全文获取类型
收费全文 | 2492篇 |
免费 | 51篇 |
国内免费 | 8篇 |
专业分类
化学 | 1611篇 |
晶体学 | 42篇 |
力学 | 93篇 |
数学 | 571篇 |
物理学 | 234篇 |
出版年
2023年 | 13篇 |
2022年 | 48篇 |
2021年 | 64篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 31篇 |
2017年 | 22篇 |
2016年 | 66篇 |
2015年 | 67篇 |
2014年 | 53篇 |
2013年 | 119篇 |
2012年 | 109篇 |
2011年 | 150篇 |
2010年 | 97篇 |
2009年 | 84篇 |
2008年 | 128篇 |
2007年 | 107篇 |
2006年 | 136篇 |
2005年 | 125篇 |
2004年 | 109篇 |
2003年 | 91篇 |
2002年 | 79篇 |
2001年 | 30篇 |
2000年 | 15篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 42篇 |
1995年 | 26篇 |
1994年 | 31篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 31篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1915年 | 9篇 |
1906年 | 7篇 |
排序方式: 共有2551条查询结果,搜索用时 15 毫秒
1.
2.
The inhomogeneous Gevrey classes, defined in terms of Fourier transform, are a natural extension of the standard Gevrey classes. We find equivalent characterizations and discuss algebraic and topological properties. We therefore introduce the dual spaces, the inhomogeneous ultradistributions, giving some equivalent definitions and corresponding algebraic and topological properties; in particular, a version of the Paley-Wiener-Schwartz theorem is proved in our framework. Finally, as an important example, the multianisotropic Gevrey classes and ultradistributions are considered. 相似文献
3.
Luigi Antonio Rosati 《Geometriae Dedicata》1987,24(3):261-267
Summary Let G be a sharply 3-transitive permutation set on a finite set E of even cardinality and let 1 be in G. The following theorems are proved.
G is one of the known examples if and only if there exists a non-identity normal subgroup N of G and an element of E such that NG
G.G is a group if and only if G for every G and for every G and for every G
.By using the classification of finite single groups a result concerning sharply k-transitive permutation sets k>3 is also proved.
Dedicato a Guido Zappa in occasione del suo 70° compleanno
Lavoro eseguito nell'ambito dei progetti finanziati dal Ministero della Pubblica Istruzione. 相似文献
Dedicato a Guido Zappa in occasione del suo 70° compleanno
Lavoro eseguito nell'ambito dei progetti finanziati dal Ministero della Pubblica Istruzione. 相似文献
4.
Luigi Ambrosone Lucia Costantino Gerardino D'errico Vincenzo Vitagliano 《Journal of colloid and interface science》1997,190(2):286
The densities and viscosities of binary aqueous mixtures of poly(ethylenoxide)hexanols [C6H13(OCH2CH2)mOH, C6Em] (m= 3, 4, and 5) have been studied in the micellar composition range. For the same surfactants the self-diffusion coefficients in mixtures with heavy water have been determined by the spin-echo pulsed field gradient method. The volumetric data are interpreted by means of the phase separation model, and values of the CMC, volume change, and standard free energy change of micellization are obtained. From the viscosity data the hydration numbers of the surfactant hydrophilic head in the micellar state are computed; they are in agreement with those obtained from HDO self-diffusion data. The surfactant self-diffusion data are used to calculate the apparent micelle radius and the aggregation number. The micellization parameters obtained for the different surfactants are compared and discussed. 相似文献
5.
Di-2-pyridylketone semicarbazone as ligand in metal complexes: synthesis and X-ray crystal structure
Luigi P. Battaglia Pier Giovanni Berzolla Anna Bonamartini Corradi Corrado Pelizzi 《Journal of chemical crystallography》1993,23(12):973-979
A series of complexes of di-2-pyridylketone semicarbazone (Hdips) and Mn(II), Co(II), Co(III), Ni(II) and Cu(II) nitrates were synthesized and characterized by means of IR spectroscopy and for cobalt and nickel by X-ray crystal structures. The results are in agreement with the formulae: Mn(Hdips)2(NO3)2·2H2O, [Co(Hdips)2](NO3)2·H2O (I), [Ni(Hdips)2](NO3)2·H2O (II), Cu(Hdips)(NO3)2·2H2O, [Co(dips)2](NO3)·2H2O (III). The structure of I and II are monoclinic, space groupP21/c, with, I,a=15.980(4),b=11.531(2),c=16.170(2)Å;=104.20(2)°,Z=4,R=0.032; II,a=16.109(5),b=11.480(3),c=16.135(6)Å;=104.15(2)°,Z=4,R=0.069. Compound III is also monoclinic, space groupP21/c witha=12.173(5),b=15.619(5),c=15.338(8)Å;=111.40(4)°,Z=4,R=0.059. In these complexes the ligand is tridentate via carbonylic oxygen, semicarbazone and pyridine nitrogens forming each two five membered chelate rings with the metal in a distorted octahedral geometry. 相似文献
6.
The potassium and sodium salts of some penicillins and cephalosporins were analyzed by thermoanalytical techniques (TG, DTG and DSC); in particular, those antibiotics whose thermal decomposition in oxygen occurs too quickly. The analyses were carried out in atmospheres of static air and oxygen, with and without the addition of ammonium sulphate or ammonium persulphate. It is possible to evaluate the purity of these antibiotics from the resultant sodium or potassium sulphate residue. Better results in terms of accuracy and precision were obtained by the addition of ammonium sulphate or persulphate to the analyzed compounds. 相似文献
7.
The interpretation of the infrared active fundamentals of TCNQ and chloranil monovalent anions is given for the first time. The rationalization of the infrared spectra was made possible by the recently achieved vibrational assignment of the corresponding neutral molecules and is mainly based on a set of judicious adjustments of their empirical valence force fields. 相似文献
8.
Andreas Stockhammer Klaus-Hermann Dahmen Tobias Gerfin Luigi M. Venanzi Volker Gramlich Walter Fetter 《Helvetica chimica acta》1991,74(5):989-992
The cluster compounds [Pt3(μ-CO)3(PR3)3] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ-CO)3(PR3)3}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]. 相似文献
9.
Luigi Fabbrizzi Piero Paoletti Markus C. Zobrist Gerold Schwarzenbach 《Helvetica chimica acta》1973,56(2):670-680
The thermodynamic functions of the proton transfer H2tn2++tn → 2 Htn+ (tn = 1,3-diaminopropane) have been determined in aqueous solutions containing different amounts of KCl (0.05 ? μ ? 3.01). The free energy (?ΔG) of the process decreases, whereas the enthalpy (-ΔH) increases with μ. There is reason to believe that the reaction is entirely controlled by the Coulomb forces between the two protonic charges. The electrostatic energy involved can be described in terms of a model incorporating an effective dielectric constant εe, such that δεe/δμ and δ2εe/δμδT are both positive. The polarisation of pure water is produced by orientation of hydrogen-bonded dipole molecules H2O, whereas the electrolyte solution is polarised in addition by dislocation of the ions K+ and Cl?. Our results demonstrate that the former type of polarisation is much more temperature dependent than the latter. 相似文献
10.
An enzyme inhibition biosensor, developed in our laboratory and previously used for the analysis of compounds with anticholinesterase activity (e.g. physostigmine, neostigmine, pyridostigmine nicotine and organophosphorus compounds) has now been tested for the analysis of another recently synthesized cholinesterase inhibitor, i.e. eptastigmine. In addition nicotinic acid and nicotinamide, although displaying weaker inhibition properties, were also tested in pharmaceutical products using the same inhibition enzyme sensor. The biosensor consisted of a hydrogen peroxide amperometric electrode coupled to a functionalised nylon membrane chemically bonding both the enzymes butyrylcholinesterase and choline oxidase; a butyrylcholine standard solution in glycine buffer acted as substrate. The response of the system to all the inhibitors considered was characterised completely and the analysis of several pharmaceutical formulations containing nicotinamide or nicotinic acid was also performed. 相似文献