全文获取类型
收费全文 | 10737篇 |
免费 | 1143篇 |
国内免费 | 939篇 |
专业分类
化学 | 6004篇 |
晶体学 | 137篇 |
力学 | 1004篇 |
综合类 | 7篇 |
数学 | 1102篇 |
物理学 | 4565篇 |
出版年
2024年 | 21篇 |
2023年 | 473篇 |
2022年 | 313篇 |
2021年 | 362篇 |
2020年 | 515篇 |
2019年 | 330篇 |
2018年 | 347篇 |
2017年 | 471篇 |
2016年 | 517篇 |
2015年 | 536篇 |
2014年 | 626篇 |
2013年 | 586篇 |
2012年 | 760篇 |
2011年 | 623篇 |
2010年 | 587篇 |
2009年 | 555篇 |
2008年 | 411篇 |
2007年 | 476篇 |
2006年 | 580篇 |
2005年 | 296篇 |
2004年 | 210篇 |
2003年 | 201篇 |
2002年 | 191篇 |
2001年 | 269篇 |
2000年 | 147篇 |
1999年 | 269篇 |
1998年 | 157篇 |
1997年 | 97篇 |
1996年 | 88篇 |
1995年 | 74篇 |
1994年 | 60篇 |
1993年 | 55篇 |
1992年 | 64篇 |
1991年 | 95篇 |
1990年 | 81篇 |
1989年 | 60篇 |
1988年 | 286篇 |
1987年 | 462篇 |
1986年 | 467篇 |
1985年 | 66篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 8篇 |
1979年 | 2篇 |
1965年 | 2篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
本文通过XRD、SEM、EDS研究了Ti0.4Zr0.1V1.1Mn0.5Cr0.1Nix(x=0,0.2,0.4,0.6,0.8)合金的相结构和电化学性能。该合金系由BCC结构的V基固溶体主相和六方结构的C14 Laves第二相组成,Ni能够促进第二相的生成,Ni含量的增加导致了各相中的化学组成和晶格参数的变化,并通过电化学方法研究了Ni含量对0.4Zr0.1V1.1Mn0.5Cr0.1合金电极的最大放电容量、自放电性能、高倍率放电性能、循环稳定性能等的影响。 相似文献
142.
《Journal of photochemistry and photobiology. A, Chemistry》2006,177(2-3):276-285
Photophysical and photochemical properties for N,α-diphenylnitrone 1a, α-p-methoxyphenyl-N-phenylnitrone 1b, N-(t-butyl)-α-phenylnitrone 1c, cis-α-cyano-N,α-diphenylnitrone 1d, trans-α-cyano-N,α-diphenylnitrone 1e, α-methoxycarbonyl-N,α-diphenylnitrone 1f and α-ethoxycarbonyl-N,α-diphenylnitrone 1g were investigated. Photolysis studies in polar and protic solvent such as ethanol revealed that the singlet-state formation was preferred in nitrones and this was confirmed by the fluorescence investigations. Absorption and fluorescence spectra indicated considerable shifts with variation in polarity of the solvent. 相似文献
143.
Ashok K. Ganguli Shalabh Gupta Jing-Tae Zhao E. Alejandro Leon-Escamilla 《Journal of solid state chemistry》2005,178(10):2959-2972
A particular pathology of certain W5Si3-type A5B3 structures (I4/mcm) appears to arise because of unduly close approaches of the A1-type atoms on the cell faces at , 0, () that occur with the larger and more electropositive A and/or in the presence of smaller B atoms. A structure refinement of binary Ba4.81Pb3 indicates such a marginal stability in that the Ba atoms in the facial Ba0.81 chains exhibit an extreme displacement ellipsoid along . Although Ca5Sn3 and La5Ga3 binaries are unknown in this structure type, five stable ternary derivatives of these have been synthesized via substitution reactions and characterized by single crystal X-ray diffraction means: Ca4Sn3.223(4)Mg0.777, Ca4Sn3Cu1.30(4), Ca4.66(6)Sn3Zn0.704(4), La4.81(1)Ga1.38(2)Al1.62, and La4.762(5)Ga1.5(1)Zn1.5. Only the Ca-Sn-Zn phase exhibits lower symmetry, P4/mbm. The problematic A1 sites exhibit diverse changes in these, whereas the surrounding B2 tetrahedra are largely unaltered. The Ca-Sn results are, respectively: direct Mg/Sn substitution at the Ca1 site; mixed fractional distribution of the smaller Cu at two sites around the A1 position with an unresolved disorder; a pair of apparently independent modes, fractional Ca in the normal position and fractional Zn rectangles thereabout. The two La-Sn phases contain normal Ga,Al (Ga,Zn) tetrahedral chains with pairs of fractional disordered La atoms along , 0, z. Each can be rationalized in terms of a reasonable incommensurate structure. Electronic effects may also be operable. 相似文献
144.
研究了水-乙腈混合溶液中SO4●-自由基氧化酪氨酸的反应.实验结果表明,SO4●-自由基氧化酪氨酸的反应机制不因乙腈的加入而改变,但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加,SO4●-的衰变速率减慢而酪氨酸中性自由基(TyrO●)的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加,SO4●-氧化酪氨酸的反应速率减慢.这一实验结果意味着,在有机溶剂存在的情况下TyrO●/ TyrOH的氧化还原电势可能发生了变化,从而旁证了关于TyrO●/ TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测. 相似文献
145.
Sn基合金负极材料具有高达990 mAh·g-1的理论比容量,但其也存在因脱嵌锂过程发生巨大的体积变化而导致循环性能较差的问题. 本文以Sn、Fe、石墨为原料利用简易的高能球磨法成功制备了具有核壳结构的FeSn2-C复合物,系统研究了球磨时间、FeSn2相含量对材料物相结构及电化学性能的影响,并分析了电极的失效机理. 研究表明,球磨时间的增加有利于FeSn2金属间化合物相的形成及材料颗粒的细化,进而有利于材料比容量的增加及循环性能的提升;FeSn2相含量的增加能够提高FeSn2-C材料的比容量,但会降低FeSn2-C电极的循环稳定性. 经工艺优化及组分调节,球磨24 h合成的Sn20Fe10C70材料具有最优的电化学性能,材料的比容量在540 mAh·g-1左右,并能稳定循环100次,是一种非常有发展前途的锂离子电池高比容量负极材料. 相似文献
146.
Hongyang Su Lanlan Chen Yizhen Chen Prof. Rui Si Yuting Wu Xiaonan Wu Dr. Zhigang Geng Prof. Wenhua Zhang Prof. Jie Zeng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20591-20596
Efforts have been devoted to achieving a highly efficient artificial synthesis of ammonia (NH3). Reported herein is a novel Fe-MoS2 catalyst with Fe atomically dispersed onto MoS2 nanosheets, imitating natural nitrogenase, to boost N2 electroreduction into NH3 at room temperature. The Fe-MoS2 nanosheets exhibited a faradic efficiency of 18.8 % with a yield rate of 8.63 μg mgcat.−1 h−1 for NH3 at −0.3 V versus the reversible hydrogen electrode. The mechanism study revealed that the electroreduction of N2 was promoted and the competing hydrogen evolution reaction was suppressed by decorating the edge sites of S in MoS2 with the atomically dispersed Fe, resulting in high catalytic performance for the electroreduction of N2 into NH3. This work provides new ideas for the design of catalysts for N2 electroreduction and strengthens the understanding about N2 activation over Mo-based catalysts. 相似文献
147.
S.H. LiuX.F. Qian J. YinL. Hong X.L. WangZ.K. Zhu 《Journal of solid state chemistry》2002,168(1):259-262
Ag2S nanoparticles in hyperbranched polyurethane matrix were prepared through the in situ reaction with thioacetamide as the sulfur source at room temperature. Transmission electron microscopic analysis revealed a uniform spherical shape for Ag2S nanoparticles, with an average size of about 4-10 nm and a narrow size distribution. X-ray powder diffraction and UV-vis spectroscopy were also used to characterize the obtained nanoparticles 相似文献
148.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2006,61(6):634-641
Matrix assisted laser desorption/ionization (MALDI) is studied at atmospheric pressure using liquid sampling methods. A time-of-flight mass spectrometer couples to an open sample stage accessed by a UV laser for desorption and ionization. Also coupled to the sampling state is a corona discharge for auxiliary ionization of desorbed neutral molecules. The interaction of the laser desorption and corona ionization is studied for a range of desorption conditions, showing enhanced analyte ionization, but the effect is analytically advantageous only at low desorption rates. The effect of corona discharge voltage was also explored. The decoupling of neutral molecule formation and subsequent ionization provides an opportunity to study each process separately. 相似文献
149.
150.
In the research on metallic glass, there are arguments against the "rigid band charge transfer", model which assumes a charge transfer from metalloid atoms to transition metal atoms to explain the experimental evidence of linear reduction of average atomic magnetic moment with the increasing concentration of metalloid atoms, but they could not explain the experimental relation of the reduction. In the present work, spin-polarized SCC-DV-X_a calculation for atomic clusters for metallic glass Co-B has been empoloyed to investigate the local electronic structure and magnetic property of the metallic glass. As opposed to the "rigid band charge transfer" model, calculation in the present work indicates that charge transfers from Co4s to both B and Co3d. It is found that there is Co3d4s-B2p hybird bonding in Co-B, which leads to the linear reduction of average atomic magnetic moment. Thus the explanation removes the above controversy. 相似文献