全文获取类型
收费全文 | 9630篇 |
免费 | 256篇 |
国内免费 | 57篇 |
专业分类
化学 | 5899篇 |
晶体学 | 39篇 |
力学 | 525篇 |
数学 | 1665篇 |
物理学 | 1815篇 |
出版年
2023年 | 81篇 |
2022年 | 211篇 |
2021年 | 227篇 |
2020年 | 194篇 |
2019年 | 179篇 |
2018年 | 157篇 |
2017年 | 158篇 |
2016年 | 343篇 |
2015年 | 276篇 |
2014年 | 280篇 |
2013年 | 533篇 |
2012年 | 523篇 |
2011年 | 573篇 |
2010年 | 379篇 |
2009年 | 317篇 |
2008年 | 544篇 |
2007年 | 531篇 |
2006年 | 464篇 |
2005年 | 455篇 |
2004年 | 404篇 |
2003年 | 352篇 |
2002年 | 299篇 |
2001年 | 143篇 |
2000年 | 127篇 |
1999年 | 124篇 |
1998年 | 90篇 |
1997年 | 96篇 |
1996年 | 126篇 |
1995年 | 108篇 |
1994年 | 105篇 |
1993年 | 91篇 |
1992年 | 82篇 |
1991年 | 72篇 |
1990年 | 65篇 |
1989年 | 63篇 |
1988年 | 73篇 |
1987年 | 74篇 |
1986年 | 54篇 |
1985年 | 100篇 |
1984年 | 88篇 |
1983年 | 59篇 |
1982年 | 65篇 |
1981年 | 61篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 41篇 |
1977年 | 51篇 |
1976年 | 39篇 |
1975年 | 39篇 |
1974年 | 39篇 |
排序方式: 共有9943条查询结果,搜索用时 15 毫秒
991.
Francesca Cal Chiara Roberta Girelli Federica Angil Laura Del Coco Lucia Mazzi Daniele Barbini Francesco Paolo Fanizzi 《Molecules (Basel, Switzerland)》2021,26(8)
Considering the growing number of extra virgin olive oil (EVOO) producers in the world, knowing the influence of olive oils with different geographical origins on the characteristics of the final blend becomes an interesting goal. The present work is focused on commercial organic EVOO blends obtained by mixing multiple oils from different geographical origins. These blends have been studied by 1H-NMR spectroscopy supported by multivariate statistical analysis. Specific characteristics of commercial organic EVOO blends originated by mixing oils from Italy, Tunisia, Portugal, Spain, and Greece were found to be associated with the increasing content of the Italian component. A linear progression of the metabolic profile defined characteristics for the analysed samples—up to a plateau level—was found in relation to the content of the main constituent of the Italian oil, the monocultivar Coratina. The Italian constituent percentage appears to be correlated with the fatty acids (oleic) and the polyphenols (tyrosol, hydroxytyrosol, and derivatives) content as major and minor components respectively. These results, which highlight important economic aspects, also show the utility of 1H-NMR associated with chemometric analysis as a powerful tool in this field. Mixing oils of different national origins, to obtain blends with specific characteristics, could be profitably controlled by this methodology. 相似文献
992.
993.
994.
Francesco Valentini Pierluigi Veltri Andr Mangeney 《Journal of computational physics》2005,210(2):730-751
We present a numerical algorithm for the solution of the Vlasov–Poisson system of equations, in the magnetized case. The numerical integration is performed using the well-known “splitting” method in the electrostatic approximation, coupled with a finite difference upwind scheme; finally the algorithm provides second order accuracy in space and time. The cylindrical geometry is used in the velocity space, in order to describe the rotation of the particles around the direction of the external uniform magnetic field.Using polar coordinates, the integration of the Vlasov equation is very simplified in the velocity space with respect to the cartesian geometry, because the rotation in the velocity cartesian space corresponds to a translation along the azimuthal angle in the cylindrical reference frame. The scheme is intrinsically symplectic and significatively simpler to implement, with respect to a cartesian one. The numerical integration is shown in detail and several conservation tests are presented, in order to control the numerical accuracy of the code and the time evolution of the entropy, strictly related to the filamentation problem for a kinetic model, is discussed. 相似文献
995.
Francesco Aldo Costabile Elisabetta Longo 《Mediterranean Journal of Mathematics》2016,13(6):4001-4017
For polynomial sequence of binomial type we propose a new recurrence formula equivalent to a determinantal form of the sequence, from which known and unknown properties are deducted. Relationships whit \({\delta}\)–functionals, \({\delta}\)–operators and generating function are pointed out. Finally, some classical examples are studied, highlighting interesting determinantal identities. 相似文献
996.
Sandro Faetti Leone Fronzoni Paolo Grigolini Vincenzo Palleschi Girolamo Tropiano 《Journal of statistical physics》1988,52(3-4):979-1003
Two models for the Freedericksz transition in a fluctuating magnetic field are considered: one is based on a dichotomic and the other on a nonlinear Gaussian noise. Both noises are characterized by a finite correlation time. It is shown that the linear response assumption leading to the best Fokker-Planck approximation in the dichotomic and nonlinear Gaussian cases can be trusted only up to the order
1 and
0, respectively. The role of the corrections to the linear response approximation is discussed and it is shown how to replace the non-Fokker-Planck terms stemming from these corrections with equivalent terms of standard type. This technique is shown to produce perfect agreement with the exact analytical results (dichotomic noise) and to satisfactorily fit the results of analog simulation (nonlinear Gaussian noise). 相似文献
997.
We study a class of degenerate elliptic second order differential operators acting on some polynomial weighted function spaces on [0,+[. We show that these operators are the generators of C
0-semigroups of positive operators which, in turn, are the transition semigroups associated with right-continuous normal Markov processes with state space [0,+]. Approximation and qualitative properties of both the semigroups and the Markov processes are investigated as well. Most of the results of the paper depend on a representation of the semigroups we give in terms of powers of particular positive operators of discrete type we introduced and studied in a previous paper. 相似文献
998.
Daniele Andreucci Paolo Bisegna Emmanuele DiBenedetto 《Comptes Rendus Mathematique》2002,335(4):329-332
We compute the homogenized-concentrated limit for a pair of non-linearly coupled diffusion equations in a perforated cylindric domain with coaxial cylindric holes periodically distributed along its axis. This problem arises from visual transduction. To cite this article: D. Andreucci et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 329–332. 相似文献
999.
Graziano Baccolini Giorgio Orsolan Elisabetta Mezzina Paolo Sgarabotto Corrado Rizzoli 《Heteroatom Chemistry》1994,5(1):37-42
Fused 1,3-benzothiaphospholes 2 (cis-2,6,10-trimethyl-[1, 3]benzothiaphospholo[2,3-b][1, 3]benzothiaphosphole) reacts with H2O2 and S8, giving the corresponding oxide and sulfide, respectively. The reactions of 2 with diethyl azodicarboxylate (DEAD)/catechol or DEAD/o-aminophenol, o-azidophenol, and tetrachloro-o-benzoquinone (TOB) give the first examples of spiro pentacoordinated phosphorus derivatives of this heterocyclic system. The X-ray structural analysis of spiro compound 3 showed a trigonal bipyramidal configuration at phosphorus in which the three rings assume axial-equatorial positions. 相似文献
1000.
Benincori T Brenna E Sannicolò F Trimarco L Antognazza P Cesarotti E Demartin F Pilati T 《The Journal of organic chemistry》1996,61(18):6244-6251
The synthesis and application of three examples of a new class of chiral (C(2)) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (-)-2,2'-bis(diphenylphosphino)-4,4',6,6'-tetramethyl-3,3'-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (-)-bitianp (1b) were synthesized. They were found to be optically stable at 100 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2'-bis(diphenylphosphino)-3,3'-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed. 相似文献