全文获取类型
收费全文 | 195篇 |
免费 | 0篇 |
专业分类
化学 | 131篇 |
力学 | 1篇 |
数学 | 52篇 |
物理学 | 11篇 |
出版年
2022年 | 2篇 |
2020年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 5篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 11篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1956年 | 2篇 |
1935年 | 1篇 |
1929年 | 2篇 |
1923年 | 2篇 |
1884年 | 1篇 |
排序方式: 共有195条查询结果,搜索用时 15 毫秒
61.
Cs2(H3O)Pr(CH3COO)6 and Cs2Pr(CH3COO)5: Synthesis, Crystal Structures and Thermolysis. Analogous Acetates with Lanthanum through Terbium Single crystals of Cs2(H3O)Pr(CH3COO)6 are obtained as green plates from an acetic acid solution (≈50%) of Cs2CO3 and Pr(CH3COO)3 · 1,5 H2O. The crystal structure monoclinic, Cm, Z = 2, a = 1 540.4(4), b = 691.3(2), c = 1 221.5(4) pm, β = 104.60(5)°, Vm = 379.1(2) cm3/mol, R = 0.040, Rw = 0.035 was determined from four-circle-diffractometer data. The structure consists of monomeric Pr(CH3COO)3 units, in which Pr3+ is surrounded by nine oxygen atoms. These monomers are linked together to infinite layers parallel (001) by common acetate oxygen atoms with two ?molecules”? of Cs(CH3COO). Together with an additional acetate ion coordinated to one of the Cs+ ions the composition of the layers is [Cs2Pr(CH3COO)6]?. Between these layers H3O+ is located for electroneutrality. Thermal decomposition of Cs2(H3O)Pr(CH3COO)6 was examined with thermoanalytical methods (TG/DTA with coupled gas analysis), Guinier-Simon technique and IR spectroscopy: beginning at 70°C the compound looses water and acetic acid. It decomposes topotactically to Cs2Pr(CH3COO)5. At 270°C this acetate decomposes to Cs2CO3 and Pr2O2CO3 which emits CO2 at 600°C form ing Pr2O3or PrO2?x Single crystals of Cs2Pr(CH3COO)5 were obtained from Pr(CH3COO)3, in molten Cs(CH3COO) at about 200°C. The crystal structure tetragonal, P43, Z = 4, a = 1 174,5(2), c = 1 480,5(3) pm, Vm = pin,307,5(1) cm3/mol, R = 0,061, Rw= 0,031 again consists of Pr(CH3COO)3, monomers where Pr3+ has 9 oxygen ligands in its first coordination sphere. They are linked together by two ”molecules“ of cesium acetate to infinite chains along [00l] around the 4, screw axis. There are also acetate bridges between these chains. Isotypic compounds Cs2(H3O)M(CH3COO)6 and Cs2M(CH3COO)5, and Cs2M(CH3COO)5with M = La? Tb, were obtained from acetic acid solutions or thermal decomposition and were characterized by X-ray Guinier techniques. 相似文献
62.
63.
Zbigniew Grobelny Andrzej Stolarzewicz Adalbert Maercker Wolfgang Demuth 《Journal of organometallic chemistry》1999,590(2):321-157
A new mechanism of the reaction of K−, K+(15-crown-5)2 with phenyl glycidyl ether is presented. The linear ether bond is attacked only to a small extent, if at all. As the main reaction path the oxirane bond in the β-position is cleaved, followed by the γ-elimination of potassium phenoxide and the formation of potassium cyclopropoxide. Crown ether ring opening also occurs in reactions with organometallic intermediates. 相似文献
64.
Robert C. Kerber 《Foundations of Chemistry》2002,4(1):61-72
In 1870–75 Markovnikov enunciatedan empirical Rule which generalized theregiochemical outcome of addition reactions tounsymmetrical alkenes. This Rule remaineduseful for about 75 years, until suchreactions came to be better understood inmechanistic terms. Thereafter the Rule couldbe deduced from principles of relativecarbocation stabilization and ceased to servean independent purpose. Nevertheless, mostorganic textbooks continue to cite it (oftenin a historically inaccurate, anachronisticway), thereby distracting student attentionfrom the underlying principles. This paperadvocates doing away with the Rule in organicchemistry textbooks and classrooms. 相似文献
65.
66.
Ohne Zusammenfassung 相似文献
67.
68.
69.
Adalbert Kerber 《Discrete Mathematics》1975,13(1):13-30
The salient point arising out of a consideration of some seemingly independent topics in representation theory, combinatorics and the theory of numerical polynomials turns out to be a result involving characters of representations of wreath products. The topics are: symmetrized inner products of representations, irreducible characters of wreath products, Frobenius' formula for the irreducible ordinary characters of symmetric groups, the Pólya-Redfield theory of enumeration under group action in combinatorics and results of Rudvalis and Snapper that certain polynomials arising from generalized cycleindices of permutation groups are numerical. 相似文献
70.
Adalbert Goertz 《Zeitschrift für Physik A Hadrons and Nuclei》1959,155(3):263-274
In order to determine the diffuse reflectivity and transmittivity of multiply scattered particles, there is not necessarily the need of solving the complete differentiointegral equation of multiple scattering. It can be shown that the problem reduces to solving a set of two simultaneous differential equations of the first order, provided that the amount of sideward scattering may be neglected. The solutions of these equations furnish all data required, if the mechanism of single scattering is known. 相似文献