全文获取类型
收费全文 | 1165篇 |
免费 | 31篇 |
国内免费 | 11篇 |
专业分类
化学 | 752篇 |
晶体学 | 6篇 |
力学 | 34篇 |
数学 | 241篇 |
物理学 | 174篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 21篇 |
2017年 | 13篇 |
2016年 | 40篇 |
2015年 | 27篇 |
2014年 | 21篇 |
2013年 | 47篇 |
2012年 | 71篇 |
2011年 | 76篇 |
2010年 | 50篇 |
2009年 | 40篇 |
2008年 | 61篇 |
2007年 | 72篇 |
2006年 | 61篇 |
2005年 | 45篇 |
2004年 | 35篇 |
2003年 | 34篇 |
2002年 | 42篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 14篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有1207条查询结果,搜索用时 15 毫秒
41.
The mass spectrometric behaviour of 2-(2-pyridyl)-2,3-dihydroxy-5-phenyl-4-pentene has been studied with the aid of B/E, B2/E linked scans, exact mass measurements, collisionally activated dissociation mass-analysed ion kinetic energy spectra, and labelling experiments. The primary loss of water is proved to involve both hydroxylic hydrogens, thus suggesting the formation of an epoxidic radical ion and the presence of extensive skeletal rearrangements. 相似文献
42.
We present a combined experimental and theoretical analysis of the dielectric and vibrational properties of crystalline lutetium oxide in its ground-state bixbyite structure. The vibrational dielectric function of Lu2O3 thin films grown by atomic-layer deposition was studied by infrared transmission and reflection-absorption spectroscopies, selectively accessing transverse and longitudinal optical frequencies. The static dielectric constant is extracted analyzing the infrared response. We also present first-principles density-functional linear-response calculations, which are in close agreement with experiment, and provide insight into the microscopic nature of vibrational spectra and dielectric properties. 相似文献
43.
Javidi B Ferraro P Hong SH De Nicola S Finizio A Alfieri D Pierattini G 《Optics letters》2005,30(2):144-146
We present three-dimensional (3D) image fusion by use of digital holography. We demonstrate experimentally that, through the image fusion technique with multiresolution wavelet decomposition, it is possible to increase the details and contrast of 3D reconstructed images obtained by multiwavelength digital holography. Although there is substantial activity in the fields of image fusion and holography, to the best of our knowledge, this is the first report of 3D image fusion by use of digital holography. 相似文献
44.
Antonello?Vicenzo Michela?Rea Luca?Vonella Massimiliano?Bestetti Pietro?Luigi?CavallottiEmail author 《Journal of Solid State Electrochemistry》2004,8(3):159-166
In the present work the electrochemical deposition of Au-Sn alloys is addressed and a cyanide-free process is presented. The electrolyte is an acidic thiourea solution containing gold as a Au[CS(NH2)2]+ complex and tin as stannous ions. Results concerning the plating process development and deposit characterization are reported. Au-Sn alloy films with a Sn content up to 50 at% and a single-phase structure can be obtained from the acidic thiourea–Au(I) solution under pulsed current plating conditions. Alloy deposits show three main crystal structures: a face centred cubic (fcc) Au(Sn) solid solution, extending up to 7 at% Sn; a hexagonal close-packed structure, of the same type as the metallurgical phase, up to about 18 at% Sn; and a NiAs-type structure, corresponding to the phase of the equilibrium diagram, with an enlarged homogeneity range. Mechanical properties of thin layers of Au-Sn alloys derived from micro-indentation measurements follow the structural modification with the alloy composition. The ordered intermetallic phases occurring in the equilibrium binary system, in particular the and phases at 8 at% and 16 at% Sn, respectively, are not detected in the electrodeposited alloys. The main factors controlling electrochemical phase formation are pointed out, considering the differences between the phase structure of the electrodeposited alloys and the equilibrium phase diagram.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany 相似文献
45.
In the presence of catalytic amounts of tetraalkylphosphonium salts and under solventless conditions, primary aliphatic amines (RNH(2): R = PhCH(2), Ph(CH(2))(2), n-decyl, and 1-naphthylmethyl) are efficiently N-benzylated to the corresponding RN(CH(2)Ph)(2), using dibenzyl carbonate as the benzylating reagent. Compared to the reaction run without salt, where the competitive formation of the benzyl carbamate is favored, the phosphonium salt promotes high selectivity toward the benzylated amine and an increase of the reaction rate as well. However, in a single case explored for an amino acidic compound, namely 4-(aminomethyl)benzoic acid [4-(NH(2)CH(2))C(6)H(4)CO(2)H], both N,N-dibenzylation and esterification of the acid group were observed. Analysis of the IR vibrational modes of benzylamine in the presence of tetrabutylphosphonium bromide supports the hypothesis that this enhanced selectivity may be due to an acid-base interaction between the salt and the amine, which increases the steric bulk of the amine and favors attack of the nucleophile on the less hindered alkyl terminus of dibenzyl carbonate. 相似文献
46.
Aime S Calabi L Cavallotti C Gianolio E Giovenzana GB Losi P Maiocchi A Palmisano G Sisti M 《Inorganic chemistry》2004,43(24):7588-7590
An innovative MRI contrast agent based on the unprecedented and easily obtained ligand AAZTA is described. The simple and straightforward synthesis of the ligand, together with the potentiometric and relaxometric behavior of the corresponding Gd(III) chelate, is reported. The complex [Gd(AAZTA)]- shows outstanding magnetic properties connected with high thermodynamic stability in aqueous solution and a nearly complete inertness toward the influence of bidentate endogenous anions, placing this compound as one of the most promising candidates for the development of high performance MRI contrast agents. 相似文献
47.
We perform a study of the nonperturbative dynamics of the light-quark sector of QCD, based on some recent results of lattice simulations with chiral fermions. We analyze some correlators that are designed to probe the Dirac structure of the quark-quark interaction at different scales. We show that, in the nonperturbative regime, such an interaction contains very large scalar and pseudoscalar components. We observe quantitative agreement between lattice QCD results and the predictions of the instanton liquid model. Moreover, we study how the quark-quark interaction is modified, when quark loops are suppressed. We observe a dramatic effect related to the loss of unitarity, which is naturally explained in the instanton picture. Such an effect cannot be explained in a Dyson-Schwinger equations (DSE) approach, if one assumes a vector quark-gluon coupling. 相似文献
48.
Let be a vector lattice of real functions on a set with , and let be a linear positive functional on . Conditions are given which imply the representation , , for some bounded charge . As an application, for any bounded charge on a field , the dual of is shown to be isometrically isomorphic to a suitable space of bounded charges on . In addition, it is proved that, under one more assumption on , is the integral with respect to a -additive bounded charge.
49.
We consider two possible zeta-function regularization schemes of quantum Liouville theory. One refers to the Laplace–Beltrami operator covariant under conformal transformations, the other to the naive noninvariant operator. The first produces an invariant regularization which however does not give rise to a theory invariant under the full conformal group. The other is equivalent to the regularization proposed by A.B. Zamolodchikov and Al.B. Zamolodchikov and gives rise to a theory invariant under the full conformal group. 相似文献
50.
V. Scuderi M. Zadro A. Di Pietro P. Figuera M. Lattuada F. Pansini M. Papa D. Vinciguerra O. Yu. Goryunov A. Khouaja V. Lyapin C. Nociforo V. V. Ostashko 《The European physical journal. Special topics》2007,150(1):53-54
The resonance scattering method in inverse kinematics on infinite target has been applied to two systems, 18O + α and 9Be + α, in order to test and to optimize an experimental apparatus in view of a set of resonance scattering experiments to
be performed with 8Li and 9Li radioactive ion beams delivered by the facility EXCYT. The scattering excitation functions, deduced for the two systems,
were compared with previous results reported in literature. Results show that reliable stopping power data are essential for
the application of this technique. 相似文献