全文获取类型
收费全文 | 266篇 |
免费 | 14篇 |
国内免费 | 12篇 |
专业分类
化学 | 119篇 |
力学 | 13篇 |
综合类 | 3篇 |
数学 | 76篇 |
物理学 | 81篇 |
出版年
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 58篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 20篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 6篇 |
1971年 | 3篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1951年 | 1篇 |
1948年 | 8篇 |
1946年 | 2篇 |
排序方式: 共有292条查询结果,搜索用时 671 毫秒
131.
132.
133.
134.
Deon DE Wet‐Roos Aletta DU Toit Dawie J. Joubert 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6847-6856
Homogeneous tandem catalysis of the bis(diphenylphoshino)amine‐chromium oligomerization catalyst with the metallocenes Ph2C(Cp)(9‐Flu)ZrCl2 and rac‐EtIn2ZrCl2, is discussed. GC, CRYSTAF, and 13C NMR analysis of the products obtained from reactions at constant temperatures show that during tandem catalysis, α‐olefins, mainly 1‐hexene and 1‐octene, are produced from ethylene by the oligomerization catalyst and subsequently built into the polyethylene chain. At 40 °C the Cr/PNP catalyst acts as a tetramerization catalyst while the polymerization catalyst activity is low. Copolymerization of ethylene and the in situ produced α‐olefins have also been carried out by increasing the temperature from 40 °C, where primarily oligomerization takes place, to above 100 °C, where polymerization becomes dominant. The melting temperature of the polymer is dependent on the catalyst and cocatalyst ratios as well as on the temperature gradient followed during the reaction, while the presence of the oligomerization catalyst reduces the activity of the polymerization catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6847–6856, 2006 相似文献
135.
Using a simple 633-nm He/Ne or diode laser, the variation of the refractive indices of four ortho-substituted dihalogenated benzenes can be obtained, demonstrating the phenomenon of polarizability. In addition, this exercise is an excellent display of the correspondence between the properties of a chemical system on the macroscopic level and the characteristics of the molecule on a microscopic scale. 相似文献
136.
Optimality of embeddings of logarithmic Bessel potential spaces 总被引:2,自引:0,他引:2
137.
Five new chloranilato-bridged binuclear chromium (III) complexes have been synthesized and identified as [Cr2(CA)L4]-(ClO4)4[L denotes 5-methyl-1,10-phenanthroline (Me-phen); 2,9-dimethyl-1, 10-phenanthroline ( Me2-phen); 5-chloro-1,10-phenanthroline(Cl-phen); diaminoethane (en) or 1,3-diaminopropane (pn)], where CA represents the dianion of chloranilic acid. Based on elemental analyses, molar conductivity and magnetic moment of room-temperature measurements, and IR and electronic spectral studies, it is proposed that these complexes have CA-bridged structures and consist of two chromium (III) ions, each in an octahedral environment. The complexes [Cr2(CA)(Me-phen)4](ClO4)4(1) and [Cr2(CA)(Me2-phen)4](ClO4)4(2) were further characterized by variable temperature (4.2-300 K) magnetic susceptibility measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, , giving the exchange parameter J = -7.8 cm-1 for (1) and J= -6.5 cm*1 for (2). This result 相似文献
138.
139.
140.
稳态实验考察经模拟道路老化的全配方稀燃Nox捕集催化剂上的Nox还原 总被引:1,自引:0,他引:1
Fully formulated lean NOx trap(LNT)catalysts of the type Pt/Rh/BaO/Al2O3 were prepared with and without incorporation of CeO2-ZrO2 in the washcoat,and their NOx reduction behavior was evaluated in steady-state,continuous flow experiments.In the fresh state, the CeO2-ZrO2 addition was found to exert little effect on NOx reduction activity using H2,CO,and NH3 as the reductants.However,after simulated road aging,NOx reduction activity was significantly impaired for the CeO2-ZrO2-free catalyst,whereas the perfo... 相似文献