全文获取类型
收费全文 | 2654篇 |
免费 | 73篇 |
国内免费 | 491篇 |
专业分类
化学 | 2751篇 |
晶体学 | 19篇 |
力学 | 18篇 |
综合类 | 12篇 |
数学 | 3篇 |
物理学 | 415篇 |
出版年
2024年 | 7篇 |
2023年 | 84篇 |
2022年 | 31篇 |
2021年 | 67篇 |
2020年 | 56篇 |
2019年 | 72篇 |
2018年 | 55篇 |
2017年 | 81篇 |
2016年 | 86篇 |
2015年 | 71篇 |
2014年 | 97篇 |
2013年 | 193篇 |
2012年 | 122篇 |
2011年 | 180篇 |
2010年 | 113篇 |
2009年 | 136篇 |
2008年 | 142篇 |
2007年 | 159篇 |
2006年 | 171篇 |
2005年 | 130篇 |
2004年 | 166篇 |
2003年 | 148篇 |
2002年 | 107篇 |
2001年 | 100篇 |
2000年 | 76篇 |
1999年 | 76篇 |
1998年 | 98篇 |
1997年 | 69篇 |
1996年 | 54篇 |
1995年 | 52篇 |
1994年 | 41篇 |
1993年 | 59篇 |
1992年 | 29篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有3218条查询结果,搜索用时 15 毫秒
101.
Kwang-il ChungJung-Do Lee Eui-Jung KimWoo-Seong Kim Jung-Hwan ChoYong-Kook Choi 《Microchemical Journal》2003,75(2):71-77
Although a lithium metal anode has a high energy density compared with a carbon insertion anode, the poor rechargeability prevents the practical use of anode materials. A lithium electrode coated with Li2CO3 was prepared as a negative electrode to enhance cycleability through the control of the solid electrolyte interface (SEI) layer formation in Li secondary batteries. The electrochemical characteristics of the SEI layer were examined using chronopotentiometry (CP) and impedance spectroscopy. The Li2CO3-SEI layer prevents electrolyte decomposition reaction and has low interface resistance. In addition, the lithium ion diffusion in the SEI layer of the uncoated and the Li2CO3-coated electrode was evaluated using chronoamperometry (CA). 相似文献
102.
A. S. Rozenberg E. I. Aleksandrova G. I. Dzhardimalieva A. N. Titkov A. D. Pomogailo 《Russian Chemical Bulletin》1993,42(10):1666-1672
The thermal decomposition of iron (III) acrylate, [Fe3O(CH2=CHCOO)6 · 3H2O]OH (FeAcr), a monomer with a complex cluster cation, has been studied at 200–370 °C. Thermal transformations of FeAcr occur
in two temperature regions. The rates of gas evolution in the low temperature region (200–300 °C) and the high temperature
region (300–370 °C) are described by first-order equations withk=4.2 · 1021exp[−59000/(RT)] s−1 andk=1.3 · 106exp[−30500/(RT)] s−1, respectively. A study of the qualitative and quantitative composition of the products of FeAcr thermolysis was carried out.
The thermal transformation of FeAcr is a complex process of dehydration, degradation, and polymerization in the solid phase
followed by decarboxylation of the metal-carboxyl groups of the polymer.
for part 33 see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1743–1750, October, 1993. 相似文献
103.
Usingn-hexadecyl acrylate, surface pressure-area (F-A) curves and equilibrium spreading pressuresF
e were measured at various temperatures (5.7°–46°C) by the Langmuir balance (F-A) and the Wilhelmy-plate method (F
e). At low temperatures (T<13 °C) condensed films and the liquid-condensed/solid condensed transition can be observed. At high temperatures (T>30 °C) liquid-expanded films occur. In the intermediate range the compression curves have two transition points. The transition pressureF
1 between liquid-expanded and condensed film has a marked temperature dependence. The transition enthalpiesH
1 decrease with increasing temperature and become zero at 29.2 °C. The second transition is related to a transition between the condensed films (F
2). The slight temperature dependence of this transition is accompanied by an increasing change of area as well as by increasing transition enthalpiesH
2.TheF
e-T curve has two distinct breaks, at the melting pointT
m and atT=30 °C. The break atT
m is due to the melting process and the break atT=30 °C is caused by a phase transition between a liquid-expanded film and a condensed film.The phase diagram was constructed from the transition pressures. It can be demonstrated that the highest pressures of the thermodynamic stable film occurs atT
m. At temperaturesT>T
m equilibrium spreading pressure and equilibrium collapse pressure are identical whereas atT
m supercompression of the monolayer occurs. The film in this state behaves like a supercooled liquid. Obviously, rupture and collapse of such a film lead to a thermodynamically metastable bulk phase. 相似文献
104.
Christelle Titier Jean-Pierre Pascault Mohamed Taha Boris Rozenberg 《Journal of polymer science. Part A, Polymer chemistry》1995,33(1):175-184
Epoxy-amine methacrylated prepolymers are prepared in a 1-step synthesis by the reaction of Bisphenol A diglycidyl ether, glycidyl methacrylate, and different diamines. The adaptation of these reactions to production processes with a reduced reaction time requires a kinetic control and the use of efficient catalysts. The comparative kinetic treatment of the epoxy-amine reaction in the frame of Horie's and Rozenberg's kinetic schemes have been made. Cases where an efficient acid catalyst is used are also examined. Structural studies of these reactions established the occurrence of a Michael amine/double bond addition, when some amines are used. © 1995 John Wiley & Sons, Inc. 相似文献
105.
阳离子无皂含氟丙烯酸酯的合成与表面性能 总被引:1,自引:0,他引:1
在合成甲基丙烯酸全氟辛酰氧基乙酯(FA)基础上,用半连续法制备了无皂阳离子含氟丙烯酸酯乳液。当乳液的粒径在100~200 nm、ζ电位大于40 mV时,乳液较稳定。阳离子亲水单体甲基丙烯酰氧乙基三甲基氯化铵(DMC)在含氟丙烯酸酯中质量分数为0.10~0.18、固含量小于20%时乳液的稳定性好,且随DMC含量的增加稳定性提高;含氟丙烯酸酯乳胶膜的附着力与耐磨性好,乳胶膜的透湿率随DMC的增加而增加。随热处理温度的提高,膜表面自由能下降;经160℃热处理后膜发生了交联,表面自由能为18 mN/m,与聚四氟乙烯(PTFE)的表面能相近,DMC含量对膜表面自由能影响不大。XPS分析也表明膜表面氟含量随热处理温度的提高而增加。 相似文献
106.
Sara Mattsson 《Tetrahedron letters》2007,48(14):2497-2499
When treated with amine bases such as triethylamine and various lithium salts in wet solvents, esters are efficiently hydrolyzed to the corresponding acids in good yields. Esters incorporating an α- or β-heteroatom with respect to the ester carbonyl group are hydrolyzed rapidly even at room temperature. To further demonstrate the usefulness of this method, one example is provided where hydrolysis of acetylated camphorsultam is mediated by LiBr. 相似文献
107.
Turbid emulsion systems of ethylacrylate/sodium dodecyl sulphate/water with monomer to surfactant (M/S) ratios 10 and 40 were transformed into stable transparent/translucent nanolatexes through emulsion polymerisation using potassium persulphate as an initiator. The latex particle size was observed to be similar to that obtained by true microemulsion polymerisation where M/S ratio is one. The kinetic plots exhibited two intervals upto M/S ratios 10. AIBN initiated systems showed separation of two phases for the M/S ratio ?10. M/S ratios were varied from 1 to 54 for the comparative study of polymerisation in emulsion and microemulsion media. Gel effect dominance was observed around 40-60% conversion for the microemulsion polymerisation of ethylacrylate. Only one chain per particle was observed for microemulsion system with M/S ratio 1 and three to four chains per particle were observed for the systems with M/S ratios 10 and 40. Unlike M/S=1 system, higher dependency of polymerisation rate on initiator concentration was observed for the systems with M/S=10 and 40. A possible mechanism for such a transformation has been proposed. 相似文献
108.
《Electroanalysis》2006,18(4):391-398
The first study of the voltammetric reduction of cyclooctatetraene (COT) in tetrahydrofuran (THF) in the presence of lithium ion is reported. A single wave is observed at ?2.23 V vs. Ag/0.1 M AgNO3. Density functional calculations have been carried out on a variety of COT/Li/THF species in order to clarify the nature and role of ion pairing in this system. The dominant species in solution are the COT/Li/(THF)2 anion radical and the COT/Li2/(THF)4 dianion. Computer simulations have been carried out to further understand the effects of ion pairing on the reduction. The simulations show that coalescence of two waves into one can occur in the presence of strong ion pairing even when the second reduction potential is negative of the first. 相似文献
109.
测定了24例甲亢治疗前后及30例健康对照的头发锌、硒、钒、锂及锗的含量,发现未治疗的甲亢头发锌、硒、钒、锂及锗含量较对照组低,Zn、Se、Li、Ge,P<0.001,V,P<0.01.甲亢经6~12周抗甲亢药物治疗后.头发中5种元素均较治疗前上升(P<0.001),且头发钒和锂含量治疗后已达到对照组水平,V,P>0.2,Li,P>0.1,而头发锌、晒及锗含量治疗后仍低于对照组(P<0 .001).结论:甲亢头发锌、硒、钒、锂及锗含量降低.经6~12周抗甲亢治疗可使头发钒及锂含量恢复正常水平,而其余3种元素则可能需要更长时间的抗甲亢治疗才能恢复至正常水平。 相似文献
110.
LiMnC2O4(Ac) precursor in which Li+ and Mn2+ were amalgamated in one molecule was prepared by solid-state reaction at room-temperature using manganese acetate, lithium hydroxide and oxalic acid as raw materials. By thermo-decomposition of LiMnC2O4(Ac) at various temperatures, a series of Li1+y[Mn2−xLix]16dO4 spinels were prepared with Li2MnO3 as impurities. The structure and phase transition of these spinels were investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. Results revealed that the Li-Mn-O spinels with high Li/Mn ratio were unstable at high temperature, and the phase transition was associated with the transfer of Li+ from octahedral 16c sites to 16d sites. With the sintering temperature increasing from 450 to 850 °C, the phase structure varied from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. A way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated. 相似文献