = 10.389(2)Å, b = 13.888(16)Å, c = 18.198(3)Å, β = 103.1(2)°, Z = 8) adopts the K2Ni4(P2O7)(PO4)2 structure. Tl2Ni4(P2O7)(PO4)2 could also be prepared in nearly single phase form by reaction of Tl2CO3, NiO, and (NH4)2HPO4. 相似文献
68.
A novel molecular entity vacancy model was proposed to describe thermodynamic properties in a multicomponent solution system using its binary interaction parameters only. A derivation of the model for its general expression has been shown in detail. Under some special conditions, this model may be reduced to Flory–Huggins equation, Wilson equation and non-random two liquids (NRTL) equation as well as molecular interaction volume model (MIVM), respectively, and can be verified by Gibbs–Duhem equation, and can express thermodynamic properties of partially miscible systems. The predicted activities are in good agreement with experimental data of some liquid alloys. The results show that the model is of better predictability and reliability because it has a certain physical basis. 相似文献
69.
Kanibolotsky D. S. Golovataya N. V. Lisnyak V. V. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):323-327
The enthalpies of mixing of liquid Gd-Si (1770±5 K) and Al-Gd (1760±5 K) alloys have been measured by high-temperature isoperibolic
calorimetry. The calorimetric study of the gadolinium-based liquid alloys demonstrates the great negative enthalpies of mixing,
which is associated with the contribution of GdSi and GdAl2 intermetallides into the liquid-state thermodynamics. The comparison of obtained results with literature data has been performed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
70.
Dr. George Serghiou Dr. Nicholas Odling Dr. Hans Josef Reichmann Dr. Gang Ji Prof. Dr. Monika Koch-Müller Prof. Dr. Daniel J. Frost Dr. Jonathan P. Wright Dr. Reinhard Boehler Dr. Wolfgang Morgenroth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(57):14217-14224
Multi-anvil and laser-heated diamond anvil methods have been used to subject Ge and Si mixtures to pressures and temperatures of between 12 and 17 GPa and 1500–1800 K, respectively. Synchrotron angle dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy, reveal recovery at ambient pressure of hexagonal Ge−Si solid solutions (P63/mmc). Taken together, the multi-anvil and diamond anvil results reveal that hexagonal solid solutions can be prepared for all Ge−Si compositions. This hexagonal class of solid solutions constitutes a significant expansion of the bulk Ge−Si solid solution family, and is of interest for optoelectronic applications. 相似文献