全文获取类型
收费全文 | 6068篇 |
免费 | 95篇 |
国内免费 | 30篇 |
专业分类
化学 | 3805篇 |
晶体学 | 20篇 |
力学 | 169篇 |
数学 | 1326篇 |
物理学 | 873篇 |
出版年
2022年 | 45篇 |
2020年 | 58篇 |
2016年 | 88篇 |
2015年 | 74篇 |
2014年 | 83篇 |
2013年 | 208篇 |
2012年 | 180篇 |
2011年 | 192篇 |
2010年 | 132篇 |
2009年 | 132篇 |
2008年 | 188篇 |
2007年 | 215篇 |
2006年 | 179篇 |
2005年 | 201篇 |
2004年 | 165篇 |
2003年 | 138篇 |
2002年 | 155篇 |
2001年 | 69篇 |
2000年 | 95篇 |
1999年 | 73篇 |
1998年 | 59篇 |
1997年 | 83篇 |
1996年 | 79篇 |
1995年 | 85篇 |
1994年 | 83篇 |
1993年 | 76篇 |
1992年 | 93篇 |
1991年 | 64篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 91篇 |
1987年 | 73篇 |
1986年 | 90篇 |
1985年 | 122篇 |
1984年 | 119篇 |
1983年 | 85篇 |
1982年 | 124篇 |
1981年 | 125篇 |
1980年 | 112篇 |
1979年 | 123篇 |
1978年 | 108篇 |
1977年 | 106篇 |
1976年 | 96篇 |
1975年 | 110篇 |
1974年 | 83篇 |
1973年 | 87篇 |
1972年 | 55篇 |
1971年 | 61篇 |
1970年 | 64篇 |
1966年 | 47篇 |
排序方式: 共有6193条查询结果,搜索用时 15 毫秒
31.
The LLW-parametersx andW of dilute rare earth impurities (RE=Pr, Nd, Tb, Dy, Ho, Er, Tm;c0.05), in the cubic matrices YPd3 and YAl2 could be determined unequivocally in the crystal field scheme of Lea, Leask and Wolf by inelastic neutron scattering. The crystal field parameters derived fromx andW are not consistent with the point charge model. The ratio of N(E
F)Jex for the (REY)Pd3 and (REY)Al2 extracted from the RE-linewidths correlates with the corresponding ratio extracted from their magnetic ordering temperatures.Supported by Sonderforschungsbereich 125, Deutsche Forschungsgemeinschaft 相似文献
32.
Walter Borho 《Inventiones Mathematicae》1977,40(2):143-169
Summary Let g be a complex Lie-algebra,G its adjoint algebraic group, and the space of primitive ideals in the enveloping algebra of . For solvable , J. Dixmier has defined a map from the dual space g* into, and R. Rentschler has proved the injectivity of the corresponding map g*/G defined on the space of orbits ofG in g*. The aim of the present paper is to define a similar map g*/G forg=sl(n,C). In a joint paper with J. C. Jantzen we shall prove that it is also injective. 相似文献
33.
Synthesis and Chirality of (5S,6R)-5,6-Epoxy-5,6-dihydro-β,β-carotene and (5R,6R)-5,6-Dihydro-β,β-carotene-5,6-diol, a Compound with Unexpected Solubility Characteristics Wittig-condensation of azafrinal ( 1e ) with the phosphorane derived from 7 leads to a (1:3)-mixture of (E)-9′- and (Z)-9′-β,β-carotene-diol 3 , from which pure and optically active 3 ((5R,6R)-5,6-dihydro-β,β-carotene-5,6-diol) has been isolated as bright violet leaflets, m.p. 168°. Due to the trans-configuration of the diol moiety and to severe steric hindrance, hydrogen bonding is reduced to such an extent, that 3 behaves much more as a hydrocarbon than as a diol. There is good evidence that the so-called ‘β-oxycarotin’ obtained by Kuhn & Brockmann [15] by chromic acid oxidation of β, β-carotene is the corresponding racemic cis-diol. 3 has been converted into (5S, 6R)-5,6-epoxy-5.6-dihydro-β,β-carotene ( 4 ), m.p. 156°. This transformation establishes for the first time the chirality of a caroteneepoxide (without other O-functions). Full spectral and chiroptical data including a complete assignement of 13C-chemical shifts for azafrin methyl ester and 3 are presented. 相似文献
34.
Rate constants for the removal of Cl atoms in the reaction Cl + O3 → ClO + O2 were measured by the flash photolysis resonance fluorescence technique over the temperature range 213–298 K. The rate constant is given by the Arrhenius expression (2.94 ± 0.49) × 10?11 exp[?(298 ± 39)/T] in units of cm3 molecule?1 s?1. Comparison with recent results from other laboratories are presented. 相似文献
35.
The thermal expansion of VN1?x was determined from measurements of the lattice parameters in the temperature range of 298–1000 K and in the composition range of VN0.707–VN0.996. Within the accuracy of the results the expansion of the lattice parameter with temperature is not dependent on the composition. The lattice parameter as a function of composition ([N]/[V]=0.707?0.996) and temperature (298–1000 K) is given by $$\begin{gathered} a([N]/[V],T) = 0.38872 + 0.02488([N]/[V]) - \hfill \\ - (1.083 \pm 0.021) \cdot 10^{ - 4} T^{1/2} + (6.2 \pm 0.1) \cdot 10^{ - 6} T. \hfill \\ \end{gathered} $$ . The coefficient of linear thermal expansion as a function of temperature (in the same range) is given by $$\alpha (T) = a([N]/[V],T)^{ - 1} [( - 5.04 \pm 0.01) \cdot 10^5 T^{ - 1/2} + (6.2 \pm 0.1) \cdot 10^{ - 6} ].$$ . The average linear thermal expansion coefficient is $$\alpha _{av} = 9.70 \pm 0.15 \cdot 10^{ - 6} K^{ - 1} (298 - 1 000K).$$ . The data are compared with those of several fcc transition metal nitrides collected and evaluated from the literature. 相似文献
36.
Walter Huber 《Mikrochimica acta》1969,57(5):897-904
Zusammenfassung Durch Hydrolyse in siedender, hochkonzentrierter Phosphorsäure läßt sich anscheinend aus allen Kohlensäurederivaten quantitativ Kohlendioxid abspalten. Dieses wird nach Reinigung und Trocknung gravimetrisch bestimmt. Folgende Verbindungen wurden analysiert: lineare und cyklische Harnstoffe, Thioharnstoffe, Urethane, Carbamate, Kohlensäureester, Phenylisocyanat, Melamin, Guanidin, Cyanursäure und Dicyandiamid. Die Anwendung verschiedener Phosphorsäurekonzentrationen erlaubt auch selektive Bestimmungen.
Herrn Prof. Dr.B. Timm zum 60. Geburtstag gewidmet. 相似文献
The determination of derivatives of carbonic acid via an acidic hydrolysis
Summary Hydrolysis in boiling highly concentrated phosphoric acid seemingly results in the quantitative splitting off of carbon dioxide from all derivatives of carbonic acid. The latter is determined gravimetrically after purification and drying. The following compounds were analyzed: linear and cyclic ureas, thioureas, urethanes, carbamates, esters of carbonic acid, phenylisocyanate, melamine, guanidine, cyanuric acid, dicyandiamide. The use of various concentrations of phosphoric acid permits selective determinations.
Herrn Prof. Dr.B. Timm zum 60. Geburtstag gewidmet. 相似文献
37.
A measuring system is described which permits study of all stages of combustion processes as functions of carrier gas, temperature, residence time and tube filling. The organic sample is fed at constant speed into a stream of carrier gas. The mixture reaches the combustion chamber within a few milliseconds via a transfer capillary. With the help of a viscous inlet system, a sample of the resulting reaction products is taken and fed into a mass spectrometer. Reaction time and temperature can be adjusted within wide ranges or varied continuously. A plot of the extent of reaction of the various combustion products against temperature at a chosen reaction time yields an oxidation-thermogram which gives a clear picture of the combustion process. It is evident from thermograms of selected compounds that the samples decompose in the presence of oxygen at appreciably lower temperatures than in inert gas. The primary step of the decomposition is “oxidative pyrolysis” which often leads to other products than “inert pyrolysis”. The intermediate products found are partly structurally specific and, especially with nitrogen-containing samples, are numerous and long-lived (for example, carbon monoxide, nitric oxide, cyanogen, hydrocyanic acid, cyanic acid and methyl cyanate). The notorious “difficult combustibility” is largely due to the fact that carbon monoxide, cyanic and hydrocyanic acids undergo complete combustion only at very high temperature. The combustion properties of the “empty tube” can be improved noticeably by a filling of quartz wool and markedly by partly filling with platinum wool. 相似文献
38.
39.
Günther Ohloff Wolfgang Giersch Walter Thommen Bruno Willhalm 《Helvetica chimica acta》1983,66(5):1343-1354
A series of compounds possessing a ‘Steroid-type’ scent and related to 4-(4′-t-butylcyclohexyl)-4-methyl-2-pentanones ( 1 and 2 ) has been synthesized. The odor of these compounds has been found to be dependent on their conformation; only when the molecule can assume a steroid-like shape there is an interaction with the odor chemoreceptor. 相似文献
40.