全文获取类型
收费全文 | 1347篇 |
免费 | 76篇 |
国内免费 | 119篇 |
专业分类
化学 | 1487篇 |
晶体学 | 3篇 |
力学 | 5篇 |
综合类 | 6篇 |
物理学 | 41篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 32篇 |
2020年 | 37篇 |
2019年 | 41篇 |
2018年 | 32篇 |
2017年 | 44篇 |
2016年 | 50篇 |
2015年 | 46篇 |
2014年 | 41篇 |
2013年 | 118篇 |
2012年 | 73篇 |
2011年 | 62篇 |
2010年 | 47篇 |
2009年 | 49篇 |
2008年 | 64篇 |
2007年 | 72篇 |
2006年 | 77篇 |
2005年 | 63篇 |
2004年 | 78篇 |
2003年 | 66篇 |
2002年 | 47篇 |
2001年 | 48篇 |
2000年 | 44篇 |
1999年 | 44篇 |
1998年 | 25篇 |
1997年 | 39篇 |
1996年 | 29篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 35篇 |
1992年 | 24篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1542条查询结果,搜索用时 12 毫秒
71.
以对甲苯胺为原料,经重氮化、KI分解得到对-碘甲苯.在NH4Cl存在下,对-碘甲苯在过硫酸铵的氧化下与异丁苯反应,得到(4-甲苯基)(4-异丁基苯基)碘鎓氯.在丙酮溶剂中,(4-甲苯基)(4-异丁基苯基)碘鎓氯与六氟磷酸钾进行离子交换,得到目的产物(4-甲苯基)(4-异丁基苯基)碘鎓六氟磷酸盐.总收率为46.7%.通过紫外光谱、红外光谱和核磁共振测定,对产物进行了结构确证. 相似文献
72.
Organometallic rhodium complexes are described which are highly efficient initiators for the ring-opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy-functional silanes in high yields without competing ring-opening polymerization. 相似文献
73.
Y. Yaci A. Kornowski W. Schnabel 《Journal of polymer science. Part A, Polymer chemistry》1992,30(9):1987-1991
The polymerization of n-butyl vinyl ether (BVE), cyclohexene oxide (CHO) and 3,4-epoxycyclohexyl(methyl)-3′,4′-epoxycyclohexane carboxylate (EEC) was initiated upon UV irradiation (λinc > 300 nm) of dichloromethane solutions containing N-ethoxy-2-methylpyridinium ( V ), N-ethoxy-4-phenyl-pyridinium ( VI ) or N-ethoxy-isoquinolinium hexafluorophosphate ( VII ). Whereas the bifunctional EEC was converted into an insoluble gel, BVE and CHO formed polymers of molar mass: Mw = 2 X 104?2 X 105 (PCHO) and Mw ≈ 2 X 104 (PBVE). Protons are formed with a rather high quantum yield [ø(H+) = 0.48 on irradiating VII in dichloromethane; titration with sodium p-nitrophenolate] and it is, therefore, assumed that the polymerization is initiated by photochemically generated protons. © 1992 John Wiley & Sons, Inc. 相似文献
74.
In this preliminary report we present the mesomorphic properties and electro-optic investigations of three new 'banana-shaped' mesogens. The materials are structurally similar to Niori's the original bent-core materials but possess alkylthio substituents in place of alkoxy substituents. Microscopic investigations revealed an unusual 'spiral-domain texture', similar to that observed in the 'B7' phase of related materials. Further investigations support our earlier observations that the materials display antiferroelectric switching in this phase, in two of the new materials studied. The nature of this phase, in comparison with the 'switchable' (B2) and 'chiral-domain' (B4) phases of the original materials, is discussed. 相似文献
75.
阴阳离子型表面活性剂双水相萃取色氨酸衍生物和牛血清白蛋白 总被引:7,自引:0,他引:7
溴化十二烷基三乙胺(C12NE)和十二烷基硫酸钠(SDS)在一定条件下混合可以形成具有清晰界面的两个水相,称为阴阳离子型表面活性剂双水相。作者研究了利用该双水相萃取3种色氨酸衍生物和牛血清白蛋白的可能性.文中采用工作曲线校正扣除表面活性剂背景的影响,萃取结果准确可信。 相似文献
76.
环糊精包结作用下水溶液共聚合制备疏水改性阳离子聚丙烯酰胺及其絮凝效果研究 总被引:1,自引:0,他引:1
在水溶液中制备了甲基环糊精(Me-β-CD)/疏水单体2-苯氧乙基丙烯酸酯(POEA)的包结物(1a)。利用紫外-可见光谱及核磁共振波谱等检测手段研究了Me-β-CD与POEA的包合作用,并对包合物的结构、性能进行了表征和分析。同时在水溶液中引发丙烯酰胺(AM)、阳离子单体丙烯酰氧乙基三甲基氯化铵(DAC)以及1a的均相共聚合得到疏水修饰的阳离子聚丙烯酰胺P(AM-DAC-POEA),实现了用绿色方法合成高效高分子絮凝剂的目的,并对该高分子对高岭土模拟污水的絮凝效果进行了考察。 相似文献
77.
V. B. Murachev A. I. Nesmelov E. A. Ezhova V. S. Byrikhin A. V. Orlinkov I. S. Akhrem 《Russian Chemical Bulletin》1998,47(1):50-54
The ionic complex of mesitoyl bromide with aluminum bromide in a 1∶1 composition (Mst-1) does not initiate the isobutylene
polymerization inn-hexane or methylene dichloride at −78 °C. The corresponding ionic complex of the 1∶2 composition (Mst-2) acts as a cationogenic
initiator of the polymerization. The addition of excess Lewis acid or introduction of organic electron acceptors increases
the initiating activity of the Mst-1 complex and activates acyl complexes of the 1∶2 composition including Mst-2. The results
are discussed in terms of the effect of specific solvation on the nucleophilicity of counteranions, which makes the addition
of the monomer to the carbocation possible.
For Part 9, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52–56, January, 1998. 相似文献
78.
D. Duracher F. Sauzedde A. Elaissari A. Perrin C. Pichot 《Colloid and polymer science》1998,276(3):219-231
Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization
of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride
as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly
homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering
(QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of
a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without
affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided
that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell
layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease
of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic
particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle
morphology information were inferred for discussion of the polymerization mechanism of this system.
Received: 21 August 1997 Accepted: 22 October 1997 相似文献
79.
Cationic polymer as a kind of flocculant is widely applied in purification treatment of waste water. Because it has positive charge group, it is able to connect strongly the suspended matters, short cellulose and other microparticles. The research on synthesis of cationic polymer and application in treatment of waste water is very universal abroad. But domestic research on those is not general. The technology of synthesis of PEM is simple, and the production cost is low. It is easy to apply in treatment of waste water.Synthesis of PEM Emulsion FlocculantSome distilled water, PVA(poly(vinyl alcohol)), EA(ethyl acrylate), and K2S2O8(potassium persulfate) were put into reaction vessel. Kept stirring up under nitrogen. When heated the solution to 40℃, dropped the water solution of MTA[(2-methacryloxylethyl)trimethyl ammonium].Maintained the temperature at 70℃, reacted about 7-8 hours. Then got the PEM emulsion. Changed the ratio of EA and MTA. Obtained a series of PEM emulsions.Stability and Convertibility of PEM EmulsionThe test results showed that when the EA/MTA was 85/15, the PEM emulsion was most stable.When the total monomer quantity was 35%, the convertibility of PEM emulsion was the highest,i.e.98.6%.The MTA Copolymerization Ratio and Morphology of PEM EmulsionWhen the monomers EA/MTA=85/15 and total monomer quantity was 35%, the MTA copolymerization ratio of PEM emulsion was 95.15%(the highest), and the PEM emulsion was some microspheres with 100-180nm of diameter.The Test Results of PEM Emulsion in Treatment of Waste Water The PEM emulsion flocculant was applied in treatment of waste water of paper mill, and measured the precipitation time(t) and transmittancy(T). The test results were showed in table 1. The optimum value of PEM which was able to make the waste water of paper mill into clear water was 0.008%. 相似文献
80.
V. B. Murachev A. L. Nesmelov V. S. Byrikhin E. A. Ezhova A. V. Orlinkov L. S. Akhrem M. E. Vol'pin 《Russian Chemical Bulletin》1996,45(5):1115-1119
Polymerization of isobutylene inn-hexane at -78 °C in the presence of the complex of benzoyl chloride with AIBr3 (1 : 2) was investigated. The results were compared to those obtained previously for the polymerization of this monomer induced by the complex of acetyl bromide with AlBr3. Both complexes initiate the polymerization only by acyl cations. The number average molecular weight (M
n
) of the polymer linearly increases as the degree of isobutylene conversion increases. The polymerization restarts after repeated addition of the monomer, andM
n
continues to increase linearly. The efficiency of the initiaton by the benzoyl chloride complex does not exceed 6.2 %; the reaction has the second order with respect to the initiator in the case of PhCOCI · A12Br6; and the chain-propagation rate constant is 13.9 L mol–1 s t. The use of PhCOCI Al2Br6 as the initator of the polymerization of isobutylene allows one to prepare macromolecules with very low contents of the terminal C=C double bonds and with narrow molecular weight distributions. Unlike the MeCOBr·AlBr3 complex, PhCOCl · AlBr3 does not initiate polymerization of isobutylene.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1175–1179, May, 1996. 相似文献