全文获取类型
收费全文 | 356061篇 |
免费 | 2391篇 |
国内免费 | 640篇 |
专业分类
化学 | 170373篇 |
晶体学 | 5410篇 |
力学 | 18521篇 |
综合类 | 9篇 |
数学 | 52541篇 |
物理学 | 112238篇 |
出版年
2019年 | 2291篇 |
2018年 | 11090篇 |
2017年 | 11870篇 |
2016年 | 8211篇 |
2015年 | 3410篇 |
2014年 | 4389篇 |
2013年 | 10777篇 |
2012年 | 12033篇 |
2011年 | 21168篇 |
2010年 | 13568篇 |
2009年 | 13463篇 |
2008年 | 18860篇 |
2007年 | 22218篇 |
2006年 | 9055篇 |
2005年 | 13927篇 |
2004年 | 10448篇 |
2003年 | 9878篇 |
2002年 | 7943篇 |
2001年 | 7474篇 |
2000年 | 5963篇 |
1999年 | 4396篇 |
1998年 | 3897篇 |
1997年 | 3861篇 |
1996年 | 3756篇 |
1995年 | 3434篇 |
1994年 | 3580篇 |
1993年 | 3266篇 |
1992年 | 3731篇 |
1991年 | 3735篇 |
1990年 | 3672篇 |
1989年 | 3540篇 |
1988年 | 3655篇 |
1987年 | 3543篇 |
1986年 | 3359篇 |
1985年 | 4444篇 |
1984年 | 4730篇 |
1983年 | 3959篇 |
1982年 | 4091篇 |
1981年 | 4017篇 |
1980年 | 3990篇 |
1979年 | 3975篇 |
1978年 | 4293篇 |
1977年 | 4140篇 |
1976年 | 4229篇 |
1975年 | 3897篇 |
1974年 | 3938篇 |
1973年 | 4127篇 |
1972年 | 2883篇 |
1971年 | 2399篇 |
1970年 | 2205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
P. K. Sazonov G. A. Artamkina I. P. Beletskaya 《Russian Journal of Organic Chemistry》2006,42(3):438-447
The nucleophilic aromatic and vinyl substitution using diaza-18-crown-6 as nucleophile afforded a number of its N,N’-diaryl-[aryl = 2,4-(NO2)2C6H3, 4-C5F4N, 4-CF3C6F4] and N,N’-dialkenyl-substituted derivatives [alkenyl = PhC(O)CH=CH, MeOCOCH=CH, (EtO2C)2C=C(Ph), etc.]. Arylation of diaza-18-crown-6 with nonactivated aryl bromides, such as 4-Me2NC6H4Br, 4-MeOC6H4Br, C6H5Br, and 4-CF3C6H4Br, was effected under catalysis by palladium complexes. N,N’-Diaryldiaza-18-crowns-6 having electron-acceptor substituents in the aromatic rings turned out to be incapable of forming complexes with metal cations, while their analogs containing electron-donor para-methoxy and para-dimethylamino groups gave complexes with barium perchlorate. 相似文献
982.
Within the framework of fractal analysis and percolation theory, an alternative model of reinforcement of filled polymers
is offered. Practically, this model can be used only to describe the reinforcement of nanocomposites, because, according to
the treatment considered, a pronounced reinforcement can be reached only at ratios of filler particle diameter to the statistical
segment length of about 10 and less. A theoretical calculation showed a good qualitative and quantitative agreement with experiments.
The type of reinforcement mechanism of composites is determined by the type of the space (fractal or Euclidean) in which the
structure of the polymeric matrix is formed.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 797–802, November–Decem ber, 2006. 相似文献
983.
A one-dimensional nanodusty plasma was modeled by self-consistently coupling a plasma model with nanoparticle growth, charging,
and transport models. As nanoparticles grow from subnanometer to tens of nm in diameter, the numerical results predict a rich
spatiotemporal structure, including four distinct temporal phases: a charge-limited phase, a charge accumulation phase, an
early ion drag phase, and a sheath interaction phase. 相似文献
984.
A theory that predicts the effect of the counterion size on the swelling and collapse of a weakly charged polyelectrolyte gel was developed. In addition to excluded-volume interactions between monomer units of the gel, the theory involves the counterion-monomer unit and counterion-counterion interactions in terms of the virial approximation. The character of interactions between different units in the system varies from repulsion to attraction depending on the type of solvent, counterion, and dielectric permittivity of the solvent. For solvents with a low permittivity, the effect of condensation of counterions resulting in the formation of ion pairs is taken into account. 相似文献
985.
B. D. Kabulov K. A. Akhundzhanov F. U. Yunusov O. A. Shpigun S. S. Negmatov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):354-356
The hydrolytic polycondensation of tetraethoxysilane in the presence of various polymers (polyacrylonitrile, polycaproamide, and chitosan) as templates was performed with the use of the sol-gel technology to obtain nanohybrid composite polymer-silica sorbents-nanofractals. 相似文献
986.
987.
V. G. Baklykov V. N. Charushin O. N. Chupakhin V. N. Drozd 《Chemistry of Heterocyclic Compounds》1987,23(4):465-469
Thiobenzhydrazides undergo cyclization with N-alkyl-quinoxalinium salts to give 5-alkyl-substituted 1,4,4a,5,10,10a-hexahydro-1,3,4-thiadiazino[5,6-b]quinoxalines, which undergo isomerization to 10-alkyl-substituted thiadiazinoquinoxalines when they are heated in ethanol or in the presence of acids.See [1] for Communication 20.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 557–561, April, 1987. 相似文献
988.
989.
990.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities. 相似文献