全文获取类型
收费全文 | 1065篇 |
免费 | 25篇 |
国内免费 | 4篇 |
专业分类
化学 | 702篇 |
晶体学 | 2篇 |
力学 | 30篇 |
数学 | 212篇 |
物理学 | 148篇 |
出版年
2023年 | 8篇 |
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 39篇 |
2015年 | 32篇 |
2014年 | 31篇 |
2013年 | 58篇 |
2012年 | 54篇 |
2011年 | 56篇 |
2010年 | 49篇 |
2009年 | 38篇 |
2008年 | 58篇 |
2007年 | 60篇 |
2006年 | 42篇 |
2005年 | 42篇 |
2004年 | 33篇 |
2003年 | 38篇 |
2002年 | 40篇 |
2001年 | 17篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1972年 | 6篇 |
1969年 | 4篇 |
排序方式: 共有1094条查询结果,搜索用时 0 毫秒
1.
In this article we study the well-posedness of the initial value problem for quasi-linear weakly hyperbolic equations of second order. We obtain a sufficient condition for the Cauchy problem to be locally solvable in the class of smooth function. 相似文献
2.
We introduce a family of matrices that define logics in which paraconsistency and/or paracompleteness occurs only at the level of literals, that is, formulas that are propositional letters or their iterated negations. We give a sound and complete axiomatization for the logic defined by the class of all these matrices, we give conditions for the maximality of these logics and we study in detail several relevant examples. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Domenico Spinelli Giovanni Consiglio Renato Noto 《Journal of heterocyclic chemistry》1977,14(8):1325-1329
The rates of piperidino substitution of some 2-L-3-nitrothiophenes (I) and 2-L-5-nitrothiophenes (II) (L = Cl, Br, I, OC6H4NO2-p, and SO2Ph) have been measured in methanol and in benzene at various piperidine concentrations. The reactivity of compounds (I) is not affected by the piperidine concentration in both methanol and benzene, except for the case of L = I (Ic). Probably due to association effects, the reactivity of Ic in benzene decreases as the piperidine concentration is increased. The reactions of compounds II follow overall second order kinetics in methanol while in benzene a different behaviour is observed as a function of the nature of the leaving group. In fact, the piperidino substitutions of IIa-c (L = Cl, Br, I) are mildly accelerated at high piperidine concentrations (a moderate solvent effect); on the contrary the reactivity of IId and e shows a strong dependence on the piperidine concentration, pointing out a genuine base catalysis. 相似文献
4.
5.
Kyle Siegrist 《Journal of Theoretical Probability》1994,7(4):725-737
Three fundamental characterizations of the standard exponential distribution on [0, ) are the remaining life, memoryless and constant failure properties. Analogs of these properties are studied for distributions on a class of semigroups in which the semigroup operation replaces addition, a compatible partial order replaces the ordinary order, and a left-invariant measure replaces Lebesgue measure. Partial characterizations of exponential distributions on such semigroups are obtained and the semigroup formulation provides new characterizations of certain aging properties studied in reliability-increasing failure rate, new better than used, and increasing failure rate average. 相似文献
6.
7.
Renato Spigler Marco Vianello 《Proceedings of the American Mathematical Society》1996,124(6):1763-1771
Rigorous asymptotic approximations of the WKB (or Liouville-Green) type are obtained for a basis of solutions to in the framework of -algebras. Both cases and are included, thus generalizing the classical theory for scalar equations developed by F.W.J. Olver to matrix as well as to infinite-dimensional equations.
8.
We have studied the reduction of SeIV in acidic medium (1 M HCl and 1 M HClO4) by classical and alternating current polarography and single sweep linear voltammetry with dropping mercury electrode and hanging mercury drop (HMDE). Two steps are observed distinctly: (1) The reduction of SeIV→Seo leads to a deposit of adsorbed elementary selenium. A mathematical expression is shown for the variation of current which is related to the surface covered at the HMDE. (2) The second step is the reduction of Seo→Se2? which takes place at more negative potentials. The accumulation of Seo may be used for the determination of traces in trace analysis by cathodic stripping. It appears that the behavior of selenium in these two mineral acids is similar. But sometimes it behaves in a different manner, especially in a.c. polarography (in this connection the influence of frequency and demodulation angle are important). 相似文献
9.
Pier G. Desideri Luciano Lepri Roberto Udisti Leonardo Checchini Massimo Del Bubba Renato Cini 《International journal of environmental analytical chemistry》2013,93(3-4):331-351
Abstract Organic compounds extractable with n-hexane were identified and quantitatively determined in pack, surface and deep snow samples taken at different depths and collected at several altitudes above sea level from Antarctica during the 1993/94 Italian expedition. The comparison between the composition of organic compounds in snow and the ones in pack and sea-water samples pointed out that the three matrices substantially contain the same biogenic and anthropogenic organic compounds. The contribution of marine aerosol to organic content in the snow is confirmed by the enrichment ratios calculated for the more representative classes of identified compounds (n-alkanes, phthalates and low molecular weight alkylbenzenes). The changes in the composition of organic compounds in snow as the altitude increases seem to depend on the dimensional spectrum of the aerosol. Thus, smallest particles, richest in surfactant material, reach the highest altitudes. 相似文献
10.
Renato Barbieri M. Teresa Musmeci 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):103-107
Abstract The title compounds, representative of classes of diorganotin (IV) derivatives active against murine leukemia P-388. interact with rat hemoglobin (selected as a model protein) by: i) co-crystallization. with formation of microcrystalline pellets, and: ii) diffusion into hemoglobin crystals from the supernatant solution (as determined for the 2-mercaptoethanesulfonato derivative). The nature of the Me2SnIV species in hemoglobin has been investigated by 119Sn Mössbauer spectroscopy, and a C2SnS2 tetrahedral geometry has been assigned by the point-charge model rationalization of the nuclear quadrupole splitting parameter. Binding into crystalline hemoglobin has been ascribed to Coulomb interactions and to hydrogen bonding between the sulfonate and the aminoacid tails of the organotin (IV) derivatives and functional groups of the globin. 相似文献