全文获取类型
收费全文 | 147334篇 |
免费 | 1466篇 |
国内免费 | 396篇 |
专业分类
化学 | 80437篇 |
晶体学 | 2388篇 |
力学 | 6065篇 |
综合类 | 3篇 |
数学 | 13670篇 |
物理学 | 46633篇 |
出版年
2021年 | 1034篇 |
2020年 | 1188篇 |
2019年 | 1255篇 |
2018年 | 1639篇 |
2017年 | 1694篇 |
2016年 | 2548篇 |
2015年 | 1565篇 |
2014年 | 2359篇 |
2013年 | 6048篇 |
2012年 | 4866篇 |
2011年 | 5964篇 |
2010年 | 4203篇 |
2009年 | 4223篇 |
2008年 | 5748篇 |
2007年 | 5528篇 |
2006年 | 5397篇 |
2005年 | 4954篇 |
2004年 | 4459篇 |
2003年 | 4124篇 |
2002年 | 4011篇 |
2001年 | 5558篇 |
2000年 | 3980篇 |
1999年 | 3083篇 |
1998年 | 2112篇 |
1997年 | 2218篇 |
1996年 | 2072篇 |
1995年 | 1923篇 |
1994年 | 1917篇 |
1993年 | 1733篇 |
1992年 | 2224篇 |
1991年 | 2302篇 |
1990年 | 2142篇 |
1989年 | 2103篇 |
1988年 | 2082篇 |
1987年 | 2088篇 |
1986年 | 1911篇 |
1985年 | 2374篇 |
1984年 | 2395篇 |
1983年 | 1914篇 |
1982年 | 1917篇 |
1981年 | 1759篇 |
1980年 | 1744篇 |
1979年 | 2039篇 |
1978年 | 2107篇 |
1977年 | 2051篇 |
1976年 | 1982篇 |
1975年 | 1868篇 |
1974年 | 1848篇 |
1973年 | 1878篇 |
1972年 | 1243篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
T. Radul 《Topology and its Applications》2007,154(8):1794-1798
R. Pol has shown that for every countable ordinal number α there exists a universal space for separable metrizable spaces X with trindX?α. W. Olszewski has shown that for every countable limit ordinal number λ there is no universal space for separable metrizable space with trIndX?λ. T. Radul and M. Zarichnyi have proved that for every countable limit ordinal number there is no universal space for separable metrizable spaces with dimWX?α where dimW is a transfinite extension of covering dimension introduced by P. Borst. We prove the same result for another transfinite extension dimC of the covering dimension.As an application, we show that there is no absorbing sets (in the sense of Bestvina and Mogilski) for the classes of spaces X with dimCX?α belonging to some absolute Borel class. 相似文献
982.
R. Cristescu G. Dorcioman E. Axente A. Moldovan T. Kocourek M. Albulescu D. Mihaiescu D.B. Chrisey 《Applied Surface Science》2006,252(13):4647-4651
We report the first successful deposition of triacetate-pullulan polysaccharide thin films by matrix assisted pulsed laser evaporation. We used a KrF* excimer laser source (λ = 248 nm, τ ≈ 20 ns) operated at a repetition rate of 10 Hz. We demonstrated by FTIR that our thin films are composed of triacetate-pullulan maintaining its chemical structure and functionality. The dependence on incident laser fluence of the induced surface morphology is analysed. 相似文献
983.
R. M. Vafina A. T. Gubaidullin O. N. Kataeva I. A. Litvinov Yu. G. Shtyrlin E. N. Klimovitskii 《Russian Journal of Organic Chemistry》2006,42(10):1563-1567
Conformationally heterogeneous 2-substituted 1,3-dithiacyclohept-5-enes (R = Ph, Me, t-Bu), which exist in solution as chair and boat conformers, react with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate with high exo-diastereoselectivity: only the chair conformer is involved. The steric structure of 4-methyl-3,5-dithia-9,10-diazabicyclo[5.4.0]undeca-7,10-diene was determined by X-ray analysis. Its crystal packing and supramolecular structure were also analyzed. 相似文献
984.
985.
T. V. Esipova A. A. Borisenko P. B. Terent’ev G. V. Grishina R. Herzshuh 《Russian Journal of Organic Chemistry》2006,42(5):742-747
A new class of endocyclic enamines, 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines, was synthesized from 4-piperidone imines by successive subjecting the latter to lithiation with lithium diethylamide, to alkylation with 1-bromo-3-chloropropane, and to intramolecular cyclization. All stages were carried out as a unique process without isolation of the intermediate compounds. A thorough optimization of the process conditions, workup, and product storage was carried out. The conformational study of 1,6-disubstituted 1,2,3,4,5,6,7,8-octahydro-1,6-naphthiridines was performed. 相似文献
986.
A new Co–Fe-based ferromagnetic bulk metallic glass (BMG) was synthesized by copper mould casting method. The thermal stability and crystallization processes were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The soft magnetic behavior was studied by DC magnetic measurements. The high glass formation ability was interpreted in terms of the effective suppression of nucleation and growth of the intermetallic compounds which appear in the multicomponent system during solidification. The high thermal stability indicates that the new Co–Fe-based BMG could be used as high-temperature magnetic material. The low coercivity which was as low as 8 A/m for the as-cast sample was found in the Co–Fe-based metallic glass cylinder with a diameter of 1.5 mm. 相似文献
987.
988.
T. Linss 《BIT Numerical Mathematics》2007,47(2):379-391
A non-monotone FEM discretization of a singularly perturbed one-dimensional reaction-diffusion problem whose solution exhibits
strong layers is considered. The method is shown to be maximum-norm stable although it is not inverse monotone. Both a priori
and a posteriori error bounds in the maximum norm are derived. The a priori result can be used to deduce uniform convergence
of various layer-adapted meshes proposed in the literature. Numerical experiments complement the theoretical results.
AMS subject classification (2000) 65L10, 65L50, 65L60 相似文献
989.
We study the equilibrium statistical mechanics of classical two-dimensional Coulomb systems living on a pseudosphere (an infinite surface of constant negative curvature). The Coulomb potential created by one point charge exists and goes to zero at infinity. The pressure can be expanded as a series in integer powers of the density (the virial expansion). The correlation functions have a thermodynamic limit, and remarkably that limit is the same one for the Coulomb interaction and some other interaction law. However, special care is needed for defining a thermodynamic limit of the free energy density. There are sum rules expressing the property of perfect screening. These generic properties can be checked on the Debye–Hückel approximation, and on two exactly solvable models, the one-component plasma and the two-component plasma, at some special temperature. 相似文献
990.
KL Britton HF Rogers Y Asano T Dairi Y Kato TJ Stillman DW Rice 《Acta crystallographica. Section D, Biological crystallography》1998,53(4):124-126
The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres. 相似文献